Advanced Experimental Psychology Notes PDF

Subject: Advanced Experimental Psychology – I Basic Book: Experimental Psychology - Methodology, Psychophysics and Learning by Michael R. D'Amato Kavisha Shah, Ph.D. Research Scholar, Department of Psychology, Gujarat University Unit-1: Psychological research and concepts of variables ...

Subject: Advanced Experimental Psychology – I Basic Book: Experimental Psychology - Methodology, Psychophysics and Learning by Michael R. D'Amato Kavisha Shah, Ph.D. Research Scholar, Department of Psychology, Gujarat University Unit-1: Psychological research and concepts of variables  Definition of psychological research:- “The term ‘Psychological Research’ includes all inquiries into problems within the sphere of psychology.” - M. R. D’Amato  Types of psychological research:- There are mainly 2 types of psychological research according to D’Amato. [A] Theoretical research [B] Empirical research [A] Theoretical research:- ➔ The primary aim of theoretical research is to construct theories. For example; Newton constructed the theory of gravitation after he watched an apple falling from the tree. → In these types of psychological researches, old facts are collected and new theories are constructed. → In these types of theories, direct experience is not a necessary condition. → There are two types of theoretical research. Library research Theory construction  Library research:- → In library research, the researcher attempts to integrate the findings or the data in a particular problem area of psychology. → They also attempt to derive hidden generalization from seemingly diverse data. → On some level, any new research is based on previously conducted researches. These previously conducted researches are mentioned in the ‘references’ section at the end of any research article or research paper. → Examples of such research are found in the frequent “review” articles that are published in the journal Psychological Bulletin. → In these articles, the accumulated research in circumscribed (limited) problem area of psychology is examined in depth. → Also, an attempt is made to draw generalizations or formulate hypothesises from the data, which help us organize and understand them. → Thus, some theory construction, limited in depth and scope, is often involved in library research. Theory Construction:- → The main purpose of this type of research is to collect information or data, generalize the findings and construct specific theories. → The researcher does not go out on the field to collect information rather he collects information or data through certain organizations or government bodies. For example, researcher can get information such as, name, age, gender, education, type of crime etc from a police station. He then analyzes this information and draws some common conclusions. Such as males are more involved in criminal activities compared to females or criminal activities are more prominent in young generation. → The development in psychology of systematic theories does not, of course, occur in isolation from empirical research; rather, theory construction and empirical research are complementary activities. → One may nevertheless distinguish activities that are primarily theoretical in nature. → Such theories may be formal or informal. For example, Psychoanalytical theories generally fall under formal category.  A classic example of informal theories may be found in mathemetico- Deductive Theory of Rote Learning by Hull and others (1940) and in Hull’s later work Principles of Behaviour (1943). → More recently, psychology has seen the development of thoroughly mathematical theories, as in the field of learning. For example, Three volumes of Handbook of Mathematical Psychology were launched in 1963 and inauguration of Journal of Mathematical Psychology in 1964. [B] Empirical Research:- → Empirical research is based on experience. → In empirical research, the researcher directly collects the information or the data. He draws conclusion based on his own observations and research data. → Methods such as observation and experiment are used in empirical research → Empirical research can be divided in to 3 research approaches. Observation (a) Natural Observation (b) Laboratory Observation Correlational research Experimentation Observation:- ➔ Observation is one of the oldest methods described in sciences like Astronomy and Astrology. → Careful observation of animal and human behaviour is a preliminary point of psychology. → This is not to say that observation alone can sustain the development of any science; at the very minimum, correlational research should also be used along the observation method. → However, very often, observation is the source of many interesting and important problems as well as the origin of many hypothesises. ➔ According to D’Amato “Observation involves the noting and recording of events without any formal manipulation of variables operating under study.” For example, Suppose a researcher wants to learn something about the group processes of children. So he will observe a group of children playing in the schoolyard. From his observations he might arrive at the hypothesis that “Individual aggressiveness and Group leadership are positively related. In other words, more aggressive children tend to engage in group leadership behaviour more frequently than the less aggressive children. In this type of observation, researcher has not manipulated any variables formally. → Going a step further, the researcher might obtain the measurement of aggressiveness of the child through either a psychological test or a rating scale. → On the basis of such measurement, the researcher will likely select children who have scored high and low on aggressiveness for future observations. → And if the hypothesis were correct then the children scoring high on aggressiveness should engage more often in group leadership behaviour than the children scoring low on aggressiveness. → We may consider the psychological test or the rating procedure as means of ‘manipulating’ through observation, the variable of aggressiveness. → Thus the researcher, in manipulating the variable of aggressiveness and relating it to the variable of group leadership, is no longer engaged in observation only, but has advanced to what is called “correlational research”. → Observation is mainly divided into 2 types. (a) Natural observation (b) Laboratory observation  (a) Natural observation:- When observation is employed on events in their natural setting, it is called natural observation. For example, the study of aggression and group leadership in children is the instance of natural observation. Many studies of animal behaviour are conducted using the natural observation method. Many social and anthropological studies are also conducted using this method. The main benefit of natural observation is that it provides us primary information and hypothesises required for laboratory experiments. (b) Laboratory observation:- Natural observation often gives way to laboratory observation. The control of relevant variables is more practicable in a laboratory setting. Events observed under natural conditions are often influenced by the factors which the researcher cannot control. Furthermore, in natural observation, many a times, the researcher must wait for certain events to occur in order to observe it. Whereas, in laboratory observation it is often possible to initiate events of interest through manipulation of environmental and related factors. Correlational Research:- ➔ A very important segment (section) of psychological research makes use of correlational techniques. → According to Cronbach (1957), scientific psychology can be divided in to two parts, Experimental psychology and correlational psychology. → Areas such as construction and application of psychological tests, differential psychology, developmental psychology, and some instances of comparative psychology can be included in the correational psychology. → An important defining feature of correlational research is that the variables under study are not directly (experimentally) manipulated by the researcher. → Rather, variation in the variable of interest is achieved by some sort of selection procedure. → In psychology, selection procedure often takes the form of psychological tests. → Thus, if one were interested in the relationship between intelligence and problem-solving ability, the variable of intelligence would be manipulated by using some reasonable test of intelligence to select individuals of different levels of intelligence. → Quite clearly the researcher cannot directly (experimentally) manipulate intelligence in his subjects. He cannot convert one group of subjects into highly intelligent individuals and second group into subnormal intelligent individuals. → Special aptitudes and many personality variables are examples of variables that can be manipulated by the researcher only through the selection procedure and not directly. ➔ The correlation between two variables can be either positive or negative. → When the change in the two variables occurs in a single direction, then it is known as positive correlation. Meaning that if the value of one variable increases so does the value of other variable and if the value of one variable decreases so does the value of other variable. → But when the change occurs in the opposite direction in two variables then we call it negative correlation. Meaning that when the value of one variable increases, the value of second variable decreases and when the value of one variable decreases, the value of second variable increases. → The researcher cannot directly manipulate the variables. So he establishes relationships and differences between the variables through certain selection methods. For example: The hypothesis in the experiment of intelligence and problem- solving ability is that “as the level of intelligence increases, the level of problem-solving abilities of the individual increases as well” Here, to decide the level of intelligence, the researcher will use an IQ test and will sort the subjects in different groups according to their IQ score. Each group will be given the same problem and the amount of time that takes to solve the problem will be recorded.  The result shows that the level of intelligence and the speed of problem solving are positively related. In other words, there is positive correlation between the two variables. Same way, we cannot directly manipulate the scholastic aptitude, but we can use certain aptitude tests and select the subjects of various scholastic aptitudes from the population. ➔ Although correlational research has certain limitations, particularly with respect to controlling relevant variables and drawing conclusions concerning cause and effect relationship, in certain important areas of psychology, the use of correlational research is unavoidable. → However, researchers use advanced statistical tools such as factorial analysis that can be useful in the analysis of complex phenomena. ➔ Cronbach, an arch-correlational psychologist, said this about the potentials of correlational research. → The well known virtue of the experimental method is that it brings situational variables under tight control. → It thus permits the testing of hypothesises and confident statements about causation. → The correlational method, for its part, can study what man has not learnrd to control or can never hope to control. → The researcher’s (correlator’s) mission is to observe and organize the data from Nature’s experiments. → As a minimum outcome, such correlations improve immediate decisions and guide experiments. → For example, Theories of Newton and Darwin. ➔ Cronbach and others have argued that experimental and correlational techniques should be combined to study difficult research problems. → In summary, correlational research, unlike observation, involves the manipulation of specific variables chosen from the area of research interest. → IN correlational research the manipulation is always accomplished by some sort of selection procedure.  