The running theme of this textbook is that humans have very creative brains that assemble or synthesize our experience. Chapter 2 argued for the fundamental point that the brain constructs mental experience. Chapter 3 discussed (among other things) some of the strange effects due to dreaming, hypnosis, and psychoactive drugs. Now we come back down to earth. Here in Chapter 4 we see how mental constructions are made accurate, anchored in reality through the guidance of sensory processes.
The study of sensation and perception is one of the oldest specialties in psychology. The earliest psychologists studied sensory inputs to the nervous system as a first step in understanding how we built up our experience of the world. Psychophysics is the study of how physical energy like light or sound is converted to psychological sensations. We will discuss psychophysics briefly in this chapter. College courses with titles like Sensation and Perception give a more thorough introduction to the topic.
Information from the environment is analyzed by sensory systems operating in conjunction with the brain. We will take a look at sense organs like the eye and the ear and how specialized sensory receptors convert physical energy into nerve impulses within the nervous system. Recent decades have provided a few surprises, like the discovery of an extra sense organ in the nose (the vomeronasal organ) which some researchers suspect may provoke an unconscious sexual response in humans.
Most controversial are proposals about extrasensory abilities like ESP. Starting with the research of Rhine at Duke University, many serious experimenters have looked for subtle effects which might point to the existence of previously-undiscovered "psi energy" or other influences beyond the ken of modern physicists. Your author takes the position (common among psychologists) that forms of ESP involving forms of energy unknown to physics do not exist...or, at least, there is no compelling evidence that they exist. Nevertheless, people have many strange ESP-like experiences, and the last part of the chapter offers possible explanations for some of them.
How this chapter is organized
We start with a discussion of basic receptor types and the waveforms of light and sound. Then we look at the eyeball, moving from the surface of the eye inward to the receptor layer in the retina. Finally, we discuss visual perception, using depth perception as an example.
The next section describes the auditory system, beginning with a discussion of ear structures and the processes of hearing and ending with a tip of the hat to the constructive processes in auditory perception, illustrated by musical hallucinations in deafness. After that we review the other senses such as touch and taste. This is followed by a section on psychophysics, the oldest experimental psychology.
The last section in the chapter is titled Extra Sensory Perception. By breaking the word extrasensory into two words, we open the door to a scientific discussion of unusual (extra) sensory capabilities that go beyond the classic seven. We will also discuss claims about ESP or psychic abilities and why many but not all psychologists prefer non-supernatural explanations of ESP-like experiences.
Related topics in other chapters
The sensory registers, which some psychologists want to banish from Memory chapters because they are actually sensory systems, remain in Chapter 6 (Memory) for reasons of history and tradition. Visual scene analysis, a spin-off from computer science that grapples with the cognitive mechanisms of visual perception, is discussed in greater detail in Chapter 7 (Cognition) because it relies on some principles that are important to other forms of cognition discussed in that chapter.