September 2011
Volume 11, Issue 11
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2011
Investigating the role of intra-collicular excitatory connections in the generation of vertical saccades: A Human behavioural study
Author Affiliations
  • Soazig Casteau
    Laboratoire de Psychologie Cognitive, CNRS - Université de Provence
  • Françoise Vitu
    Laboratoire de Psychologie Cognitive, CNRS - Université de Provence
Journal of Vision September 2011, Vol.11, 544. doi:10.1167/11.11.544
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      Soazig Casteau, Françoise Vitu; Investigating the role of intra-collicular excitatory connections in the generation of vertical saccades: A Human behavioural study. Journal of Vision 2011;11(11):544. doi: 10.1167/11.11.544.

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Abstract
 

In neural models of saccade generation, lateral interactions between neurons in the topographic motor map of the Superior Colliculus play a major role in determining saccade metrics. By reshaping the activity profile that initially arises from visual stimulation, short-distance excitatory and long-distance inhibitory interactions favor the emergence of a main peak of activity, which determines in turn where the eyes move. Thus, when two spatially-proximal stimuli are displayed simultaneously in the same hemifield, the eyes land at an intermediate location between the two stimuli (i.e. the Global Effect) because short-distance excitations resume the two initially active peaks into one intermediate peak. Recently, we provided Human behavioural evidence for this assumption; we showed that the global effect cancels out when the spatial separation between two stimuli presented on the horizontal meridian exceeds a threshold distance of about 1mm of collicular surface, as previously suggested by electrophysiological investigations in the monkey [Casteau & Vitu, 2009]. Here, we investigated whether this 1-millimeter threshold distance generalizes to stimuli presented on the vertical axis. A singleton peripheral target was presented on the vertical meridian either in isolation, or simultaneously with a less eccentric distractor displayed also on the vertical meridian. Both the eccentricity of the distractor (0°, 2 and 4°) and the angular separation between distractor and target (1° to 7°) were manipulated. In the target-alone condition, vertical saccades were relatively accurate. In the distractor condition, saccade accuracy was virtually the same, meaning that there was almost no trace of a global effect. The eyes were rarely deviated towards the distractor, and this was mainly when the separation between the stimuli was extremely small. A way to reconcile these findings with the lateral-interaction hypothesis is to assume that short-distance excitatory connections within the motor maps are not oriented along the representation of the vertical meridian.

 
French-German ANR-DFG grant (#ANR-07-FRAL-014). 
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