Visual perception


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Visual perception

  1. 1. Visual Perception Individual Differences, Purposes and Needs  Conformity may sometimes influence perception. Sometimes, influenced by a group or crowd we tend to see things as the group sees it.  Some factors related to personality may have an influence on perception. One such factor is 'tolerance of ambiguity'. Some people can tolerate randomness more than others. They can accept and live with disorder. Others can not. They must create order.  People tend to have various levels of prejudice. Some people prefer simplicity and clarity. Others can tolerate and function well with variety.  Prejudice can affect perception as Gordon Allport and Leo Postman showed in a famous study (1945). After briefly looking at a drawing of figures inside an underground train - five men, two women and a baby, with two of the men standing - a black man and a white man face-to-face in the centre of the picture. Observers were asked to describe what they had seen. Over half of the observers reported having seen a cut-throat razor in the hands of the black man. Some even claimed that he had been 'brandishing it widely' or 'threatening' the white man whereas it was actually in the left hand of the white man standing with him. This
  2. 2. experiment was part of a study of rumour so memory as well as perception was involved.  impulsivity vs. reflectivity. When asked to find a match for a 'familiar figure' (such as a drawing of a telephone) from a choice of 6, some people seem habitually 'leap in' with a response before checking the alternative fully - these are the impulsives - whilst others seem unwilling to respond until they are sure that they have made the correct choice these are the reflective types.  Another kind of cognitive style was referred to as 'field dependence or independence’. Field independence refers to an aptitude for disembedding figures from their contexts. This means they have a high sense of discrimination and can identify something they are searching for in a confusing field. o Someone who finds words easily in word-search grids has considerable field independence. o Where's Wally? books in which one has to find a recurrent character amidst a crowd of people and a frenzy of depicted activity on a very detailed double-page spread. o Those who are good at this are field independent. o Similarly children's puzzles sometimes include the task of identifying faces, objects or animals 'hidden' in a relatively detailed  Gender plays a part in perception too. One gender-related influence concerns how our attention may be drawn to different aspects of a scene or image.  Using ambiguous doodle-like black-and-white figures found gender differences in interpretation.
  3. 3. • A figure which was more likely to be viewed as a brush or a centipede by males was more likely to be viewed as a comb or teeth by females. • Another figure viewed as a target mostly by males was more likely to be viewed by females as a dinner plate. • And a third figure which was viewed mostly by men as a head was viewed mostly by females as a cup. Other roles can also influence perception. An aerial photograph of a river delta may appear obvious to a geographer or a pilot, but if the image lacked an explicit label, others might have quite different interpretations. What is Corvus corax to a professional ornithologist is simply a pest to some farmers, an ill omen to the superstitious, 'Old Grandfather' to the Koyukon Indians of the subarctic forest of North America, a crow to most of us, and a raven to the amateur naturalist.  Many factors which play a part in influencing how things are perceived are relatively 'stable' or long-term individual factors. These include personality, cognitive styles, gender, occupation, age, values, attitudes, long-term motivations, religious beliefs, socio-economic status, cultural background, education, habits and past experience. o But there are other factors which may contribute to individual differences in perception which are more transitory. These include current mental 'set', mood (affective/emotional state), goals, intentions, situational motivation and contextual expectancies.
