Perception

Perception Perception refers to the ways in which information is received through our sense organs. Perception is a cognitive process involving the recognition and interpretation of stimuli once they have registered.

Our perception of the world appears to be immediate and we have no conscious awareness of the brain activity underlying this ability. However, in spite of this it involves complex brain processes.

Illusions

These are visually perceived images that are different from objective reality. The information received by the eyes is processed and gives a perception that is not in line with that of the source.

Two types of illusion include:– Physiological illusions– Cognitive illusions

Physiological Illusions

These are presumed to be the effects on the eyes or brain of excessive stimulation of a specific type, e.g. brightness, colour or movement.

An example of this is the Hermann grid illusion. Grey spots appear at the intersections, a result of the dark surround.

Cognitive Illusions

These are thought to arise from our own assumptions on the world leading to us making unconscious conclusions. They are divided into the following:-

Ambiguous Illusions

These involve a perceptual switch between alternative interpretations. E.g. Necker Cube or Rubin Vase.

Distorting Illusions

These are characterised by distortions of size or length. Examples include the Muller- Lyer illusion or Café wall illusion.

Paradox IllusionsThese are generated from objects that are impossible

such as the Penrose triangle or impossible staircase.

The triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join.

Kanizsa Triangle The brain has a need to see familiar simple objects and

has a tendency to create a whole image from individual elements. Our brain makes sense of shapes and symbols putting them together like a jigsaw puzzle, formulating that which isn't there to that which is believable.

A floating white triangle, which does not exist, is seen.

The Ponzo Illusion This uses cues of depth perception to fool the

eyes. The converging parallel lines tell the brain that

the image higher in the visual field is further away and therefore perceived to be longer although the two yellow lines are of equal length.

Colour and brightness constancies

The contrast of an object will appear darker against a black field which reflects less light compared to a white field even though the object itself has not changed in colour. The horizontal bar is the same shade of grey throughout.

The Spinning Dancer

Some observers initially see the figure as spinning clockwise and some counter clockwise. Additionally, some may see the figure suddenly spin in the opposite direction. The illusion derives from an ambiguity from the lack of visual cues for depth.

http://upload.wikimedia.org/wikipedia/commons/2/21/Spinning_Dancer.gif

The Poggendorff Illusion This is an optical illusion that involves the brain's perception of

diagonal lines and horizontal and vertical edges.In the picture, a straight black and red line is obscured by a

grey rectangle. The blue line, rather than the red line, appears to be a continuation of the black one, which is clearly shown not to be the case on the second picture. To this day, it is not known why this illusion happens.

GIBSON'S :BOTTOM UP PROCESSING

THEORY

What is bottom up processing?• Based on the assumption that we work from bottom upwards in processing.• It assumes that there is enough information provided in the sensory input to allow

the individual to make sense of the world around, without experience. analysis of

sensory

informatio

n

Information is

relayed to the retina where the process of transducti

on into electrical impulses begins.

Impulses are then passed

into the brain and triggers further

responses along visual

pathways until they are in the

visual cortex for final

processing.Flow diagram showing bottom up processing

Main components of his theoryHis theory of direct perception originated from the work he carried out training pilots during WW2. He found all the information that a pilot required to land an aircraft was the total pattern of light that reached the eye. There was sufficient information from the horizon line, ground texture, movement and so on to be able to land a plane.

From this he developed three main components:• Optic flow patterns • Role of invariance• Affordances

Optic flow patterns • Changes in the flow of the optic array

contain important information about what type of movement is taking place.

• The flow of the optic array will either move from or towards a particular point. If the flow appears to be coming from the point it means you are moving towards it. If the optic array is moving towards the point you are moving away from it.

• Think about when you are on a train sitting backwards everything appears to flow past you towards the back of the train.

red = direction of travel star = point of which array flows frompurple = flow of optic array

Role of invariants• Invariants play a part in our everyday lives, they are aspects of the environment

that don't change, even when the observer does move. These invariants supply us with information that is crucial for accurate perception.

• Texture is also associated with changes in distance as an invariant feature of visual perception.

• Another invariant is the horizon-ratio relation. The ratio above and below the horizon is constant for objects of the same size standing on the same ground, even though they change in size.

