Cortical fMRI Activation to Sequences of Tones Alternating in Frequency: Relationship to Perceived Rate and Streaming

Abstract

Wilson EC, Melcher JR, Micheyl C, Gutschalk A, Oxenham AJ. Cortical fMRI activation to sequences of tones alternating in frequency: relationship to perceived rate and streaming. J Neurophysiol 97: 2230-2238, 2007. First published January 10, 2007 doi:10.1152/jn.00788.2006. Human listeners were functionally imaged while reporting their perception of sequences of alternating-frequency tone bursts separated by 0, 1/8, 1, or 20 semitones. Our goal was to determine whether functional magnetic resonance imaging (fMRI) activation of auditory cortex changes with frequency separation in a manner predictable from the perceived rate of the stimulus. At the null and small separations, the tones were generally heard as a single stream with a perceived rate equal to the physical tone presentation rate. fMRI activation in auditory cortex was appreciably phasic, showing prominent peaks at the sequence onset and offset. At larger-frequency separations, the higher-and lower-frequency tones perceptually separated into two streams, each with a rate equal to half the overall tone presentation rate. Under those conditions, fMRI activation in auditory cortex was more sustained throughout the sequence duration and was larger in magnitude and extent. Phasic to sustained changes in fMRI activation with changes in frequency separation and perceived rate are comparable to, and consistent with, those produced by changes in the physical rate of a sequence and are far greater than the effects produced by changing other physical stimulus variables, such as sound level or bandwidth. We suggest that the neural activity underlying the changes in fMRI activation with frequency separation contribute to the coding of the co-occurring changes in perceived rate and perceptual organization of the sound sequences into auditory streams.

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

“…Instead, the changes are likely attributable to the ⌬f 0 -related differences in the temporal properties of the A and B tones. This dependence on temporal rather than spectral differences between A and B represents a crucial difference compared with previous imaging studies of streaming, all of which have used repeating sequences of pure tones (Gutschalk et al, 2005;Snyder et al, 2006;Wilson et al, 2007) or complex tones with gross spectral differences (Deike et al, 2004).…”

“…In fMRI, auditory cortical activation increased with increasing difference in f 0 in the present study, just as activation increased with increasing frequency difference in pure-tone paradigms (ABAB) . A mechanism previously proposed to underlie the increases in cortical activity seen in pure-tone studies is neural "adaptation" or "forward suppression" in which (1) the neural response to one tone suppresses the responses to subsequent tones, and (2) as successive tones are made increasingly different in frequency (or the time interval between tones is increased), the degree of suppression decreases (Gutschalk et al, 2005;Wilson et al, 2007). This frequency-selective forward suppression model maps straightforwardly to the data of the present study if it is assumed that the strength of suppression in some auditory cortical neurons depends on the f 0 difference between tones (i.e., is f 0 selective).…”

“…The ABBB pattern used in the present study offers both advantages of the triplet pattern, because the only difference is that the silent gap between triplets has been filled with another B tone. Filling the gap was important for the fMRI part of this study, in which we examined the time course as well as the magnitude of blood oxygen level-dependent (BOLD) responses, because actual (or perceived) gaps lead to changes in BOLD time course (Harms and Melcher, 2002;Wilson et al, 2007). By ensuring no physical temporal gaps, we were able to investigate the effect perceived temporal gaps introduced when the percept shifts from one to two streams.…”

“…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.…”

Grouping Mechanisms in Music

“…A number of studies exploring the neural correlates of streaming based on pitch have found either no difference in activation between the left and right hemispheres, or activation primarily in the right hemisphere (Cusack, 2005;Gutschalk et al, 2005Gutschalk et al, , 2007Snyder et al, 2006;Wilson et al, 2007). In contrast, Deike, Gaschler-Markefski, Brechmann, and Scheich (2004) and Deike, Scheich, and Brechmann (2010) found activation primarily in the left hemisphere when subjects were asked to segregate A from B tones continuously in sequences where the tones differed in timbre or in pitch.…”