  4. 4.  WE mentioned the subjectivity of the photographic image It is worth reminding ourselves that photographs reflect not only the scene they depict but the purposes of the photographer. A photograph is a particular photographer's selection from the world of something which they regarded as significant for some reason and is framed in a way which reflects certain considerations. Such purposes include: making a record of something  aesthetic reasons - the subject and/or the framing seemed aesthetically interesting (e.g. 'beautiful')  'self-expression' - to express how they felt about something  persuasion (social/political) e.g. to shock Furthermore, each photograph alludes to photographic conventions:       of a particular historical period for photographs of particular types (e.g. news photos, snapshots, portraits, passport photos) composition/framing, lighting, point of view of other photographs by the same photographer Thematic Apperception Test (TAT) cards are sometimes used in psychoanalysis as a way of exploring the thoughts
  5. 5. and feelings of the person interpreting the ambiguous but figurative situational images depicted on the card. The scenes depicted are emotionally charged but open to interpretation in a variety of ways. The use of such images acknowledges the role of personal concerns in perception. Mood may also influence perception. Leuba and Lucas (1945) conducted an experiment involving the description of 6 pictures by 3 people when in each of 3 different moods. Each mood was induced by hypnosis and then the pictures were shown. Here are the descriptions that one person gave for a picture of 'four college men on a sunny lawn, listening to radio':    Happy mood: 'Complete relaxation. Not much to do just sit, listen and relax. Not much at all to think about.' Critical mood: 'Someone ruining a good pair of pressed pants by lying down like that. They're unsuccessfully trying to study.' Anxious mood: 'They're listening to a football game or world series. Probably a tight game. One guy looks as if his side wasn't winning.' We need to remind ourselves that it was the same picture each time. Mood can clearly play an important part in perception. Albert Hastorf and Hadley Cantril (1954) conducted what became a famous study of the reactions of opposing fans to an American football game between two university teams the Princeton Tigers and the Dartmouth Indians (Princeton won). It was a rough and tense game. One Dartmouth player was taken off with a broken leg and a star Princeton player suffered a broken nose. Both sides were penalized. Undergraduate students from each of the universities were asked for their reactions to the game a week later. 69% of the Princeton students who had seen the game saw it as 'rough and dirty' compared to only 24% of the Dartmouth supporters, whilst 25% of the Dartmouth students invented their own category of 'rough and fair'. When shown a film of
  6. 6. the game later, the Princeton students 'saw' the Dartmouth team make over twice as many rule infractions as were seen by Dartmouth students. Hastorf and Cantril comment that: The data here indicate that there is no such 'thing' as a 'game' existing 'out there' in its own right which people merely 'observe'. The game 'exists' for a person and is experienced by him only insofar as certain happenings have significances in terms of his purpose. For these students, the perception and recall of what might seem to be 'the same event' involved a very active construction of differing realities. Hastorf and Cantril's classic case-study emphasizes the crucial role of values in shaping perception. Context and Expectations Someone once said that there is no meaning without context. Various kinds of context are important in shaping our interpretation of what we see. As a reminder of the importance of making clear what is meant by the importance of 'context' in perception I briefly list here several very different uses of the term. However, I would not suggest that in practice tidy distinctions can always be usefully made. The largest frame is that of the historical context of perception. Some theorists, such as Marshall McLuhan (1962), Walter Ong (1967) and Donald Lowe (1982), have argued that there have been shifts over time in the human 'sensorium' - that is, in the 'balance' of our senses or the priority which we give to some compared with others. Such argue that in western urban cultures we have come to rely more on sight than on any other sense (this was referred to in Visual Perception 1 as 'ocularcentrism'). Another major framework is that of the socio-cultural context of perception. Just as there may be subtle differences in human perception over time there may also be differences
  7. 7. attributable to culture. Some of these were alluded to in Visual Perception 3. Constance Classen (1993) in her book Worlds of Sense shows that different cultures accord priority to different senses - the Ongee of the Andaman Islands, for instance, live in a world ordered by smell. A native American Indian writer called Jamake Highwater, who is of Blackfeet/Cherokee heritage, draws attention in the following extract to radically different ways of seeing the world: Evidence that Indians have a different manner of looking at the world can be found in the contrast between the ways in which Indian and non-Indian artists depict the same events. That difference is not necessarily a matter of 'error' or simply a variation in imagery. It represents an entirely individual way of seeing the world. For instance, in a sixteenth-century anonymous engraving of a famous scene from the white man's history an