POSITIONAL, DIRECTIONAL AND SPEED SELECTIVITIES IN THE PRIMARY AUDITORY-CORTEX OF THE CAT

Responses of high-frequency primary auditory cortex (Al) neurons of th e cat to noise stimulation were obtained in a quasianechoic chamber us ing a static and an apparently moving stimulus presented at similar az imuths. Simulated motion toward right or left as well as different sim ulated velocities were used. Under static stimulation, most units were contralateral-preferring followed by ipsilateral-and midline-preferri ng. Some were omnidirectional and a few were unclassifiable. Width of tuning was similar for contralateral-, ipsilateral-and midline-preferr ing units. Overall, about 25% were finely tuned (<20 degrees) and the remaining were broadly tuned (greater than or equal to 20 degrees). Al l cells sampled with static stimulation responded to apparent motion. About one quarter of the units were sensitive to the direction of the simulated moving noise in that they responded at least twice as much t o one direction as to the other. Almost all directional contralateral- preferring units responded more when the apparent motion was directed toward ipsilateral azimuths, whereas all directional ipsilateral-prefe rring units responded preferentially to contralaterally oriented motio n. In some units, up to five apparent speeds were tested. About half t he units were not speed-selective (46%). The other cells were tuned to a preferential speed (40%), decreased their response as the apparent speed increased (10%) or displayed direction-dependent speed selectivi ty (4%). These results indicate that moving-sound sources are processe d by some Al single units.