Trends in Cognitive Sciences
Volume 5, Issue 8, 1 August 2001, Pages 340-348
Journal home page for Trends in Cognitive Sciences

Opinion
On the role of space and time in auditory processing

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Abstract

Unlike visual and tactile stimuli, auditory signals that allow perception of timbre, pitch and localization are temporal. To process these, the auditory nervous system must either possess specialized neural machinery for analyzing temporal input, or transform the initial responses into patterns that are spatially distributed across its sensory epithelium. The former hypothesis, which postulates the existence of structures that facilitate temporal processing, is most popular. However, I argue that the cochlea transforms sound into spatiotemporal response patterns on the auditory nerve and central auditory stages; and that a unified computational framework exists for central auditory, visual and other sensory processing. Specifically, I explain how four fundamental concepts in visual processing play analogous roles in auditory processing.

Section snippets

Lateral inhibition: extracting the spectral profile

The spatiotemporal representation of sounds in the frequency range <4 kHz in the auditory nerve has given rise to a range of opinions on how the early stages of the auditory system extracts the acoustic spectrum of the stimulus. At one extreme is the purely spatial representation 11, which views the cochlea as a frequency analyzer that maps the stimulus spectral profile onto the tonotopic axis. A simple, central neural network would estimate this profile from the short-time average firing-rate

Multiscale cortical decomposition: spectral profile analysis

The spectral profile extracted at the cochlear nucleus is projected to the auditory cortex via a tonotopically organized pathway through the midbrain and thalamus. However, the details of the representation of the spectral profile in these structures are vague 16. As with other cortical sensory areas, the auditory cortex is subdivided, with a primary auditory field (AI) in the center, surrounded by a belt of secondary areas that are distinguished both anatomically and physiologically. The

Temporal coincidence: estimating periodicity pitch

Pitch is a fundamental percept of sound that is critical to our appreciation of prosody of speech and the melody in music, and in organizing the acoustic environment into different sources 32, 33. Pitch refers to many distinct percepts that are illustrated in Fig. 4. These include: (1) spectrally pitch evoked by a single tone; (2) periodicity pitch (also known as virtual and missing fundamental pitch) evoked by harmonic tone complexes that are spectrally resolved by the cochlea 34; and (3)

Spatial coincidence: binaural localization

In binaural sound processing the central auditory system compares the signals impinging on the two ears, detecting and utilizing various imbalances (e.g. sound level, time of arrival and phase) to perform such perceptual tasks as sound localization in space and signal-to-noise enhancement 45. In this sense, binaural hearing is analogous to binocular vision in endowing perception with an extra spatial dimension based primarily on disparity measures in the stimulus projection upon the sensory

Conclusion

The perception of sound involves a complex array of attributes, ranging from the sensation of timbre and pitch to the localization and fusion of sound sources. Computational strategies proposed to describe these phenomena have emphasized temporal cues and features in the representation of sound in the auditory system. They have also postulated temporal algorithms, such as correlations and absolute period measurements, and utilized delay-lines, intrinsic oscillators and other temporal structures

Acknowledgements

This work has been supported in part by a grant from the Office of Naval Research under the ODDR\ &E MURI97 Program to the Center for Auditory and Acoustic Research.

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