This chapter provides a brief introduction to the physical nature of sound, the manner in which it is transmitted and transformed within the ear, and the nature of auditory neural responses.

The nature of auditory stimuli

The sounds responsible for hearing consist of rapid changes in air pressure that can be produced in a variety of ways – for example, by vibrations of objects such as the tines of a tuning fork or the wings of an insect, by puffs of air released by a siren or our vocal cords, and by the noisy turbulence of air escaping from a small opening. Sound travels through the air at sea level at a velocity of about 335 meters per second, or 1,100 feet per second, for all but very great amplitudes (extent of pressure changes) and for all waveforms (patterns of pressure changes over time). Special interest is attached to periodic sounds, or sounds having a fixed waveform repeated at a fixed frequency. Frequency is measured in hertz (Hz), or numbers of repetitions of a waveform per second; thus, 1,000 Hz corresponds to 1,000 repetitions of a particular waveform per second. The time required for one complete statement of an iterated waveform is its period. Periodic sounds from about 20 through 16,000 Hz can produce a sensation of pitch and are called tones.