Gibson's Direct Theory (1979) is bottom up, information is pieced together to make sense of it.
- Environmental stimuli projects visual information, which is processed by one's cognitive system then made sense of by the person.
- The Optic Array is the pattern of light made up of all the light rays reflecting off all the objects and surfaces in view, this enters the eye allowing things to be seen. It consists of Texture Gradient (objects that are further away take up less of the optic array and look closer together, it provides information on depth and distance of an object.) Horizon Ratio, where objects that are the same height are cut in the same place by the horizon, regardless of distance. It provides information on the size and distance of an object. The Optic Flow Patterns show that when moving towards something, it stays stationery, wheread other objects appear to move past us. Objects close move faster, and those further away move slower, due to changes in Optic Array. It gives information on position and depth of objects.
- The optic array doesn't explain how we're able to perceive what objects are or how they're used, so affordance comes in. An object 'affords' an action, for example a door knob affords turning.
- The theory has been studied in real-world situation, therefore has high ecological validity.
- It has practical applications, for example optic flow has been used to train pilots.
- Affordance has been criticised, as the uses of some objects can't be perceived without previous knowledge.
Gregory's Indirect Theory (1966) is top down, perception is steered by context and prior knowledge.
- The concept is useful when the stimuli is ambiguous or information provided is limited.
- Visual Illusions support, for example the Necker Cube, our perception of which face is the front changes, Gregory says this is your brain testing different 'hypotheses'. No context is present to help you decide, so your brain continues to switch between the faces.
- Stimuli alone don't provide enough information for perception by cognitive system.
- There is a lot of research supporting, but many lab experiments, so lack ecological validity.
- Theory can explain errors in perception, for example visual illusions. However if perception was based entirely on hypotheses testing, we would make more errors than we do.
Perception is a combination of bottom-up and top-down processes. Bottom-up is useful for unambiguous situations, top-down is useful when information provided is reduced.
Development of Perception
- Depth Perception allows us to change a 2D image on the retina into 3D, using cues such as relative size and texture gradients.
- Gibson and Walk (1960) studied depth perception in babies. A visual cliff was created, with a shallow and a deep level. 36 6 month old babies wouldn't crawl from the shallow side to the deep side. This shows that…