Perception

From Sense to Object

John M. Wilding

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781315464435
• Edition: 1
• Topic: Psicología
• Subtopic: Historia y teoría en psicología

Originally published in 1982, this book introduces the student to the central problem of all perceptual theories: just how does the perceiver identify particular objects? In focusing on the problem, Dr Wilding provides a coherent, well organized framework for its study, bypassing the conventional split between perception and reaction time evidence which was common to most textbooks at the time.

The author draws on evidence from a wider number of research traditions and argues that each has a contribution to make to any account of perception. Throughout he emphasizes the methodological basis of the research discussed, in order to provide students with a solid foundation for their own practical work.

1 Questions

As I look out of my window, I see grass and trees, gently swaying in the wind, with a lake beyond. The smell of new-mown grass drifts in through the open window and the warmth of the afternoon sun pours into the room. An asphalt path leads down through the trees to the lake and two squirrels are chasing each other to and fro across it, ignoring the woman coming up the path. A sudden screech of brakes calls my attention to the constant whirr of traffic on the road beyond the lake and now I hear geese honking, and a murmur of voices from the next room.

This is the scene I experience, a world of objects with back-ground, acted upon and sometimes acting and interacting in events. I have no problem seeing and hearing and smelling and feeling all these things because they affect my senses directly and they make up the real world.

Or do they? I can look again and notice things I missed before, or see the scene in new ways. There is a white wall framing the window I am looking through and the window in fact fills less of my field of view than the wall, but I did not even notice the wall at first, and my impression was that the scene through the window was a panorama right across in front of me. There are metal bars dividing the window into squares and the glass is obscured with dust and spots, but for me the view seemed complete and unobscured. The ‘grass’ is patches of colour ranging from nearly white in the bright sun to nearly black in the shade, but I ‘saw’ green grass in light and shade. Other changing greenish shapes were for me permanent leafy branches moved by a wind I neither saw nor felt, and two constantly varying grey shapes were squirrels moving with a purpose. Another shape increasing in size and changing in position was an approaching woman. A particular pattern of sound frequencies was immediately linked to memories of geese, and another pattern to anxiety, sudden deceleration and images of a suddenly stopping car. A particular sensation of smell evoked memories of lawn-mowers and heaps of grass with children throwing them at each other.

Differences between experience and sensory information

What we experience, apparently directly, is actually very different from what is recorded by our sense organs. Yet it is very difficult to get away from the former and try to get back to the latter. Here is a list of some of the ways in which the information at the sense organs differs from the perceptual experience upon which it is based.

1 Perceptual experience is of a world of segregated objects and events (I will use the word ‘object’ in a broad sense to include such things as sounds, spoken words, and tunes, as well as visually defined objects like people, buildings and hills). But the sensory input is an unsegregated flux, which does not arrive ready for division like a bar of chocolate. We hear words separated by gaps, but physically there are as many gaps in the middle of words as there are between, and frequently there are none in between. Recall how a foreign language sounds.

The situation is not very different for visual perception. Admittedly, visually presented words are usually printed with spaces in between, but most of the other input to our eyes is a patchwork of contours and colours which is far from being neatly organized to suit our needs. Occasionally we gain a glimpse of what the unorganized deluge of stimulation is like when we wake in a strange room or are confronted with a puzzle picture or a photo in which it is not clear which side is the top (Figure 1). Such situations are disturbing, and the sudden realization of where we are, or the sudden organization of the picture so that everything falls into place, produces relief and satisfaction, like we feel having solved a knotty problem. In fact the solution does often come by trying out a number of different possible guesses about the answer. Certain drugs and meditational methods are sometimes used to induce a similar state of non-organization, with the aim of experiencing the ‘reality’ behind normal experiencing. Our immediate visual experience is also of a three-dimensional world, with objects at different distances from us, while the eye receives only a two-dimensional pattern of excitation.

2 Second, the input to our senses is varying in many ways, while our experience is of a stable world. Every time we move our eyes or our head, every time the sun goes in or comes out, the pattern delivered to our eyes changes. We move around in a room but do not believe the walls change shape and the objects in it move around, depending on the angle from which we see them. Sounds of cars or other voices come and go, mingling with the speaker’s voice. The same word is uttered or written differently by different speakers and by the same speaker at different times. Faces change with emotion and age, tunes are played by different instruments and in different keys. Yet we can derive from the variation an underlying stability and disregard the change, or interpret it as having a significance of its own.

Figure 1 Sacks stacked in a warehouse

Another example of our ignoring variability is the grouping together or categorizing together of things which are physically different. In some cases the physical difference is actually unnoticed. Say to yourself ‘keep calm and cool’. Three of the words begin with a ‘k’ sound, but in fact these three sounds differ considerably, You should be able to feel that they are produced differently. An Arab can hear the differences because in Arabic they are sometimes important for meaning, and a Spaniard confuses ‘ice’ and ‘eyes’, which are clearly different for an English speaker, because in Spanish this difference is never important. In other cases the differences can be perceived, but they do not stop us treating a class of objects as similar; the puzzle in these cases is often how we manage to select the similarity. Think of the difficulty of explaining to a Martian how to decide the thing in front of him was a dog or the sounds he could hear were Reggae. No simple clue is apparent and we cannot easily say how we do it.

