Ludimar Hermann discovered the Hermann Grid. It was characterized by “ghostlike blobs” at the intersections where a grey grid is displayed on a background of black (Spillmann&Levine 1971). Baumgartner believed this effect is caused by inhibition in retinal neurons called ganglions. Hermann’s grid can only provide a biological description of visual perception. If we want to fully understand visual perception, then we should also look for an explanation that includes the environment.
There is more light at the intersection’s center than there is in the field of receptivity located on the other side. In the intersection, more light means there is greater lateral inhibiting. Lateral inhibition prevents action potentials spreading from neurons that are excited to their neighbors in the lateral directions (Yantis and Steven, 2014). This contrast allows for greater sensory perception. This is due to the fact that the receptive zones in the central retina are much smaller and therefore cannot cover an intersection.
Likewise, Hermann’s grid is only a partial explanation of visual perception. Schiller & Tehovnik (2015) point out three flaws. The illusion remains the exact same even when our receptive areas remain the same. Second, by distorting or skewing the grid even by 45 degrees you can greatly reduce or eliminate the illusion. Thirdly it is not so simple to arrange retinal ganglions and the corresponding receptive zones as Baumgartner had assumed. Parasol cells have much larger receptive centers and surrounds than Midget ganglions. The Hermann grid is not explained by Baumgartner’s localized processes because of the complex arrangement between excitatory centers, and inhibitory surrounds that operate at different distances across the 2-D image.
We can therefore conclude that the visual processing process cannot be explained only by lateral inhibitory inhibition. Other explanations must exist. Cognitive explanations claim that we process information visually through cognitive processes including attention and recall. James Gibson’s and Richard Gregory’s work are two of the most important cognitive explanations.
James Gibson’s bottom-up hypothesis suggests that the mechanisms of perception are innate and have evolved over time. Learning is not necessary. It is clear that perception would be necessary to survive, as the environment without it would be extremely dangerous. In order to avoid predators or to determine which fruits are poisonous and safe to eat, our ancestors must have had the ability to perceive.
Gibson’s Theory began with the idea that the pattern or array of light that reaches the eye contains all the information needed for visual perception. The optic array is a way to get unambiguous data about objects’ layout in space. The flow changes of the optical array provide information about the movement type. The flow will move either from or toward a certain point. If you move towards the point and the flow seems to come from it, then it is likely that you are. You are moving away if the optic array appears to be moving towards the object.
Gibson’s Theory is a strong one because he can apply it to many different situations. If you paint a line on the runway to guide pilots in the right direction, it can gradually get smaller or wider. Gibson’s concept is applicable to all species. It highlights the information richness within an optical array.
It is, however, a reductionist theory as it tries only to explain the perception of an object in terms that are based on its environment. It is well-established that the brain, and especially long-term memories, can affect perception. Richard Gregory’s work shows that we use our pre-existing visual schemas to process information.
Richard Gregory asserted that perception relies on top down processing. As the stimuli from our surroundings are frequently ambiguous, additional information is needed to interpret them. Gregory performed the Hollow Face test to prove his hypothesis. He explained how we reconstruct present information using previous experience by rotating a Charlie Chaplin face. We know that a nose is prominent on a normal-looking face, so we subconsciously transform the hollow face to a face with a protruding nose.
The Necker Cube provides proof that Gregory’s claim about perceptions being ambiguous often is true. The cube’s orientation can change suddenly when you stare at the cross on it. It can be unstable. One physical pattern could produce two perceptions. Gregory claimed that the object appeared to change orientation because of two equally plausible hypotheses, and was unable to choose between them. It is impossible for the appearance to change due to bottom up processing when the perception alters, but there are no changes in the sensory information. The perceptual hypothesis must be used to determine the distance and nearness of objects.