AffordancesThe term affordance, is the potential for action offered by objects;

they afford opportunities for particular action. The concept of affordance further links perception and movement.

Gibson argued that the meaning of an object can be directly perceived and this meaning communicates action potential. Some objects are shaped in a way that make them look like seats, for example in the case of a flat stone, of a particular height. As a result, we are more likely to sit on a flat stone than do anything else with it.

Evaluation of his theoryGibson argued that we don’t make mistakes, but we do (illusions). He argued that they are presented to us in an artificial setting however they do appear in real life (mirages)He argued that we know what objects are used for but surely we learn this. Therefore affordances must be leant. Would an African tribesman know what a post box is used for?Infants and animals perceive depth innately. Wraga(2000) there is no Muller lyer effect when participants are allowed to walk around a 3D displayGibson exaggerated the role of the optic array/flow to move successfully around our environment (Eysnck) – we use binocular disparity as well

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+

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Appears that there is water on the road even though there isn’t.

Neisser developed the perceptual cycle which combines both Gregory and Gibson's theories.

Gregory’s Top Down theory of Perception

Stimulus information from our environment is frequently

ambiguous so to interpret it, we require higher cognitive

information either from past experiences or stored knowledge in

order to draw conclusions and perceive.

• A lot of environmental 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 using higher cognitive input. In this way we are actively constructing our perception of reality based on our environment and stored information.Senso

ry stimuli from environme

nt

Higher cognitive input from past

experiences and stored

information

Perception

• Gregory proposed that often when we construct our perception of reality it involves making more than one hypothesis about what we actually perceive.

• If we form a correct hypothesis we will perceive correctly, however if we form an incorrect hypothesis it will lead to errors in our perception and this explains why we are sometimes tricked by optical illusions.

• Our brain has formed an incorrect hypothesis or two equally plausible hypotheses and is jumping between the two in our actual perception.

Size Constancy

• As we walk around our visual world, it is constantly changing however our perception of the world is stable.

• If our perception is only based on retinal image (proximal image) objects would appear to grow and change in shape.

• Size constancy refers to our ability to see objects as more or less the same regardless of changes to the stimulus.

• Therefore size constancy is a way of maintaining a stable visual world.

Perceptual ErrorsGregory believed that we

make perceptual errors, and that our retinal images are innately ambiguous.

Of course there are some properties that our eyes cannot signal e.g. weight, Temperature etc.

Sometimes we formulate the wrong hypotheses, optical illusions are a good example of this.

Research also suggests that our perception of objects are influenced by prior expectations or stored knowledge. It has been proposed that stored set knowledge makes perception more efficient by reducing the choices available and speeds up the recognition process.

If you look at this illusion for a while you will notice that it originally looks like two intersecting squares, however with further attention it changes orientations, and jumps backwards and forwards.

Gregory explained this in terms of hypothesis testing.

There are various examples of illusions that can be applied to Gregory’s hypothesis testing theory. One is the Rat-man, because no context is provided we assume it is both a rat and a man, our brain switches between both images.

A popular illusion is the young and old woman that can be applied similarly to Gregory’s hypothesis testing theory.

Our Research on Rat ManBased on the study by BugelskiWe wanted to see if a set of stimulus images

influenced perception of an ambiguous image.E.g. Looking at an old woman and cat and

then looking at the rat man illusionOur results were non conclusive.

What would you expect to find in your kitchen?

Schema

Schemas are sets of ideas about an object or activity

which come from past experiences and may be taken

in from the wider culture.

Our Investigation

Hypothesis: Biederman, Glass and Stacy suggested that when we are presented with a photograph of an organised setting, we are able to remember more objects compared to if we were shown the same objects but in an unorganised pile. They said that this

was because people have developed schemas for everyday familiar settings.

We aimed to prove this statement correct by undergoing our own adaptation of the study!

Results: Unfortunately we could not accept our hypothesis as our results were actually the opposite of what we had expected!

Procedure: We used 24 St Gabriel’s sixth formers. We showed 12 girls in group 1 a slide for 2 seconds of an organised everyday place setting. They were then asked to

immediately recall as many objects in the photograph for 15 seconds. 12 girls from group 2 were shown the same objects as group 1, however, these were shown against a blank background and were presented in an unorganised pile. They also had to recall as many

objects immediately after for 15 seconds.