Experimentation:- An essential condition of most of any sciences, including psychology is experimentation. ➔ Zimney (1961, p. 18) defines a psychological experiment as “objective observation of phenomena which are made to occur in a strictly controlled situation in which one or more factors are varied and the others are kept constant.” Following points can be derived from the definition. 1. The experiment is a type of an observation. 2. The experiment is the type of an objective observation. The object is observed in its original form. Observation is unbiased. 3. Observation of the phenomenon. Webster’s dictionary defines phenomenon as “an observable fact or event.” (In psychological experimentation, phenomenon refers to any publicly observable behaviour, such as actions, appearances, verbal statements, responses to questionnaires, and physiological recordings.) 4. In experiment, the phenomenon is made to occur. 5. Phenomenon is observed under strictly controlled situation. 6. One or more factors are varied and the others are kept constant. → The experimental method has enabled science to take many giant leaps. The essence of this method is simple. The experimenter- 1. Changes or varies something. 2. Keeps other conditions as constant as possible. 3. Looks for some effects of the changes or variations on the thing being studied. ➔ In an ideal experiment, the investigator controls and directly manipulates the important variables of interest. Example: Temperature, humidity, lighting, task instructions, materials, and procedures are some of the variables that can be manipulated directly. → In experiment, some subject relevant variables cannot be manipulated directly, in which case these variables are manipulated through the manipulation through selection method. Example: Age, Gender, Intelligence, academic achievements are some of the subject relevant variables that can be manipulated through selection procedure. → It is important to know the difference between direct manipulation and manipulation through selection.  The difference between direct manipulation and manipulation through selection. 1. Subsidiary change: → The difference between direct manipulation of variables and manipulation through selection procedure is important for several reasons. → First, when a variable is manipulated through selection, often, other quite relevant variables are concomitantly manipulated with the variable of interest. (IV) (concomitantly = naturally accompanying or associated) → Such concomitant manipulation of variables can lead to very misleading interpretations of research results. For example, Suppose a researcher is interested in the relationship between height and food intake initiates a study comparing the food intake of people of various heights. He would undoubtedly find that the two variables are positively related; that is, taller people eat more than shorter people. Although this empirically obtained result may be undeniable, the question arises that “does height itself influence the amount eaten?”  Consider, for example, a hypothesis that in taller people the heart must work harder to pump the blood into the head region and that this added work consumes extra energy, requiring, in turn, greater food intake. A little thought will make it clear that probably height is not the important relevant variable. The relationship obtained by the researcher most likely results from the close relationship of height and weight. In manipulating height, through, through selection of individuals of different heights, the researcher concomitantly manipulated weight, because taller people tend to weight more. Thus, the tall people were not only taller than the short people, but they also weighted more-and it is quite likely that the latter is the important one. It should be noted that, this conclusion could be checked by measuring the food intake of one group of individuals who vary in height but not in weight and of a second group who vary in weight but not in height. → Of course, the misleading interpretation arises when the concomitantly manipulated variable is subtle and goes unnoticed by the researcher-not an uncommon occurrence. → For this reason, as well as others, it is often difficult in correlational research to make confident statements about concerning cause and effect relations. 2. Errors in manipulation through selection: → A second reason for distinguishing between direct manipulation and manipulation through selection relates to the accuracy (precision) of manipulation attained by two methods. → Although with some variables manipulation through selection is very precise, with others a considerable margin of error is involved. → Errors occur with reference to the true value of variable and the value attained by the manipulation of the variable. → Thus, any error committed in manipulating age as a variable is likely to be small, but this is not true for variables such as aptitudes, intellectual ability, and personality. → It is generally true that directly manipulated variables are subject to very little error in their manipulation. 3. Direct manipulation is more powerful: ➔ The third difference between the two methods of manipulation is that certain powerful research techniques, developed with directly manipulated variables, are inapplicable to most variables manipulated by selection procedure. → Among the more important of these is the single-group or within- subjects design. A technique in which each subject serves as his own control. → Single-group (within subjects) design is the method in which a single group of subjects serves under all conditions of research. For example, Suppose we want to determine whether nicotine has any harmful effects on motor co-ordination. One powerful means of approaching this problem is as follows. We would select a group of subjects and give them a series of motor co-ordination tests, one test daily. Before some of the tests, subjects will be given a dose of nicotine and before others they would receive placebo. Hence, all subjects are tested under both the drug and no-drug conditions. If the drug has a harmful effect on motor co-ordination, we will observe that, in general, the performance of our subjects is poorer when tested under the nicotine than when tested after receiving the placebo. Note that because each subject is tested under both conditions, we don’t need to concern ourselves with individual differences in motor coordination ability. ➔ Now imagine that the only way in which we could obtain the subjects was by choosing smokers and non smokers from general public. → In this instance we would be forced to use separate-groups or between- subjects design. → In separate-groups, one group of subjects (smokers) would be tested under the drug condition, and a second group of subjects (non-smokers) would be tested under the no-drug condition. → In separate group design, a separate group of subjects serves under each of the conditions of the research. → By comparing the performance of the two groups of subjects, we can evaluate the effect of nicotine on motor co-ordination. → Note that the motor co-ordination ability is radically changed with respect to individual differences. → We are now vitally interested in any dimension of individual differences that might significantly affect motor co-ordination, such as age, sex, and occupation. → Obviously we would want smokers (drug group) and non-smokers (no- drug group) to be well equated with respect to such individual characteristics. → However, these precautions are not necessary with the single-group design because every subject is tested under all the conditions of the research. ➔ In summary, the fundamental (basic) feature of experimentation is that the variables under study are directly manipulated by the researcher. → And it may be stated as a general principle that the more directly the researcher can manipulate his variables of interest, the more reliable and precise his results are likely to be → Direct manipulation of variables possesses several advantages over manipulation of manipulation by selection. 1. The dangers of concomitant manipulation of relevant but extraneous variables are considerably less potent with direct manipulation. 2. There is generally less error of manipulation involved when variables are directly manipulated. 3. Certain powerful research techniques, such as single-group designs, are possible with many variables that are manipulated directly but are possible with only few variables that are manipulated by selection.  Psychology and the concept of variables:- ➔ Consider the following experiment. → A subject (S) is seated before a table on which a small telegraph key and, next to it, a white electronic light bulb is placed. And the subject is made to wear earphones. → Subject is instructed by the experimenter (E) to press the telegraph key as quickly as possible whenever he sees the white light illuminate or hear a tone through earphones. → The stimuli, the white light and the tone, are presented individually and in a random (irregular) order so that the S cannot predict whether the net stimuli will be the light or the tone. → During each stimulus presentation, E accurately measures S’s reaction time (RT), that is, the time elapsing between the onset of the stimulus and the time S presses the telegraph key. → After 50 presentations of each stimulus, the experimental session is terminated. ➔ Although relatively simple, the preceding situation contains many of the important features common to most experiments in psychological research. → Our present interest is the concept of variables, in particular independent variables, dependent variables, and relevant variables. ❖ Definition of variable: “Variable is any measurable attribute of object, things or beings.” - M.R.D’Amato → For example, height, weight, temperature, light, time, intelligence, motivation, memory etc are all variables. → The term ‘variable’ has a very wide application, but it is not all inclusive. For example, Extrasensory perception (ESP) is thought to be an attribute of human beings, but it is apparently incapable of reliable measurement, thus we would not call it a variable. → The measurability required of an attribute need not be quantitative. → Race, sex, and religion, for example, are the variables that are only “qualitatively” measurable. ❖ Classification of variables according to D’Amato:  Independent variable:- ➔ “An independent variable is any variable manipulated by the experimenter, either directly or indirectly, in order to determine its effects on dependent variable (behavioural measure)” - M.R.D’Amato For example, 1. The effect of noise on work. 2. The effect of light intensity on the speed of reading. 