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Gregory's indirect theory (1974)
A lot of information reaches the eye, but much is lost by the time it reaches the brain
(Gregory estimates about 90% is lost).Therefore, the brain has to guess what a person sees
based on past experiences. We actively construct our perception of reality. Gregory
proposed that perception involves a lot of hypothesis testing to make sense of the
information presented to the sense organs. Our perceptions of the world are hypotheses
based on past experiences and stored information. Sensory receptors receive information
from the environment, which is then combined with previously stored information about the
world which we have built up as a result of experience. The formation of incorrect
hypotheses will lead to errors of perception (e.g. visual illusions like the Necker cube).
Perception is based on 3 things:
1. Sensory data What you actually see on the back of your retina
2. Previous knowledge expectations of what you have previously seen with that data
3. Forming a hypothesis based on the two looks at the information given from sensory
data and what previous knowledge you associate together to produce an image that
you perceive.
What we see is an interaction of what we actually see (sensory data) and previous
The MullerLyer illusion:
Two lines are the same size however Gregory suggests that this illusion occurs because of
our experience with depth, one looks like the edge of a building
Khorasani et al (2007) found that once the person knew the illusion it didn't work as well as
if they didn't, however Shopland and Gregory found that visual reversals of the Necker
cube were not prevented when the participants handled the threedimensional selfluminous
model in a dark room. Thus hypothesis testing may sometimes but not always contribute to
the end perception.
Bruner and Minturn (1955) showed that the digits 1 and 3 will be perceived as the letter B if
displayed within a set of letters but as 13 when in a set of numbers.
Visual illusions offer main support for this theory. Segall et al (1963) found that people who
do not live in carpentered environments (i.e. they live in round huts) are less likely to
perceive differences in the lengths of the lines of the illusion as they are not used to seeing the
edges of buildings or the corners of rooms.

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The indirect approach explain the way our perceptual system deals with ambiguous
situations where the retinal image is poor.
However most studies are done in an artificial set up therefore fails to explain our own
realworld perception.
Theory fails to explain why we continue to see visual illusions even though we know that
they are illusions and that our brain is misleading us.
Lack of precision regarding key concepts, the notion of perceptual hypotheses may appear
to make sense, but there are unanswered questions, i.e.…read more

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Three important components of Gibson's Theory are
1. Optic Flow Patterns
2. Invariant Features and
3. Affordances.
These are now discussed.
1. Optic Flow Patterns
Changes in the flow of the optic array contain important information about what type of
movement is taking place. For example:
i) Any flow in the optic array means that the perceiver is moving, if there is no flow the
perceiver is static.…read more

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Are, in short, cues in the environment that aid perception. Important cues in the environment
OPTICAL ARRAY: The patterns of light that reach the eye from the environment.
RELATIVE BRIGHTNESS: Objects with brighter, clearer images are perceived as closer
TEXTURE GRADIENT: The grain of texture gets smaller as the object recedes. Gives the
impression of surfaces receding into the distance.
RELATIVE SIZE: When an object moves further away from the eye the image gets smaller.…read more

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Gibson and Walk (1960) found that infants and animals perceive depth innately and thus
supporting Gibson's idea of perception.
Sahin et al (2007): the concept of affordance has been successfully applied to autonomous
robots, which are able to learn about the meaning of objects in their environment.
Wraga et al (2000) found that there was no MullerLyer effect when participants walked
around a three dimensional display shows that movement is important in perception because
a static display leads to the illusion.
E.g. Ames room.…read more

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Newborn infants: shown preference to face like patterns than nonface patterns. Show
greater interest in more complex images. Brennan et al (1966) shows infants checkerboard
patterns of increasing complexity (2 by 2, 4 by 4, and then 24 by 24) 1 month old infants
preferred most complex ones. Youngest infants so not have sufficient visual acuity to see the
smaller squares in a 24 by 24 display but the preference by older infants indicates
preference for more complex visual stimuli.…read more

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Forest Dwellers: Colin Turnbull (1963): Bambuti pygmy saw buffalo grazing in distance
(only used to seeing forest) not used to distance so asked what insects they were. Replied
they were buffalos he laughed. His lack of experience with perception led to inability to use
distance perception to interpret size.
Pictorial cues: Hudson (1960) studied influence of culture on depth perception using Bantu,
European and Indian children in South America.…read more

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Fantz (1961) showed infants as young as 4 days old three
pictures. All the infants seemed slightly more interested in
the picture that was closest to a real face rather than them
being jumbled up.
Goren et al (1975): face recognition make sense to be
innate as has adaptive value so a newborn can attach and
relate to own species.
All units are linked to the cognitive system which provides
information as required about stereotypes or information
about people we know.…read more


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