Sensory, Attentional and Perceptual Processes PDF

Sensory Sensory,, AAttentional ttentional and Perceptual Processes Chapter 4 After reading this chapter...

Sensory Sensory,, AAttentional ttentional and Perceptual Processes Chapter 4 After reading this chapter, you would be able to understand the nature of sensory processes, explain the processes and types of attention, analyse the problems of form and space perception, examine the role of socio-cultural factors in perception, and reflect on sensory, attentional and perceptual processes in everyday life. Contents Introduction Knowing the World Nature and Varieties of Stimulus Sense Modalities Attentional Processes Selective Attention Divided Attention (Box 4.1) Sustained Attention Span of Attention (Box 4.2) Attention Deficit Hyperactivity Disorder (Box 4.3) Perceptual Processes Processing Approaches in Perception The Perceiver Principles of Perceptual Organisation Perception of Space, Depth, and Distance Monocular Cues and Binocular Cues Perceptual Constancies Illusions Socio-Cultural Influences on Perception Key Terms The quality of life is determined Summary by its activities. Review Questions Project Ideas – Aristotle 60 Psychology Rationalised 2023-24  Introduction While some of our receptors are clearly observable (for example, eyes or ears), others lie inside our body, and are not observable without the help of electrical or mechanical devices. This chapter will introduce you to various receptors that collect a variety of information from the external and internal worlds. You will also know some important things about attention, which helps us to notice and register the information that our sense organs carry to us. Different types of attention will be described along with the factors that influence them. At the end, we will discuss the process of perception that allows us to understand the world in a meaningful way. You will also have an opportunity to know how we are sometimes deceived by certain types of stimuli such as figures and pictures. kinds of information about various objects. KNOWING THE WORLD However, in order to be registered, the objects The world in which we live is full of variety of and their qualities (e.g., size, shape, colour) objects, people, and events. Look at the room must be able to draw our attention. The you are sitting in. You will find so many things registered information must also be sent to the around. Just to mention a few, you may see brain that constructs some meaning out of your table, your chair, your books, your bag, them. Thus, our knowledge of the world your watch, pictures on the wall and many around us depends on three basic processes, other things. Their sizes, shapes, and colours called sensation, attention, and perception. are also different. If you move to other rooms These processes are highly interrelated; hence, of your house, you will notice several other they are often considered as different elements new things (e.g., pots and pans, almirah, TV). of the same process, called cognition. If you go beyond your house, you will find still many more things that you generally know NATURE AND VARIETIES OF STIMULUS about (trees, animals, buildings). Such experiences are very common in our day-to- The external environment that surrounds us day life. We hardly have to make any efforts contains a wide variety of stimuli. Some of them to know them. can be seen (e.g., a house), while some can be If someone asks you, “How can you say heard only (e.g., music). There are several that these various things exist in your room, others that we can smell (e.g., fragrance of a or house, or in the outside environment?”, you flower) or taste (e.g., sweets). There are still will most probably answer that you see or others that we can experience by touching (e.g., experience them all around you. In doing so, softness of a cloth). All these stimuli provide you are trying to tell the person that the us with various kinds of information. We have knowledge about various objects becomes very specialised sense organs to deal with these possible with the help of our sense organs (e.g., different stimuli. As human beings we are eyes, ears). These organs collect information bestowed with a set of seven sense organs. not only from the external world, but also from These sense organs are also known as sensory our own body. The information collected by receptors or information gathering systems, our sense organs forms the basis of all our because they receive or gather information knowledge. The sense organs register several from a variety of sources. Five of these sense 61 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24 organs collect information from the external cannot hear very faint or very loud sounds. The world. These are eyes, ears, nose, tongue, and same is true for other sense organs also. As skin. While our eyes are primarily responsible human beings, we function within a limited for vision, ears for hearing, nose for smell, and range of stimulation. For being noticed by a tongue for taste, skin is responsible for the sensory receptor, a stimulus has to be of an experiences of touch, warmth, cold, and pain. optimal intensity or magnitude. The Specialised receptors of warmth, cold, and pain relationship between stimuli and the are found inside our skin. Besides these five sensations they evoke has been studied in a external sense organs, we have also got two discipline, called psychophysics. deep senses. They are called kinesthetic and In order to be noticed a stimulus has to vestibular systems. They provide us with carry a minimum value or weight. The important information about our body position minimum value of a stimulus required to and movement of body parts related to each activate a given sensory system is called other. With these seven sense organs, we absolute threshold or absolute limen (AL). register ten different variety of stimuli. For For example, if you add a granule of sugar to example, you may notice whether a light is a glass of water, you may not experience any bright or dim, whether it is yellow, red or green, sweetness in that water. Addition of a second and so on. With sound you may notice whether granule to water may also not make it taste it is loud or faint, whether it is melodious or sweet. But if you go on adding sugar granules distracting, and so on. These different qualities one after another, there will come a point when of stimuli are also registered by our sense you will say that the water is now sweet. The organs. minimum number of sugar granules required to say that the water is sweet will be the AL of SENSE MODALITIES sweetness. It may be noted at this point that the AL is Our sense organs provide us with first-hand not a fixed point; instead