Group 1: Organised -> used their schema

Group 2: Unorganised -> could not use their schema

Mail box or Toaster?

Expectations may be generated by the context

in which an object is viewed.

A famous study by Palmer showed participants

regularly mistaking the presence of a mail box for a toaster when shown in the context of a kitchen

setting.

Carpentered World Hypothesis

Segall, Campbell & Herskovitz

• People from built up areas are more likely to be fooled by the Műller-lyer illusion.

• Built up Western societies have the tendency to interpret trapezoid shapes as rectangles, and acute angles as right angles.

• Westerners are also used to interpreting two-dimensional drawings as three-dimensional objects.

ORInsect Buffalo

Colin Turnball did research on culture effecting depth perception. He took a pygmy from Congo who was used to living in dense Ituri forest, to the plains. There they saw a buffalo grazing and the Pygmy asked what insects they were. This is because in the forest, vision is so limited that there is no great need to make an automatic allowance for distance when judging size. When Turnball tired to explain that it was a buffalo the pygmy laughed it off and did not believe him.

Hudson’s Study’s1. Zambian & British school children.

Westerns are used to interpreting a 2D figure as 3D, so, the British children made a 3D model, and the Zambians, a 2D model.

2. African Cultures

• ‘What is the man is doing with the spear?’

• ‘Which is nearer the antelope or the elephant?’

African cultures could not perceive depth in the picture. This suggests that to be able to see depth, you must first learn how, as the Western culture are not fooled.

Myopia

• Short sightedness – affects perception.• Strong evidence that it runs in families.• It is found that the environment can also be a

powerful factor.

Mutti’s study on MyopiaInuit Children

• Myopia was uncommon, until the introduction of Western education.

• Myopia is more common in cultural groups that experience formal education and engage in close work.

Berson’s Study on Myopia

• Myopia is much more common in male Jewish teenagers, who study up to 16 hours a day, than Jewish females who study 8-9 hours a day.

Ames Room

Ames Room Explained

The people are in fact twins. Clever trickery

deceives the eye. The floor slopes and the

windows are trapezoid.

Nature Nurture

Gibson and WalkTested 36 babies between 6 and 14 monthsTried to encourage the baby to walk across

the visual cliff by having the mother at the other end.

Babies wouldn’t cross the cliff. If they did they would show fear

response AHHHH!!!!

Gibson and WalkAlso tested with animalsE.g. day old chicks so NO LEARNING!!Only animal that was unafraid to cross was

the rats as have poor vision and use their whiskers.

Campos, Langer & KrowitzTested this with younger babies by moving

them across the cliff. He found decrease heart rate which showed they could detect the change in depth.

Babies of 9 months had increase heart rate showing that they detected a change in depth and associated danger with it.

YonasBabies as young as 2 months showed

avoidance behaviour.Shown a video of on object appearing to fly at

them they flinched.

BowerConditioned infants between 6 and 9 weeks

to turn their head towards a 30cm cube 1m away.

He then introduced three different cubesCube 1: 30cm cube 3m awayCube 2: 90cm cube 3m awayCube 3: 90cm cube 1m away

Cube 1 had the most looks.

1 2

3

Granrud and YonasBabies were shown 2D cardboard shapes like

below.They found that babies reached for the left

shape in A but not in B or C.

A B C

Riesen – monkey manLocked baby monkeys in TOTAL darkness for

3 monthsThey were unable to recognise objects in

their environmentIf something flew at them they did not react.

Ouch!

Cooper - kittens• Kept young kittens in circler boxes that they

couldn’t see out of• Some of the boxes had horizontal lines and

the others had vertical.

(Was the closest we could find – besides they are cute.)

Ethics!

DoHave fully informed consentMaintain the right to withdrawDebrief after an experimentKeep participant unharmed (physically,

mentally and emotionally – happy campers)Help if necessaryContinue of treatment if participant wishesKeep participant’s details anonymous

Bad practiceCooper (kittens) and Riesen (monkey man)

Permanently damaged the animals by destroying nerve cells in the eyes

Gibson and WalkDidn’t gain fully informed consent – however

did get parental permission.Mild stress – but comforted asap

Remember to treat your participants correctly or they will end up like this: