CHAPTER 16 Flashcards
(13 cards)
Visual illusions
A visual illusion occurs when perception consistently di ers from objective
reality – it is consistent from person to person and from time to time. Illusions are caused by psychological factors, as opposed to other distortions of perception that can be caused by biological factors.
Ponzu illusion
TRAIN TRACK ILLUSION
In the Ponzo Illusion (Figure 16.1) the upper horizontal line in each diagram is perceived to be longer than the lower horizontal line. Why? We mistakenly perceive this because of the depth cues of linear perspective and height in the visual eld – both of which make the upper line appear to be further from us. Because it casts the same-size image on the retina, we perceive the ‘more distant’ line to be longer.
Müller-lyer illusion
Another illusion, the Müller-Lyer Illusion (Figure 16.2), consists of two lines of equal length, each having opposite-shaped patterns on the ends. One line has regular arrowheads; the other has inverted arrowheads (feather-tails). The line with feather- tails is perceived as being longer than the arrow-headed line.
Carpentered world hypothesis
British psychologist Richard Gregory proposes the carpentered world hypothesis (see Figure 16.3) – he believes that the Müller-Lyer Illusion involves the ‘misapplication of size constancy’. In a 3D world, we maintain a constant perception of the size of a familiar object by considering its distance from us. Gregory argues that we mentally make a 3D form of each gure, using familiar features of buildings to do so. This causes the observer to perceive the arrow-headed line as the leading vertical edge of a building’s outer wall (closest to the observer). The line with the feather-tails is perceived as being further away (the inside corner of a room). Because the feather- tailed line is perceived as being the more distant of the two, and each line produces an equal length image on the retina, we interpret the line with feather-tails to be longer.
Evidence to support this theory came when the illusion was shown to country- dwelling Zulu people who live in round huts with rounded doors and windows. They did not perceive the lines to be di erent lengths as they had never learned to judge distance from corners and angles. Zulu people living in cities in South Africa were fooled by the illusion like everyone else.
Perceptual compromise theory
Ross Day, an Australian psychologist, proposes the perceptual compromise theory.
1 Both parallel lines cast identical-sized images on the retina.
2 The arrowhead or feather-tail lines at the ends of the gures create ‘open’ gures that
cause us to apply the Gestalt principle of closure.
3 This creates a more ‘solid’ gure as shown by the blue lines in Figure 16.4.
4 Because of the perceptual compromise made, we perceive each gure to be the length
of the average between the internal (black) line and the external (blue) lines (see
Figure 16.5).
5 As a result of this, Figure A is perceived to be much shorter than Figure B, each being
perceived to be as long as the distance between the green lines shown in Figure 16.5.
Evidence in support of this theory is that the illusion occurs even when the ends of the lines are ‘U’-shaped or completed circles, as shown in Figure 16.6.
Ames room illusion
FIGURE 16.7 The Ames Room is not really rectangular, but because of our lifetime of experience with rectangular rooms, we perceive it to be bounded by right-angles. In fact the ‘smaller’ person is simply twice as far from the observer as the ‘larger’ person.
The Ames Room Illusion shows that we maintain shape constancy (of a room) at the expense of size constancy.
The Ames Room is constructed in a trapezoidal shape, but is made to appear
square when observed through a peephole. It
is necessary to prevent the use of both eyes in this way, so that the strongest (binocular) depth cues do not work. The rear wall actually runs from right to left, away from the viewer. The far-left corner is twice as far from the peephole as the far-right corner. To add to the illusion, the ceiling is not parallel to the oor. It slopes upwards from right to left, while the oor slopes downwards from right to left, so that the height of the room at far left is double that at far right.
When a person walks from the left corner to the right corner, the observer maintains shape constancy, but cannot also maintain size constancy – so the person appears to be growing rapidly in size.
Waterfall illusion
In 1834, Robert Addams was watching the Falls of Foyers, a waterfall
in Scotland, and noticed an odd e ect (Addams, 1834). After staring at the waterfall for about 30 seconds, he noticed that the rocks beside the falls appeared to drift upwards. He coined the term ‘Waterfall Illusion’ to describe this phenomenon.
Motion after effect
The Waterfall Illusion is an example of a motion after-e ect (MAE) illusion. The MAE refers to the apparent motion of a stationary stimulus (object) following the extended viewing of a continuously moving stimulus. The stationary stimulus appears to move in the opposite direction. It is thought that this illusion is due to the fact that neurons coding a particular direction of movement decrease their response over time; when looking at a stationary surface, the motion then appears in
the opposite direction.
Perceptual set gustatory perception distortion
Visual cues play a large role in the way we perceive avour, by allowing us to make predictions about whether or not we should eat something. When we inspect our food, a lot of what we base our expectations on is past experience. From an early age, visual cues such as shape and colour are learned as indicators of a food’s taste
or quality, which continues into adult life (Ndom, Elegbeleye & Ademoroti, 2011) While the pale green chicken might be perfectly ne, most people have learned to associate the colour green with mould or food that has gone bad, and will not eat meat of that colour. If, on the other hand, the vegetables were pale green, they would still not seem appealing, yet they would be marginally more appealing than the green chicken as the colour is closer to what we typically expect of vegetables.
Colour intensity distortion
Colour intensity plays an important role, not just on our assessment of food, but in our prediction of the type of avour we will experience. For example, foods coloured pink and purple are often associated with sweet avours. Yellow colours are often associated with sour avours. Our expectations of avour are tied to colour and its intensity. Even when not true we often perceive yellow foods to taste sour because of our previous experience with yellow foods such as lemon.
Texture of food definition
The texture of food can be de ned as its physical structure and the way it breaks down in our mouth to release avour and sensations including size, surface feeling, wetness, and viscosity
How texture effects taste perception
Again, we expect certain things to feel a certain way when we eat them. Texture helps us determine whether something tastes normal. Additionally, flavour is affected by texture. Apple flavour, for instance, is affected by what form it takes: grated, pureed, baked or juiced. Variations in texture can also give us a different experience of food or flavour, Studies have found that texture of food or drinks can change the extent to which we can taste. For instance, one study found that banana avouring was stronger, or more apparent, in solutions containing more thickening agent than when it was added in the same concentration to solutions containing less thickening agent.
Synaesthesia
Synaesthesia is a condition in which stimulation of one of the senses causes perception of another sense. This ‘mixing’ occurs after the primary sensory cortex has accurately registered the initial stimulus. Sean Day is a synaesthete. He
sees tastes as colour – cucumber creates flashes of pink, spinach a dark purple, zucchini a dull yellow and chicken a light blue. His tastes are very normal, but he shops for food combinations based on colours that go well together. A meal could therefore consist of chicken with ice cream because he enjoys the colour combination!
Sean also sees music as colour and enjoys listening to different colours. However, he doesn’t get to choose the colours different instruments create – he loves the sound of the French horn, for example, but does not enjoy the colour it creates!
