Detection of Tones and Their Modification by Noise in Nonhuman Primates

Abstract

A fundamental function of the auditory system is to detect important sounds in the presence of other competing environmental sounds. This paper describes behavioral performance in a tone detection task by nonhuman primates (Macaca mulatta) and the modification of the performance by continuous background noise and by sinusoidally amplitude modulating signals or noise. Two monkeys were trained to report detection of tones in a reaction time Go/No-Go task using the method of constant stimuli. The tones spanned a wide range of frequencies and sound levels, and were presented alone or in continuous broadband noise (40 kHz bandwidth). Signal detection theoretic analysis revealed that thresholds to tones were lowest between 8 and 16 kHz, and were higher outside this range. At each frequency, reaction times decreased with increases in tone sound pressure level. The slope of this relationship was higher at frequencies below 1 kHz and was lower for higher frequencies. In continuous broadband noise, tone thresholds increased at the rate of 1 dB/dB of noise for frequencies above 1 kHz. Noise did not change either the reaction times for a given tone sound pressure level or the slopes of the reaction time vs. tone level relationship. Amplitude modulation of tones resulted in reduced threshold for nearly all the frequencies tested. Amplitude modulation of the tone caused thresholds for detection in continuous broadband noise to be changed by smaller amounts relative to the detection of steady-state tones in noise. Amplitude modulation of background noise resulted in reduction of detection thresholds of steady-state tones by an average of 11 dB relative to thresholds in steady-state noise of equivalent mean amplitude. In all cases, the slopes of the reaction time vs. sound level relationship were not modified. These results show that macaques have hearing functions similar to those measured in humans. These studies form the basis for ongoing studies of neural mechanisms of hearing in noisy backgrounds.

Detection of Modulated Tones in Modulated Noise by Non-human Primates

“…The monkeys were prepared for chronic experiments using standard techniques used in primate research (e.g., Ramachandran and Lisberger 2005;Dylla et al 2013), and their audiograms as well as the effects of noise on their audiograms were consistent with previous reports on non-human primates, including studies from our laboratory (Stebbins et al 1966;Pfingst et al 1975Pfingst et al , 1978Dylla et al 2013). All procedures were approved by the Institutional Animal Care and Use Committee at Vanderbilt University and were in strict compliance with the guidelines for animal research established by the National Institutes of Health.…”

“…Consistent with such a hypothesis, detection thresholds of a steady-state signal in a modulated masker were lower relative to when the signal and the masker were not temporally modulated or when the modulation of the masker is uncorrelated across different spectral regions (e.g. Hall et al 1984;Schooneveldt and Moore 1989;Fantini 1991;Langemann and Klump 2001;Dylla et al 2013). When both signals (local stimulus to an auditory filter) and masker (global stimulus) were temporally modulated, behavioral performance was highly dependent on temporal correlations between the signal and the masker: detection thresholds were lower when the modulation of the signal and the masker were different relative to when the signal and the masker were modulated similarly (e.g., McFadden 1987;Cohen and Schubert 1987;Fantini and Moore 1994).…”

“…The surgical and experimental procedures have been described in detail earlier (Dylla et al 2013). Briefly, monkeys were prepared for this study with a surgical procedure conducted using isoflurane anesthesia and performed under sterile conditions.…”

“…Lever state was sampled at a rate of 24.4 kHz, with a temporal resolution of about 40 μs on the lever release. The details of the task, basic stimulus, and experimental conditions have been described elsewhere (Dylla et al 2013). Briefly, the monkeys initiated trials by holding down a lever (Model 829 Single Axis Hall Effect Joystick, P3America, San Diego, CA).…”

“…Studies have found that macaques have U-shaped audiograms, similar to humans (e.g., Stebbins et al 1966;Pfingst et al 1975Pfingst et al , 1978, and the modification of the audiograms by noise are similar to humans (compare results from Dylla et al (2013) with Hawkins and Stevens (1950)). An early indication of modulation-based release in masking in macaques was observed when tone detection thresholds were lower when either the signal or the noise was modulated (Dylla et al 2013), consistent with findings in humans and other species (e.g., Gustafsson and Arlinger 1994;Bacon et al 1998;Langemann and Klump 2001;Velez and Bee 2010). In this paper, we extend the findings of our previous behavioral study to further investigate how detection is modified when both tones and noise were timevarying (temporal variation was created by amplitude modulation) and suggest a model for the computation underlying the detection.…”