UCL Discovery

Abstract

Auditory pattern processing may be associated with changes in cortical gamma-band activity (Kaiser & Lutzenberger, 2003). Auditory pattern analysis was investigated by recording changes in cortical activity associated with the build-up and break-down of auditory streaming based solely on temporal cues. Each complex tone of a tonal triplet was composed of unresolved harmonics with a fundamental frequency, f0=62.5 Hz, summed either in sine phase (S) or alternating sine and cosine phase (SC), with a pitch corresponding to f0 and 2* f0 respectively. In the 1-stream condition, a repeating triplet of S-SC-S tones was presented with an inter-stimulus interval (ISI) of 50 ms and inter-triplet-interval (ITI) of 200 ms; this presentation evoked the percept of a single stream. Temporal jitter was imposed by the occasional presentation of a deviant triplet with an ISI of either 40 ms or 30 ms. In the 2-stream condition, a repeating triplet of S-SC-S tones was presented with an ISI of 30 ms and ITI of 200 ms; this presentation evoked the percept of two streams. In this case, temporal jitter was imposed by the occasional presentation of a deviant triplet with an ISI of 20 ms. Psychophysical results showed that for the 1-stream condition, increasing amount of temporal jitter was associated with an increased perception of 2-streams. For the 2-stream condition, introduction of temporal jitter had minimal effect on the perception of the 2-streams. In the corresponding EEG study, the build-up of steaming was associated with a slight overall increase in gamma-band activity. Whilst introduction of temporal jitter in the 1-stream condition was associated with a decrease in the gamma-band activity, there was no change in the gamma-band activity with the introduction of temporal jitter in the 2-stream condition.