The effect of temporal context on the sustained pitch response in human auditory cortex.

Recent neuroimaging studies have shown that activity in lateral Heschl's gyrus covaries specifically with the strength of musical pitch. Pitch strength is important for the perceptual distinctiveness of an acoustic event, but in complex auditory scenes, the distinctiveness of an event also depends on its context. In this magnetoencephalography study, we evaluate how temporal context influences the sustained pitch response (SPR) in lateral Heschl's gyrus. In 2 sequences of continuously alternating, periodic target intervals and a more irregular baseline interval, the distinctiveness of the target was decreased in 1 of 2 ways--either by increasing the pitch strength of the baseline or by decreasing the pitch strength of the target. The results show that the amplitude of the SPR increases monotonically with the distinctiveness of the target. Moreover, SPR amplitude is greater for the sequence, where the pitch strength of the target is varied, compared with the condition, where the baseline is varied. Two subsequent experiments show that the amplitude of the SPR increases as duty cycle decreases, in a pitch "strength" contrast and in a pitch "value" contrast. These results indicate that the SPR adapts to recent stimulus history, enhancing the response to rare and brief events.