Perception in psychology can be defined as the analysis of sensory information within the brain. As we go through our day, we are surrounded by the rich stimuli of modern life and we rely heavily on our sight to inform us of where we are placed within this world. Through perception we obtain a description of our surroundings and what they mean.
Debate has been ongoing for many years on exactly what role sensory visual information plays within perception and how important our memories and past experiences are in this process.
Visual perception is generally given more attention in psychology due to the sheer volume of research available on vision compared to other sensory areas.
The human eye is a remarkable organ which takes in visual stimulus and sends this sensory information to the brain.
- The eye relies on light which passes through the cornea
- This light is focused by the lens and the cornea onto the retina, a light sensitive membrane on the back surface of the eye
- It is the receptor cells in the retina that translate the light into images.
- Our retina has two classes of receptor cells called rods and cones, both of which are sensitive to light.
Rods respond better to low light levels; therefore they are the cells responsible for maintaining some vision in poor light. Cones are responsible for our ability to detect fine detail and different colours and are the basis of our vision at higher (daylight) light levels.
A significant area of retina is the macula and the fovea. The fovea is an area that contains the highest density of cones and is responsible for perception of fine detail. The optic nerve can then take this information up into the brain.
There are two processes associated with vision which are dependent on the directional flow of information; top-down processing and bottom-up processing.
Various theories of visual perception have been proposed within psychology.
Some fall very much within the bottom-up processing viewpoint where all the information required for perception comes from the visual sensory input.
In contrast, others favour a top-down processing viewpoint, that prior knowledge and past experience is the key to accurate perception of the world around us.
James Gibson was a leading psychologist in the theory of direct realism. Put simply the realist view is that we perceive objects as they really are in the world.
This is a bottom-up approach to perception in that our senses are able to provide us with accurate direct information from the external world.
Gibson’s approach to perception is an ecological one. He claimed the visual information we take in from our environment is so rich that cognitive processing and internal representations to make sense of that information are not required.
Gibson worked with aeroplane pilots in World War II.
He concluded that a pilot’s point of focus on a runway remained stationary as they flew towards it. However, the areas and landscapes around this point flowed outwards as the pilots got closer to landing.
It is from this work Gibson created the term ‘optical flow’ and he believed its principles gave the pilots he worked with more detailed information regarding their distance from the runway and their speed.
Our heads are rarely stationary and neither are our eyes, therefore our world is almost always in motion.
If this movement flows outward from a centre point of focus we are moving towards this point. However, if movement flows inward towards a centre point we are moving away from it.
Gibson claimed the series of angles formed by light reflecting into our eyes from surfaces within the environment are crucial to how we understand what we are seeing.
He suggested this ‘optic array’ provided vital information to aid our perception including distance and speed.
This theory of optic flow patterns is useful in everyday life to inform us of which direction we are moving relative to the objects around us. Simply, if there is movement within our optic array then we are moving.
A key criticism of Gibson’s theories is that they don’t explain how information is picked up from the environment.
Marr (1982) attempted to address this by examining exactly how the brain is able to take information sensed by the eyes and turn it into accurate, internal representations of our surrounding world.
Like Gibson, Marr says information from the senses is enough to allow perception to occur. But unlike Gibson, Marr’s approach puts processes responsible for analysing retinal images at the centre of his theory.
Marr’s theory is strongly ‘bottom-up’ as it views the initial retinal image as the starting point of perception and explores how it might be analysed to produce a description of the environment.
Optical visual illusions are an area of great interest to visual researchers but also cannot be explained by Gibson’s direct realism theory.
In visual illusions we often see movement within patterns and two-dimensional images such as ripples or rotations that are not really there. The well-known ‘Rotating Snakes’ illusions is a good example of this.
When prompted, Gibson’s explanation, is that such illusions are artificial. They are not real-world images and not the type of stimulus we encounter on day to day basis. Therefore, they are not representative of how our visual system operates.
The leading opposing view of Gibson’s visual perception is that of Gregory (1970). Gregory’s view is termed a ‘constructive’ view of perception as it is a top-down processing theory based on construction of our world from past experiences alongside real-time visual information.
Gregory claims the visual information available to us is not always of a high enough quality and therefore the brain needs to fill in the gaps by using prior knowledge, memories and similar experiences to understand what is around us.
Gregory suggests a great deal of information taken in by our eyes is lost en route to the brain.
The information the brain uses to understand this visual input does not always match the reality of what we are actually seeing. This he says, is why we see visual illusions and other similar phenomena.
The Necker Cube is a good example. Upon looking at the cube, our brain concludes that what we are seeing could be a cube with a coloured side closest to us and the cube facing toward the right.
Equally, it could be a cube with a coloured side furthest away and the rest of cube coming towards us. Both of these are possible but our brain is unable to decide which one it is actually seeing.
It is claimed this is why the cube seems to switch perspectives from one view to the other as you continue to look at it.
If this is the case, this cannot be due to bottom-up processing as the visual information of the cube has not changed, however the perspective or our perception of the cube changes nevertheless.
The constructive theory of perception has been criticised for its inability to explain how, if our perception process is based on past experiences, people from different cultures and lifestyles still perceive the world in a similar way.
The direct theory of perception has been highlighted as being unable to account for visual illusions and areas of perception where prior knowledge is more likely to have had influence, such as some of the examples in the above video.
In conclusion it is likely our visual perception processes are the result of a hybrid of these two theories, using our memories, experiences and knowledge to aid understanding of visual information where required.
Perception within psychology is not something we can measure directly and it is a complex phenomenon. We may never know for sure the answers to these questions. However, as we evolve and learn more about our abilities and as science continues to develop, we are moving closer to a much deeper level of understanding.
Gibson, J. J. (1966). The senses considered as perceptual systems. Oxford, England: Houghton Mifflin
Gregory, R, L. (1997) Knowledge in Perception and Illusion, Phil. Trans. R. Soc. Lond. B (1997) 352, 1121–1128
Gregory, R. L. (1980) Perceptions as hypotheses. Phil. Trans. R. Soc. Lond. B 290, 181 – 197
Marr, D., & Vision, A. (1982) A computational investigation into the human representation and processing of visual information. WH San Francisco: Freeman and Company