3. The effect of tranquilizer on memory. 4. The effect of age on reaction-time. In the above instances, noise, light intensity, tranquilizer and age are independent variables. → In the Reaction-Time experiment, the experimenter’s interest lies in determining whether the type of stimulus employed, tone or light, has an effect on the subject’s reaction time. → The experimenter question being asked is: Does, in general, an individual’s Reaction-Time (RT) depend on whether the stimulus being used is a tone or a light? → To answer this question, Experimenter systematically manipulates the stimulus presented to the Subject and observes whether subject’s reaction- time (RT) is faster with the light or the tone. → Because the type of stimulus employed (tone or light) is a variable manipulated by Experimenter in order to determine the Subject’s reaction- time, it is called any “independent variable.” ➔ Note that in this case Experimenter is able to manipulate directly the type of stimulus, tone or light, presented to the subject. → However Experimenter encounter situation in which he can manipulate only through a selection procedure. → For example, suppose Experimenter wished to investigate the question, Does the reaction-time of an individual depend on his age? → In order to manipulate the variable of interest-age, Experimenter would select Subjects on the basis of their age, for example he would select subjects ranging from ages 20 to 40. → The subject’s age is a variable manipulated by Experimenter by means of selection in order to determine the effects on subject’s reaction-time; it is therefore an independent variable. ➔ Now, we want to distinguish between independent variables that are directly manipulated and that are manipulated trough selection. → The variables manipulated directly or experimentally are referred to as “Type-E” independent variables. For example, in the experiment of effect of tonal stimulus on the reaction time, the independent variable ‘tonal stimulus’ is manipulated by the experimenter directly. Thus it is a Type-E independent variable. → The variables manipulated through a selection procedure are referred to as “Type-S” independent variables. For example, in the experiment, the effect of age on reaction-time, the independent variable ‘age’ is manipulated by the experimenter through the selection of subjects of various ages. Thus is a Type-S independent variable.  Dependent variable:- ➔ “A dependent variable is any behavioural variable measured by the experimenter to assess the effects of independent variable.” - M.R.D’Amato For example, 1. The effect of noise on work. 2. The effect of age on reaction-time. 3. The effect of tranquilizer on sleep. In the above instances, work, reaction-time and sleep are dependent variables. → In simple words, dependent variable is the result. → In any experiment, at least one dependent variable should be present. In some experiments, there are 2 or more dependent variables are present. For example, Maze learning through trial and error. In this experiment, there are two dependent variables, Time and Error. ➔ The reason why dependent variable is also called behavioural variable is because in psychological research the experimenter is always interested in some aspect of behaviour of a living organism. → The term “behaviour” is applied in its most general sense and includes not only overt, directly observable responses, such as reaction time and choice behaviour, but also language responses-from which we can deduce facts concerning perception, imagery and similar phenomenon-and relevant physiological reactions, such as pulse rate and the galvanic skin response. → Experimenter’s concern is in observing the effects of manipulation of the independent variable on the measured behavioural variable. → In summary, any measured behavioural variable of interest in a psychological experiment is called a dependent variable.  Interdependence of Independent and Dependent Variables:- ➔ It is clear from the definitions of independent and dependent variable that neither concept is defined independently of other. → It is not possible to identify the independent variable without specifying or identifying the dependent variable and vice versa. → However, in most research it is quite easy to identify independent and dependent variables. ➔ On the other hand, there is a good reason there is a good reason for the interdependence of the two definitions. → Sometimes, experimenter manipulates certain independent variables solely for the purpose of control. (i.e., to eliminate differential effects of the variable from research results.) → In such cases experimenter is not directly interested in the effects of the manipulated variables on the dependent variable. For example, In reaction-time experiment, experimenter manipulated the stimulus sequence, that is, the order of presentation of the light and tone. Experimenter presented the stimuli in an irregular order until 50 presentations of each stimulus were completed. Suppose experimenter first presented the tone on trials 1 to 50 and then the light on trials 51 to 100, adopting this procedure with all subjects. If it turned out that in general subjects’ reaction-time to the light was faster than the tone, then can we confidently say that there is a distinctive difference between the two stimuli? It can be argued that the difference in the RT occurred due to the fact that all 50trials with light came after the 50 tone trials and, therefore, had the benefit of practice effect. In other terms, if the light stimulus had been employed on all 100 trials, it is quite likely that the reaction-time on the last 50 trials would have been faster than the reaction-time of the first 50 trials, simply because of the practice effects. “Order of the stimulus presentation,” then, is a variable manipulated by the experimenter directly to control its effects on the  experimental results but not to determine its effects on the dependent variable; hence, it is not an independent variable. → It is important to note that a variable manipulated by the experimenter is not classified as an independent variable unless manipulation is for the purpose of observing its effects on the dependent variable. ➔ A complementary situation exists for measured behavioural variables. → Sometimes experimenter will measure a behavioural variable for control purposes. For example, to equate groups of subjects for certain characteristics. For example, Suppose experimenter wished to determine the effects of learning task B on the retention of task A. Task will B will be learned after task A. The experimental group will learn task A, then learn task B, and finally be tested on the retention of task A. The control group will learn task A and then after a short period rest will be tested on the retention of task A. The effect of learning task B on the retention of task A will be revealed by comparing the retention scores of experimental and control groups. Because, in general, the amount retained by an individual might vary with the speed with which they learned the material, experimenter would want to have the experimental and control groups fairly equal with respect to the speed of learning task A. One simple way of accomplishing this is for experimenter to assign the subjects to the two groups after all subjects have learned the task A. He would then assign subjects to the experimental and control groups taking into consideration each subject’s speed of learning task A. → It is clear that speed of learning task A is a measured behavioural variable, but it is also clear that the experimenter is not directly concerned with its effects on the dependent variable, that is retention of task A. Thus, speed of learning task A is not a dependent variable.  Relevant Variables:- ➔ We have already seen that variables other than the independent variable can have an effect on the dependent variable. → In reaction-time experiment, there are number of variables, other than the order of presentation of the stimuli, whose variation can affect reaction-time. → Intensity of the tone and light stimuli, force required to press the telegram key, and location of the visual stimulus in the visual field are such variables that can have an effect on the dependent variable. → However, there are other countless variables, such as atmospheric pressure, subject’s income and religion that have no visible effect on the reaction-time. ➔ The class of variables that have an effect on the dependent variable are called “relent variables.” → The class that have no visible effect on the dependent variable are called “irrelevant variables.” → The purpose of much of the psychological research can be described as the classification of independent variable as either relevant or irrelevant variables. → For example, the question stated in the reaction-time experiment could be: “Is the type of stimulus, tone or light, a relevant variable with respect to reaction-time?” ➔ One of the most critical tasks for the experimenter becomes: the identification and control of all relevant variables operating in the research stimulus. → This is a challenging and difficult task that has not been approached in the psychological research to a greater or lesser degree. → The topic of identification and control of relevant variables has received a fair share of attention in the experimental psychology. → A detailed and historical aspect of this topic has been presented by Boring (1954). ❖ Types of relevant variables:- 1. Physical environment and situational relevant variable 2. Apparatus relevant variable 3. Sequence relevant variable 4. Experimenter relevant variable 5. Subject relevant variables 1. Physical environment and situational relevant variable: → These variables are related to things in the environment that may impact how each participant responds. → For example, if a participant is taking a test in a chilly room, the temperature would be considered a situational relevant variable. Some participants may not be affected by the cold, but others might be distracted or annoyed by the temperature of the room. → Other situational relevant variables are light, humidity, noise etc. → All these variables can have an effect on the dependent variable. Therefore, they must be controlled. 2. Apparatus relevant variable: → Stop watch, list of poems or prose, length of learning material, meaningfulness of learning material are some of the examples of apparatus relent variables that can directly or indirectly have an effect on dependent variable. 3. Sequence relevant variable: → In an experiment the sequence of sessions or the sequence of stimulus presentation can also affect the results. → Technique such as counter-balancing is used in order to control these variables. 4. Experimenter relevant variable: → Experimenter’s behaviour, language, pronunciation, talking speed, temperament, uniform, appearance etc are experimenter’s relevant variables and need to be controlled. 