Neural Correlates of Auditory Perception, Attention and Expectation

This dissertation examined the neural correlates of auditory perception, attention
and expectation in three experiments. Experiment 1 analyzed neural correlates of auditory
perception and expectation in an electroencephalography (EEG) experiment using a
temporally perturbed metronome to establish an expectation for auditory events, then
violate and reestablish that expectation. High frequency evoked (phase-locked) gamma
band activity (GBA) was observed to follow the onset of tones whereas induced (nonphase-
locked) GBA reached maximum power simultaneously with the occurrence oftone
onset. Moreover, the latency of induced GBA was perturbed after an expectancy violation
and relaxed back into synchrony as the expectation was reestablished.
Experiment 2 was a methodological study to compare two functional magnetic
resonance imaging (fMRJ) scanning techniques and assess their influence on auditory
processing. Subjects passively listened to isochronous tone sequences at three rates while
sparse or continuous scanning was employed. Sparse and continuous scanning was observed to yield comparable fMRI data, however, continuous scanner notse was
observed to perturb known EEG evoked response potentials. Moreover, high frequency
evoked activity, as identified by spectral analysis, was attenuated in the presence of
continuous fMRl noise.
Experiment 3 was conducted to study auditory expectancy and attention. First,
subjects were tested behaviorally to determine their ability to tap the beat of ten highly
syncopated patterns. Subjects were asked to return for one EEG and one fMRl session. In
these sessions, they were instructed to attend to a syncopated pattern, mentally rehearse
the pattern, and then reproduce the pattern. During the control condition, subjects heard
the auditory patterns, however, they were instructed to study a list of words, remember
the words during the retention interval, and then recall as many words as possible. Brain
activity was localized to frontal and auditory regions when attending to the patterns and
occipital-auditory areas when attending to the words. Evoked activity was shown to
reflect the subject's anticipation of the beat and was attenuated when ignoring the
auditory stimulus.
Taken together, these results suggest that GBA indexes auditory perception,
attention and expectation. The current results suggest that attention and task engagement
may elicit stronger neural phase locking.