Lossy compression of uninformative stimuli in the auditory system

Abstract

Despite its temporal precision, the auditory system does not encode fine detail of some classes of natural sounds. For example, sounds known as “auditory textures” seem to be encoded and retained with a lossy, compressed representation consisting of time-averaged statistics. One explanation is that the auditory system compresses stimuli that exceed its informational bandwidth. Decreased sensitivity to temporal detail of sound would reflect a limit of the auditory system to transmit sensory information above a certain rate. Here we instead propose a normative explanation. We assume that to minimize energy expenditure, the auditory system compresses stimuli that do not carry novel information about the environment. We developed practical measures of stimulus coding cost (the number of simulated auditory nerve spikes required to encode the sound) and stationarity (degree of change to the sound spectrum across successive time windows). We found that coding cost is not predictive of the ability to discriminate exemplars of a sound. In a second experiment we found that human listeners are sensitive to temporal detail of sounds with high coding cost provided they are unexpected. Our results are consistent with the hypothesis that perceptual compression of auditory textures is a manifestation of an adaptive coding strategy.