5. Subject relevant variables: → These extraneous variables are related to individual characteristics of each participant that may impact how he or she responds. → These factors can include background differences, mood, anxiety, intelligence, awareness, motivation, boredom, intelligence, age, and other characteristics that are unique to each person. → There are two types of subject relevant variable depending on the type of experimental design (a) Inter-subjective relevant variable: → When an experiment is conducted on two groups then certain inter- subjective variables affect the results. → Variables such as age, gender, intelligence, education qualification should be controlled in both groups. (b) Intra-subjective relevant variable: → When experiment is conducted on a single group then certain intra- subjective variables affect the results. → Variables such as tiredness, boredom, practice, motivation should be controlled.  Classification of variables:- ➔ A variable is generally defined as any measurable attribute of objects, things, beings. → Despite the requirement of measurability, qualitative variables such as sex, race, and religion are included in psychological experiment.  Qualitative and Quantitative Variables Variables can be classified as qualitative (aka, categorical) or quantitative (aka, numeric). ❖ Qualitative Variables:- “Qualitative variables are variables composed of categories which cannot be measured with respect to magnitude” -M.R.DAmato → Qualitative variables are also called categorical variables because their values can be discrete categories. For example: Race, occupation, religion, gender, political affiliation, health status, personality classification, in humans etc. → Qualitative variables may also be called nominal variables because their values are simply names and so they are said to be measured on nominal scale. For example, if we are interested in political affiliation, the value of our nominal variable will be conservative and liberal. → In psychology, qualitative variables often relate to aspects or properties of the organism under study. → In psychology, qualitative variables are associated with the characteristics of the stimulus. For example: In reaction-time experiment, variable presented to the subject, tone or light, is an example of qualitative variable. → The essential feature of qualitative variable is that they are composed of categories which do not bear a quantitative relation to each other. → With qualitative variables you cannot make statements such as “Category A possesses more magnitude (value) than the category B” For example, A researcher wants study how emotionality and strain membership are related in rats. (for example, Wistar strain vs. Sprague-Dawley strain) Here, strain membership (Wistar strain and Sprague-Dawley strain) is the independent variable and emotionality is dependent variable. The separate category of strains cannot be placed in order based on magnitude. Meaning that it is absurd to state that the Wistar have more “strain membership” than the Sprague-Dawleys. → Unlike quantitative variables, whose values are numbers, there is no natural ordering to the values of qualitative variables. For example, we can’t say that blue is greater than orange or that conservative is greater than liberal. → The term categorical and nominal both captures the fact that qualitative variables are just names for particular qualities and there is no natural order to the values of such variables.  Quantitative Variables:- ➔ “Quantitative variables are variables that can be measured with respect to magnitude.” -M.R.DAmato → A quantitative variable is a variable which can have some numerical value. For example, age, intelligence, number of trials to learn a specific task and intensity of and auditory stimulus are all quantitative variables. → Because individuals may vary in magnitude of age, intelligence, and number of trials to learn a specific task, and an auditory stimulus can  differ in the magnitude of intensity, they are known as quantitative variables. ➔ Needless to say, quantitative variables are preferred in scientific work than qualitative variables for the simple reason: precise measurement. → In addition, there is little power in explanatory power in qualitative variables. → When a qualitative independent variable influences a quantitative dependent variable, the experimenter tries to explain the relationship between manipulated qualitative variable and dependent quantitative variable. For example, In the reaction-time experiment, it is well established that reaction time to sound is usually faster than reaction time to light. One possible interpretation of this result is that sound stimuli activate their receptors in the cochlea faster than light stimuli excite their corresponding receptors in retina (rods and cones) because relatively slow photochemical processes are involved in the latter. (Woodworth and Schlosberg) → Thus, differences in reaction time caused by manipulation of qualitative independent variable, type of stimuli (visual or auditory), are explained by the changes occurred in the associated quantitative dependent variable, time to excite the respective receptors. ➔ These variables can also be compared with each other to obtain meaningful results. → Quantitative variables can be of two types – (1) Continuous (2) Discrete. → Discrete variables have whole numbers as their values whereas continuous variables can even have values in between the whole numbers. → In the above number line, ‘x’ is a discrete variable and ‘a’ is continuous variable. For example, There are 4 apples in the basket. Here, the number of apples is a discrete variable Temperature is 35.5 degree C. Here, temperature is a continuous variable. → Quantitative variable are separable into continuous and discrete variables. → Majority of quantitative variables in psychology fall under continuous variables. Continuous variable:- ➔ “Variables that can take on an infinite number of possible values are called continuous variables.” → Continuous variables are numeric variables that have an infinite number of values between any two values. → A continuous variable is one which can take on infinitely many, uncountable values. For example, 1. Reaction-time is a continuous variable. It can be measured with any degree of exactness one chooses, limiting only to the capacity of the measuring instrument. In the beginning, because of the lack of instruments, reaction-time could only be measured in milliseconds. Now in current times, reaction-time can be measured in microseconds, a thousandfold reduction in the size of the measuring unit. 2. Another example of continuous variable is weight or height - a person doesn't have to be either 65 kg or 72 kg. They could be 65.8 or 72.666 kg. 3. Temperature is a continuous variable. It can be 50°, 50.1°, 50.11°, 50.111°, 50.1111°, …  Discrete Variable:- ➔ “Variables that can only take on a finite number of values are called "discrete variables.” → As a general rule, in psychology discrete variables are variables whose values are obtained by counting. → All qualitative variables are discrete. For example, 1. Number of children is an example of discrete variable. You cannot say that you have two and a half children. The number of children is a natural number (i.e. 1, 2, 3, 4, 5…) 1 No amount of advanced instrument can produce a value of, say, 2 2 children. 2. Suppose we flip a coin and count the number of heads. The number of heads could be any integer value between 0 and plus infinity. We could not, for example, get 2.5 heads. Therefore, the number of heads must be a discrete variable. 3. Numbers of subjects, number of trials, number of pages in the book, gender etc. are examples of discrete variable. ➔ One must be careful, though, in distinguishing between the basic nature of quantitative variable and the means by which it is measured. For example, Level of achievement in a college psychology course can be measured by the number of items correctly answered on a final examination. Clearly, the underlying variable, level of achievement in the course, is a continuous variable, even though it is measured by the number of items correctly answered on a final examination. In fact, the physical measurement of all continuous variables can be interpreted to involve counting.  Age, height, and weight, all of which are continuous variables, are often measured in terms of the number of months of age, the number of inches in height, and the number of pounds of weight. But unlike true discrete variables, the measurement of these variables can be refined almost endlessly so that, if one wished, their measurement could be in terms of the number of days of age, the number of hundredths of an inch in height, and the number of grams of weight. ➔ In summary, all variables in psychology may be classified as either qualitative or quantitative. → Qualitative variables are composed of categories that cannot be ordered with respect to magnitude. → Quantitative variables, in contrast, do lend themselves to ordering with respect to magnitude. Quantitative variables may be classified into those that can be measured with an arbitrary degree of fineness and those that cannot. → The former quantitative variables are called continuous variables; the latter, discrete variables. → It follows that type-E independent variables may be qualitative, continuous, or discrete variables, and the same holds true for type-S independent variables. → Dependent variables are sometimes qualitative, as often found in studies involving personality projective tests, though most often they are quantitative, in particular, continuous, variables. ❖ Characteristics of A Good Psychological Experiment: A good psychological experiment must possess the following characteristics: 1. Control: → Like any other scientific experiment, psychological experiments have the quality of control. → In a psychological experiment, attempts are made to conduct an experiment under controlled conditions by keeping the relevant variables under control or constant. → Various relevant variables such as subject RVs, sequence RVs, situational RVs, Experimenter RVs and apparatus RVs can influence the dependent variable and the results are contaminated. → Lack of control over the extraneous factors may contaminate the findings of the study. Only independent variables are allowed to vary. → For the purpose of control over extraneous variables, arrangements are made in the design of the experiment. For example, An experimenter may be interested in knowing the effects of reward on learning. In such an experiment, the experimenter tries to keep under control some of the important factors, like age, gender, intelligence, etc., of the subjects as these variables are likely to affect the findings of the experiment, because there is ample chance that the performance of the subject is affected by these extraneous factors. → Various techniques of control are used in the experiment, such as single- blind, double blind technique, matching, randomization and counterbalancing. 