A John Van Opstal

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The superior colliculus in the monkey contains a topographically organized representation of the target in its upper layers and saccade-related activity in its deeper layers. Since collicular movement fields are quite large, a considerable region of the colliculus is active whenever a saccade is made. We have modelled the collicular role in saccade(More)
1. Most recording studies on the role of the monkey superior colliculus (SC) in eye movement generation have so far indicated that the code of the recruited population of cells is a fixed vector command representing the desired saccadic eye displacement vector, irrespective of the position of the eyes in the orbit. Experimental evidence from(More)
Because the inner ear is not organized spatially, sound localization relies on the neural processing of implicit acoustic cues. To determine a sound's position, the brain must learn and calibrate these cues, using accurate spatial feedback from other sensorimotor systems. Experimental evidence for such a system has been demonstrated in barn owls, but not in(More)
The midbrain inferior colliculus (IC) is implicated in coding sound location, but evidence from behaving primates is scarce. Here we report single-unit responses to broadband sounds that were systematically varied within the two-dimensional (2D) frontal hemifield, as well as in sound level, while monkeys fixated a central visual target. Results show that IC(More)
This study addresses the integration of auditory and visual stimuli subserving the generation of saccades in a complex scene. Previous studies have shown that saccadic reaction times (SRTs) to combined auditory-visual stimuli are reduced when compared with SRTs to either stimulus alone. However, these results have been typically obtained with high-intensity(More)
A procedure is described to calibrate three-dimensional eye position with a dual-search coil implant in rhesus monkeys using a two-field magnetic system. The method allows one to determine the sensitivity of the search coils taking into account the presence of d.c. offset voltages. The orientation of the implant on the eye relative to a space-fixed(More)
Auditory and visual target locations are encoded differently in the brain, but must be co-calibrated to maintain cross-sensory concordance. Mechanisms that adjust spatial calibration across modalities have been described (for example, prism adaptation in owls), though rudimentarily in humans. We quantified the adaptation of human sound localization in(More)
Saccades to combined audiovisual stimuli often have reduced saccadic reaction times (SRTs) compared with those to unimodal stimuli. Neurons in the intermediate/deep layers of the superior colliculus (dSC) are capable of integrating converging sensory inputs to influence the time to saccade initiation. To identify how neural processing in the dSC contributes(More)
Human sound localization relies on implicit head-centered acoustic cues. However, to create a stable and accurate representation of sounds despite intervening head movements, the acoustic input should be continuously combined with feedback signals about changes in head orientation. Alternatively, the auditory target coordinates could be updated in advance(More)
Saccades are controlled by neurons in the brainstem reticular formation that receive input from the superior colliculus and cortex. Recently two quantitative models have been proposed for the role of the colliculus in the generation of three-dimensional eye movements. In order to test these models, three-dimensional eye movements were measured in the alert(More)