Pre-saccadic perceptual facilitation can occur without covert orienting of attention.
Blangero A., Khan AZ., Salemme R., Deubel H., Schneider WX., Rode G., Vighetto A., Rossetti Y., Pisella L.
The pre-motor theory of attention suggests that the mechanisms involved in target selection for eye movements are the same as those for spatial attention shifts. The pre-saccadic facilitation of perceptual discrimination at the location of a saccadic goal (paradigm of Deubel and Schneider, 1996) has been considered as an argument for this theory. We compared letter discrimination performance in a saccade (overt attention - pre-saccadic facilitation) and a fixation (covert attention) task in a patient with right posterior parietal damage and 4 controls. In the overt attention condition, the patient was instructed by a central cue to make a saccade to a target located at a peripheral location. During the saccade latency (in a period of time of 250 msec following the presentation of the cue), a letter was presented at the target location. Accuracy of leftward saccades was impaired compared to rightward saccades. To evaluate letter discrimination performance in this saccade task (i.e., the presence of pre-saccadic facilitation), we selected only those leftward saccades that were equivalent in accuracy (and latency) to the rightward ones. Within these selected trials, the patient was able to discriminate letters equally well in both visual fields. In contrast, he performed at chance level during the fixation task (covert attention condition) for letters presented at the same peripheral location with the same timing with respect to the cue presentation. The patient could thus discriminate the letter presented at 8° of visual eccentricity while he was preparing a saccade, whereas he was unable to perceive the letter in the fixation task. Remarkably, in the left visual field, letter discrimination was impossible even when a letter was presented as close as 2.5° of visual eccentricity in the fixation task. Altogether, these results suggest that pre-saccadic perceptual facilitation does not rely on the same processes as those of covert attention, as tested by fixation task. Instead, we propose that pre-saccadic perceptual facilitation results from a form of attention specific to action, which could correspond to a pre-saccadic remapping process.