2. Manipulation: → “In an experiment, when any change is brought about deliberately, with a specific objective or purpose in the independent variable, it is known as manipulation. → In a good scientific experiment, the experimenter can manipulate the independent variable. → The manipulation of independent variable is done by introducing it to the treatment at least at two levels, and their corresponding effects on the dependent variable are observed. → The manipulation is done under control conditions.  For example, In the experiment to study the effect of noise on the reading ability, noise is the experimental variable which can be manipulated by the experimenter either by increasing or decreasing its intensity, or with the help of absence or presence method. In any experiment, when the intensity of the independent variable is increased or decreased, it is referred to as the value of that variable. 3. Repetition: → Repetition is also an important feature of a good experiment. → Repetition means the experimenter should be in a position to repeat the whole or part of the experiment time and again so that consistency of the findings can be ensured. → When an experimenter obtains similar results on repetition of the experiment, the results are considered as reliable; inconsistencies in the results obtained on various occasions indicate weaknesses of the experiment. 4. Objectivity: → Objectivity means neutrality. → A good psychological experiment must be free from all sorts of biases. → There are various sources of biasness. Biasness can be from the experimenter side, as well as from the subject side. → Biasness of any form tends to damage the results of the experiment. → While conducting an experiment the experimenter, as well as the subject must be neutral, objective and honest in their approaches. → Any kind of subjectivity, prejudice, attitude, etc., may ruin the purpose of an experiment. 5. Experimental design: → In a psychological experiment, two types of experimenter design are used. (1) Single group design (2) Separate group design → A good psychological experiment follows the format of either a single group design or a separate group design. → An experimental design is a blueprint of the procedures that enables the experimenter to test the hypothesis. → Selection of a proper experimental design ensures control over the experiment. For example, In a separate group design, experimenter needs to decide which technique is to be used to divide the subjects into the experimental group and control group. Whether to use the technique of randomization or matching. In the single group design, there is a possibility of sequence relevant variable affecting the results of the experiment. Then the experimenter needs to decide, would the technique of counterbalancing be used or not? Which type of counterbalancing technique would be used? Complete or partial? → Thus, a proper experimental design provides a guideline and control over the experiment.  Unit-2: Control Techniques and Experimental Designs  Types of control techniques: ❖ Introduction: → In psychology, various scientific methods such as observation, questionnaire, interview, survey methods, psychological tests and experiments are used to study behaviour of humans and animals. → Of all these scientific methods, the experimental method is considered to be the best. → The reliability and validity of the experimental result depends on the controls that are used in the experiment. → This helps in establishing the cause and effect relationship. On the other hand, lack of control results in experimental error. → Mostly, it is the variable related to the physical environment, experimenter, apparatus, and subjects that are likely to affect the dependent variable. Therefore, the experimenter should control these variables. → In any experiment, variables related to the physical environments such as temperature, lighting, amount of humidity in the atmosphere, noise, movement of people etc need to be controlled or results can be affected. To control these variables, the experimenter may use air-conditioned rooms, fans, sound proof rooms, artificial lights, one way screen etc. → Similarly, the apparatus used can also result in experimental error. For this, the experimenter must first and foremost check whether it is proper working condition or not. → Experimenter variables like facial expressions, voice tone, expectations of the experimenter can affect the result. In such an experimental situation, “Double blind technique” is an ideal method. → If the experiment is too long or has to be conducted in two sessions and on the same subjects, then intra-subject relevant variables such as hunger, fatigue, boredom etc. needs to be controlled. ❖ Techniques of control: 1. Single blind, Double blind 2. Matching 3. Randomization 4. Counterbalancing (1). Single blind, Double blind: (a) Single blind technique: → If the subjects are aware of the presence-absence of the independent variable in the experimental group and control group, then this is likely to affect the results. For example, Effect of Vitamin A on night blindness. The subjects of experimental group are given Vitamin A tablet and subjects of control group are not given any Vitamin A. The subjects of the experimental group may feel they have been given some special tabs and control group subjects may feel left out. This awareness is likely to affect the behaviour (dependent variable). Therefore, subjects of control group should be given similar tabs, but without medical value, and of the same size, shape and colour, which are called placebo’s → Thus, the experimenter knows which group of subjects are given Vitamin tabs and which group is given placebo. The subjects are not aware of this, and this is referred to as Single Blind Technique. (b) Double Blind Technique: → The use of Single Blind Technique may result in lack of control. → Here the subjects are unaware about the administration of the independent variable but the experimenter is aware of this. As a result, the experimenter may give different reactions to the responses given by the subjects of the both group. The facial expressions, verbal remarks or expectations of the experimenter may affect the performance of the subject and therefore affect the results. To control this effect, Double Blind Technique is used. → In this technique, experiments and subject both are unaware about the administration of the independent variable. → Here the third person who is not familiar gives the tablets to the two groups. Even the experimenter does not which group is given (Vitamin A) and which group is given Placebo. → This is done by keeping Vitamin A tabs in one bottle and Placebos in the other. → The details of the Placebos and Vitamin A tablets are written on a chit that is glued at the bottom of the two bottles.  → The experimenter rotates the bottles with his eyes closed not knowing which contains Vitamin A and which Placebos. → Thereafter the third person gives the tablets from one bottle to one group and tablets from the other bottle to the second group. → In this way, the experimenter does not know which group gets the tablets and which group gets the placebos. → Thus, this method is referred to as Double Blind Technique. (2). Matching: → When the experiment is conducted with the help of the separate group design, i.e. the experimental group and the control group, then both groups have to be alike with regards to all the relevant variables. Except the experimental variable. → The inter subject relevant variable should be same for both the groups. Example-1: In the experiment on effects of Vitamin A on the night vision, besides the independent variable i.e. Vitamin A, variables such as age, gender, diet, general state of mental health of the subjects are likely to affect the night vision. Therefore, both the groups have to be alike in these variables. If, for example, there are young subjects in the experimental groups and older subjects in the control group, then one can argue that difference in night vision is due to age and not vitamin A. So both the groups have to be same on the variable of age. For this, the technique of matching may be used, by which the number of subjects belonging to different ages are in equal number in both the groups. Example-2: Similarly, if 20 subjects are taken from MBA and divided into two groups of 10 each, then it is likely that all of their ages will not be the same. There may be four students aged 22 years, and others may be 20 tears. If all the four students aged 23 years are present in one group, then it will affect the results. Hence the technique of matching is used in which two students each aged 23 are placed in both the groups.  Even in the case of gender, the experimenter can have all the male subjects or all the female subjects in both the groups and if there are not enough subjects of one gender and experimenter is forced to use both male and female gender, here the effect of gender on dependent variable can be controlled by matching the two groups on the variable of gender. Example: If there 40 males and30 females, then there should be 20 males and 15 females in each group. → Limitation: The limitation of this technique is that it can match only one or two relevant variables. It is not possible to use all the relevant variable. → So the variables that are likely to have maximum effect on the result of the experiment should be matched. → For the other variables, the technique of randomization is used. (3). Randomization: → This is a technique which is based on probability or chance. → In this technique, each individual gets a unique chance of being selected. For example, The prizes won by the lottery system, tossing of a coin are examples of randomization technique. For instance, if the Gujarat housing board receives applications from 500 candidates of the sale of 100 flats, then the name of the each applicant is written on a chit, out of 500 chits, 100 chits are picked randomly. This type of selection is known as the chance selection. Here each candidate gets an equal chance to buy the flat. → In an experiment, the technique of randomization is used for the selection of subjects or for the presentation of the stimulus or the independent variable. → Here, the effect of relevant variable is not controlled or removed completely, but the effect is randomly distributed. For example, The experimenter assigns the number 1-2, 1-2…to all the subjects Then all the subjects belonging to number 1 would form group 1, i.e. the experimenter group and all those assigned number 2 will form control group.  