Revisiting Hafter and De Maio: How precision of coding of interaural delay varies with both magnitude of interaural delay and center frequency

Abstract

Erv Hafter’s contributions span a broad range of topics fundamental to the understanding of monaural and binaural auditory perception. His publications and presentations are typified by historically important empirical, conceptual, and theoretical analyses. One issue he studied concerned how precision of neural coding of interaural time delay (ITD) varies with the magnitude of the delay and the spectral content of the stimulus. Such information remains central to contemporary quantitative models of binaural processing. Extending Erv’s efforts, we have developed a new way to measure precision of ITD-coding as a joint function of ITD-magnitude and center frequency. The novel twist entails transforming the classic NoSπ condition into (NoSπ)τ by imposing an ITD on the entire signal-plus-masker waveform. With that stimulus, uniform internal compensation of external ITDs would yield thresholds both independent of ITD and equal to those obtained under NoSπ. In accord with the results of Hafter and De Maio [J. Acoust. Soc. Am. 57, 181–187 (1975)], however, thresholds increased with ITD and did so more rapidly at 4 kHz than at 500 Hz. Our data were accounted for by assuming an internal, interaurally uncorrelated “processing noise,” the power of which increases exponentially with the magnitude of the internal, “matching,” delay.