Experimental Psychology - Theory PDF

Experimental Psychology - Theory Unit 1 - Psychophysics Book Reference - Experimental Psychology - an Introduction by L. Postman and J. Egan. Brief on Experimental Psychology Experimental Psychology examines the re...

Experimental Psychology - Theory Unit 1 - Psychophysics Book Reference - Experimental Psychology - an Introduction by L. Postman and J. Egan. Brief on Experimental Psychology Experimental Psychology examines the relationships between human behaviour and the mind. It is centered on fact based, scientific research and experimentation. Experimental Scientists manipulate research variables in order to discover relationships between cognition and behaviour. They explore basic concepts such as memory, motivation, emotion, learning. Mostly conducted in laboratories in controlled environment. Applying Experimental methods to Psychological study and the processes that underlie it. Studies external as well as internal processes of different stages of human development. Experimental Psychology as Method - Experimental psychoogy attempts to apply the rules of scientific method to its subjec matter: to discover the lawful relationships that govern behavior. Whether the behavior be as simple as pressing a telegraph key or as complex as painting a picture, experimental psychologists search for the determinants of these actions in the behaving organism and its environment. Variables - Behaviour occurs under which conditions or the antecendents of the behaviour. We aim to understand the determinants of behavior by discovering the relations among clearly defined variables. a variable is a characteristic or attribute that can take on a number of values. Thus, the number of items that an individual solves on a particular test is a variable. the size o our pupil in different degrees of illumination, these and many others are examples of variables which experimental psychology studies. The experimenter distinguishes between two basic types of variables: independent and dependent. The phenomena which we wish to explain and predict are the dependent variables. These variables are called dependent because they depend upon the occurrence ot particular antecedent conditions. The antecedent conditions that the experimenter manipulates freely are called the independent variables. In the above example - we may choose intensity of illumination as our independent variable, manipulating it freely, and measure the pupillary area of the eye as the dependent variable. Stimuli and Responses as Variables - The variables of experimental psychology are stimuli and responses: events in the environment and the organism’s responses to them. Any stimulus is a selected aspect of the total environmental situation, and any response is a selected characteristic of the total complex of behavior occurring at any moment. Experimental Control of Variables - study the relation between a dependent variable y, and an independent variable, x: the number of trials required to learn a list of words as determined by the length of the list. There might also be other factors that might influence the response such as difficulty of the words(z), time interval between trials (w), speed of presentation (u) - To only study the influence of x on y it is important to keep the other factors constant in all trials so they do not have an effect on the response. In our example, we would prepare lists of different length (variable x) but of equal difficulty (variable z), and present these lists at the same rate (variable u ), and with a constant time interval between successive trials (variable w). Thus, we would determine variations in y as a function of variations in x with z, u, and w held constant. The variables z, u, and w, which are constant during a particular experiment but which may be varied from experiment to experiment, are called parameters. The use of several subjects for each value of the independent variable, x, serves to minimize the effects of individual differences. By using several different subjects under each condition, we hope to average out the effects of such individual differences. Experimental and Control Groups. - An experimental group consists of participants exposed to a particular manipulation of the independent variable. These are the participants who receive the treatment of interest. Researchers will compare the responses of the experimental group to those of a control group to see if the independent variable impacted the participants.A control group consists of participants who do not receive any experimental treatment. The control participants serve as a comparison group.The control group is matched as closely as possible to the experimental group, including age, gender, social class, ethnicity, etc. The difference between the control and experimental groups is that the control group is not exposed to the independent variable, which is thought to be the cause of the behavior being investigated. Statistical Significance of Experimental Results - In a well designed experiment it is not necessary that the uncontrolled factors will be averaged out and these may be responsible for observed changes in dependent variable. Statistical techniques play an important role in giving an estimate how probable it is that the observed changes in y are due merely to the random action of uncontrolled variables. If that probability is very low, say, one in a hundred, we conclude that it is the independent variable, x, which is responsible for the change in y. Description and Explanation - systematic and unbiased account of the observed characteristics of behaviors. When we have explained a behavior, we also understand what causes it to occur. Explanation includes knowledge of the conditions that reliably reproduce the occurrence of a behavior. Most Important areas covered by experimental psychology include Psycho-physics, animal psychology, clinical psychology, psych of individual differences, child psychology etc. Includes Components like Variables, Stimuli, Experimental and control Groups. Psychophysics