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CORTEX. A. S. Trause, U. Werner-Reiss, A. M. Underhill, J. M. Groh*. Dept. of
Psychol. and Brain Sci., Dartmouth, Hanover NH 03755. 739.11. Soc. Neuro. Abstr.
Localization of visual and auditory information relies on very different kinds of
evidence. Visual stimulus locations are initially encoded using an eye centered frame of
reference: information about the position of a visual target is based solely on the site of
retinal activation. In contrast, the brain computes the location of a sound by comparing
the sound's pressure level and arrival time across the two ears. These cues indicate the
direction of the sound with respect to the head and ears -- a head-centered frame of
reference. Yet, a variety of studies have shown that auditory information is ultimately
translated into an eye-centered frame of reference to permit integration with visual
In our previous abstract (Clark et al., 2000, Soc. Neuro. Abstr.), we presented evidence
that this transformation begins within the brainstem auditory pathway: eye position
influenced the auditory responses of about 45 % of cells in the primate inferior colliculus
(IC). Here we examined the frame of reference of responses in auditory cortex. The
monkey fixated visual stimuli at one of three locations while noise bursts were presented
from 15 different speakers. We found that eye position modulated the auditory responses
of about 70 % (25 out of 35) of cortical neurons. The response magnitude was affected
by eye position, but the receptive fields did not appear to shift systematically when the
eyes moved. Together, these results suggest that the frame of reference in auditory cortex
lies on a continuum between head- and eye-centered, but is closer to being eye-centered
than are the signals in IC.
Supported by ONR, Whitehall, McKnight, Sloan, and Merck grants to JMG.