In this way, the relevant variables, such as age, intelligence level, and educational qualification of the subjects are randomly distributed. → When counterbalancing technique proves to be a failure in controlling the effect of relevant variables, then the technique of randomization is useful. → The limitation of this technique is that it is not effective for a large group. → Randomization removes the effects of constant error. (4). Counterbalancing: → The effect of relevant variables can be controlled in two ways, i.e. by elimination and equal distribution. For example, If exams are held in the month of May, then the temperature is likely to affect the results of the subjects answering the exam. To eliminate the effect of temperature, one can put ACs inall the college, which is not possible. So the other alternative is to conduct al the exams in the month of May. In this way, the effects of temperature will get equally distributed on all the results. → The technique of counterbalancing is used to nullify or to equally distribute the effect of the order of the sessions in the experiment. → Many a times only one session may be conducted, but the stimulus may be presented more than once. → In such cases, the order of sequence of the sessions or sequence of the presentation of the stimulus is likely to affect the dependent variable. Hence the technique of counterbalancing is used, which can be defined as follows: “When the effect arising as a result of the order in which the stimulus is presented or the sequence of the sessions that are conducted is distributed equally, then it is referred to as counterbalancing” (a) Partial counterbalancing: In the experiment on fluctuation of attention, method of partial counterbalancing is used. Position 1 2 3 Sessions A B C C B A  Here, the experiment is conducted keeping the intra-subject design, i.e. for all the six sessions, one subject is used for the experiment. (b) Complete counterbalancing In the example of fluctuation of attention complete counterbalancing can also be achieved Position 1 2 3 Sessions A B C – S1 C B A – S2 A C B – S3 C A B – S4 B C A – S5 B A C – S6 For complete counter balancing to be achieved, which is possible with 18 sessions in this example, inter-subjective design has to be used. i.e. total six subjects are required to do the experiment. Here A-B-C sessions occur in each of the three positions equal number of times. ➔ The following formula is used to determine the number of sessions for complete counterbalancing. Number of sessions = n x n! = 3 x (3 x 2 x 1) = 18 ➔ If complete counterbalancing is used, then it takes a very long time do the experiment. Therefore, partial counterbalancing is used most of the time.  Experimental design: ❖ Introduction: → In psychology, various scientific methods such as observation, questionnaire, interview, survey methods, psychological tests and experiments are used to study behaviour of humans and animals. → Of all these scientific methods, the experimental method is considered to be the best. → In the experiment, different control techniques are used. As a result true effects of independent variable can be studied, we can get more accurate information, and we can establish cause and effect relationship. → Anderson has stated that the experimental method is the perfect example of the scientific method. → At present, this method is widely used in various fields of psychology. → The extent of accurate information that can be obtained depends on the experimental design. ❖ Experimental design Definitions: “A design tells us what observations to make, how to make them and how to analyze the quantitative representations of the observations.” - Kerlinger “Experimental design is the blue print of the procedures that enables the researchers to test the hypothesis by reaching valid conclusions about the dependent variable.” - Best and Kahn Explanation: → The planning done by the researcher, keeping in mind the purpose of the experiment and thinking about the specific questions with regards to how to conduct the experiment is known as experimental design. The experimenter keeps in mind the following points while planning the experimental design. 1. Whether to use a single group or separate groups. 2. If the experiment is to be performed with the help of the experimental group and control group method (separate group  design), then which technique to be used to divide the subjects into two groups. 3. How would the difference variables be controlled? Which techniques of control would be used? 4. How many values of the independent variable would be used? How many sessions would be conducted? How would the independent variable be manipulated, using the E-type or S-type? ❖ Types of experimental design: → There are at least two values of an independent variable (experimental variable). Thus, two conditions would arise from this: Experimental condition and control condition. → Based on whether to use one or two groups for the two conditions, there are two types of experimental designs. 1. Single group design 2. Separate group design 1. Single group design: ➔ In this experimental design, different conditions or different sessions in an experiment are conducted on the same subjects. → As a result, inter-subject relevant variables such as age, gender, intelligence, and educational qualifications of the subjects need not be controlled. But intra-subject relevant variables such as hunger, fatigue, boredom etc needs to be controlled. For the control of intra-S-relevant variable counterbalancing technique is used. → This design is also referred to as ‘Within subjects experimental design’. a) Before-After Technique: ➔ Many a times, the behaviour of the subjects is tested before administrating the independent variable. And then it is again measured after administrating the independent variable. This technique is called ‘Before- After Technique’ For example, → Suppose the experimenter wants to study the effects of tranquilizers on the memory span. → If the before-after technique is used, then the memory effect of the subject has to be measured before giving the tranquilizer, and again after giving the tranquilizers.  → If there is a difference in the memory span of the subject that was measured before and after, then it is therefore of the tranquilizer. Experimental design: 1. Prior selection of the group Yes 2. Before measurement Yes (Y1) 3. Administration of the experimental variable Yes (X) 4. Presence of the uncontrolled variable Yes 5. After measurement Yes (Y2) D = Y2 – Y1 2. Separate group design: ➔ The nature of some experiments is such that two groups are required to conduct the experiment, especially with regarding to problems in which the effect of some type of drug on behaviour and development has to be studied. → Though it may be possible to conduct, such as an experiment on one group or one subject, yet for the purpose of control, the experiment is conducted on two groups. This type of experimental design is known as Separate Group Design. ➔ Many a times, the effect of experimental variable is examined by using the presence-absence method. → If the experiment is to be conducted by this method, then two conditions have to be applied: i. Experimental variable is administrated ii. Experimental variable is not administrated → These two conditions are known as Experimental condition and Control condition respectively. → When the experiment is conducted on two groups, then the subjects are different in both the groups, i.e., Experimental group (presence of experimental variable) has one set of subjects and Control group (absence of experimental variable) has another set of subjects. → Both these groups have to be alike with regards to all those relevant variables, which are likely to affect the Dependent variable. → The difference in both the groups should be in terms of the presence- absence of experimental variable. → In this way, both the groups are alike as far as possible and the different in terms of experimental variable. ➔ On the basis of whether the dependent variable is measured once or twice in the separate group design, there are two sub-types: a) Before-After Technique: → In the before-after technique, the behaviour of the subjects is tested before administrating the independent variable. And then it is again measured after administrating the independent variable. → The behaviour of the subjects is tested twice, once before administrating the independent variable and once after administrating the independent variable. Example, → Suppose the experimenter is interested in examining whether or not Vitamin A has any effect on night vision. → If an experiment has to be conducted on this, then two groups are required. This experiment cannot be conducted on a single group. → For this, the subjects are divided into two groups after having been given the test of night vision. The night vision of the subjects in both groups should be same. → Both the groups are as much alike as practically possible in all those aspects that are likely to affect the night vision such as age, sex, health, occupation, die etc. → After, experimental group subjects were given a high dose of Vitamin A and the control group is given normal doses of Vitamin A. → If at the end of the experiment, the experimental group shows significantly superior performance of night vision compared to control group, then this improvement can be attributed to high dose of Vitamin A. Experimental design Experimental Control group group 1. Prior selection of the group Yes Yes 2. Before measurement Yes (Y1) Yes (Y1’) 3. Administration of the experimental variable Yes (X) No 4. Presence of the uncontrolled variable Yes Yes 5. After measurement Yes (Y2) Yes (Y2’) d d’ d = Y2 – Y1 d’ = Y2’ – Y1’ D = d – d’ b) Only-After Technique: → In the only after technique, dependent variable is not measured in any of the group in the beginning. → The behaviour of the subjects is tested only once, after administrating the independent (experimental) variable and not before. Example, → Hovland and his associates conducted a study using this type of experimental design. → The purpose of this experiment was to examine the effect of movies on the morale of the soldiers. → The experiment was conducted on soldiers who had been selected from British Army. → Two groups were selected that were alike related to variables such as IQ (measured by AGCT intelligence test), age, area of residence, experience of working in the army etc. → After that, the experimental group was shown the movie “The Battle of Britain”, while no movie was shown to control group. → Then both the groups were given a questionnaire and their morale was measured. → After comparing the results of both the groups, a conclusion was drawn. Experimental design Experimental Control group group 1. Prior selection of the group Yes Yes 2. Before measurement No No 3. Administration of the experimental variable Yes (X) No 4. Presence of the uncontrolled variable Yes Yes 5. After measurement Yes (Y1) Yes (Y1’) D = Y1 – Y1’  Unit-3: Classical psychophysics  Basic concepts of psychophysics ❖ Introduction: ➔ Human life at all times is involved in the perception of the external world that consists of various stimuli. → These stimuli stimulate our senses resulting in sensory processes such as seeing, hearing, smelling, tasting and touching. → When we react or respond to these stimuli, it is referred to as behaviour in physical terms. → We may react to the stimuli in terms of accepting, or rejecting certain stimuli. → The whole human life and behaviour is based upon these processes. → All these phenomena indicate that on one hand there are physical dimensions of the stimuli and on the other hand is the behaviour or the experience that is produced by the stimulus. → Thus, one aspect is physical and the other is psychological. → The study of the relationship between these two aspects is the subject matter of psychophysics. ➔ One needs to keep in mind that every stimulus or object is mutli- dimensional in nature i.e., it has several qualities or characteristics. → It is the physical dimension of the stimuli that leads to the experience in the form of behaviour. → The relationship of the sensory experiences and the stimulus had earlier been discussed in philosophy. - This question was discussed in terms of the relationship between the mind and the body. - Questions such as Are the two different or one? Does the mind influence the body or vice versa? → Psychology took up the task of scientifically studying the relation between mind and body, resulting in the development of psychophysics. → Thus, in the mid 19th century, the German physicist Gustav Fechner evolved a general law which he referred to as the psychophysical law and published the same in 1860 under the title, “Elements of Psychophysics”. - In which he explained the various methods of determining the relationship between the mind and the body.  