it varies considerably information about our external or internal across individuals and situations depending world. The initial experience of a stimulus or on the people’s organic conditions and their an object registered by a particular sense motivational states. Hence, we have to assess organ is called sensation. It is a process it on the basis of a number of trials. The through which we detect and encode a variety number of sugar granules that may produce of physical stimuli. Sensation also refers to the experience of “sweetness” in water on immediate basic experiences of stimulus 50 per cent of occasions will be called the AL attributes, such as “hard”, “warm”, “loud”, and of sweetness. If you add more number of sugar “blue”, which result from appr opriate granules, the chances are greater that the stimulation of a sensory organ. Different sense water will be reported more often as sweet than organs deal with different forms of stimuli and plain. serve different purposes. Each sense organ is As it is not possible for us to notice all highly specialised for dealing with a particular stimuli, it is also not possible to differentiate kind of information. Hence, each one of them between all stimuli. In order to notice two is known as a sense modality. stimuli as different from each other, there has to be some minimum difference between the Functional Limitations of Sense Organs value of those stimuli. The smallest difference Before we move on to a discussion of sense in the value of two stimuli that is necessary to organs, it is important to note that our sense notice them as different is called difference organs function with certain limitations. For threshold or difference limen (DL). To example, our eyes cannot see things which understand it, we may continue with our are very dim or very bright. Similarly our ears “sugar water” experiment. As we have seen, 62 Psychology Rationalised 2023-24 the plain water is experienced as sweet after ATTENTIONAL PROCESSES the addition of certain number of sugar granules. Let us remember this sweetness. The In the previous section we have discussed some next question is: how many sugar granules will sensory modalities that help us in collecting be needed in the water in order to experience information from the external world and also its sweetness as different from the previous from our internal system. A large number of sweetness. Go on adding sugar granules one stimuli impinge upon our sense organs after another tasting the water each time. After simultaneously, but we do not notice all of addition of a few granules, you will notice at a them at the same time. Only a selected few of point that the water is now sweeter than the them are noticed. For example, when you enter previous one. The number of sugar granules your classroom you encounter several things added to the water to generate an experience in it, such as doors, walls, windows, paintings of sweetness that is different from the previous on walls, tables, chairs, students, schoolbags, sweetness on 50 per cent of the occasions will water bottles, and so on, but you selectively be called the DL of sweetness. Thus, difference focus only on one or two of them at one time. threshold is the minimum amount of change The process through which certain stimuli are in a physical stimulus that is capable of selected from a group of others is generally producing a sensation difference on 50 per cent referred to as attention. of the trials. At this point it may be noted that besides You may realise by now that understanding selection, attention also refers to several other of sensations is not possible without properties like alertness, concentration, and understanding the AL and DL of different types search. Alertness refers to an individual’s of stimuli (for example, visual, auditory), but readiness to deal with stimuli that appear that is not enough. Sensory processes do not before her/him. While participating in a race depend only on the stimulus characteristics. in your school, you might have seen the Sense organs and the neural pathways participants on the starting line in an alert state connecting them to various brain centers also waiting for the whistle to blow in order to run. play a vital role in this process. A sense organ Concentration refers to focusing of awareness receives the stimulus and encodes it as an on certain specific objects while excluding electrical impulse. For being noticed this others for the moment. For example, in the electrical impulse must reach the higher brain classroom, a student concentrates on the centers. Any structural or functional defect or teacher’s lecture and ignores all sorts of noises damage in the receptor organ, its neural coming from different corners of the school. In pathway, or the concerned brain area may lead search an observer looks for some specified subset of objects among a set of objects. For to a partial or complete loss of sensation. example, when you go to fetch your younger sister and brother from the school, you just Activity 4.1 look for them among innumerable boys and girls. All these activities require some kind of Vision and hearing are generally believed to be effort on the part of people. Attention in this the two most highly prized senses. What would sense refers to “effort allocation”. your life be if you lost any one of your senses? Attention has a focus as well as a fringe. Which sense would you find more traumatic to lose? Why? Think and write down. When the field of awareness is centered on a What if you could magically improve the particular object or event, it is called focus or performance of one of your senses, which sense the focal point of attention. On the contrary, would you choose to improve? Why? Could you when the objects or events are away from the improve the performance of this one sense without center of awareness and one is only vaguely magic? Think and write down. aware of them, they are said to be at the fringe Discuss with your teacher. of attention. 