Sensation & Perception


Our sensory organs contain receptors which encode vibrations, sound waves, light waves, scents, and flavors... We call this sensation
Structures in our brain receive input from these receptors and interpret the coded information... We call this perception

The cells of the retina are organized in layers, which pass information from the part of the retina farthest from the eyes towards the front.

Horizontal cells synapse with similar cells on the same "level", while Ganglion cells synapse with cells on adjacent levels in a heirarchical manner. Rod cells respond to varying levels of light, without respect to wavelength. Thus, "dark-light" vision is attributed to the rod cells which are located at the periphery of the retina.

Cone cells respond to light of specific wavelengths and are concentrated in the center of the retina. Color vision is primarilly handled by the cone cells.

The opponent process theory is based upon the assumption that cone cells respond to light of complementary wavelengths, such as red/green or blue/yellow. When stimulated with one "side", the cells will rebound with an "opponent" display of the other complementary color.

Vision Pathways
The primary receptor is the retina, which transmits information to the brain.

The lateral geniculate nucleus of the thalamus relays visual information to cortex.

Gestalt Principles

Similarity:

Things which share visual characteristics such as shape, size, color, texture, value or orientation will be seen as belonging together.

Proximity:

Things which are closer together will be seen as belonging together.

Closure:

We tend to see complete figures even when part of the information is missing, perhaps a survival instinct which allows us to complete the form of a threat or predator in the absence of complete information.

Continuity:

We prefer continuous figures over discontinuous figures, and perceive the figure above as two crossed lines instead of 4 lines meeting at the center.

Visual Illusions

Figure-Ground:

When viewing images with ambiguous elements of figure and ground, we tend to favour one interpretation over the other (though altering the amount of black or white which is visible can create a bias towards one or the other). Once we have identified a figure, the contours seem to belong to it, and it appears to be in front of the ground.

Ponzo:

Identical figures placed over parallel lines which converge into the infinite distance appear different; the "farther" line appears larger.

Necker Cube:

Adaptation, Brightness/Contrast:

Colors tend to fade and brighten relative to adjacent information. As well, brightness and contrast are perceived relative to adjacent information.

Depth:

We rely on depth to determine the relationship between objects. 2-dimensional representations of 3-dimensional space are a product of perception, which is developmentally, culturally, and anthropomorphically based.

Shading/Shadows:

Shading and shadows dictate whether we see an item from the "top" or "bottom".