Cognitive Psychology: Sensation and Perception

Recognizing Patterns

Every movement we make involves the ability to recognize various kinds of patterns that we see, hear, touch, taste, and smell. Pattern recognition is crucial to identifying objects and landmarks, moving through a building or a city, reading books, appreciating art, listening to speech and music, even savoring a good meal. Indeed, research has revealed that the essence of expertise in a specialty area lies less in overall reasoning ability than in the ability to recognize large numbers of different patterns as meaningful and significant for action.

In any given domain, experts differ from novices largely in terms of how many patterns they can recognize quickly and respond to appropriately. For example, a chess grand-master's skill depends in large part on the ability to recognize about 50,000 different chessboard patterns of attack and defense. Experts in activities as diverse as detecting cancer cells under a microscope, interpreting speech, and identifying schizophrenic delusions all share mastery in recognizing patterns that recur in their domains.

Recognizing Shapes

Research in perception has focused on such fundamental problems as how we separate a figure from its background and how we organize different figures into coherent patterns. For example, behavioral scientists have found that we tend to see small figures against larger backgrounds, rather than the reverse, even though both perceptions are logically possible.

Researchers have also discovered how perceptions remain constant despite changing patterns of stimulation. A person approaching down a hallway is not perceived as growing larger, even though on the retina, that person's image is expanding dramatically. This occurs, in part, because the observer knows that people stay the same size over short time intervals a contribution of memory to perception. The mind also uses distance cues to compensate and correct for apparent changes in size.

This finding tells us something important about how visual perception operates. The cues to distance, size, and motion are not simple physical attributes but rather ratios of these attributes, such as the retinal height of the approaching man relative to the height of a nearby telephone pole. To maintain perceptual constancy, the visual system keeps track of a large number of different ratios a tribute to the computational power of the human mind.

One of the most difficult research problems is understanding how shape is perceived and recognized. Shape is the most important attribute humans use in identifying objects; for this reason, simple line drawings often suffice to communicate the essential aspects of objects and scenes. Because written words are composed of letter shapes, each with a unique configuration of lines and angles, even reading can be regarded as a shapeprocessing task.