63 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24  Attention has been classified in a number bright, and moving stimuli easily catch our of ways. A process-oriented view divides it into attention. Stimuli, which are novel and two types, namely selective and sustained. moderately complex, also easily get into our We will briefly discuss the main features of focus. Studies indicate that human these types of attention. Sometimes we can photographs are more likely to be attended to also attend to two different things at the same than the photographs of inanimate objects. time. When this happens, it is called divided Similarly, rhythmic auditory stimuli are more attention. Box 4.1 describes when and how readily attended to than verbal narrations. the division of attention is possible. Sudden and intense stimuli have a wonderful capacity to draw attention. Selective Attention Internal factors lie within the individual. Selective attention is concerned mainly with the These may be divided into two main categories, selection of a limited number of stimuli or viz. motivational factors and cognitive factors. Motivational factors relate to our biological objects from a large number of stimuli. We or social needs. When we are hungry, we notice have already indicated that our perceptual even a faint smell of food. A student taking an system has a limited capacity to receive and examination is likely to focus on a teacher’s process information. This means that it can instructions more than other students. deal only with a few stimuli at a given moment Cognitive factors include factors like interest, of time. The question is, which of those stimuli attitude, and preparatory set. Objects or events, will get selected and processed? Psychologists which appear interesting, are readily attended have identified a number of factors that by individuals. Similarly we pay quick determine the selection of stimuli. attention to certain objects or events to which we are favourably disposed. Preparatory set Factors Affecting Selective Attention generates a mental state to act in a certain way Several factors influence selective attention. and readiness of the individual to respond to These generally relate to the characteristics of one kind of stimuli and not to others. stimuli and the characteristics of individuals. They are generally classified as “external” and Theories of Selective Attention “internal” factors. A number of theories have been developed to External factors are related to the features explain the process of selective attention. We of stimuli. Other things held constant, the size, will briefly discuss three of these theories. intensity, and motion of stimuli appear to be Filter theory was developed by Broadbent important determinants of attention. Large, (1956). According to this theory, many stimuli B o x 4.1 Divided Attention In day-to-day life we attend to several things at time. However, this becomes possible only with highly the same time. You must have seen people driving practiced activities, because they become almost a car and talking to a friend, or attending to phone automatic and require less attention to perform than calls on a mobile set, or putting on sunglasses, or new or slightly practiced activities. listening to music. If we watch them closely, we Automatic processing has three main will notice that they are still allocating more effort characteristics; (i) It occurs without intention, (ii) It takes to driving than to other activities, even though place unconsciously, and (iii) It involves very little (or some attention is given to other activities. It no) thought processes (e.g., we can read words or tie indicates that on certain occasions attention can our shoelaces without giving any thought to these be allocated to more than one thing at the same activities). 64 Psychology Rationalised 2023-24 simultaneously enter our receptors creating a consciousness. It is also suggested that more kind of “bottleneck” situation. Moving through processing requires more mental effort. When the short-term memory system, they enter the the messages are selected on the basis of stage selective filter, which allows only one stimulus one processing (early selection), less mental to pass through for higher levels of processing. effort is required than when the selection is Other stimuli are screened out at that moment based on stage three processing (late of time. Thus, we become aware of only that selection). stimulus, which gets access through the selective filter. Sustained Attention Filter-attenuation theory was developed While selective attention is mainly concerned by Triesman (1962) by modifying Broadbent’s with the selection of stimuli, sustained attention theory. This theory proposes that the stimuli is concerned with concentration. It refers to not getting access to the selective filter at a given moment of time are not completely our ability to maintain attention on an object blocked. The filter only attenuates (weakens) or event for longer durations. It is also known their strength. Thus some stimuli manage to as “vigilance”. Sometimes people have to escape through the selective filter to reach concentrate on a particular task for many higher levels of processing. It is indicated that hours. Air traffic controllers and radar readers personally relevant stimuli (e.g., one’s name in provide us with good examples of this a collective dinner) can be noticed even at a phenomenon. They have to constantly watch very low level of sound. Such stimuli, even and monitor signals on screens. The though fairly weak, may also generate occurrence of signals in such situations is response occasionally by slipping through the usually unpredictable, and errors in detecting selective filter. signals may be fatal. Hence, a great deal of Multimode theory was developed by vigilance is required in those situations. Johnston and Heinz (1978). This theory believes that attention is a flexible system that Factors Influencing Sustained Attention allows selection of a stimulus over others at three stages. At stage one the sensory Several factors can facilitate or inhibit an representations (e.g., visual images) of stimuli individual’s performance on tasks of sustained are constructed; at stage two the semantic attention. Sensory modality is one of them. representations (e.g., names of objects) are Performance is found to be superior when the constructed; and at stage three the sensory and stimuli (called signals) are auditory than when semantic representations enter the they are visual. Clarity of stimuli is another B o x 4.2 Span of Attention Our attention has a limited capacity to receive span of attention varies within the limit of seven plus stimuli. The number of objects one can attend to at or minus two. This is popularly known as the “magic a brief exposure (i.e. a fraction of a second) is called number”. It means that at a time, people can attend to “span of attention” or “perceptual span”. More a set of five to seven numbers, which can be extended specifically, the span of attention refers to the to nine or more under exceptional conditions. That is amount of information an observer can grasp from perhaps the reason why motorbikes or cars are given a complex array of stimuli at a single momentary a number plate that contains only four digit numbers exposure. This can be determined by the use of an with some alphabets. In case of violation of driving rules instrument, called “tachistoscope”. On the basis of a traffic police can easily read and note these numbers several experiments, Miller has reported that our along with the alphabets. 