Definitions: “The study of the functional relationship between the mind and the body.” -Gustav Fechner “Psychophysics is a branch of psychology that studies the relationship between the physical stimulus and the sensory reaction (psychological experience)” -American Heritage Dictionary “The oldest branch of experimental psychology concerned with the relationship between the physical magnitude of sensations and physical intensity of the stimuli that produce them.” -Oxford dictionary of physical science ❖ Basic concepts of psychophysics: 1. Sensitivity: → We respond to the physical world with our sense organs. → It is the receptors in the sense organs that respond to the environmental stimuli. → The organism is equipped with a number of receptor organs specialized to respond to particular energy changes in the environment. → The receptors of the eye are responsive to light i.e., the rods and cones in the retina are responsive to a certain range of wavelengths. In the same way, the receptors (hair cells) in the ear are responsive to the sound waves within a certain range of frequency and so on. → Thus, the action of these receptor organs, constitutes an important link in the chain of responses which occurs between the application of the stimulus and the subject’s responses. “The capacity of the receptor organs to respond to a particular physical energy or stimulation is known as sensitivity.” → As peer the experimental measurements there are two types of sensitivity: (a) Absolute (b) Differential a) Absolute Sensitivity: It refers to the minimum and maximum levels required for the organ to be stimulated. → In every type of sensation, the maximum and minimum limit of sensitivity of each sensory organ already exists. → The stimulus too has the intensity which is less than the minimum limit and the intensity which is more than the maximum limit that would fail in arousing the sensation. → For instance, with regards to auditory pitch, the range of auditory sensation per second is from a minimum of 20 vibrations, to a maximum of 22,000 vibrations. → We cannot hear the sound having less than 20 vibrations or more than 22,000 vibrations. → In the same way the wavelength of light measuring less than 360 nm ad more than 760 nm are not visible to the human eye. (millimicron) b) Differential Sensitivity: Differential sensitivity refers to the minimum intensity between two stimuli required to notice the difference. → It defines the organisms’ capacity to respond difference between stimuli. → It is related to the minimum difference between stimuli needed for reliable discrimination. → If the difference between the two stimuli is very less, the none can not discriminate. For example, If a 100-watt light is on in a room and a night lamp is also switched on, then there is an increase in the intensity of the light. But, the individual cannot notice this increase in the intensity of light, as the increase is very little. → Thus, the increase or decrease in the stimulus should be such that the difference between the two stimuli is noticeable. 2. Threshold: → All the stimuli do not evoke a response in an organism. → Some stimuli are so weak that they always fail to evoke an effective response in the organism. Other stimuli are so intense that they always produce a reaction. → The line separating these two kinds of stimuli, those that never produce response and those which always produce a response can never be sharply drawn. → This line is known as threshold. → The Latin word for threshold is ‘Limen” which essentially means a boundary separating the stimuli that elicit response from the stimuli that elicit a different response. For example, If a very light weight is placed gently on the subject’s palm and if the weight is below a certain value, he says, “No, I don’t feel it.” But if the weight is increased trial by trial, it eventually reaches a value, where he says “Yes, now I feel it.” Thus, this value of the weight, has produced a response, therefore this is threshold. a) Absolute Threshold “The minimum intensity or value of the stimulus that is necessary to arouse sensation is known as absolute threshold” For example, We wish to measure the subject’s absolute sensitivity to sound. We begin with a very weak value of the sound, which the subject fails to hear on repeated trials. We then increase the intensity of thee sound. At this second level, the subject may sometimes hear the sound and sometimes fail to hear it. This happens due to internal and external factors. When we increase the intensity of stimulation to a level at which the subject never fails to hear the sound. This shows that there is no one stimulus value that produces a response. It varies from trial to trial. → For the purpose of measurement, one needs to measure absolute threshold repeatedly and an average needs to be found i.e., a single value of the stimulus has to be found. → In this context, absolute threshold is a statistical concept. “Absolute threshold is that stimulus value which yields a response 50% of the time i.e. on half the test trials.” - Postman and Egan → Thus, it is essential to understand that absolute threshold is not a fixed point on the stimulus scale, but it is variable. → Absolute threshold is also known as Absolute Limen, in short as AL. → The range of intensity of the stimulus that evokes the sensation is referred to as the range of sensitivity. → Stimulus sensitivity beyond this range, cannot evoke a sensation.  For example, The range of visual sensitivity is between 360 nm and 760 nm. The wavelengths, less than 360 nm’s and more than 760 nm’s are not visible to the human eye. → This indicates that absolute threshold has two limits, the maximum limit and the minimum limit. → The minimum limit is referred to as the lower threshold and the maximum threshold is referred to as the upper threshold. b) Differential Threshold: “The minimum amount of difference needed between two stimuli so that they can be recognized as different, is known as differential threshold.” → One of the characteristics of the stimulus is delectability. → This is the other characteristic of the stimulus which is referred to as discriminability. → What is the minimum or the smallest amount of difference required to tell, that the two stimuli are different? This small amount of stimulus difference that is noticeable is called differential threshold. For example, If we present a subject with two tones differing very little in intensity, then he will fail to report the difference between the intensity of the two sounds, then on half of the trials the subject will be able to judge the difference between the 2 sounds. This point of difference is the differential threshold of the subject. It is also known as, Just Noticeable Difference (JND). “That stimulus difference that gives rise to the judgement of difference 50% of the times is called differential threshold.” -Postman and Egan ➔ Thus, absolute threshold deals with one stimulus only and it passes from ‘no experience’ to ‘some experience’ → Similarly, differential threshold deals with two stimuli and it passes from ‘no difference to ‘some difference’. → There are many variations in the limits of these two thresholds. This may be due to internal or the external factors. → The values of the absolute and differential threshold are measured with the help of psychophysics. 3. Point of Subjective Equality (PSE) ➔ One fundamental category of relational judgment is sameness vs. difference. → Sometimes stimuli whose physical characteristics are identical may give rise to a judgment of different, and stimuli which differ physically may be judged same. → Thus, there is no necessary correspondence between physical quality of stimuli and judgments of sameness, nor is there a necessary correspondence between physical differences and judgment of different. For example, In the experiment on the method of average error, where the Muller-Lyer figure has been used, the subject is presented with 2 lines. One is the standard line and the other is the variable line. The standard line is kept constant while the length of the variable line can be increased or decreased. The subject’s task is to adjust the variable line by increasing or decreasing it in length to make it appear equal to the standard line. The point where he finds the variable line to be equal to the standard line is called the point of subjective equality. The length of the standard line is 160 mm and if the variable line adjusted at 145 mm then the subject’s PSE is 145 mm. This means, that though the length of the variable line is 15mm less than the length of the standard line but the subject finds the variable line to be equal to the standard line at that point. Thus, the point of subjective equality means, that the value of the variable stimulus is equal to the value of the standard stimulus. 4. Errors: Error in the psychological experiments does not imply that one judgment is right and the others wrong. Error here simply refers to the fluctuation in judgment. There are two types of experimental errors (1) Random error or variable error (2) Constant error  (1) Random error or variable error: “Due to lack of control when the effect of variables other than the IV on the DV occurs at times and doesn’t occur at other times is referred to as Random error.” → This type of error doesn’t occur in the same direction, i.e. sometimes it may have appositive effect and sometimes it may have negative effects. For example: When the experiment on the effect of noise on learning ability, the experimenter group is sometimes given learning material in the morning, while the control group is sometimes given the learning material in the evening. As a result, there may be positive effect at times and there may be negative effect at other times. (2) Constant error: “Due to the lack of control when the effect of variables other than the IV on the DV occurs in the session or in all the trials and is continuous and in the same direction, then it is known as constant error.” → The important characteristic of this type of error is that its effect is continuous in the entire experiment and it may be positive or negative, thereby occurring in the same direction. For example, In the experiment on maze learning, if the piece of cloth used to blindfold the subject is tied loosely and the subject is able to see the maze pattern, then it is likely that he will make less errors in all the trials. This results in positive effects in all the trials. On the other hand, if the piece of cloth used to blindfold the subject is dirty and it stinks, then the subject is likely to experience discomfort. As a result, he may make more errors in all the trials. This results in negative effect. There are two types of constant error (a) Time error (b) Space error  (a) Time error: → If two identical stimuli, A and b, are presented inn succession, we find, for different time intervals between A and B, systematic tendencies to underestimate or overestimate the second stimulus, B. → In the case of judgment on loudness, for example, if two equally intense tones are separated from each other by an interval of 1⁄2 second, the second tone will usually be judged as less loud than the first. → If the two tones are separated by a longer time interval say, 6 seconds, the second will usually be judged as louder than the first. → This tendency to underestimate or overestimate the second of two successive stimuli constitutes the time error. → The time error has been found to occur with a variety of other stimulus material, such as judgments of weight and the extent. (b) Space error: → Judgments may be influenced systematically by the special position of the stimuli, whether they are, for instance, on the right or left of the subject.  