Abstract
We used magnetoencephalogram (MEG) in two experiments to investigate spatio-temporal profiles of brain responses to gaps in tones. Stimuli consisted of leading and trailing markers with gaps between the two markers of 0, 30, or 80 ms. Leading and trailing markers were 300 ms pure tones at 800 or 3200 Hz.Two conditions were examined: the within-frequency (WF) condition in which the leading and trailing markers had identical frequencies, and the between-frequency (BF) condition in which they had different frequencies. Using minimum norm estimates (MNE), we localized the source activations at the time of the peak response to the trailing markers. Results showed that MEG signals in response to 800 and 3200 Hz tones were localized in different regions within the auditory cortex, indicating that the frequency pathways activated by the two markers were spatially represented.The time course of regional activity (RA) was extracted from each localized region for each condition. In Experiment 1, which used a continuous tone for the WF 0-ms stimulus, the N1m amplitude for the trailing marker in the WF condition differed depending on gap duration but not tonal frequency. In contrast, N1m amplitude in BF conditions differed depending on the frequency of the trailing marker. In Experiment 2, in which the 0-ms gap stimulus in the WF condition was made from two markers and included an amplitude reduction in the middle, the amplitude in WF and BF conditions changed depending on frequency, but not gap duration.The difference in temporal characteristics betweenWF and BF conditions could be observed in the RA.
Highlights
The human auditory system is sensitive to temporal changes in sounds
The results showed no significant effect of gap duration on mismatch negativity (MMN) amplitude and suggested that primary auditory cortex plays a central role in the computation required for WF- and BF-gap detection
Responses to the 800-Hz tone appeared concentrated in a single area regardless of condition (Figures 3A,B), while those to the 3200-Hz tone were dispersed across the auditory cortex (Figures 3C,D)
Summary
The human auditory system is sensitive to temporal changes in sounds. Gap detection is a frequently used task that measures auditory temporal resolution by requiring a listener to judge whether a stimulus contains a brief silent interval (gap). When leading and trailing markers share the same frequency, this task is referred to as a within-frequency (WF) detection task (Formby and Forrest, 1991; Formby et al, 1998; Phillips, 1999), and the gap-detection threshold (i.e., the minimally detectable gap duration) is usually found to be around 2–3 ms (Plomp, 1964; Penner, 1977). Psychophysical evidence has shown that gap detection becomes more difficult as the frequency difference between the leading and trailing markers increases; the gap-detection threshold can be as high as 50 ms when the frequencies are separated by two octaves (Formby and Forrest, 1991; Phillips et al, 1997; Formby et al, 1998; Phillips, 1999). The results showed no significant effect of gap duration on MMN amplitude and suggested that primary auditory cortex plays a central role in the computation required for WF- and BF-gap detection
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
