Abstract
Much evidence points to an interaction between vision and audition at early cortical sites. However, the functional role of these interactions is not yet understood. Here we show an early response of the occipital cortex to sound that it is strongly linked to the spatial localization task performed by the observer. The early occipital response to a sound, usually absent, increased by more than 10-fold when presented during a space localization task, but not during a time localization task. The response amplification was not only specific to the task, but surprisingly also to the position of the stimulus in the two hemifields. We suggest that early occipital processing of sound is linked to the construction of an audio spatial map that may utilize the visual map of the occipital cortex.
Highlights
Space representation is one hard problem that the brain has to face, given the continuously changing flow of information collected by our mobile sensors, for review see refs 1–3
Sensor Level Analysis. 16 blindfolded naïve subjects performed an auditory bisection task (Fig. 1) to a sequence of 3 sounds provided in the lower visual hemifield, where the middle sound could be delivered at two different spatial positions and two different temporal lags independently
Mean Event Related Potentials (ERP) amplitude was computed by averaging the voltage in the early occipital ERP component time windows
Summary
Space representation is one hard problem that the brain has to face, given the continuously changing flow of information collected by our mobile sensors, for review see refs 1–3. Despite the demonstration of neuronal activity and pathways in animal models, and the clear evidence from fMRI, previous studies using scalp Event Related Potentials (ERP) in sighted humans have failed to demonstrate a reliable early response involving striate areas to a unimodal auditory stimulation[22, 23]. In contrast to the paucity of studies showing early visual cortical response to sound alone in normal human subjects, clear evidence demonstrates a neuronal interaction between vision and audition in early visual cortex, for example an amplification/reduction of the visual response to a congruent/incongruent audio-visual stimuli[13, 19, 24, 25, 28, 29] All these data demonstrate that the visual cortex plays an important role in audio-visual integration[17, 30,31,32,33,34,35]. We hypothesized the existence, in this purely auditory bisection task, of an ERP component which 1) is elicited by a task involving the development of a spatial metric; 2) occurs in an early time window involved in multisensory integration
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