3 Third, much that we experience is either not present in the input at all, or the basis for it is very different in form from our experience. I have already pointed out that gaps between spoken words are often not physically present; the same is true of stress and loudness in speech, which often depend far more on interpretation of the speaker’s intentions than the physical characteristics of the sounds. Sound waves varying in frequency and amplitude are all that arrive at the ear, but the experience is rich and varied. In vision, fragmentary information, partly obscured, can provide experience of unfragmented objects. Contours may be seen where none exist (Figure 2) and one line may be seen as longer than another though they are really equal (Figure 3). We even claim to be able to judge hardness from appearance. The visual information at the eye consists of a two-dimensional pattern of points of light varying in location, intensity and wavelength, but our experience is of a three-dimensional world of solid objects, such as trees and squirrels. Even such an apparently simple matter as seeing straight lines need not be due to straight lines being projected on to the eye. It is possible to devise spectacles containing prisms which make all vertical straight lines project a curved line. At first these seem curved but after some experience of wearing the spectacles they seem straight again, and if the spectacles are removed they appear curved in the opposite direction for a time. This process of adapting can occur even if no such lines are actually experienced, but only a world of dots (Held and Rekosh 1963). In this environment, movement of the head up and down will produce not the usual ‘flow’ of the image in the opposite direction to the head movement, but a flow along the curved path produced by the spectacles. This unusual result of head movements can, it seems, give the necessary clue about the nature of the distortion, so that a correction to the sensory input can be made. Perception depends on interpreting the result of an action.

Figure 2 Phantom contours (after Kanizsa 1955)

4 On the other hand, much of what arrives at the senses is disregarded – the wall and the window frame and the spots on the glass when I look out of my window at the scene beyond. The ticking of the clock, the pressure of our clothes, the nose in front of our eyes are all there but we usually remain unaware of them. This does not, of course, mean that we cannot become aware of these things if we need to, nor that we take no account of them – indeed, when looking through the window I must avoid looking at the frame, but so long as it remains unchanging and irrelevant this can be done automatically without difficulty. It is change which causes attention to switch, when the automatic taking into account fails. It is obviously important to survival to respond to changes in the environment, and this is exactly how the nervous system reacts, with a burst of activity in response to changes, settling back to a steady state once monotony prevails. Indeed, when by special techniques the image on the eye is kept in exactly the same place, moving with the eye’s movement, it soon disappears altogether, and in very uniform surroundings, such as smooth snow, a form of blindness can develop. Similarly, once we are in the bath we can find we need to keep adding more hot water to maintain a pleasant feeling of warmth.

Figure 3 The Mueller-Lyer illusion
Although the line with outward pointing fins looks longer, both lines are really equal in length.

Figure 4 Plan of a room giving the illusory perception shown in Figure 5 The solid outline is that of the actual room, which projects the same retinal image as a normal room, which is shown with broken lines. The viewer interprets the walls and windows as if they were a normal room and consequently does not correct for the smaller retinal image of the more distant face.

Minor irregularities or inconsistencies are also disregarded, such as misprints and a cough replacing a word in speech (Warren 1970), though this last experiment also showed that a silent gap was noticed; the cough was heard as a word, but the gap could not be so heard.

5 Sensory input is frequently ambiguous but perceptions are usually confident and correct. A given visual patter at the eye could be produced by an infinite number of physical possibilities out in the world, but we are rarely in doubt or mistaken. For example, a large tree far away and a small one closer can project the same sized visual patter on my eye. Nearly always we see the right-sized object at the right distance, though it is possible to devise situations which deceive us, such as the Ames room (Figures 4 and 5), which looks like an ordinary room viewed fom an angle, but is really an odd-shaped room viewed fom directly in front. Sometimes an unchanging input can be seen in more than one way (Figure 6).

6 Because our nervous systems respond mainly to changes and are therefore bad at recording exact copies, perceptions tend to be relative to recent experience or the prevailing context. If you test the bath water after putting one hand under the cold tap and the other under the hot one, the first hand will tell you the bath is hot and the other will tell you it is cool. A kilogramme weight will feel light after lifting ten kilogrammes, but heavy after lifting a few grammes. The house seems dark when you come in out of the bright sunlight but not after a time indoors. The perceived size of objects depends on the company they are in (Figure 7). If you cover your eyes with halves of a table tennis ball and shine a coloured light on them, you soon cease to see any colour at all (Hochberg, Triebel and Seaman 1951).

Figure 5 The Ames room (from Ittelson and Kilpatick 1951)

Figure 6 Two Necker cubes
The upper one can be seen in two different ways with diff...