Mach bands in hearing.

Abstract

It is difficult to explain the extraordinary capacity of the ear in discriminating pitch without assuming the existence of laterally inhibitory neural nets fed by cochlear potentials. On such an assumption, we have sought to show edge effects in direct auditory masking analogous to Mach bands found in vision. Noise bands having theoretically infinite attenuation rates outside the passband were generated by computer from 56 sinusoids spaced randomly by frequency. Monaural pure-tone-masked audiograms were obtained for each of four subjects for each of two such noise bands (480–580 Hz and 960–1160 Hz) at sensation levels of 20, 30, 40, 50, and 60 dB. Edge effects, as measured by contours of threshold shift, were revealed for all subjects, at every loudness, and were similar for both noise bands. Sharpening was greater at the low frequency end of a band and grew nonlinearly with loudness, as did upward spread of masking. Sharpening was greater for an interrupted than for a continuous masked tone and may be maximal for relatively low interruption rates. The data are consistent with the existence of laterally inhibiting neural nets and are discussed in relation to their neural basis and to other phenomena such as the pitch of noise bands and the regions of increased sensitivity often found in abrupt hearing loss.