artist depicted a sailing vessel anchored offshore with a landing party of elegantly dressed gentlemen disembarking while regal, Europeanized Indians look on - one carrying a 'peace pipe' expressly for this festive occasion. The drawing by an Indian, on the other hand, records a totally different scene: Indians gasping in amazement as a floating island, covered with tall defoliated trees and odd creatures with hairy faces, approaches. When I showed the two pictures to white people they said in effect: 'Well, of course you realize that what those Indians thought they saw was not really there. They were unfamiliar with what was happening to them and so they misunderstood their experience.' In other words, there were no defoliated trees, no floating island, but a ship with a party of explorers. Indians, looking at the same pictures, pause with perplexity, and then say, 'Well, after all, a ship is a floating island, and what really are the masts of a ship
  8. 8. but the trunks of tall trees?' In other words, what the Indians saw was real in terms of their own experience. The Indians saw a floating island while white people saw a ship. Isn't it also possible - if we use the bounds of twentieth-century imagination - that another, more alien people with an entirely different way of seeing and thinking might see neither an island or a ship? They might for example see the complex networks of molecules that physics tells us produce the outward shapes, colours and textures that we simply see as objects. Albert Einstein showed us that objects, as well as scientific observation of them, are not experienced directly, and that common- sense thinking is a kind of shorthand that attempts to convert the fluid, sensuous animation and immediacy of the world into illusory constructs such as stones, trees, ships and stars. We see the world in terms of our cultural heritage and the capacity of our perceptual organs to deliver culturally predetermined messages to us. (Highwater 1981, 6-8) Both the historical and socio-cultural context of perception are vast themes which will not be explored further here, but such studies do help to emphasize that 'the world' is not simply indisputably 'out there' but is to some extent constructed in the process of perception. Within a given socio-cultural context, there are widely-shared interpretive conventions and practices. Whilst the basic processes of human perception are largely universal there is scope for subtle but significant variations over space and time. Several other kinds of context are commonly referred to. I have referred already, in Visual Perception 3, to the importance of individual factors which can have an influence on perception. An emphasis on the individual as a context emphasizes the role of the various long-term characteristics of individual perceivers such as values, attitudes, habits and so on. An emphasis on the situational context considers such transitory situational factors as goals, intentions, situational constraints and contextual expectancies. Finally, an emphasis
  9. 9. on the structural context stresses structural features and relationships (such as the relationship between one line and another) 'in' what is perceived - though the extent to which there is agreement about even such low-level formal features may vary. Five main definitions of the scope of the term 'context' have been listed here in relation to their potential influence on perception:      historical socio-cultural individual situational structural Whilst it may be useful to be alert to the very different meanings that the word 'context' can have, disentangling them is problematic. A very well-known study by Bugelski and Alampay (1961) can be seen as showing the importance of situational context. Their experiment is often used as an example of the influence of what psychologists call 'perceptual set': a predisposition to perceive something in relation to prior perceptual experiences. Perceptual set is broader than situational context, since it may involve either long-term (for instance, cultural) prior experience or, as in this case, short-term or situational factors (Murch 1973, 300-301). Groups of observers in the experiment were shown an ambiguous line drawing which was designed to be open to interpretation either as a rat or as a bald man wearing spectacles. Prior to seeing this image, two groups were shown from one to four drawings in a similar style. One group was shown drawings of various animals and the second group was shown drawings of human faces (see illustration below). A control group was shown no pictures beforehand. 81% of the control group reported seeing the ambiguous image as a man rather than a rat. The more pictures of animals that the 'animal' group had seen, the more likely they were to see a rat rather than a man (with 4 prior images of animals 100% then saw a
  10. 10. rat). From 73-80% of the 'faces' group subsequently saw a man rather than a rat. The influence of perceptual set has also been explored in relation to the famous image shown below: This image was designed to be interpreted as either a young woman or an old woman. It was introduced into the psychological literature by Edwin G Boring (1930) (though it was published by the British cartoonist W E Hill in 1915, and is thought to be based on a French version of 15 years earlier). It is sometimes given the chauvinistic label of 'The Wife and the Mother-in-Law'. In order to study the role of perceptual set Robert Leeper (1935) had the image redrawn in two 'biased' forms: one which emphasized the old woman and the other which emphasized the young woman (see image below).
