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    Resourcd File Resourcd File Presentation Transcript

    • Theories of Perceptual Organisation
    • (Buddhist proverb) When a tree falls down in a wood and nobody is there, does it make a noise? What is perception? Do we always see what is there?
    • The Eye
    • The Eye • The Lens is situated behind the pupil and completes the process of bringing light into the eye. The lens can change its shape to bring objects at various distances into focus. • The retina at the back of the eye consists of three main layers of cells; o Photoreceptors (light sensitive cells) o Bipolar cells o Ganglion cells.
    • The Eye Photoreceptors consist of 2 different types of cell – cones and rods – which allow humans to see in a wide range of lights. Cones are responsible for vision under bright conditions and colour vision. There are about 5 million cones in each retina and about 50,000 are packed into the small central area called the fovea. Rods are responsible for vision under dim lighting conditions.
    • The Eye Once light has been focused on the retina by the lens, it is changed into neural impulses and sent along the optic nerve to the brain for processing and integration. The optic nerve leaves the eye at the blind spot – an area at the back of the retina that is free of photoreceptors. We are not usually aware of the blind spot – partly because we have 2 eyes, so if the image falls on the blind spot of one eye it will be picked up by receptors in the other eye.
    • The Visual Pathways The optic nerves from each eye come together at the base of the brain to form the optic chiasma. The optic nerve fibres from the nasal retinas (closest to the nose) cross to the opposite side of the brain at this point, while the fibres from the temporal retinas (closest to the temples) continue on the same side of the brain. After they pass through the optic chiasma, most of the nerve fibres lead to the lateral geniculate nucleaus (LGN) in the thalamus. From here, they lead to the primary visual cortex where additional processing is carried out.
    • Gibson’s bottom-up theory Gibson (1979) believed that there was enough information within the pattern of light reaching the eyes (the optic array) for perception to occur directly. Gibson saw perception as due to the direct detection of environmental invariances – unchanging elements of the visual environment. These contain enough sensory data to enable individuals to perceive features such as depth, distance and spatial relationships.
    • Gibson’s bottom-up theory According to Goldstein (1999), Gibson’s theory is based on four main assumptions: 1. The pattern of light reaching the eye can be thought of as an optic array which contains all information necessary for perception. 2. Important information is provided by the movement of the observer. 3. The optic array contains invariant information (information that remains constant as the observer moves). 4. This invariant information leads directly to perception.
    • The Optic Array The optic array contains all the visual information from the environment that enters the eye. Gibson believed that the starting point for perception is the light that enters the eye. To perceive objects, the light has to be structured by the presence of objects, surfaces and textures. According to Gibson, the optic array contains unambiguous , invariant information about how and where objects are situated in space. This information comes in a number of forms...
    • Optic Flow Patterns Gibson described optic flow patterns as unambiguous sources of information concerning height, distance and speed that directly inform perception. The term refers to the changes in the light patterns that reach an observer when either the person, or the visual environment moves.
    • Optic Flow Patterns Flow patterns are created when objects in the visual field move past the observer. The flow provides information about position and depth (consider the way a road sign first appears in the distance, then grows and eventually passes to your left as you pass). Information regarding distance is also gained; distant objects like hills appear to move more slowly while closer objects move more quickly, this is known as motion parallax. The optic flow also varies in relation to the angle between an observer’s direction of movement and the direction of an object being regarded. When travelling forwards – the optic flow is quickest when the object is at 90 degrees to the observer’s side, directly above or directly below.
    • Optic Flow Patterns Johansson (1973) found that a black-clad actor wearing lights on his joints walking in a darkened room, was seen as a moving person, but standing still, he was not perceived as a stationary person. Maher and West (1993) filmed the movement of black-clad animals with light on their joints and found that participants could recognise the species of animal. This demonstrates the strength of movement information in determining optic flow patterns and shows that there is enough sensory information for perception to occur directly.
    • In this painting, the bricks and other features of the front of the building are mainly parallel. The building looks flat, as if seen straight on.
    • Texture Gradient Texture gradients are surface patterns providing sensory information about the depth, shape etc. of objects. There are several classic texture gradients – for example frontal surfaces project a uniform gradient, while longitudinal surfaces, like roads, project gradients that diminish with greater distance from the observer. Texture gradient also indicates the orientation of a surface – sudden changes in texture often signals a change in the direction of a surface, such as a wall meeting a floor. Linear perspective can also be identified – lines are seen to converge as they move further away, helping us to determine depth and distance.
    • Here, texture gradient is used in the form of cobblestones that get progressively smaller to show that the street recedes.
    • Texture Gradient Gibson and Bridgeman (1987) showed participants photographs of surface textures. Participants could correctly identify objects, state their colour, identify the light conditions and say whether they were lying flat etc., suggesting that there is sufficient sensory information in surface textures to permit direct perception. Frichtel et al. (2006) presented participants with a film of a car driving through scenery. Evidence was found that infants as young as 4 months old could perceive using texture gradient, implying that the ability is innate.
