3rd French conference on acoustics
J. Phys. IV France 04 (1994) C5-419-C5-425
Units in the primary auditory cortex of the Japanese monkey can demonstrate a conversion of temporal and place pitch in the central auditory systemH. RIQUIMAROUX and T. HASHIKAWA
Neural Systems Laboratory, Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan
The present study has examined whether the temporal pitch known as the "missing fundamental" is co-place-coded with the place pitch in the auditory cortex, using adult Japanese monkeys (Macaca fuscata) prepared for chronic recordings. The stimuli were white noise bursts, tone bursts and bursts of a combination of higher harmonics of a low frequency. Unit recordings were made from the contralateral (left) primary auditory cortex (AI). During recording sessions, the animal was anesthetized with a mixture of nitrous oxide and oxygen, supplemented by ketamine and xylazine injections. The data have confirmed a tonotopicity, low frequency anteriorly while high frequency posteriorly, in AI when the recording time window was short (< 20 msec) with stimulus at threshold levels. For longer time windows andlor suprathreshold stimulus levels, determining the best frequency (BF) for a neuron was often difficult. In the low frequency area (≤ 500 Hz), the same neuron responded to BF as well as a combination of successive higher harmonics of BF without BF. However, they did not or little responded to the harmonics themselves. The findings imply that the temporally-coded pitch at the periphery appears to be already place-coded together with the place pitch by the same neuron at AI. This evidence agrees well with previous psychoacoustical findings.
© EDP Sciences 1994