Sensitivity to the temporal structure of rapid sound sequences - An MEG study.
Bottom Line: Analysis of the latency of offset responses revealed that the temporal structure of (even rather simple) regular sequences is not learnt precisely when the sequences are ignored.Pattern coding, supported by a network of temporal, parietal and frontal sources, improved considerably when the signals were made behaviourally pertinent.Thus, contrary to what might be expected in the context of an 'early warning system' framework, learning of temporal structure is not automatic, but affected by the signal's behavioural relevance.
Affiliation: UCL Ear Institute, 332 Gray's Inn Road, London WC1X 8EE, UK.Show MeSH
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Mentions: Fig. 1A schematizes the stimuli used in Experiment 1. The signals were sequences of 25 ms tone bursts (500 Hz) separated by silent intervals of a fixed duration, resulting in an isochronous rhythm. In different conditions, the duration of the silent interval was set to one of three values (50, 100 or 200 ms), corresponding to inter-onset-intervals (IOI) of 75, 125 and 225 ms, respectively. These IOI durations were chosen because rapid temporal patterns remain under-investigated, despite the fact that the temporal properties of many natural sound sequences are within this range. The sequences were of variable overall duration, consisting of a minimum of 24 and maximum of 36 tone-bursts. The stimulus set also contained long pure-tone stimuli (‘CONT’), used to measure the latency of ‘simple’ auditory cortical offset responses. The length of the constant tone varied randomly between 1500 and 3500 ms. The signals were created off-line at a sampling rate of 44.1 kHz and saved in a 16-bit stereo WAV format. In total, 150 repetitions of each of the 4 experimental conditions were presented. All conditions were presented in random order with the inter-sequence interval (ISI) randomized between 750 and 1500 ms.
Affiliation: UCL Ear Institute, 332 Gray's Inn Road, London WC1X 8EE, UK.