    • Horizon Ratio Horizon ratios are another form of invariant sensory information allowing direct perception. They concern the position of objects in relation to the horizon. Objects of different sizes at equal distance from an observer have different horizon ratios, which can be calculated by dividing the amount of an object above the horizon by the amount below the horizon. Objects of equal size standing on a level surface possess the same horizon ratio. When nearing an object, it seems to get bigger, but the proportion of the object above and below the horizon stays constant and is a perceptual invariant.
    • Horizon Ratio Bingham (1993) asked participants to judge the height of cylinders under various conditions where they were provided with cues in the form of tree silhouettes and a horizon. The heights of cylinders were judged inaccurately when they appeared with the horizon but without trees. Judgements were more accurate when the cylinders also appeared in the context of trees, demonstrating how horizon ratios are used to estimate the height of objects in the visual field. Rogers (1996) found horizon ratios were an effective source of information when judging the relative size of objects in pictures, even when horizons were not provided. Participants could impose their own horizon ratio based on eye level and the contents of the picture – showing the degree to which we rely on this source of information.
    • Affordances
    • Affordances Affordances are the most controversial aspect of Gibson’s theory and involve attaching meaning to sensory information. Affordances are the action possibilities of an object – they are what objects suggest or mean to observers and are linked to psychological state and physical abilities. Gibson saw affordances as giving directly perceivable meaning to objects, because evolutionary forces shaped perceptual skills so that learning experiences were not necessary.
    • Affordances Warren (1984) studied whether participants could judge whether staircases portrayed with differently proportioned steps could afford to be climbed. Whether they actually could depended on the length of a participant’s leg. It was found that participants were sensitive to the affordance of ‘climbability’, and according to Gibson this would be achieved by the light reflected from the staircase. Bruce and Green (1990) found that the idea of affordances could be used to explain the visually controlled behaviour of insects.
    • Affordances Stoffregen et al. (1995) tested the affordances of the actions of others. Participants observed tall and short actors standing next to an adjustable chair and in motion (such as walking on the spot) and had to make judgements of preferred and maximum sitting heights for each actor. In both conditions, participants gave accurate judgements, supporting the idea that affordances are available by direct perception.
    • Evaluating Gibson
    • Evaluating Gibson Horizontal lines are painted on the road, becoming closer together as driver approach junctions. These markings are often seen on the exit roads from motorways and serve to create the illusion of increasing speed, which causes the driver to slow down before joining a non-motorway road. Gibson’s theory has practical applications – such as road markings.
    • Evaluating Gibson Tan et al. (2006) used Gibson’s idea of optic patterns to investigate the effects of motion on car drivers’ perception, where cars travelling towards a viewer appear to increase in speed and size, even though their real speed and size is constant. This perceptual problem is increased by the fact that the viewer is also in motion. A camera mounted on a wing mirror was used to determine real-world speed. The data gained from such studies is used to determine speed limits and advise on braking distance. As well as contributing to knowledge of perception, Gibson’s theory also saves lives in preventing / lessening the impact of traffic accidents.
    • “Perception is not determined simply by stimulus patterns. Rather it is a dynamic searching for the best interpretation of the available data...which involves going beyond the immediately given evidence of the senses” Gregory (1966)
    • Gregory’s top-down theory Gregory (1966) believed that perception was an unconscious, continual process of generating and testing hypotheses, and as an active search for the most sensible interpretation of sensory data based on previous experience. Gregory saw sensory information as impoverished, incomplete or ambiguous. What is perceived is much richer than the information contained in the sensory data.
    • Perceptual Set Perceptual set is a concept that views individuals as biased in how they perceive due to previous experiences, cultural factors, and emotional and motivational influences. In other words, people see what they want or expect to see and this cuts down on the number of possible interpretations that data may suggest, making perception speedier, though increasing the opportunities for errors to occur.
    • Expectations Perceptual set occurs through expectations, where people perceive what they expect to based on previous experiences.
    • Expectations Bruner and Mintern (1955) showed an ambiguous figure to participants that could be seen as either the letter ‘B’ or the number ’13’. Participants who saw the figure surrounded by the consecutive numbers 12 and 14 perceived it as 13, while those who saw it flanked by the letters A and C saw it as the letter B This suggests that the context in which stimuli are viewed creates an expectation that shapes actual perception.
    • Expectations Leeper (1935) showed participants an ambiguous picture, which could either be seen as a young or an old woman. Participants previously given a description or picture of a young woman perceived a young woman, while those described or shown an old woman saw an old woman – showing the influence of expectations.
    • Expectations Brochet (2002) gave 54 experienced wine tasters an array of white wines, which they described as ‘fresh’ and so on. He then gave them an array of red wines to evaluate, some of which were white wines, made to look red by the addition of a tasteless, odourless additive. Not one expert spotted the frauds, describing them in terms reserved for red wines (such as ‘intense’ ‘spicy’). Because they had increased knowledge of wine, they were more influenced by colour. The colour created an expectation, which determined actual perception. Why do you think Brochet had his participants rate genuine white wine first?
