Abstract
Source analyses on event related potentials (ERPs) derived from the electroencephalogram (EEG) were performed to examine the respective roles of cortical areas preceding exogenously triggered saccades, combined convergences, and combined divergences. All eye movements were triggered by the offset of a central fixation light emitting diode (LED) and the onset of a lateral LED at various depths in an otherwise fully darkened room. Our analyses revealed that three source pairs, two located in the frontal lobe–the frontal eye fields (FEF) and an anterior frontal area–, and one located within the occipital cortex, can account for 99.2% of the observed ERPs. Overall, the comparison between source activities revealed the largest activity in the occipital cortex, while no difference in activity between FEF and the anterior frontal area was obtained. For all sources, increased activity was observed for combined vergences, especially combined convergences, relative to saccades. Behavioral results revealed that onset latencies were longest for combined convergences, intermediate for combined divergences, and the shortest for saccades. Together, these findings fit within a perspective in which both occipital and frontal areas play an important role in retinal disparity detection. In the case of saccades and combined divergences stimulus-locked activity was larger than response-locked activity, while no difference between stimulus- and response-locked activity was observed for combined convergences. These findings seem to imply that the electrophysiological activity preceding exogenous eye movements consists of a sensory-related part that is under cortical control, while subcortical structures may be held responsible for final execution.
Highlights
Eye movements play an integral and crucial role in human vision, as for the detailed perception of objects their respective images have to be properly projected on the fovea
Saccades were characterized by the shortest mean onset latencies, intermediate latencies were obtained for combined divergences, and the longest latencies were observed for combined convergences
The analysis revealed that latencies were not dependent on the direction of the eye movements, since there was no main effect of direction (F(1,13) < 0.01, p = 0.953, η2 < 0.001), and no eye movement type x direction interaction (F(2,26) = 0.02, p = 0.943, η2 = 0.001)
Summary
Eye movements play an integral and crucial role in human vision, as for the detailed perception of objects their respective images have to be properly projected on the fovea. Three types of eye movements are responsible for adjusting our gaze and directing the line of sight to a new object of interest: smooth pursuit, saccades, and vergences [1, 2]. The engagement of cortical areas preceding exogenous vergence eye movements the fovea, vergences move the eyes in opposite directions to project the images of an object on the fovea of both eyes simultaneously [1]. We intend to demonstrate that reflexive (i.e., exogenous) combined eye movements may involve similar cortical areas as saccades. Different types of eye movements may involve different cortical areas in varying degrees. Source analyses on event related potentials (ERPs) preceding eye movements, which can be derived from the electroencephalogram (EEG), were carried out to determine the likely involvement of different cortical areas over time
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