65 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24 factor. Intense and long lasting stimuli facilitate simply due to the problem of attention. Box sustained attention and result in better 4.3 presents some interesting information performance. Temporal uncertainty is a about a disorder of attention. third factor. When stimuli appear at regular intervals of time they are attended better than when they appear at irregular intervals. PERCEPTUAL PROCESSES Spatial uncertainty is a fourth factor. Stimuli In the previous section we have examined that that appear at a fixed place are readily the stimulation of sensory organs leads us to attended, whereas those that appear at random experience something such as, a flash of light locations are difficult to attend. or a sound, or a smell. This elementary Attention has several practical implications. experience, called sensation, does not provide The number of objects one can readily attend us with any understanding of the stimulus to in a single glance is used to design the that stimulated the sense organ. For example, number plates of motorbikes and cars so that it does not inform us about the source of the the traffic police can easily notice them in the light, sound or fragrance. In order to make case of traffic rule violations (Box 4.2). A sense out of the raw material provided by the number of children fail to perform well in school sensory system, we process it further. In doing B o x 4.3 Attention Deficit H yperactivity Disorder (AD Hyperactivity HD) (ADHD) This is a very common behavioural disorder found found to account for ADHD more reliably than other among children of the primary school age. It is factors. Currently ADHD is considered to have multiple characterised by impulsivity, excessive motor causes and effects. activity, and an inability to attend. The disorder is Disagreement remains over the most effective more prevalent among boys than among girls. If method of treatment of ADHD. A drug, called Ritalin, is not managed properly, the attention difficulties may widely used, which decreases children’s over-activity persist into adolescence or adult years. Difficulty and distractibility, and at the same time increases their in sustaining attention is the central feature of this attention and ability to concentrate. However, it does disorder, which gets reflected in several other not “cure” the problem, and often also results in such domains of the child. For example, such children negative side-effects as the suppression in normal are highly distractible; they do not follow growth of height and weight. On the other hand, instructions, have difficulty in getting along with behavioural management programmes, featuring parents, and are negatively viewed by their peers. positive reinforcement and structuring learning They do poorly in school, and show difficulties in materials and tasks in such a way that minimises errors reading or learning basic subjects in schools in and maximises immediate feedback and success, have spite of the fact that there is no deficit in their been found quite useful. Successful modification of intelligence. ADHD is claimed with cognitive behavioural training Studies generally do not provide evidence for programme in which rewards for desired behaviours a biological basis of the disorder, whereas some are combined with training in the use of verbal self- relationship of the disorder with dietary factors, instructions (stop, think, and then do). With this particularly food colouring, has been documented. procedure, the ADHD children learn to shift their On the other hand, social-psychological factors (e.g., attention less frequently and to behave reflectively — home environment, family pathology) have been a learning that is relatively stable over time. 66 Psychology Rationalised 2023-24 so, we give meaning to stimuli by using our approach lays emphasis on the perceiver, and learning, memory, motivation, emotions, and considers perception as a process of other psychological processes. The process by recognition or identification of stimuli. Studies which we recognise, interpret or give meaning show that in perception both the processes to the information provided by sense organs is interact with each other to provide us with an called perception. In interpreting stimuli or understanding of the world. events, individuals often construct them in their own ways. Thus perception is not merely THE PERCEIVER an interpretation of objects or events of the external or internal world as they exist, instead Human beings are not just mechanical and it is also a construction of those objects and passive recipients of stimuli from the external events from one’s own point of view. world. They are creative beings, and try to The process of meaning-making involves understand the external world in their own certain sub-processes. These are shown in ways. In this process their motivations and Fig.4.1. expectations, cultural knowledge, past experiences, and memories as well as values, Processing Approaches in Perception beliefs, and attitudes play an important role in How do we identify an object? Do we identify a giving meaning to the external world. Some of dog because we have first recognised its furry these factors are described here. coat, its four legs, its eyes, ears, and so on, or do we recognise these different parts because Motivation we have first identified a dog? The idea that The needs and desires of a perceiver strongly recognition process begins from the parts, influence her/his perception. People want to which serve as the basis for the recognition of fulfil their needs and desires through various the whole is known as bottom-up processing. means. One way to do this is to perceive objects The notion that recognition process begins in a picture as something that will satisfy their from the whole, which leads to identification need. Experiments were conducted to examine of its various components is known as top- the influence of hunger on perception. When down processing. The bottom-up approach hungry persons were shown ambiguous lays emphasis on the features of stimuli in pictures, they were found to perceive them as perception, and considers perception as a pictures of food objects more often than satiated process of mental construction. The top-down (non-hungry) persons. Fig.4.1 : Sub-processes of Perception 67 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24 Expectations or Perceptual Sets The expectations about what we might perceive in a given situation also influence our perception. This phenomenon of perceptual