| Abstract No.: | C-D3140 |
| Country: | Canada |
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| Title: | SEQUENCES OF VISUAL SEARCH EYE MOVEMENTS ARE PROCESSED IN ADVANCE OF VISUAL RECEPTIVE FIELD ACTIVATION. |
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| Authors/Affiliations: | 1 Kelly Shen*; 1 Martin Paré;
1 Queen's University, Kingston, ON, Canada
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| Content: | Objectives: Vision is an active process that requires a sequence of saccadic eye movements interrupted by periods of fixation during which details of the foveal image are analyzed and the next detail in the periphery is selected. While most neurophysiological studies of visual search have focused on the processing of a single saccade, visual behavior naturally entails sequences of multiple eye movements.
Materials and methods: To understand how the brain regulates this sequential behavior, we examined the activity of superior colliculus (SC) visuo-motor neurons while two monkeys performed a visual conjunction (color+form) search task. In this task, a unique target was presented with seven distractor stimuli and monkeys were required to report the location of the target by foveating it.
Results: As we have previously reported (Shen & Paré, 2007), monkeys foveated the target with a single saccade at levels well above chance (0.67), but required two saccades in a significant proportion of trials (0.27). Here, we report the activity during trials in which the monkeys foveated the target with two saccades. When the target was brought into a neuron’s receptive field following the first saccade, SC activity associated with the programming of the second saccade into the neuron’s receptive field began well before the end of the afferent delay (within 50 ms of the end of the first saccade) in nearly all recorded neurons. This first result suggests that the second saccade goal was programmed concurrently with the first. When the target first fell in a neuron’s receptive field, the activity before the initial incorrect saccade was enhanced when the second correct saccade was produced within 100 ms after the first (164 Hz) compared to when it was produced well after the first (123 Hz). This second result demonstrates that the pre-processing of visual stimuli contributes to the selection of saccade goals.
Conclusion: Altogether, these results show that visual search saccades should be considered as elements of sequences of fixations to visual objects selected by concurrent visual processing.
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