On a Psychoacoustical Equivalent of Tuning Curves

Abstract

When measuring tuning curves of single units in the auditory nerve (e. g. KIANG et al. 1965, KATSUKI 1966, EVANS 1972) the sound pressure level of a tone burst is increased until the spike rate of a single fibre reaches a particular value just above the spontaneous activity. This value is chosen more or less arbitrarily, but has to be a constant response criterion, for example 1 spike per tone burst (KIANG et al. 1970). The sound pressure level of the tone burst necessary to reach this criterion as a function of its frequency is called the tuning curve. The SPL of the tone, its frequency f, the response criterion and the single fibre are the 4 values involved in the production of such tuning curves. To produce corresponding curves in psychoacoustics, equivalents to these 4 values have to be found. Level of the tone (burst) and its frequency f can be identical values whereas the equivalent of the response criterion can be realized in some kind of a threshold. However, a single fibre has no direct psychoacoustical equivalent, but a very faint sinusoidal tone with a frequency corresponding to the characteristic frequency (CF) of the fibre may be a good approximation, although the spatial extension of a single fibre is always “narrower” than the excitation produced by a faint tone.