Psychophysics is made up of psychology and physics. Psychology - psychological variables - mainly sensation and perception. Physics - physical properties of stimulus Branch of psychological science that study the relation between psychology phenomena and physical properties of stimulus. The Lawful relationships between measurable characteristics of the stimulus, and the reportable attributes of sensory experience is the subject matter of division of experimental psychology known as PSYCHOPHYSICS Works of anatomist and physiologist Ernst Heinrich Weber on Sense of Touch and light in 1830s inspired Fechner. Psychophysics - coined by Gustav Theodore Fechner - 1860 (German Physicist and philosopher) To describe mathematically the relation between Physical stimuli and reported conscious experience. - In his book Elemente der Psychophysik (1860) (Elements of Psychophysics) It is one of the earliest branch of Experimental psychology and its theoretical value lies in the fact that it provides one important psychological approach to the study of sensory processes and of judgement. Its practical value lies in it receiving wide application in fields such as personnel selection and equipment design. Weber - Fechner Law The Weber–Fechner laws are two related scientific laws in the field of psychophysics, known as Weber's law and Fechner's law. Weber’s law is a principle in psychology that indicates the relationship between the intensity of a stimulus and the minimum amount of change required to detect a difference in that stimulus. (Pednekar et al., 2023). Both relate to human perception, more specifically the relation between the actual change in a physical stimulus and the perceived change. Both Weber's law and Fechner's law were formulated by Gustav Theodor Fechner (1801–1887). In simple terms, Weber’s law means that the difference you can detect between two things, such as brightness or weight, depends on how big those things are. That means that if the initial stimulus is very large, the difference between two things also has to be very large in order for you to detect the difference. Weber gave the observation that the size of the difference threshold is proportional to the intensity of the standard stimulus. This ratio is constant. The size of the difference threshold, a constant ratio of the standard stimulus, is often referred to as Weber Fraction. For eg - Suppose that you can just tell the difference between 100 and 104 grams then you will be able to just distinguish between 200 and 208 grams, 400 and 416 grams and so forth. The formula for Weber’s Law is ΔI/I = k, where ΔI represents the smallest noticeable difference, I represent stimulus intensity, and k is known as Weber’s constant The formula for Fechner's Law - S = k* log I where S = sensation, the psychological experience, the Just Noticeable Difference (JND), k = Weber constant for the task (ΔI/I ), I is the physical intensity/magnitude. Basic Problems of Psychophysics ⦁ Detection of Minimal Stimuli - What is the minimum stimulation required for the detection of the stimulus. What kind of stimulus is needed? How intense must it be to distinguish its absence or presence in the environment or to the subject. ⦁ Detection Of Minimal Stimulus Differences - What is the minimal difference qualitative or quantitative needed between two stimuli so that they can be reliably recognized as different by the subject? How great a difference in intensity is required for a discrimination of brilliance. Eg. White and Ivory light. ⦁ Judgment of Relations Among Stimuli - The experimental problems are not limited only to the study of stimuli and stimulus differences. An important area of investigation is Judgement of stimuli well above minimum needed for discrimination. For eg. Under what conditions are two stimuli judged to be equal or standing in relation to one another? What is the extent of error when subjects attempt to equate two stimuli with respect to quantity or quality. How reliably can a subject respond to stimulus being half or twice as intense. The Basic Concepts of Psychophysics Sensitivity Organism is equipped with receptor organs specialized to respond to changes in the environment. The receptor organs constitutes an important link between the application of stimulus and the subject’s response. The capacity of receptors and reaction system to respond selectively and deferentially to physical stimulus is known as Sensitivity. The laws governing sensitivity are inferred with the aid of psychophysical procedures, from variations in response resulting from variations in stimulation. Experimental measurements allow us to distinguish between two types of sensitivity - Absolute and Differential 1. Absolute Sensitivity - Limits of the subject’s capacity to respond to a stimulus. Inversely related to Minimal Stimulus that is easily detected by the subject. 2. Differential Sensitivity - The subject’s capacity to respond to differences both qualitative and quantitative between stimulus. Inversely related to minimal difference between stimuli required for reliable discrimination Thresholds / Limen Some stimuli are so weak that they always fail to evoke a response while others are so intense that they never fail to produce a reaction.The line separating theses two kinds of stimuli can never be sharply drawn rather the transition from one to other is gradual and continuous. While measuring a subject’s absolute sensitivity to sound, suppose we begin at a very weak or low sound which the subject fails to hear on repeated trials. During the experimentation this sound is then increased in intensity. During 2nd level the subject may sometimes hear the sound while they may fail to hear it at times. Finally the increment of intensity of stimulation is at a level at which the subject never fails to report the presence of the sound. Clearly, then, there is no one stimulus value which represents the minimum necessary for a response.  > Absolute Threshold. That stimulus value which yields a response 50% of the time ; that is on half the test trials, is known as Absolute Threshold. This is not a fixed point on the stimulus scale but rather is inherently variable in time. A single value representing the absolute threshold must necessarily be a statistical concept. > Differential / discrimination Threshold. It is defined as the stimulus difference which gives rise to judgement of difference (JND) 50% of the time. When presenting a subject with 2 different tones but of similar intensity the subject will fail to report a difference most of the time. Just as we increase the intensity difference between the ties the subject will be able to report the difference between the stimulus presented. Similar to the absolute threshold when the subject is able to report the difference is half of the trial it is known as differential threshold. It produces a just noticeable difference, that is j.n.d. The j.n.d. indicates subject’s capacity to discriminate. The difference threshold is the amount by which a given stimulus must be increased or decreased so that the subject can perceive a just noticeable difference (j.n.d.) 50% of the times. There are many variation in experimentation and statistical procedures of absolute and differential thresholds but the general purpose of it is same. I,e. to make as good as possible of a judgment or estimate of that stimulus value which will yield a given judgement - presence vs absence, same vs different on half of the trials of the series. Point of Subjective Equality 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 equality of stimuli and judgments of sameness, nor is there a necessary correspondence between physical differences and judgments of different. For this reason, experiments on discrimination often include an estimate of the point of subjective equality. PSE is defined as - the value of a comparison stimulus that, for a given observer, is equally likely to be judged as higher or lower than that of a standard stimulus. (APA dictionary of psychology). E.g - Suppose we present a subject with pairs of stimuli, one member of the pair being fixed and the other member varying from trial to trial, sometimes being equal to the first stimulus, sometimes larger, sometimes smaller. The subject is required to make a judgment of same or different in response to each pair. In such an experiment the point of subjective equality is defined by that comparison stimulus which is most likely to result in a judgment of same. The point of subjective equality (PSE) is a term used in psychology and neuroscience to describe the point at which two stimuli are perceived as equal in intensity or magnitude by an individual.In other words, it's the point where a person can't distinguish between two different stimuli, and they seem identical. This concept is often used in experiments to measure perception, sensation, and decision-making. For example, in a study on sound perception, a participant might be asked to adjust the volume of two different tones until they sound equally loud. The point at which they perceive the tones as equal is their point of subjective equality. PSE can vary from person to person, as it's based on individual subjective experience. It's a useful concept for understanding how our brains process and interpret sensory information. Here are some examples of Point of Subjective Equality (PSE): 1. Sound: Two different sound frequencies are played, and the volume of one is adjusted until they sound equally loud. 2. Light: Two light sources of different intensities are shown, and the brightness of one is adjusted until they appear equally bright. 3. Weight: Two objects of different weights are lifted, and the weight of one is adjusted until they feel equally heavy. 4. Taste: Two solutions with different concentrations of a sweetener are tasted, and the concentration of one is adjusted until they taste equally sweet. 5. Pain: Two different pressures are applied to the skin, and the pressure of one is adjusted until they feel equally painful. 6. Color: Two different shades of color are displayed, and the saturation of one is adjusted until they appear equally vibrant. 7. Smell: Two different concentrations of a fragrance are presented, and the concentration of one is adjusted until they smell equally strong. 8. Temperature: Two different temperatures are applied to the skin, and the temperature of one is adjusted until they feel equally warm or cool. Errors - Variable and Constant Errors Variable Error It is a characteristic of psychological judgments that they are variable in time. When a subject responds repeatedly to the same stimulus or stimulus configuration his judgments may not be the same every time the stimulus is presented. Such Variability is especially characteristic of judgments which are rather difficult for the subject For eg., when tested with stimuli close to his absolute or differential threshold. Several Probable sources of this variability, when subject’s sensitivity may vary from moment to moment; and at any instant the condition of the organism may be more or less favorable to the performance of a fine discrimination. There also may be at times slight unavoidable changes in the physical characteristics of the stimulus, for no matter how carefully controlled the instrumentation, ascertain margin of fluctuation cannot be eliminated. Factors such as interest, attitude etc as difficult to measure may exercise influence on the subject’s performance. The degree to which judgments differ from trial to trial provide an index of the amount of VARIABLE ERROR - Extent to fluctuations in judgments. (Does not imply that one judgement is right and other is wrong) In psychophysics, variable error refers to the random fluctuations in a participant's responses that occur due to various factors, such as: 1. Attention and focus: Momentary lapses in attention or changes in focus. 2. Fatigue and motivation: Changes in energy levels or motivation during the experiment. 3. Sensory noise: Random fluctuations in the sensory system. 4. Cognitive processing: Variability in how information is processed in the brain. 