familiarisation or perceptual generalisation reflects a strong tendency to see what we expect to see even when the results do not accurately reflect external reality. For example, if your milkman delivers you milk daily at about 5.30 A.M., any knocking at the door around that time is likely to be perceived as the presence of the milkman even if it is someone else. Activity 4.2 To demonstrate expectancy tell your friend to close Fig.4.2 : An Item to test the ‘Field Dependent’ and her eyes. Write 12, 13, 14, 15 on the board. Ask ‘Field Independent’ Cognitive Style her to open her eyes for 5 seconds, look at the board, and note down what she saw. Repeat replacing only the 12, 14, 15 with A, C, D viz. ‘A Cultural Background and Experiences 13 C D’. Ask her again to note down what she Different experiences and learning saw. Most people write down B in place of 13. opportunities available to people in different cultural settings also influence their perception. People coming from a pictureless Cognitive Styles environment fail to recognise objects in Cognitive style refers to a consistent way of pictures. Hudson studied the perception of dealing with our environment. It significantly pictures by African subjects, and noted several affects the way we perceive the environment. difficulties. Many of them were unable to There are several cognitive styles that people identify objects depicted in pictures (e.g., use in perceiving their environment. One most antelope, spear). They also failed to perceive extensively used in studies is the “field distance in pictures, and interpreted pictures dependent and field independent” cognitive incorrectly. Eskimos have been found to make style. Field dependent people perceive the fine distinction among a variety of snow that external world in its totality, i.e. in a global or we may be unable to notice. Some aboriginal holistic manner. On the other hand, field groups of Siberian region have been found to independent people perceive the external world differentiate among dozens of skin colours by breaking it into smaller units, i.e. in an of reindeers, which we would not be able analytic or differentiated manner. to do. Look at Fig.4.2. Can you find out the These studies indicate that the perceiver triangle hidden in the picture? How much time plays a key role in the process of perception. do you take to locate it? Try to find out the People process and interpret stimuli in their time other students of your class take to locate own ways depending on their personal, social the triangle. Those who can do it quickly will and cultural conditions. Due to these factors be called “field independent”; those who take our perceptions are not only finely tuned, but long time will be called “field dependent”. also modified. 68 Psychology Rationalised 2023-24  PRINCIPLES OF PERCEPTUAL ORGANISATION Our visual field is a collection of different elements, such as points, lines, and colours. However, we perceive these elements as organised wholes or complete objects. For example, we see a bicycle as a complete object, not as a collection of different parts (e.g., saddle, wheel, handle). The process of organising visual field into meaningful wholes is known as form perception. You may wonder how different parts of an objects are organised into a meaningful whole. You may also ask if there are certain factors that facilitate or inhibit this process of organisation. Several scholars have tried to answer such Fig.4.3 : Rubin’s Vase questions, but the most widely accepted answer has been given by a group of researchers, called and sky stay behind the figure and are Gestalt psychologists. Prominent among perceived as background. them are Köhler, Koffka, and Wertheimer. To test this experience, look at the Fig.4.3 Gestalt means a regular figure or a form. given below. You will see either the white part According to Gestalt psychologists, we perceive of the figure, which looks like a vase (flower different stimuli not as discrete elements, but pot), or the black part of the figure, which looks as an organised “whole” that carries a definite like two faces. form. They believe that the form of an object We distinguish figure from the ground on lies in its whole, which is different from the sum the basis of the following characteristics: of their parts. For example, a flower pot with a 1. Figure has a definite form, while the bunch of flowers is a whole. If the flowers are background is relatively formless. removed, the flower pot still remains a whole. 2. Figure is more organised as compared to It is the configuration of the flower pot that has its background. changed. Flower pot with flowers is one 3. Figure has a clear contour (outline), while configuration; without flowers it is another the background is contourless. configuration. 4. Figure stands out from the background, The Gestalt psychologists also indicate that while the background stays behind the our cerebral processes are always oriented figure. towards the perception of a good figure or 5. Figure appears more clear, limited, and pragnanz. That is the reason why we perceive relatively nearer, while the background everything in an organised form. The most appears relatively unclear, unlimited, and primitive organisation takes place in the form away from us. of figure-ground segregation. When we look The discussion presented above indicates at a surface, certain aspects of the surface that human beings perceive the world in clearly stand out as separate entities, whereas organised wholes rather than in discrete parts. others do not. For example, when we see words The Gestalt psychologists have given us several on a page, or a painting on a wall, or birds laws to explain how and why different stimuli flying in the sky, the words, the painting, and in our visual field are organised into meaningful the birds stand out from the background, and whole objects. Let us look at some of these are perceived as figures, while the page, wall, principles. 