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Navon 1977
Navon investigated the Gestalt law according to which ‘the whole is more then the sum of its parts’. Participants were asked to identify either the small letters making up the large letters, or the large letter. The small letters were sometimes the same as the large letter and sometimes different. It took longer to identify the small letters when these conflicted with the shape of the large letter. But there was no difference in the time taken to identify the large letters. This could be because the whole large letter could be perceived before the parts (small letters), thus supporting the Gestalt rule. The iv included was whether the small letters were the same as the large letters or conflicting with it. Dv was the time taken to identify the small letters and the large letters.

Proximity-items close together will tend to be grouped together.
Similarity- we tend to group together similar items.
Closure- we tend to fill in missing information to make figures and characters whole.
Good communications-we have preference for continuous figures.
Pragnanz- Gestalt principle states that we are predisposed to see our world in the simplest way possible that requires us to make the smallest effort.

Depth cues-monocular(cue from 1 eye only)/binocular(cue from both eyes)
Binocular- convergence/ used for perceiving the distance of an object at close range. When the eyes converge on a near object(turns inwards as the object is brought closer)the angle between the eyes is greater then when the converge on a distant object. When looking at the object in the distance, eyes are parallel. It is from the stretching of the eye muscle the brain can determined the distance of the object from us.
Retinal disparity-because the yes are 6 cm apart, there is a difference between the images that fall on the retina at the back of each eye. Closer an object is to us, the greater this difference is.

Monocular-motion parallax/ this is where movement of the head produces apparent movement of nearby objects in the opposite direction to us and distant objects in the same direction. In addition when we are moving, objects close to use seem to pass more quickly than object in the distance. Texture gradient- a coarser texture appears closer and a finer texture looks more distant, e.g. sand appears smooth in the distance but grainy close up. Linear perspective- this refers to the tendency for parallel lines that recede from us to appear to converge. Interposition- objects that are closer to us partially obscure objects that are further away. Height in plane or elevation- when an object is further away from us, it appears higher in our visual field.

Size constancy- when we move closer to an object, the size of the retinal image becomes larger, but the perceived size of the object remains constant. This is because the brain receives information about both the size of the retinal image and the distance of the object, and the visual system automatically makes allowance for distance. Shape constancy- when we look at an object in real life, our viewpoints might be quite different and yet the perceived shape is the same. i.e. when we see a door open, it makes a trapezium image on the retina, and yet we perceive it as a normal door. Different viewpoints of an object don’t stop us recognising it.

Ambiguous figures- two hypotheses are presented to us and we are unable to make a definite interpretation of what our senses tell us. But the image on the retina stays the same. The Necker cube- is a lined drawing of a cube that appears to change back and forth spontaneously between two distinct images. Rubin’s vase- we can either perceive a green vase or two red faces. Distortion illusions- the Muller lyer illusion/ ponzo illusion. Muller lyer- arrows on top of the lines are perceived as linear perspective depth cues. Arrows that are outwards are perceived longer then the arrows that point towards us, but they are both the same size. Ponzo- converging lines give us a depth cue of linear perspective, as the top line seems longer than the line below. Both lines are horizontal. These two lines must have the same retinal image because they are both the same size.

Perception is our sense organs (eye, ears, nose) transmitting sensory information to our brain.

Gibson’s
Gibson argued that our perception of surfaces is important and cues from the surfaces are given off and interpreted in a bottom up fashion. This means that visual perception starts with sensory input from the object to the retina and finishes in the brain, where it is interpreted. Gibson thus proposed an ecological theory of perception whereby our perceptual system both perceives simple stimuli and decides what the object affords us i.e whether a surface can be sat on, slid on, grasped ect. He implied that not only in visual perception of an object, but also its meaning, are directly available. Gibson’s theory therefore is a direct theory of perception. In addition to the concept of affordances, which is the intrinsic properties of an item, Gibson made two further fundamental points about the sensory input.

One of which is Optic array. In the natural environment the light source from say a window gives off millions of rays of light. Some of these arrays come directly from the object to the eye, and some comes from the surface on which the object stands. Gibson’s proposed the optic array from objects in our environment gives us a lot of helpful direct sensory data. The second fundamental point to sensory input is invariants. Texture expands as you approach a object and contract as you move away. This flow of texture always occurs I the same way and is therefore ‘invariant’. This direct information from the environment provides an important cue to distance and depth.

Study -lee and lishman 1975
A study was carried out by lee and lishman to investigate optic flow. This is the changing sensory information that is given off from the environment with movement and is received by the eyes. They prepared a ‘swaying room’ where the floor moved and the texture flow could be manipulated. Participants were placed in the room to see if they could remain standing as the floor moved. Adults were able to make mental adjustments and they did not fall over. But the children were not able to make these judgment and they did fall over. It was concluded that participants could monitor changes in the optic flow and send signals to their muscles to prevent them from falling over.

