Visual perception: Gregory and Gibson

Perception is basically the principle of how we perceive information of the world through our senses and how it is then processed to allow us interaction with the environment. In our natural environment we are surrounded with sensory information but we only take in a small amount of that information. For the purpose of this assignment the general principle which will be researched into, is the theory of having a two-way flow of information or more simply the bottom-up and top-down processors (Daniels, 2010).

According to Gross (2010), The major theorists involved in the bottom-up and top-down processors are Gibson (1966-1979) and Gregory (1966, 1972-1980), so the direct and indirect theories proposed by Gibson and Gregory on visual perception will be compared and contrasted respectively.

Bottom-up processing is also known as the data driven process because the data induced by the senses, drives on what is perceived. Huitt (2003) stated this theory is based upon believing that we gain an understanding of the world in a direct way through the analysis of sensory input. Information we already have stored in our memory or prior knowledge about our surroundings based on psychological factors such as expectations, is known as top-down processing and is an indirect approach to visual perception (Douglas A. Bernstein, Peggy W. Nash, 2008).

“…The perception of space between objects, in this theory, depends on the experience of contours against a general background, and on the impression of one surface behind another.” (Gibson, 1950: 367-834).

Direct bottom-up processing

The direct approach of bottom-up processing was proposed by Gibson, Douglas A. Bernstein et al (2008) mentioned in his book that “Bottom up processing uses aspects of recognition that depend first on information about stimuli that come up to the brain from the sensory systems”. Gibson believed that biology and genetics are dependable in order for our senses to react to stimuli, and we require no previous knowledge to our environment, alongside the theory that processing information is not done cognitively but on a neural level (Vicki Bruce et al, 2003).

According to Gross (2010) in World War Two Gibson created a training film for pilots who had trouble landing and taking off, he named the information available to pilots as the optical flow pattern (OFP), he suggested that light bounces off different surfaces with different textures and gradients, that then creates patterns through the perception of the eye, the light extended over time and space is known as the optic array, the information processed by the optic array contains three forms: optical flow patterns, texture gradients and affordance.

Affordance is one of Gibson’s notions that link perception and actions in opposite tendencies or basically that perception is independent of the action; it is the connection between the environment and the perceiver.

Draper (2009) wrote in relation to affordance:

“It may also be a surprise to those who think perception is about measuring the absolute attributes of objects, because affordance is obviously not an object attribute, but a relationship between object and perceiver…. Even when we are measuring an object carefully with a ruler, we are using our perception of the object’s relationship with the ruler to derive an absolute property.”

By using the OFP film that Gibson created he was able to give the pilot’s unambiguous information like the speed, altitude and the direction the pilots were going as they approach the landing strip. Gibson argued that optical illusions occur when there is inadequate information available in the optical array; he did not see a distinction between perception and sensation, therefore suggesting that perception is a direct process involving both sensation and perception. (Gross, 2010).

Top-down processingGibson’s theory involves starting at the bottom and relays on stimulus to be processed in order to reach the higher cognitive state, using this stimuli in a direct way to form light patterns and give the perceiver hints about the environment and its relationship. This theory is a complete contrast to Gregory’s top-down indirect approach that uses the cognitive state as a starting point and works its way down, so that visual data relays on prior knowledge of the environment to explain how we perceive, The diagram below shows the flow of stages.

Cognitive state

Stimulus

Bottom-up processing

Indirect top-down processing

The indirect approach of top-down processing was proposed my Gregory, he argued that relevant experience and past knowledge play an important role in visual perception, because using this knowledge will help us perceive current objects, therefore the top-down theory is an indirect active process which goes beyond what is actually being perceived; we utilise inferences, the active process of visual perception results in a perceptual hypothesis being created. (Daniels, 2010).

Visual illusions support the idea of having an active indirect approach of which we use previous experience, however sometimes the brains perceptual area, misinterprets the visual information received and then we get a discrepancy in between cues, this is what Gregory describes as an optical illusion. (Vicki Bruce, et al, 2003).

Gregory (1966) suggests that illusions usually fall into one of these four main categories, first are those based on the top-down processing, secondly are those based on bottom-up processing, the third reflects upon the misuse of mechanisms which are neither bottom-up or top-down which Gregory has named the ‘side-ways rules’, he used this to refer to operations such as depth perception, grouping and scaling, the fourth rule depends on physiological states such as fatigue in specific orientated cells. (David Groome, Hazel Dewart, 1999).

The Muller-lyer and the ponzo illusions can be explained using side-ways rules and the physiological mechanisms. The Muller-lyer illusion occurs because of size consistency scaling and depth perception, he argued it’s the way we interpret 2-D data that causes the illusion, below is the Muller-lyer illusion:

D

C

B

A

According to Daniels (2010) the outward pointing arrow heads represent right angles formed in a room by the floor and ceiling. The inward arrows on the line CD can be thought of as the outside corners of a building. The retinal size of images AB and CD will be the same, but our brain uses size consistency and scales up AB so it appears longer then CD. The Ponzo illusion with the masks relies on a similar effect.

Cardwell (1996) stated that using experience and past knowledge with this indirect approach gives us clues or inferences to how our brain makes sense of visual images, Individual differences and culture can effect this prior knowledge because we all have different experiences that are bias upon our perception, the interpretation on incoming sensory information differs upon what is already known about the environment and is known as schemas.

Together both top-down and bottom-up help recognise the perceptual world, these two work together on many occasions, one example of this is through the process of reading, when the quality of the writing or stimuli on the page is hard to read or poor, top-down processes compensate and make continued reading possible by filling in the gaps where the words were not well processed and perceived. The gaps can be filled in because the world is redundant which provides clues about what is going on, a quote from Douglas A. Bernstein (2008) in his book Essentials of psychology says:

“There is so much redundancy in written language, for instance, that many of the words and letters you see are not needed. Fo- ex-mp-e, y-u c-n r-ad -hi- se-te-ce -it- ev-ry -hi-d l-tt-r m-ss-ng.”

This shows we can create clues to depth making and recognition of a distance easy and clear to recognise. Top-down processing compensates for ambiguous stimuli, an example of this would be to re-arrange a sentence compiled of nonsense to make sense and be put into a meaningful order which can then be recognised. (Douglas A. Bernstein, Peggy W. Nash, 2008).

Conclusion

Both top-down and bottom-up play important roles in visual perception, they contrast with direct and indirect theories but also compensate each other when visually tough tasks occur. Both approaches give details and explain how visual illusions occur through the information processing of visual perception. The top-down approach clearly states that learning and prior knowledge is an important part of the process. Virtually every visual perception task faced in everyday life will involve the use of both approaches and has been a major contribution within the field of visual perception and cognitive psychology.

As quoted in Gross (2010: p239) by Harris (1998):

“Perception is not just a single task but…contributes in many different ways to everyday life… Some of these … are obviously more difficult than others and it seems very likely that some can be accomplished directly, as Gibson maintained, whilst others may require sophisticated internal knowledge and are thus better described by the indirect approach”.