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CIM - REPARTI Perception Seminars

Can different strategies for head and eye coordination during gaze shifts to a remembered target after passive rotation shed light on the relationship between the programming of gaze saccades and visual attention?


Prasun Lala, PhD student
Artificial Perception Laboratory, Centre for Intelligent Machines McGill University

March 13, 2008 at  3:00 PM
George Zames Room MC437

This short talk will present the outline of an intended protocol being investigated and some of the associated background material.

Many current theories of spatial attention propose a link between shifts in spatial attention and the programming of saccadic eye movements. The superior colliculus (SC) of the brain stem has been implicated as having a possible role in this system. I am suggesting that incorporating passive vestibular stimulation to protocols measuring performance in spatial attention tasks might offer insight into the relationship between shifts in attention and shifts in gaze.

Based on evidence that the SC programs saccades in terms of gaze (head + eye) rather than purely eye, Guitton and Munoz have proposed a model of collicular commands for gaze saccades that is based on the availability of an *instantaneous* gaze error signal. Their model proposes that neurons in the deep layers of the SC are active for a particular vector error between the intended saccade target and the visual axis, and project to neurons in the gaze motor system responsible for a saccade. In the rostral SC are 'fixation' neurons active for a vector error of 0 deg, that project to neurons in the gaze motor system that prevent initiation of saccades during fixation. In their model, before a gaze saccade there is excitation in the rostral 'fixation' area representing present gaze position, and a build up of activity at a more caudal area representing the *intended* saccade. Commencement of a saccade is contingent upon the attenuation of activity in the rostral fixation area, and *during* the gaze shift, activity representing gaze vector error (gaze saccade amplitude signal) moves towards the rostral fixation area until target fixation is accomplished.

The Vestibular Memory Contingent Saccade (VMCS) protocol requires a subject to fixate a head-fixed LED during a passive rotation in the dark, and then to look back to the remembered position of a just seen earth-fixed target while still in the dark. The goal directed motor output, gaze refixation of the remembered target, must be based solely on the subject's perception of how much the subject was rotated. In the Guitton-Munoz model, the VMCS protocol presumably would maintain neural activity in the SC's rostral fixation area throughout the turn (because of LED fixation) while concurrent neural activity would move away caudally from the 'fixation' area based on the intended saccade amplitude for the VMCS task. I will suggest some ideas of how incorporating tasks measuring spatial attention during the VMCS protocol might shed light on the link between spatial attention shifts and intended shifts in gaze.