Evaluation- the experiment by lee and lishman lacked ecological validity because it would be rare to encounter a ‘swaying room’ in real life.
-One of the problems with Gibson's theory is that it cannot explain perceptual errors i.e. visual illusions.
+Gibson's theory has ecological relevance and his work was stimulated by his interest in errors made by pilots in the Second World War.
+The concept of invariants has led to interesting empirical research, i.e. into the perception of aging faces.

Gregory's
Gregory 1972 proposed a constructivist approach which is perceptual experiences is more then a direct response to stimulation but includes hypotheses based on constructed from past experiences is relied on the top down processing. This means the expectations stored in the brain works downwards to influence the way we interpret the sensory information from a stimulus. In visual perception, sensory receptors in the retina trigger neural activity, and knowledge in the brain interacts with inputs from the stimulus to enable us to make sense of the world around us. One type of evidence for Gregory theory lies in the way we perceive what we expect to see in a particular context, thereby drawing on stored knowledge.

Evidence for Gregory’s active approach to perception can be found in his explanation of the muller lyer illusion. He proposed that the arrows at the end of the lines provide cue to depth. The outgoing arrows suggest the inside corner of the room, and the ingoing ones resemble the outside corner of a building. In the real world these inwards and outwards facing corners are cues to distance. Gregory’s misapplied size constancy theory states the out going arrows are giving off depth cues that suggest that the lines are further away. The retinal image is off to lines that are equal in length. If this is so, then the one that is assumed to be further away must be longer. As a result, our perception of this line is mentally ‘scaled up’.

Evaluation- when arrows are removed from Muller lyer illusion and replace by circles, there are no depth cues. The illusion however persists and this is a problem for the ‘misapplied size constancy theory’ proposed by Gregory. – Lacks ecological validity because most of Gregory’s research is done I the laboratory. +Unlike Gibson, Gregory can explain visual illusions. +It is likely that both Gibson's and Gregory’s approaches are used in perception depending on the environmental conditions.

Perceptual set is a tendency to notice particular features of the information that enters our sensory system. Vernon 1955 said there is two ways that set acts in -selector/ we focus our attention on what we expect to perceive. -Interpreter/ we already know how to interpret the incoming information and we are biased towards interpreting it this way “the dog chewed the bona”, we might interpret bona as bone.

Perceptual set and motivation- studies seem to show when we are deprived of something, our desire or motivation increases so we are more likely to perceive it. i.e. if we were hungry, we may more readily smell food, or interpret the spoken words’ scream’ as something to eat like ice cream. Study- Gilchrist and Nesberg 1952. Gilchrist and Nesberg carried out an experiment with two groups of participants. One group was deprived of food, whiles the other group had eaten. All participants were then shown a picture and asked to rate them for brightness. Those who had been deprived of food rated the pictures of food and drink as visually brighter then the non-food pictures. The control group who had eaten showed no difference in the ratings of the food and non-food items. –Depriving participants of food in studies can be criticised on ethical ground. – Lacked ecological validity because materials used were pictures not real food.

Perceptual set and expectations- a number of studies have shown we tend to perceive what we expect to see. Study- Bruner and Minturn 1955. Bruner and minter showed participant an ambiguous figure ‘B’ or the number ‘13’. Those shown the figure in the context of numbers ’12 B 14’ were more likely to interpret the figure as a ‘13’, while those show the figure in the context of letters ‘A B C’ interpreted the figure as a letter. This shows how the interaction of context and expectation effects our perception. +Findings can be used in the real world. i.e police training where personnel can be trained to notice and remember car registrations. Important for Gregory.

Perceptual set and emotion-our emotional state affect the way we perceive. Sometimes we are more likely to recognise something because of perceptual sensitisation. This is when the recognition threshold for a stimulus is lowered. At other times our perceptual system defends us from upset or offence. This is known as perceptual defence. Perceptual defence means that we are less likely to perceive a stimulus. Things that cause us anxiety are more difficult to perceive at a conscious level. Study- McGinnis 1949. McGinnis investigated perceptual defence by presenting participants with emotionally neutral words i.e. ‘glass, apple’ and taboo words i.e. ‘rape, penis’ and then asking them to rename the word as soon as it was recognised. It was concluded that emotionally arousing taboo words lead to perceptual defence. – use of taboo words may cause embarrassment and upset is also ethically unsound.

Perceptual set and culture-refers to the idea, information, code of behaviour i.e. that makes up the environment in which we live. Early cross culture studies consisted of presenting participants with visual illusions such as the Müller lyer illusion to different culture groups. Result found that non-Europeans did not make the error on the Müller lyer illusion to which European adults and children were prone. Study- deregowski1972. Deregowski investigated whether pictures were perceived in the same way in different cultures. Participants from Africa and European cultures were shown pictures that were either a split type drawing or the same article showing perspective, and were asked to choose which they preferred. Africans preferred the split type drawings, whereas the Europeans chose the perspective drawings. Deregowski argued that perceiving perspective in drawings is a learned skill, and therefore culture must influence our perceptions.