HUMAN AUDITORY-CORTEX RESPONSES TO RISING VERSUS FALLING GLIDES

A 24-channel SQUID magnetometer was used to record signals from the ri ght auditory cortex to tone glides with 16 different centre frequencie s (ranging from 0.5 to 2 kHz), sweeping over one octave. The stimulus sequence, presented with an interstimulus onset interval of 0.6 s, con sisted of infrequent 'deviant' rising (falling) glides and frequent 's tandard' falling (rising) glides; the rising glides were identical to the falling glides but presented in the reverse direction. Deviant gli des elicited significantly larger responses than standards at a latenc y of about 100 ms. This amplitude difference presumably arises from a mismatch response to the deviants. These results suggest that the audi tory cortex extracts the direction of frequency transition even when t he stimuli do not contain same frequencies.