Cognitive Psychology: Sensation and Perception

As adaptive creatures, we humans need to know what is happening in the world around us. Sensation tells us there are objects in the world outside ourselves; perception tells us what and where they are and what they are doing. Together, our sensations and perceptions link our brains to the world and allow us to form mental representations of reality.

We know the world through many senses, including seeing, hearing, touching, smelling, and tasting. With more than 50 percent of our cerebral cortex devoted to visual functions and much of the remainder devoted to audition (including speech), seeing and hearing are by far the most studied.

The visual sense is amazing because we can create vivid, detailed representations of the world from rather fuzzy patches of light momentarily projected through the lens of the eye onto the retina. From this highly impoverished two-dimensional array of light and dark, we construct a complex three-dimensional mental model of the world around us. This model identifies people and objects of specified shapes, sizes, and colors, located at specific places or moving across our field of view. The processes underlying this everyday miracle are still somewhat mysterious, but behavioral scientists specializing in sensation and perception are discovering the steps that transform retinal nerve firings into the internal cinema of daily life.

In tracing those steps, researchers have found that very small aspects of the retinal array provide a basis for leaping to gigantic conclusions about what is "out there." One fuzzy edge of darkness on the retina may come from a building a certain distance away, while another may come from a man leaning out the building's window. Our brain combines that information from the retinal array with knowledge, beliefs, and expectations to make reasonably informed guesses about what is present in the scene. Our inferences about the location, movement, size, color, and texture of objects also involve a huge amount of guesswork. In our everyday lives, we hardly know anything for sure, but because the world is a fairly regular place, we usually surmise correctly. The fact that perception relies so much on our knowledge of the world implies that it cannot be studied and understood in isolation; scientists must link perception with other cognitive processes, such as learning, memory, judgment, and problem solving.

The study of perception is one of the most advanced areas of psychology. Many perceptual processes, especially those involving vision and audition, are well understood and provide a vital bridge between neuroscience and behavioral science. But much more must be learned. One major mystery is how we identify the shapes of things the configuration of contours and edges that populate our visual world with poodles, people, potholes, and Picassos. Another is how we move from identifying the shapes of objects to identifying the objects themselves. A third is how perception is influenced by a person's experiences, motives, expectations, and goals.