Spatial and temporal disparity in signals and maskers affects signal detection in non-human primates

Abstract

Detection thresholds for auditory stimuli (signals) increase in the presence of maskers. Natural environments contain maskers/distractors that can have a wide range of spatiotemporal properties relative to the signal. While these parameters have been well explored psychophysically in humans, they have not been well explored in animal models, and their neuronal underpinnings are not well understood. As a precursor to the neuronal measurements, we report the effects of systematically varying the spatial and temporal relationship between signals and noise in macaque monkeys (Macaca mulatta and Macaca radiata). Macaques detected tones masked by noise in a Go/No-Go task in which the spatiotemporal relationships between the tone and noise were systematically varied. Masked thresholds were higher when the masker was continuous or gated on and off simultaneously with the signal, and lower when the continuous masker was turned off during the signal. A burst of noise caused higher masked thresholds if it completely temporally overlapped with the signal, whereas partial overlap resulted in lower thresholds. Noise durations needed to be at least 100 ms before significant masking could be observed. Thresholds for short duration tones were significantly higher when the onsets of signal and masker coincided compared to when the signal was presented during the steady state portion of the noise (overshoot). When signal and masker were separated in space, masked signal detection thresholds decreased relative to when the masker and signal were co-located (spatial release from masking). Masking release was larger for azimuthal separations than for elevation separations. These results in macaques are similar to those observed in humans, suggesting that the specific spatiotemporal relationship between signal and masker determine threshold in natural environments for macaques in a manner similar to humans. These results form the basis for future investigations of neuronal correlates and mechanisms of masking.

Neuronal adaptation to sound statistics in the inferior colliculus of behaving macaques does not reduce the effectiveness of the masking noise

“…As we have previously discussed, we did only observe a significant difference in detection thresholds when the noise level was varied (gated noise thresholds across subjects: F(3, 3) ϭ 367.2, P ϭ 0.0002; noise distribution across subjects: F(3, 3) ϭ 841.7, P Ͻ 0.0001). These results are consistent with our recent study (Rocchi et al 2017), showing no significant differences between tone detection thresholds with gated noise and continuous (steady-state) noise maskers.…”

“…However, this discrepancy might be due to differences in the stimuli used (e.g., stimulus duration). Consistently with Rocchi et al (2017), our results suggest that behavioral detection threshold shifts did not vary as a function of the characteristics of the noise surrounding the signal. Dahmen et al (2010) investigated how auditory spatial processes lead to adaptation depending on the variance of the distribution of the input interaural level differences, showing that the variability within the auditory scene affects perceptual and neurophysiological sensitivity.…”

“…Subsequently, Rees and Palmer (1988) reported similar results recording from IC neurons of guinea pigs. Recent work (Rocchi et al 2017) has shown that psychometric detection thresholds in macaques did not significantly vary depending on whether a 200-ms tone is masked by either simultaneously gated noise or continuous steady-state noise. The present study investigates whether the noise background surrounding target sounds may affect sound detection and the underlying neuronal mechanisms.…”