tuning curve
a graph of neuronal response (usually measured in action potentials or spikes per unit time) as a function of a continuous stimulus attribute, such as orientation, wavelength, or frequency. A neuron is said to be “tuned” for the stimulus that evokes the greatest response, and the width of the curve from the half-maximum response on either side of the peak indicates how broadly or narrowly tuned a neuron is for a particular stimulus attribute. In the auditory system, it is a measure of frequency selectivity. For example, in recordings from an auditory nerve fiber, the threshold is usually defined as a fixed increase in firing rate in response to a pure tone. Typically, tuning curves are V-shaped with a characteristic frequency (CF) or best frequency (BF) at which the fiber requires the minimal sound level to reach the threshold response. A psychophysical tuning curve (PTC) shows the relationship
between the level and frequency of a pure-tone masker (see auditory masking) that is necessary to just mask a probe signal of fixed level and frequency. PTCs bear a strong resemblance to the actual tuning curves measured in auditory nerve fibers. See critical band; tonotopic organization.