Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration

Abstract

Auditory stream segregation refers to the organization of sequential sounds into "perceptual streams" reflecting individual environmental sound sources. In the present study, sequences of alternating high and low tones, "...ABAB...," similar to those used in psychoacoustic experiments on stream segregation, were presented to awake monkeys while neural activity was recorded in primary auditory cortex (A1). Tone frequency separation (AF), tone presentation rate (PR), and tone duration (TD) were systematically varied to examine whether neural responses correlate with effects of these variables on perceptual stream segregation. "A" tones were fixed at the best frequency of the recording site, while "B" tones were displaced in frequency from "A" tones by an amount = delta F. As PR increased, "B" tone responses decreased in amplitude to a greater extent than "A" tone responses, yielding neural response patterns dominated by "A" tone responses occurring at half the alternation rate. Increasing TD facilitated the differential attenuation of "B" tone responses. These findings parallel psychoacoustic data and suggest a physiological model of stream segregation whereby increasing delta F, PR, or TD enhances spatial differentiation of "A" tone and "B" tone responses along the tonotopic map in A1.

Human Cortical Activity during Streaming without Spectral Cues Suggests a General Neural Substrate for Auditory Stream Segregation

“…Microelectrode studies in animals provide clear evidence for forward suppression at a neuronal level in auditory cortex (Calford and Semple, 1995;Brosch and Schreiner, 1997;Fishman et al, 2001Fishman et al, , 2004Kanwal et al, 2003;Ulanovsky et al, 2003;Klump, 2004, 2005;Wehr and Zador, 2005). Much of the data illustrates frequency-dependent suppression, with a greater effect of one tone on subsequent ones when the tones are close in frequency than when they are far apart.…”

“…The present findings indicate a more broadly distributed sensitivity to f 0 that may reflect neuronal sensitivity to the differing temporal properties of tones of different f 0 , rather than a sensitivity to pitch per se. Frequency-selective forward suppression of neural responses in the auditory cortex (or the equivalent in nonmammalian species) has been proposed to play an essential role in auditory streaming (Fishman et al, 2001(Fishman et al, , 2004Kanwal et al, 2003;Klump, 2004, 2005;Micheyl et al, 2005Micheyl et al, , 2007. Specifically, it has been suggested that whether a sequence of pure tones is perceived as a single coherent stream or as two separate streams depends on the degree to which one tone influences the responses to subsequent tones.…”

“…The neural underpinnings of auditory stream segregation have been investigated with intracortical recordings in animals (Fishman et al, 2001(Fishman et al, , 2004Kanwal et al, 2003;Klump, 2004, 2005;Micheyl et al, 2005), and noninvasively in humans, using electroencephalography (EEG) (Sussman et al, 1999, Sussman, 2005Snyder et al, 2006), magnetoencephalography (MEG) (Gutschalk et al, 2005), and functional magnetic resonance imaging (fMRI) (Deike et al, 2004;Cusack, 2005;Wilson et al, 2007). All of these studies have used pairs of sounds that differed in frequency content, and were presented alternately, or in other repeating temporal patterns.…”

Multistability in auditory stream segregation: a predictive coding view

“…In this case, links between same-feature events are established first, because the reduction of link strength between adjacent sounds owing to high feature separation (e.g. by topological distance in a tonotopically organized area of the auditory cortex; [60,61]) exceeds that caused by longer temporal separation between the non-adjacent (but same feature) sounds. In other words, the cost of establishing the link between topologically highly separate focuses of neural activity exceeds that of establishing the link between the neural activity elicited by the incoming sound and a relatively more decayed neural after-effect of the previous (less recent) same-feature sound.…”

Neurophysiological evidence for context-dependent encoding of sensory input in human auditory cortex

“…The context, or environment surrounding a probe tone, modulates the amplitude of both single-and multi-unit neural activity. Contextual factors such as temporal sound density (Blake and Merzinich, 2002;Brosch and Schreiner, 2000), temporal onset time (Steinschneider et al, 2005), interaural phase disparity (Malone et al, 2002), or forward (Brosch and Schreiner, 1997;Fishman et al, 2004) and backward (Brosch et al, 1998) masking, arising from properties of adjacent sounds, have been shown to influence the way that auditory cortical neurons respond to the probe tone. What is unique in the current study is that the cortically generated response to the probe tone was modified by sounds not in its immediate proximity.…”