5. Response variability: Natural fluctuations in motor responses. Variable error can lead to: 1. Increased response variability, 2. Decreased precision, 3. Reduced reliability, 4. Increased uncertainty. To minimize variable error, researchers use techniques such as: 1. Averaging responses, 2. Increasing the number of trials, 3. Using control conditions, 4. Randomizing stimulus presentation, 5. Providing regular breaks, 6. Monitoring participant engagement, 7. Using data analysis techniques to account for variability. Constant Error If such judgments are merely a manifestation of variable error, A should sometimes be overestimated and sometimes underestimated. Frequently, however, we find a systematic tendency on the part of the subject toward overestimation or underestimation. Such a systematic tendency is known as constant error! constant error refers to a systematic and consistent deviation from the true value in a participant's responses. It is a type of bias that occurs when a participant consistently overestimates or underestimates the magnitude of a stimulus. Constant error can arise from: 1. Methodological biases: Flaws in the experimental design or procedure. 2. Participant biases: Systematic differences in how participants perceive or respond to stimuli. 3. Stimulus biases: Inherent properties of the stimuli that affect perception. 4. Instrumental biases: Calibration errors or flaws in the measurement instruments Examples of constant error include: 1. Constant overestimation: Consistently rating stimuli as more intense than they actually are. 2. Constant underestimation: Consistently rating stimuli as less intense than they actually are. Factors contributing to time constant error in sensory stimulation include: 1. Attention and arousal: Changes in attention or arousal levels can affect time perception. 2. Sensory adaptation: Prolonged exposure to the stimulus can lead to decreased sensitivity.  3. Stimulus intensity: The strength or intensity of the stimulus can impact time perception. 4. Modality-specific factors: Unique characteristics of each sensory modality (e.g., visual, auditory) can influence time constant error. 5. Methodological factors: Experimental design or procedure flaws can contribute to time constant error. To minimize time constant error, researchers use techniques like: 1. Controlled attention tasks, 2. Stimulus calibration & Stimulus validation, 3. Sensory adaptation control, 4. Careful experimental design, 5. Data analysis techniques (e.g., regression analysis). Time Constant Error - TIME ERROR If two identical stimuli, A and B, are presented in succession, we find, for different time intervals between A and B, systematic tendencies to underestimate or overestimate the second stimulus, B. For eg. in the Judgments of Loudness - 2 equally intense tones are separated by sometime. (A and B by 1 second) and (A and B by 10 seconds) In the 1st trial presented B will be judged as less loud while in the 2nd trial when given a longer interval between tones presented B will be judged as more louder than A. This tendency to underestimate or overestimate the 2nd of two successive stimuli constitutes to time error. The degree of time error can be plotted as a function of length of time interval between two tones. The time error has been found to occur with a variety of other stimulus materials, such as judgments of weights and of extent. When presenting a sensory stimulus (e.g., visual, auditory, tactile, olfactory, gustatory) in psychophysics, time constant error refers to the consistent bias in judging the duration of the stimulus. This error can manifest in various ways, including: 1. Overestimation: Participants consistently judge the stimulus duration to be longer than its actual duration. 2. Underestimation: Participants consistently judge the stimulus duration to be shorter than its actual duration. Space Constant Error - Space Error Judgments may be influenced systematically by the spatial position of the stimuli, whether they are, for instance, on the right or left of the subject. - Location (e.g., left/right, up/down), Distance (e.g., length, depth), Size (e.g., width, height), Orientation (e.g., angle, direction) This error occurs when a participant consistently overestimates or underestimates the spatial properties of a stimulus, resulting in a biased perception of the stimulus's spatial characteristics. For example: - A participant consistently judges a line to be 10% longer than its actual length. - A participant consistently misjudges the location of a visual stimulus by 5 degrees to the right. Again, we must be careful not to be misled by the word error in the term constant error. Such systematic tendencies as we have described should not be dismissed merely as inaccuracies of judgment which need to be somehow eliminated or corrected. On the contrary they are of interest to the psychophysicist because they represent the reliable correlation between certain conditions of stimulation and judgement. Other potential errors to consider 1. Subjective bias: Participants' expectations, experiences, and biases can influence their responses. 2. Context effects: The surrounding environment, instructions, and stimuli can impact perception. 3. Adaptation: Prolonged exposure to stimuli can lead to decreased sensitivity. 4. Attention and fatigue: Participants' focus and energy levels can affect responses. 5. Individual differences: People's perceptions can vary significantly. 6. Stimulus range and spacing: Inadequate stimulus selection can lead to inaccurate results. 7. Methodological limitations: Techniques like magnitude estimation or forced-choice tasks have inherent constraints. 8. Data analysis errors: Incorrect statistical analysis or modeling can lead to flawed conclusions. 9. Participant compliance: Participants may not follow instructions or provide accurate responses. 10. Experimenter effects: Researchers' expectations or behaviors can unintentionally influence participants' responses. By acknowledging and addressing these potential errors, researchers can improve the validity and reliability of psychophysical studies.