    • Expectations See Palmer’s research on p75. and the role of hypothesis testing
    • Emotion Perceptual set also occurs through emotional factors, which affect perception by creating a bias to perceive, or not, certain features of incoming sensory data. Perceptual defence is important here, where emotionally threatening stimuli takes longer to perceive.
    • Emotional Influences McGinnies (1949) found that emotionally threatening words took longer to recognise than neutral ones, suggesting that perceptual defence influences perception through emotional factors. However, the results may be due to the embarrassment of speaking the words aloud. Bitterman and Kniffin (1953) found no differences in recognition time if the words were written down. Lazarus and McCleary (1951) found that nonsense syllables presented so swiftly that they could not be consciously perceived raised anxiety levels if they were previously paired with electric shocks. This implies that emotional factors have an unconscious affect.
    • Emotional Influences Phelps et al. (2006) manipulated emotion by showing participants, for a brief instance, either fearful or neutral faces in various locations on a screen. An image then appeared briefly and participants selected in which direction it tilted. Participants were more able to do this when the figure was paired with fearful faces, especially those in the same orientation as the tilted figure. This suggests that emotion facilitates perception early in the processing system.
    • Motivation Draw a picture of your lunch
    • Motivational Influences Perception can be influenced by factors such as thirst or hunger. Images of food appear more enticing as the individual becomes more hungry. What evolutionary purpose might this serve?
    • Motivational Influences Solley and Haigh (1948) found that children drew a bigger Santa and sack of toys as Christmas approached, but after Christmas Santa and his sack both shrank. Bruner and Goodman (1947) got children to manipulate a patch of light so it was the same size as various coins. All children overestimated the size of the coins compared to cardboard control discs, but poor children even more so. What does this imply? Balcettis and Dunning (2006) briefly flashed an ambiguous figure, that could be the letter B or number 13. Participants told that a letter would get them a nice drink, perceived the letter, while those told that a number would earn them a drink saw the number. Which previous aspect does this link to?
    • Cultural Influences Cultural factors influence perceptual set by predisposing individuals to perceive environmental features in certain ways. People from different cultural backgrounds may perceive identical sensory information differently, as they have had different environmental experiences. In the Muller-Lyer illusion, line A is only perceived as longer in cultures where individuals live in a manufactured world of straight lines and right angles because they unconsciously read the dimension of depth into it. Those from cultures where buildings are made from natural materials do not experience the illusion.
    • Cultural Influences Segall (1963) found that Africans living in open country, where occasional vertical objects were important features, were susceptible to the horizontal-vertical illusion, while those living in dense jungle, were less likely to see the illusion. Pettigrew et al. (1978) presented a picture of one South African ethnic group to one eye of a participant and another ethnic group to the other eye. White South Africans were not able to distinguish black and mixed-race people, suggesting that the cultural influence of their racial prejudice affected their perception.
    • Illusions Gregory believes that visual illusions are experienced because expectations based on past experiences are used to create and test hypotheses from incoming sensory information – but sometimes errors happen and false perceptions are experienced.
    • Illusions Necker Cube Hollow Face Penrose Triangle Kanizsa Triangle
    • Evaluating Gregory • Gregory's theory has increased the understanding of perception and inspired a wealth of research. • It seems logical that we would draw on previous experience when viewing conditions are incomplete or ambiguous. • The idea of indirect processing explains how individuals perceive the same stimuli in different ways. • Gregory give a more satisfactory explanation of visual illusions than Gibson. • However – according to Gregory’s theory, once an illusion is understood, perception should alter so that it should not be experienced any more.
    • Evaluating Gregory • Eysenck and Keane (1990) believe that Gregory’s theory is better at explaining perception of illusions than real objects, because illusions are unreal and easy to misperceive, while real objects provide enough data to be perceived directly. • Most supporting research comes from lab experiments, which are biased to favour his theory as fragmented and briefly presented stimuli are often used, so would be difficult to perceive directly. •Gregory underestimates how rich and informative sensory data can be. • In general, people’s perceptions are similar. This would not be true if perceptions were created from individual experience. • The theory suggests that we constantly search memory to find the best interpretation of stimuli. This would be time-consuming and inefficient.
    • Evaluating Gregory •Gibson and Gregory both see perception as being hypothesis based, and they both agree that visual perception occurs from light reflected off surfaces and objects, and that a specific biological system is necessary to perceive. •Perhaps a combination of Gregory and Gibson’s ideas form the best explanation of perception. Gibson’s theory works best for ideal viewing conditions, while Gregory’s works best for less than ideal conditions. This approach was utilised in Neisser’s (1976) Perceptual Cycle Theory.
    • Evaluating Gregory Where is the IDA? • Gregory and Gibson’s theories can be seen in terms of the nature vs nurture debate. Gregory’s indirect theory emphasises learning (nurture), while Gibson’s direct theory sees more of a role for nature. • Research into emotional factors can be considered unethical by causing psychological harm through exposure to threatening material.