Auditory lateralization in monkeys: An examination of two cues serving directional hearing

Abstract

In assigning binaural ongoing time differences (phase) as the cue for localization of low frequencies, and binaural intensity differences as the cue for localization of high frequencies, the duplex theory has successfully accounted for human directional hearing of tones. Sensitivity of monkeys to these cues was examined in two experiments. The dependencies on frequency of interaural intensity difference thresholds (lateralization experiment I) and time difference thresholds (lateralization experiment II) were determined behaviorally on three monkeys (M. nemestrina). The range of frequencies was from 125 Hz to 8 kHz in experiment I and from 250 Hz to 2 kHz in experiment II. The results indicate that the duplex theory is applicable to monkeys. However, monkeys are less sensitive than man to both binaural cues. The shortest time disparity monkeys discriminate is 42 microseconds at 1.5 kHz and the smallest intensity difference is 3.5 dB at 500 Hz. Good agreement between the present findings and localization measurements [C. H. Brown et al., J. Acoust. Soc. Am. 63, 1484-1492 (1978)] suggests: (a) that monkeys utilize time disparity cues through higher frequencies than man; and (b) that inaccurate localization by monkeys at high frequencies reflects decreasing sensitivity to interaural intensity cues.

Effect of Behavioral Context on Representation of a Spatial Cue in Core Auditory Cortex of Awake Macaques

“…Few previous studies have examined the ability of macaques to localize pure tones, either in the free field (Brown et al, 1978;Recanzone et al, 2000b) or using closed-field presentation of binaural cues (Wegener, 1974;Houben and Gourevitch, 1979). Thresholds for ILD reported here are lower than those in Macaca nemestrina (Fig.…”

“…2 B, dynamic IPD data shown). As a reference, at 1000 Hz, an IPD of (Houben and Gourevitch, 1979). Base SPL was 90 or 80 dB (monkey Z and X, respectively).…”

Interaural Level Difference Discrimination Thresholds for Single Neurons in the Lateral Superior Olive

“…The shaded area marks the typical human ILD discrimination threshold of tones (for which there is often considerable intersubject variability), which is approximately constant between 0.5 and 4 dB across the bulk of audible frequency range 200 Hz to 10 kHz (Mills, 1960;Grantham, 1984;Yost and Dye, 1988;Wright and Fitzgerald, 2001;Stellmack et al, 2004). The best ILD thresholds in nonhuman primates also range from 1 to 4 dB for frequencies from 0.5 to 10 kHz (Houben and Gourevitch, 1979;Scott et al, 2007). And cats can discriminate ILDs of 1 dB with stimuli in the range of 0.5-3 kHz (Wakeford and Robinson, 1974), suggesting comparable performance between humans, cats, and nonhuman primates.…”

“…Humans, primates, and cats can discriminate differences in ILDs of sounds presented over headphones as small as 1-4 dB (Mills, 1960;Houben and Gourevitch, 1979;Scott et al, 2007;Wakeford and Robinson, 1974). The behavioral resolution of sound source location will be ultimately limited by the variability in the neural representation of the localization cues such as ILDs.…”

“…Instead, location must be computed centrally based on neural representations of minute differences in direction-dependent spectral and temporal characteristics of the sounds arriving at the two ears. The difference in the sound pressure levels (SPLs) of stimuli at the two ears is a primary acoustical cue for horizontal sound location by humans (Rayleigh, 1907;Stevens and Newman, 1936;Mills, 1958), nonhuman primates (Houben and Gourevitch, 1979), cats (Casseday and Neff, 1973;May and Huang, 1996), and other mammals, particularly for sounds with high-frequency content. These interaural level differences (ILDs) arise from the spatial-and frequency-dependent acoustic shadow that is cast by the head and varies systematically with source azimuth (Martin and Webster, 1989;Wightman and Kistler, 1989;Spezio et al, 2000).…”