Illusory Sound Perception in Macaque Monkeys

Abstract

In most natural listening environments, noise occludes objects of interest, and it would be beneficial for an organism to correctly identify those objects. When a sound of interest ("foreground" sound) is interrupted by a loud noise, subjects perceive the entire sound, even if the noise was intense enough to completely mask a part of it. This phenomenon can be exploited to create an illusion: when a silent gap is introduced into the foreground and high-intensity noise is superimposed into the gap, subjects report the foreground as continuing through the noise although that portion of the foreground was deleted. This phenomenon, referred to as auditory induction or amodal completion, is conceptually similar to visual induction, fill-in, illusory motion, and illusory contours. Two rhesus macaque monkeys performed a task designed to assess auditory induction. They were trained to discriminate complete stimuli from those containing a silent gap in the presence of two types of noise. Interrupting noise temporally coincided only with the gap, and in humans this causes induction. Surrounding noise temporally encompassed the entire foreground, and in humans this causes masking without auditory induction. Consistent with previous human psychophysical results, macaques showed better performance with surrounding masking noise than interrupting noise designed to elicit induction. These and other control experiments provide evidence that primates may share a general mechanism to perceptually complete missing sounds.

The auditory continuity illusion: A parametric investigation and filter model

“…Thus, the auditory system might smoothly embed continuous sounds of interest in the ongoing context irrespective of the background noise level. The finding that the continuity illusion becomes increasingly prominent with decreases in SNR and NW is consistent with previous results (Houtgast, 1972;Kluender & Jenison, 1992;Petkov et al, 2003;Sugita, 1997;Warren et al, 1972;Warren et al, 1988) and supports the spectral proximity principle. In the SNR experiments, the masker contained the on-frequency band and thus had spectral-temporal overlap with the target.…”

“…For example, it is unknown whether the proximity principles vary with center frequency. A conceptual problem in the study of the continuity illusion arises with the use of very brief (100 msec or less) maskers (see, e.g., Darwin, 2005;Petkov et al, 2003) and of maskers that contain power in the target's frequency band-that is, the on-frequency band (see, e.g., Darwin, 2005;Lyzenga, Carlyon, & Moore, 2005). Without comparison of continuity illusions to nonillusory continuity percepts of appropriate control stimuli, it remains unclear whether listeners could hear the actual targets in very brief maskers.…”

Grouping Mechanisms in Music

“…In order to maintain a stable representation of the auditory world, our perceptual system needs to restore the masked portions of each sound, by estimating their characteristics based on other sounds that occur before, during, and after the masking sound. The continuity effect is widespread, and has been shown to occur in nonhuman species such as cats (Sugita, 1997), monkeys (Petkov, O'Connor, & Sutter, 2003), and birds (Braaten & Leary, 1999;Seeba & Klump, 2009), as well as in human listeners (Houtgast, 1972;Miller & Licklider, 1950;Vicario, 1960;Warren, Obusek, & Ackroff, 1972).…”

Hearing Illusory Sounds in Noise: Sensory-Perceptual Transformations in Primary Auditory Cortex

“…This continuity illusion illustrates the constructive nature of perception that may serve to enhance sensitivity to expected signals and to ensure robustness against background noise. Psychoacoustic research investigated the continuity illusion for various sounds (tones, sweeps, melodies, vocalizations, and speech), and in several species [birds (Braaten and Leary, 1999), cats (Sugita, 1997), monkeys (Miller et al, 2001;Petkov et al, 2003), humans (e.g., Warren, 1999)], suggesting that common perceptual mechanisms may operate at multiple levels of abstraction. The current view holds that the gap induces sudden energy changes in the frequency channel of the interrupted sound (target) which are therefore perceptually interpreted as target off-and onsets.…”