Chapter 3: Sensation, Perception and Human Potential
Chapter 3: Sensation, Perception and Human Potential
Perception and Human Potential
The beginning of human knowledge is through the senses, and the fiction writer begins where human perception begins.
Flannery O’Connor
Perception – Interpreting Stimuli
We have completed consideration of the stimulation processed through Aristotle’s five major senses along with balance and movement. At this point the body has received input that something has happened in an exclusively bottom-up process.
Not all environmental stimulation relates to survival or achievement of one’s goals. Adapting to one’s environment requires interpretation and prioritization. Once an event is detected, it is important to determine where it originated and what it is. One way the brain has evolved to interpret and prioritize sensory input is the development of feature detectors (Hubel and Wiesel, 1959, 1962). These are cells in the visual cortex which respond to stimuli likely to convey adaptive information. Specialized cells have been discovered for movement, lines, edges, and angles. These characteristics are frequently associated with biologically significant stimuli. For example, movement might signal the presence of a predator. Lines and edges could signal the presence of solid stationary objects or a sudden drop off in height. As shown in Figure 3.21, even infants and other animals are cautious upon approaching a visual cliff (Gibson and Walk, 1960).
Figure 3.21 The visual cliff.
The ability to perceive depth (the relative location of objects) and distance (how far objects are from you) in three-dimensional space is essential to survival and responsible for the visual cliff. In addition to feature detectors for edges and lines, there are additional visual cues which facilitate depth perception. Some of these are dependent on the information obtained from both of our eyes (i.e., binocular cues) whereas others are based upon the information available to one eye (i.e., monocular cues). Not all animals with two eyes have them located so that they are facing in the same direction (e.g., fish). When both eyes face forward there is overlap as well as differences in the visual fields providing potential information regarding the location of objects. The human visual field covers approximately 200 degrees of which there is 120 degrees of overlap between the two eyes.
The major binocular cues are retinal disparity and convergence. Retinal disparity results from your eyes being separated in space, producing stimulation from slightly different angles. The stimulation from objects which are far away is much more similar for both eyes than the stimulation from close objects. Similarly, your two eyes converge (i.e., move closer to each other) as objects move closer. This provides depth and distance information from the muscles controlling eye movements.
It is counter-intuitive but most of the cues related to perceiving objects as three-dimensional are monocular and two-dimensional. Artists