Visual calibration of auditory spatial perception in humans and monkeys
Norbert Kopco1, I-Fan Lin2, Barbara Shinn-Cunningham2, Jennifer Groh3
1Technical University of Kosice, Slovakia, 2Boston University, 3Duke University
At the early stages of auditory and visual processing, space is represented in different coordinate frames: the location of auditory stimuli is detected relative to the orientation of the head, while visual stimuli are detected relative to the orientation of the eyes. Since visual signals are known to help calibrate auditory spatial perception, the two modalities must align at some processing stage. Following up on previous results [Lin et al., JASA 121, 3095, 2007, and Kopco et al. SFN Abstract # 662.4, 2007], this study investigated the influence of visual spatial cues on auditory localization to determine the frame of reference in which the visually-guided auditory calibration occurs.
Visually-guided shifts in sound localization were induced in seven human subjects and two monkeys who made eye saccades to auditory or audio-visual stimuli. On the audio-visual (training) trials, the visual component of the targets was displaced laterally by 5� to 6�. Interleaved auditory-only (probe) trials served to evaluate the effect of experience with mismatched visual stimuli on auditory localization. To dissociate head- from eye-centered reference frames, the initial fixation position of the eyes in the auditory-only trials either differed from or equaled the location used during the audio-visual training trials.
In both the humans and the monkeys, the displaced visual stimuli shifted the endpoints of saccades on the probe trials by 30 to 50%. The shifts were induced in a mixture of head- and eye-centered coordinate frames and at multiple temporal scales. These findings suggest that the neural mechanisms underlying spatial plasticity are not strictly head-centered but incorporate information about eye position, possibly at distinct processing stages. This is reminiscent of demonstrations of eye-position-dependent modulation of neural responses in the auditory pathway of non-human primates [e.g. Groh et al., Neuron, 29:509-518, 2001]. [Supported by NIH and VEGA]