  11. 11. Leeper varied the conditions of viewing for five groups. A control group was shown only the ambiguous drawing, and 65% of this group spontaneously described the image as that of a young woman. The second and third groups were first given a verbal description of the old woman and the young woman respectively. The fourth and fifth groups were first shown the 'old' version and the 'young' version respectively. Groups 2 to 5 were then shown the original ambiguous image. Leeper found that each of the primed groups was 'locked-in' to their previous interpretation. 100% of group 5, which had seen the young version first, interpreted the ambiguous image as a young woman. 94% of group 4, which had seen the old version first, reported seeing the old woman in the ambiguous image. The percentages opting for each interpretation amongst those given verbal descriptions were much the same as for the control group. Gerald Murch (1973, 305) was unable to replicate these findings (94% of his control group first saw the young woman) and suggested that the image was by then so well-known that this may have influenced the results. Particular situational contexts set up expectations in the observer. Bruner and Postman (1949) conducted an experiment in which playing-cards were used, some of which had the colour changed from red to black or vice versa. The cards were exposed in succession for a very short time. Subjects identified them as follows:   some normalized the colours of the anomalous cards; some normalized the suits to make them compatible with the anomalous colours;
  12. 12.  some compromised and saw the anomalous cards as brown or purple. Interpretation here was dominated by what the situational context suggested that people ought to be seeing. A shorter time of exposure was necessary for people to name the normal cards than the anomalous ones. In one experiment, Steven Palmer (1975) first presented a situational context such as a kitchen scene and then briefly flashed on a target image. When asked to identify a loaf-like image, people who had first seen the kitchen correctly identified it as a loaf 80% of the time. Obviously, a loaf of bread is the kind of thing you’d expect to find in a kitchen. They were asked to identify an image like an open US mailbox and an image resembling a drum - two objects not usually associated with the kitchen. The images were a little ambiguous: the mailbox was a little like the shape of a loaf with a slice of bread lying next to it, and the drum could have been interpreted as the lid of a jar. People who had first seen the kitchen only identified these as a mailbox and a drum 40% of the time. The ability to identify objects was affected by people’s expectations concerning what is likely to be found in a kitchen. I have mentioned that situational contexts generate certain (short-term) expectations but it is worth noting in passing that expectations may also be set up by longer-term influences - such as by stereotypes, prejudices and past experience. To return to contexts, here is an example of structural context. This pattern of circles is known as the Ebbinghaus (or Titchener) illusion. It is an illusion of relative size (or more strictly, area). Here the formal relationship between the
  13. 13. parts of the image leads the small white circle (which is the same size in both images) to seem larger in the structural context of the tiny black circles than amongst the large black circles. There is no shortage of examples of the role of structural context amongst the geometrical illusions which can be found in psychology textbooks so no further examples of the role of structural context will be discussed here. At this point it is useful to introduce schema theory briefly. A schema (plural 'schemata' or 'schemas') is a kind of mental template or framework which we use to make sense of things. Particular circumstances seem to activate appropriate schemata, which set up various standard expectations about such contexts. Such schemata develop from experience. They help us to ‘go beyond the information given’ (as Jerome Bruner famously put it) by making assumptions about what is usual in similar contexts. They allow us, for instance, to make inferences about things which are not currently directly visible. The application of schemata and the expectations which they set up represents 'top-down' processes in perception (whilst the activation of schemata by sensory data is a 'bottom-up' process). A good example of the role of topdown processes is where you think that you recognize someone in the street and then realize (from sensory data) that you are wrong. We are often misled in this way by situational contexts, by wishful thinking and so on, ignoring contradictory sensory data in favour of our expectations. In an experiment by Brewer and Treyens (1981), individual participants were asked to wait in an office. The experimenter said that this was his office and that they should wait there whilst he checked the laboratory to see if the previous participant had finished. After 35 seconds, he returned and took the participant to another room where they were asked to recall everything in the room in which they had been waiting. People showed a strong tendency to recall objects consistent with the typical ‘office schema’. Nearly everyone remembered the desk and the chair next to it. Only eight out of the 30 recalled the skull (!), few recalled the wine bottle or the coffee pot, and only one recalled the picnic basket. Some recalled items that had not been there at all: 9
