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

Abstract

In natural environments, many sounds are amplitudemodulated. Amplitude modulation is thought to be a signal that aids auditory object formation. A previous study of the detection of signals in noise found that when tones or noise were amplitude-modulated, the noise was a less effective masker, and detection thresholds for tones in noise were lowered. These results suggest that the detection of modulated signals in modulated noise would be enhanced. This paper describes the results of experiments investigating how detection is modified when both signal and noise were amplitude-modulated. Two monkeys (Macaca mulatta) were trained to detect amplitude-modulated tones in continuous, amplitude-modulated broadband noise. When the phase difference of otherwise similarly amplitude-modulated tones and noise were varied, detection thresholds were highest when the modulations were in phase and lowest when the modulations were anti-phase. When the depth of the modulation of tones or noise was varied, detection thresholds decreased if the modulations were antiphase. When the modulations were in phase, increasing the depth of tone modulation caused an increase in tone detection thresholds, but increasing depth of noise modulations did not affect tone detection thresholds. Changing the modulation frequency of tone or noise caused changes in threshold that saturated at modulation frequencies higher than 20 Hz; thresholds decreased when the tone and noise modulations were in phase and decreased when they were anti-phase. The relationship between reaction times and tone level were not modified by manipulations to the nature of temporal variations in the signal or noise. The changes in behavioral threshold were consistent with a model where the brain subtracted noise from signal. These results suggest that the parameters of the modulation of signals and maskers heavily influence detection in very predictable ways. These results are consistent with some results in humans and avians and form the baseline for neurophysiological studies of mechanisms of detection in noise.

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

“…However, the post-hoc tests showed that only the thresholds obtained with a 500 Hz tone were significantly higher than the others. This is consistent with higher audiometric thresholds for 500 Hz tones for macaques (see Bohlen et al 2014 for audiometric thresholds of monkeys C and D).…”

“…This is consistent with a model of auditory detection previously developed (Bohlen et al, 2014), that implicates accumulation/integration, and it is generally consistent with models of sensory processing and sensorimotor integration (Vickers 1970; Usher and Mclelland 2001). Models of central neurons have also incorporated accumulation as an important aspect of computing decision (e.g., Wang 2008).…”

“…Monkeys A, B, C and D ( Macaca mulatta ) were 10, 9, 7 and 6 years old, respectively at the start of the study, while Monkey G (M acaca radiata ) was 7 years old. All monkeys showed audiometrically normal hearing thresholds measured (in dichotic conditions) over the range of frequencies spanning 0.125 to 40 kHz (Dylla et al, 2013; Bohlen et al 2014). All the procedures were approved by the Animal Care and Use Committee of the Vanderbilt University Medical Center and were strictly consistent with the guidelines for animal research established by the National Institutes of Health.…”

“…Detection performance was measured only when the monkeys consistently performed the task. The behavioral procedures are described in Dylla et al (2013) and Bohlen et al (2014). Briefly, all trials started with the monkeys pressing down on the lever (Model 829 Single Axis Hall Effect Joystick, P3America, San Diego, CA).…”

Noise-induced cochlear synaptopathy in rhesus monkeys ( Macaca mulatta )

“…Threshold shifts at 32 kHz are undefined because baseline thresholds ranged from 50-75 dB SPL and all post-exposure thresholds at this frequency exceeded the limit of the acoustic system (90 dB SPL). This frequency approaches the upper limits of audibility, where the audiogram steeply slopes in monkeys as young as 5-7 yrs, so high baseline thresholds at 32 kHz may not be pathological (Pfingst et al, 1978; Dylla et al 2013; Bohlen et al 2014). Note that ABR threshold shifts in the naïve macaque (M4 in Fig.…”