69 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24 The Principle of Proximity The Principle of Smallness Objects that are close together in space or time According to this principle, smaller areas tend are perceived as belonging together or as a to be seen as figures against a larger group. For example, Fig.4.4 does not look like background. In Fig.4.7 we are more likely to a square pattern of dots, but as a series of see a black cross rather than a white cross columns of dots. Similarly, Fig.4.4 also looks within the circle because of this principle. like a group of dots together in rows. Fig.4.4 : Proximity The Principle of Similarity Fig.4.7 : Smallness Objects that are similar to one another and The Principle of Symmetry have similar characteristics are perceived as a This principle suggests that symmetrical areas group. In Fig.4.5 the little circles and squares tend to be seen as figures against asymmetrical are evenly spaced both horizontally and backgrounds. For example, in Fig.4.8 the black vertically so that the proximity does not come areas are seen as figures (as they have into play. Instead, we tend to see alternating symmetrical properties) against their white columns of circles and squares. asymmetrical background. Fig.4.5 : Similarity Fig.4.8 : Symmetry The Principle of Continuity This principle states that we tend to perceive The Principle of Surroundedness objects as belonging together if they appear to According to this principle, the areas form a continuous pattern. For instance, we surrounded by others tend to be perceived as are more likely to identify two lines a-b and c- figures. For example, the image in Fig.4.9 looks d crossing than to identify four lines meeting like five figures against the white background at the center p. rather than the word ‘LIFT’. Fig.4.6 : Continuity Fig.4.9 : Surroundedness 70 Psychology Rationalised 2023-24 The Principle of Closure Monocular Cues (Psychological Cues) We tend to fill the gaps in stimulation and Monocular cues of depth perception are perceive the objects as whole rather than their effective when the objects are viewed with only separate parts. For example, in Fig.4.10 the one eye. These cues are often used by artists small angles are seen as a triangle due to our to induce depth in two dimensional paintings. tendency to fill the gaps in the object provided Hence, they are also known as pictorial cues. by our sensory input. Some important monocular cues that help us in judging the distance and depth in two dimensional surfaces are described below. You will find some of them applied in Fig.4.11. Fig.4.10 : Closure PERCEPTION OF SPACE, DEPTH, AND DISTANCE The visual field or surface in which things exist, move or can be placed is called space. The space in which we live is organised in three dimensions. We perceive not only the spatial attributes (e.g., size, shape, direction) of various objects, but also the distance between the objects found in this space. While the images of objects projected on to our retina are flat Fig.4.11 : Monocular Cues and two dimensional (left, right, up, down), we The above picture will help you to understand some still perceive three dimensions in the space. monocular cues: Interposition and relative size (see the Why does it happen so? It occurs due to our trees). Which other cues can you locate in the picture? ability to transfer a two dimensional retinal vision into a three dimensional perception. The Relative Size : The size of retinal image allows process of viewing the world in three us to judge distance based on our past and dimensions is called distance or depth present experience with similar objects. As the perception. objects get away, the retinal image becomes Depth perception is important in our daily smaller and smaller. We tend to perceive an life. For example, when we drive, we use depth object farther away when it appears small, to assess the distance of an approaching and closer when it appears bigger. automobile, or when we decide to call a person walking down the street, we determine the Interposition or Overlapping : These cues occur loudness with which to call. when some portion of the object is covered by In perceiving depth, we depend on two main another object. The overlapped object is sources of information, called cues. One is considered farther away, whereas the object called binocular cues because they require that covers it appears nearer. both eyes. Another is called monocular cues, Linear Perspective : This reflects a phenomenon because they allow us to perceive depth with by which distant objects appear to be closer just one eye. A number of such cues are used together than the nearer objects. For example, to change a two dimensional image into a three parallel lines, such as rail tracks, appear to dimensional perception. converge with increasing distance with a 71 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24 vanishing point at the horizon. The more the when we travel in a bus, closer objects move lines converge, the farther away they appear. “against” the direction of the bus, whereas the farther objects move “with” the direction of the Aerial Perspective : The air contains microscopic bus. particles of dust and moisture that make distant objects look hazy or blurry. This effect Binocular Cues (Physiological Cues) is called aerial perspective. For example, distant mountains appear blue due to the Some important cues to depth perception in scattering of blue light in the atmosphere, three dimensional space are provided by both whereas the same mountains are perceived to the eyes. Three of them have particularly been be closer when the atmosphere is clear. found to be interesting. Light and Shade : In the light some parts of the Retinal or Binocular Disparity : Retinal object get highlighted, whereas some parts disparity occurs because the two eyes have become darker. Highlights and shadows different locations in our head. They are provide us with information about an object’s separated from each other horizontally by a distance. distance of about 6.5 centimeters. Because of this distance, the image formed on the retina Relative Height : Larger objects are perceived of each eye of the same object is slightly as being closer to the viewer and smaller objects different. This difference between the two as being farther away. When we expect two images is called retinal disparity. The brain objects to be the same size and they are not, interprets a large retinal disparity to mean a the larger of the two will appear closer and the close object and a small retinal disparity to smaller will appear farther away. mean a distant object, as the disparity is less Texture Gradient : It represents a phenomenon for distant objects and more for the near by which the visual field having more density objects. of elements is seen farther away. In the Fig.4.12 Convergence : When we see a nearby object the density of stones increases as we look our eyes converge inward in order to bring the farther away. image on the fovea of each eye. A group of muscles send messages to the brain regarding the degree to which eyes are turning inward, and these messages are interpreted as cues to the perception of depth. The degree of convergence decreases as the object moves further away from the observer. You can experience convergence by holding a finger in front of your nose and slowly bringing it closer. The more your eyes turn inward or converge, the nearer the object appears in space. Accommodation : Accommodation refers to a Fig.4.12 : Texture Gradient process by which we focus the image on the retina with the help of ciliary muscle. These Motion Parallax : It is a kinetic monocular cue, muscles change the thickness of the lens of the and hence not considered as a pictorial cue. It eye. If the object gets away (more than 2 meters), occurs when objects at different distances the muscle is relaxed. As the object moves move at a different relative speed. The distant nearer, the muscle contracts and the thickness objects appear to move slowly than the objects of the lens increases. The signal about the that are close. The rate of an object’s movement degree of contraction of the muscle is sent to provides a cue to its distance. For example, the brain, which provides the cue for distance. 