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Gregory’s top down/indirect theory of perceptual organisation

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  • Category: Mind Sense

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Gregory proposed that our past experience, knowledge, expectations and motivations can affect how we interpret the visual information we receive, therefore affecting our perception. He suggested that how we see objects is highly brain driven and indirect, and the process takes place so fast that we are unaware of the object in ‘normal perception’; Gregory would say that ‘a perceived object is a hypothesis’. Perceptual constancies show how the brain compensates to provide a constant perception of things despite changes in the sensory information received by the retina. For example size constancy. When we see a person an extremely small person walking next to a person of normal size we understand that a person cannot physically be that small, and therefore must be further away. Another perceptual constancy is shape constancy, where we understand that a shape is the same regardless of which angle we see it from, even though it may produce different shapes on the retina.

We also see different shades of a colour (changed due to illumination) as the same colour due to colour constancy. Similarly we see the world as the same even when we are in different positions or in movement, due to location constancy. The Top Down Theory is supported by studies of perceptual set which show how perception is affected by expectation and context. Palmer’s study supports the Top Down Theory. In this Palmer showed participants a familiar scene (such as a kitchen) and then shown a picture on a screen very quickly. This would either be an appropriate object to the scene like a loaf of bread or an inappropriate object to the scene like a drum. It was found that the loaf of bread was correctly identified 84% of the time and the drum was identified only 50% of the time.

This supports Gregory as it shows that perception is influenced by the brain and what it expects to see, not what is actually there. To evaluate Palmer’s study his study could be argued to lack ecological validity as it was performed in a laboratory meaning this is not an activity you would perform in everyday life, however this would also make the study more standardised and allow the experimenters to repeat it at will. Also, Palmer anticipated people would expect to see a loaf of bread, however in some cases people might also expect to see a drum, making the study lack validity. Minturn and Bruner’s study, conducted in 1951, supports Gregory and Palmer. In this, the experimenters showed that the middle figure (of a board that appeared to read ABC horizontally and 12 13 14 vertically) was more likely to be seen as a number 13 if presented with 12 and 14, and more likely to be seen as a B if presented with A and C.

This supports Gregory and Palmer because it shows that the brain sees what it wants to see, not necessarily what is there as the participants saw the same picture but their brains manipulated the image each time so that it fit with its surroundings. Gregory proposed that the brain creates a hypothesis to explain sensory data. It can, therefore, be misled as demonstrated by visual illusions and draw the wrong conclusions. For example, ambiguous figures that have two equally possible explanations that the brain alternates between, such as the Necker Cube where the brain tries to interpret a 3D box from a 2D shape. Another example is distortions such as the Muller-Lyer illusion that shows two lines perpendicular to each other, one with an arrow point on each end and one with an inverted arrow point on each end. Gregory argued that culture influences the perception of the Muller-Lyer illusion.

He argued that Westernised societies live in a ‘carpentered environment’ which is a built environment, formed of lots of squares and rectangles so they relate the two lines of the Muller-Lyer illusion to the internal and external corners of buildings. As the brain compensates when objects are further away by perceiving them as bigger than they are actually seen (to estimate their size when close up) the brain also compensates for the line with the arrowhead going away from us (compared to a building going away from us) by making it appear bigger to us and making the line with the arrow head on each end (compared to a building coming towards us) smaller. Evidence for Gregory explanation of the Muller-Lyer illusion comes from cataract patients who have had their sight restored and see the lines the same length, suggesting visual experiences such as the Muller-Lyer illusion are learnt.

More evidence comes from Segall who found that people who live in less square environments do not fall for the illusion, suggesting its results are learnt not innate. However, evidence against Gregory’s explanation of the Muller Lyer illusion comes from children as they are more susceptible to the Muller-Lyer illusion than adults, even though they have had less experience of the carpentered environment. More evidence against Gregory’s explanation comes from Eysenck and Keene who in 1990 suggested that one of the lines is perceived as longer because the overall object is longer due to the fins of the inverted arrow; this suggests the result was just common sense, not the result of having lived in a carpentered environment. Gregory believed that all perception was learnt, his views falling on the nurture side of the debate. In terms of strengths, his views are widely regarded and supported by a range of research studies on perceptual set and illusions.

Gregory’s theory is supported by scientific research carried out under controlled conditions therefore could be argued to be a strong case. It also offers an explanation for why people can perceive things differently from one another. In contrast, Gibson believed that all people view the world in much the same way, as perception is a natural and automatic process, and his view falls on the nature side of the debate. He proposed that the environment provides a rich source of information that the brain can perceive directly with little processing and this view is supported by a large number of research studies such as the Visual Cliff experiment which could be argued to be more ecologically valid. Gregory’s theory has been criticised in that many of the studies used to support his views are argued to lack validity as visual illusions involve very artificial two-dimensional stimuli that give very little information about depth and context.

Also these images are often only seen for a few seconds which could suggest that a lot of the research’s results are guesswork. Another sizeable weakness in the Top Down theory comes from Eysenck. He believed that there are 2 visual systems: vision-for-perception and vision-for-action. As Gregory’s theory ignores the importance of movement and so isn’t relevant to the vision-for-action system, as it isn’t good at explaining how vision is associated with rapid and accurate responses that might be required in a natural environment, and this is better explained by Gibson. To conclude, it could be argued that although Gregory does have support from a variety of scientific studies, that these studies aren’t strong enough alone to hold up his argument as they mostly lack ecological validity due to their unrealistic stimuli. However, all in all Gregory’s Top Down theory does explain a diverse assortment of visual problems we face, explaining them by saying they are due to cognitive, environmental, emotional and motivational factors.

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