Methods of psychophysics: ❖ Definition: “The study of the functional relationship between the mind and the body.” -Gustav Fechner “Psychophysics is a branch of psychology that studies the relationship between the physical stimulus and the sensory reaction (psychological experience)” -American Heritage Dictionary “The oldest branch of experimental psychology concerned with the relationship between the physical magnitude of sensations and physical intensity of the stimuli that produce them.” -Oxford dictionary of physical science ❖ Introduction: → The main purpose of experimental psychology is to find a lawful relationship between the changes in the physical stimulus and resultant variations in our psychological experiences. → This leads to the development of psychophysics. → The main purpose of psychophysics is to determine the nature of interactional relationship between the physical stimulus and the sensational experience, and to present this relationship in the form of law. → For this psychophysical methods have been developed. → George. H. Zimny has specified the importance of psychophysical method as follows: “The psychophysical methods provide powerful, scientific tools for study of the organism’s response to stimuli.” → The psychophysical methods are widely used in the theoretical as well as applied fields of psychology; these methods have contributed a lot in the field of experimental psychology. ❖ Methods of psychophysics: I. Method of minimal changes (Method of limits) II. Method of constant stimuli III. Method of average error IV. Method of ranking V. Method of paired comparison. I. Method of minimal change (Method of limits). → This method is used to determine both absolute and differential threshold. → When we determine the threshold by this method, we make small amounts of changes or minimum possible changes in the intensity of the stimulus. So, it is known as the method of minimal changes. → With the help of this method the limits of sensation are also determined so, it is also referred to as the method of limits. (a) Basic procedure to determine absolute threshold (or absolute limen (AL) ➔ There are two types of absolute thresholds, lower threshold and upper threshold. → The procedure to determine both these thresholds is the same. → 10-30 stimulus values are required to determine absolute threshold. → 50% of the stimulus values are less than the average or normal levels of sensations. → 50% of the stimulus values are above the average or normal level of sensation. → The average stimulus value is that value which is fixed for each sensation. ➔ For example, → Suppose we want to determine the subject’s absolute threshold for auditory sensation. → For this we select 11 stimulus values ranging from 20-30 vibrations with a difference of one vibration between each value. → Thus, each stimulus value differs from the previous one by a small amount. → These stimulus values are then presented to the subject. → The subject is given following instructions, “I will present a sound to you. If you can hear the sound then give the response ‘yes’ (+) and if you are unable to her then you give the response ‘no’ (–). ➔ In the determination of absolute threshold it is customary to employ two kinds of series, ascending and descending series. → So, the stimulus values presented to the subject are ascending and descending series. → In the ascending series we start with the stimulus values that are less of less intensity, such that the subject will not be able to hear, as a result, his response would be ‘no’.  ➔ Since this is the method of minimal changes, the changes in the intensity of the stimulus occur by a small physical amount. → So, in the beginning, in almost all the trials the subject’s response would be ‘no’. → Then at a certain level due to small amount of changes in the intensity, the subject would finally report the presence of the sound and so his response would be ‘yes’. → Thus, in the ascending series, after the point where the subject gives ‘yes’ responses, further presentation of the stimulus is stopped. → In the descending series, we start with the stimulus values that would be significantly of greater intensity than the average level of sensation. And the subject’s response would be ‘yes’ here on each successive trial. → The stimulus values would keep decreasing in small amounts. In the beginning, the subject’s response would be ‘yes’ in almost all the trials. Then at a certain level, the subject would no longer be able to hear the sound, so his response would be ‘no’. → Thus, in the descending series, after the point where the subject gives the ‘no’ response, the further presentation of the stimulus value is stopped. → In this way, one ‘trial’ is presented to the subject which consists of one ascending and one descending series. → In this manner, a minimum of 5-10 trials are given to the subject. → In each series absolute threshold is obtained. → The ‘yes’ and ‘no’ responses are presented in the table as + and – respectively. ❖ *Illustration: The hypothetical results of a subject’s responses are as under. Stimulus Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Sr. no value A D A D A D A D A D (db) 1 30 + 2 29 + + 3 28 + + + 4 27 + + + + 5 26 - + + + + + + 6 25 + + + - - - + 7 24 + - - + - - - - 8 23 - - - - 9 22 - - - 10 21 - - 11 20 - Threshold (Limen) 23.5 26.5 24.5 24.5 23.5 24.5 25.5 25.5 25.5 24.5  𝑬𝑿 Absolute threshold = 𝑵 23.5+26.5+⋯+24.5 = 10 248 = 10 = 24.8 ∴ Absolute threshold = 24.8 db ❖ Calculation: ➔ For the ascending series, the stimulus values are of less intensity so the response of the subject would be ‘no’. → The values increase gradually and at a certain point the response changes to ‘yes’. → Here the response is yes for 22 vibrations in the first trial. → So, the stimulus value that lies between the stimulus value for the first ‘yes’ response and the stimulus value for the last ‘no’ response is known as absolute threshold. ➔ Similarly, for the descending series, the midpoint that lies between the stimulus value for the first ‘no’ response and the stimulus value for last ‘yes’ response is referred to as the absolute threshold. ➔ In the above table, 5 trials have been presented, in each trial there are two series, i.e. ascending and descending series. → In each series we get one threshold value. → Then the sum of all the threshold value is found, which is 202. → This is then divided by the number of series which is 10. Therefore we get 20.2 as the value of absolute threshold. ❖ Errors: (1) Error of habituation: → The stimuli are presented in the ascending and descending series. → As a result, the subject gives one particular type of response till the point where the stimulus value produces sensation, i.e., He is likely to give same kind of response for a number of stimulus values. → In the ascending series, the stimulus values are of less intensity in the beginning. As a result the subject’s response is ‘no’. Similarly, in the  descending series, the stimulus values are of greater intensity in the beginning and so the subject’s response is ‘yes’. → In this way, the subject gets into the habit of giving ‘yes’ responses for descending series and ‘no’ response for ascending series. → Because of this habit, at times even if the sensation occurs, the subject would give ‘no’ response and in the descending series, because of the habit of giving ‘yes’ responses, at times if sensation does not occur he would still give the ‘yes’ response. → Thus, when there is an error in the judgment because of the habit of giving a particular response, it is referred to as habit error. (2) Error of expectation: → In this case, a change in the stimulus values take places place in a particular direction and the subject may become familiar with this fact. → During the process of determining the threshold, the subject gets an idea that, there may be an increase or decrease in the stimulus values presented to him. → Thus, there arises an expectation in the subject regarding the change in the stimuli value. → Though there may no change in the sensation, but due to the expectation of a change, there is likely to be a change in the subject’s response. → Thus, when there is an error in the judgment due to the expectation, then it is known as the error of expectation. ➔ To overcome both these types of error, the stimuli are presented once in the ascending and once in the descending order during the entire procedure. → Each time, the starting point for the ascending and descending series should be changed. (b) Basic procedure to determine differential threshold (or differential limen (DL): ➔ Two types of stimuli are required to determine differential threshold by the method of minimal changes. (1) Standard Stimuli – The value of the standard stimili remains constant throuout the whole experiment. (2) Variable Stimuli – The value of the variable stimuli keeps changing throughout the whole experiment. ➔ 5 -10 stimulus values of grater intensity than the standard stimulusans 5 - 10 stimulus values of that are of a lesser intensity than the standard stimulus are selscted. These are called the variable stimuli. → For example, the standard stimulus is a light intensity of 100 watts and the variable stimuli ranging from 50 – 100 watts of light with the interval of 10 watts are selected. → Hence, the standard stimulus and the variable stimulus are presented in a pair and they are presented in succession. → The subject is given the following instructions, “You have to tell me each time whether the second stimulus is less, equal or more compared to the first stimulus. ➔ The stimulus values are presented in the ascending and descending series. → For the ascending series, in the beginning, the values of the variable stimuli are considerably smaller than the standard stimulus. As a result, his responses would be ‘less’. Then the values of the variable stimuli will keep increasing slowly, until the point where the subject’