72 Psychology Rationalised 2023-24  viewed from the edge). It is also called form Activity 4.3 constancy. Hold a pencil in front of you. Close your right eye Brightness Constancy and focus on the pencil. Now open the right eye and close the left eye. Keep doing it simultaneously Visual objects not only appear constant in their with both the eyes. The pencil will appear to move shape and size, they also appear constant in from side to side in front of your face. their degree of whiteness, greyness, or blackness even though the amount of physical energy reflected from them changes PERCEPTUAL CONSTANCIES considerably. In other words, our experience of brightness does not change in spite of the The sensory information that we receive from changes in the amount of reflected light our environment constantly changes as we reaching our eyes. The tendency to maintain move around. Yet we form a stable perception apparent brightness constant under different of an object seen from any position and in any amount of illumination is called brightness intensity of light. Perception of the objects as constancy. For example, surface of a paper relatively stable in spite of changes in the which appears white in the sunlight, is still stimulation of sensory receptors is called perceived as white in the room light. Similarly, perceptual constancy. Here we will examine coal that looks black in the sun also looks black three types of perceptual constancies that we in room light. commonly experience in our visual domain. I LLUSIONS Size Constancy The size of an image on our retina changes with Our perceptions are not always veridical. the change in the distance of the object from Sometime we fail to interpret the sensory the eye. The further away it is, the smaller is information correctly. This results in a the image. On the other hand, our experience mismatch between the physical stimuli and its shows that within limits the object appears to perception. These misperceptions resulting be about the same size irrespective of its from misinterpretation of information received distance. For example, when you approach by our sensory organs are generally known as your friend from a distance, your perception illusions. These are experienced more or less of the friend’s size does not change much by all of us. They result from an external despite the fact that the retinal image (image stimulus situation and generate the same kind on retina) becomes larger. This tendency for of experience in each individual. That is why illusions are also called “primitive the perceived size of objects to remain relatively organisations”. Although illusions can be unchanged with changes in their distance from experienced by the stimulation of any of our the observer and the size of the retinal image is senses, psychologists have studied them more called size constancy. commonly in the visual than in other sense modalities. Shape Constancy Some perceptual illusions are universal In our perceptions the shapes of familiar and found in all individuals. For example, the objects remain unchanged despite changes in rail tracks appear to be converging to all of the pattern of retinal image resulting from us. These illusions are called universal illusions differences in their orientation. For example, a or permanent illusions as they do not change dinner plate looks the same shape whether the with experience or practice. Some other image that it casts on the retina is a circle, or illusions seem to vary from individual to an ellipse, or roughly a short line (if the plate is individual; these are called personal illusions. 73 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24 In this section, we will describe some important light points will not appear as moving. They visual illusions. will appear either as one point, or as different points appearing one after another, without Geometrical Illusions any experience of motion. Experience of illusions indicates that people In Fig.4.13 the Muller-Lyer illusion has been do not always perceive the world as it is; shown. All of us perceive line A as shorter than instead they engage in its construction, line B, although both the lines are equal. This sometimes based on the features of stimuli and illusion is experienced even by children. There sometimes based on their experiences in a given environment. This point will be further made clear in the section that follows now. A B SOCIO-CULTURAL INFLUENCES ON Fig.4.13 : Muller-Lyer Illusion PERCEPTION are some studies that suggest that even animals Several psychologists have studied the experience this illusion more or less like us. processes of perception in different socio- Besides Muller-L yer illusion, several other cultural settings. The questions they try to visual illusions are experienced by human answer through these studies are: Does beings (also birds and animals). In Fig.4.14 perceptual organisation of people living in you can see the illusion of vertical and different cultural settings take place in an horizontal lines. Although both the lines are uniform manner? Are the perceptual processes equal, we perceive the vertical line as longer universal, or they vary across different cultural than the horizontal line. settings? Because we know, people living in different parts of the world look different, many psychologists hold the view that their ways of perceiving the world must be different in some respects. Let us examine some studies relating to perception of illusion figures and other pictorial materials. You are already familiar with Muller-Lyer Fig.4.14 : Vertical-Horizontal Illusion and Vertical-Horizontal illusion figures. Apparent Movement Illusion Psychologists have used these figures with several groups of people living in Europe, This illusion is experienced when some Africa, and many other places. Segall, motionless pictures are projected one after Campbell, and Herskovits carried out the most another at an appropriate rate. This