  14. 14. remembered books. This shows how people may introduce new items consistent with the schema. In an experiment by Baggett (1975) participants were shown a series of simple line drawings telling a story. One story showed a long-haired man entering a barbershop, then sitting in the barber’s chair, and finally leaving the shop with shorter hair. In a later test they also saw a picture showing the actual haircut, which had not been present originally. People were fairly good at remembering that this picture had not been present if the test followed immediately after the initial showing. However, if the test occurred a week after the initial presentation most people claimed that they had seen the haircutting picture in the original sequence. This shows the way in which we incorporate in our memories inferences derived from our schemata. This experiment was concerned with memory rather than perception, but it is difficult to separate these processes if you take the stance that no perception is 'immediate'. Gestalt Principles of Visual Organization In discussing the 'selectivity' of perception I have alluded to foregrounding and backgrounding. We owe the concept of 'figure' and 'ground' in perception to the Gestalt psychologists: notably Max Wertheimer (1880-1943), Wolfgang Köhler (1887-1967) and Kurt Koffka (1886-1941). The Gestalt psychologists outlined what seemed to be several fundamental and universal principles (sometimes even called 'laws') of perceptual organization. The main ones are as follows (some of the terms vary a little):  Proximity,  similarity,  good continuation,  closure,
  15. 15.  smallness,  surroundedness,  symmetry and  prägnanz. The principle of proximity can be demonstrated thus: What you are likely to notice fairly quickly is that this is not just a square pattern of dots but rather is a series of columns of dots. The principle of proximity is that features which are close together are associated. Below is another example. Here we are likely to group the dots together in rows. The principle also applies in the illustration below. We are more likely to associate the lines which are close together than those which are further apart. In this example we tend to see three pairs of lines which are fairly close together (and a lonely line on the far right) rather than three pairs of lines which are further apart (and a lonely line on the far left).
  16. 16.  The second major principle of perceptual organization - that of similarity. Look at the example below. Here the little circles and squares are evenly spaced both horizontally and vertically so proximity does not come into play. However, we do tend to see alternating columns of circles and squares. This, the Gestalt psychologists would argue, is because of the principle of similarity - features which look similar are associated. Without the two different recurrent features we would see either rows or columns or both...  A third principle of perceptual organization is that of good continuity. This principle is that contours based on smooth continuity are preferred to abrupt changes of direction. Here, for instance, we are more likely to identify lines a-b and c-d crossing than to identify a-d and c-b or a-c and d-b as lines.  Closure is a fourth principle of perceptual organization: interpretations which produce 'closed' rather than 'open' figures are favoured.
  17. 17. Here we tend to see three broken rectangles (and a lonely shape on the far left) rather than three 'girder' profiles (and a lonely shape on the right). In this case the principle of closure cuts across the principle of proximity, since if we remove the bracket shapes, we return to an image used earlier to illustrate proximity...  A fifth principle of perceptual organization is that of smallness. Smaller areas tend to be seen as figures against a larger background. In the figure below we are more likely to see a black cross rather than a white cross within the circle because of this principle. As an illustration of this Gestalt principle, Coren, Ward and Enns (1994, 377) argue that it is easier to see Rubin's vase when the area it occupies is smaller. The lower portion of the illustration below offers negative image versions in case this may play a part. To avoid implicating the surroundedness principle the conventional broad borders from the four versions have been removed. The Gestalt principle of smallness would suggest that it should be easier to see the vase rather than the faces in the two versions on the left below.
  18. 18.  The principle of symmetry is that symmetrical areas tend to be seen as figures against asymmetrical backgrounds.  Then there is the principle of surroundedness, according to which areas which can be seen as surrounded by others tend to be perceived as figures. Now we're in this frame of mind, interpreting the image shown above should not be too difficult.  All of these principles of perceptual organization serve the overarching principle of pragnänz, which is that the simplest and most stable interpretations are favoured.  The Gestalt principles of perceptual organization suggest is that we may be predisposed towards interpreting ambiguous images in one way rather than another by universal principles.
  19. 19.  The Gestalt principles can be seen as reinforcing the notion that the world is not simply and objectively 'out there' but is constructed in the process of perception