illusion extensive study of illusion susceptibility by is referred to as “phi-phenomenon”. When we comparing samples from remote African see moving pictures in a cinema show, we are villages and Western urban settings. It was influenced by this kind of illusion. The found that African subjects showed greater succession of flickering electrical lights also susceptibility to horizontal-vertical illusion, generate this illusion. This phenomenon can whereas Western subjects showed greater be experimentally studied with the help of an susceptibility to Muller-Lyer illusion. Similar instrument by presenting two or more lights findings have been reported in other studies in a succession. For the experience of this also. Living in dense forests the African illusion, Wertheimer had reported the presence subjects regularly experienced verticality (e.g., of appropriate level of brightness, size, spatial long trees) and developed a tendency to gap, and temporal contiguity of different lights overestimate it. The Westerners, who lived in to be important. In the absence of these, the an environment characterised by right angles, 74 Psychology Rationalised 2023-24 developed a tendency to underestimate the settings, such as hunters and gatherers living length of lines characterised by enclosure (e.g., in forests, agriculturists living in villages, and arrowhead). This conclusion has been people employed and living in cities. Their confirmed in several studies. It suggests that studies indicate that interpretation of pictures the habits of perception are learnt differently is strongly related to cultural experiences of in different cultural settings. people. While people in general can recognise In some studies people living in different familiar objects in pictures, those less exposed cultural settings have been given pictures for to pictures have difficulty in the interpretation identification of objects and interpretation of of actions or events depicted in them. depth or other events represented in them. Hudson did a seminal study in Africa, and found that people, who had never seen Key Terms pictures, had great difficulty in recognising objects depicted in them and in interpreting Absolute threshold, Binocular cues, Bottom- depth cues (e.g., superimposition). It was up processing, Depth perception, Difference indicated that informal instruction in home and threshold, Divided attention, Figure-ground segregation, Filter theory, Filter-attenuation habitual exposure to pictures were necessary theory, Gestalt, Monocular cues, Organ to sustain the skill of pictorial depth perception. Perceptual constancies, Phi-phenomenon, Sinha and Mishra have carried out several Selective attention, Sustained attention, studies on pictorial perception using a variety Top-down processing, Visual illusions. of pictures with people from diverse cultural Summary Knowledge of our internal and external world becomes possible with the help of senses. Five of them are external senses, and two are internal senses. The sense organs receive various stimuli and send them in the form of neural impulses to specialised areas of brain for interpretation. Attention is a process through which we select certain information by filtering out many others that appear to be irrelevant at a given moment of time. Activation, concentration, and search are important properties of attention. Selective and sustained attention are two major types of attention. Divided attention is evident in the case of highly practiced tasks in which there is much automaticity of information processing. The span of attention is the magical number of seven plus and minus two. Perception refers to the processes of interpretation and informed construction of the information received from sensory organs. Human beings perceive their world in terms of their motivations, expectations, cognitive styles, and cultural background. Form perception refers to the perception of a visual field set off from rest of the field by visible contours. The most primitive form of organisation takes place in the form of figure-ground segregation. Gestalt psychologists have identified several principles that determine our perceptual organisations. The image of an object projected on to the retina is two dimensional. Three dimensional perception is a psychological process that depends on correct utilisation of certain monocular and binocular cues. Perceptual constancies refer to invariance of our perceptions of an object seen from any position and in any intensity of light. There is good evidence for size, shape, and brightness constancies. 75 Chapter 4 Sensory, Attentional and Perceptual Processes Rationalised 2023-24  Illusions are the examples of nonveridical perceptions. They refer to misperceptions resulting from misinterpretation of information received by our sensory organs. Some illusions are universal, while others are more personal and culture-specific. Socio-cultural factors play an important role in our perceptions by generating differential familiarity with and salience of stimuli as well as certain habits of perceptual inference among people. Review Questions 1. Explain the functional limitations of sense organs. 2. Define attention. Explain its properties. 3. State the determinants of selective attention. How does selective attention differ from sustained attention? 4. What is the main proposition of Gestalt psychologists with respect to perception of the visual field? 5. How does perception of space take place? 6. What are the monocular cues of depth perception? Explain the role of binocular cues in the perception of depth? 7. Why do illusions occur? 8. How do socio-cultural factors influence our perceptions? Project Ideas 1. Collect ten advertisements from magazines. Analyse the content and message being conveyed in each advertisement. Comment on the use of various attentional and perceptual factors to promote the given product. 2. Give a toy model of a horse/elephant to visually challenged and sighted children. Let the visually challenged children feel by touching the toy model for some time. Ask the children to describe the model. Show the same toy model to sighted children. Compare their descriptions and find out their similarities and differences. Take another toy model (e.g., a parrot) and give it to a few visually challenged children to have a feel of it by touching. Then give a sheet of paper and a pencil and ask them to draw the parrot on the sheet. Show the same parrot to sighted children for some time, remove the parrot from their sight, and ask to draw the parrot on a sheet of paper. Compare the drawings of the visually challenged and sighted children and examine their similarities and differences. 76 Psychology Rationalised 2023-24