When larger visual distractors become less disruptive: Behavioral evidence for lateral inhibition in saccade generation

How neuronal activity is integrated over time may largely rely on excitatory and inhibitory mechanisms. Dynamic neural field models assume that local excitation and lateral inhibition (i.e., the "Mexican hat") shape the output of neural networks. Most models of saccade generation assume that such interactions in the superior colliculus play a key role in determining both the metrics and the latency of saccades. Here, we investigated the role of lateral inhibition in saccade metrics in humans. We used a saccade target task in which a visual distractor line was presented close to a peripheral visual target (i.e., a small circle). Models assuming lateral inhibition predict that beyond a critical size larger distractors induce less perturbation than smaller ones. To assess this prediction, we varied the length of the distractor. Results confirmed that a distractor presented along with the target deviated the saccade's landing position away from the target. This perturbation increased with distractor length but only up to a critical size as the effect reversed for larger distractors, leading to a reduced perturbation on saccade metrics. These results suggest that larger distractors induce a neuronal activity pattern wide enough to involve lateral inhibition, thereby decreasing the distractor's weight in the spatial integration of distractor and target locations. They are consistent with a critical role of lateral inhibition in the computation of saccade metrics.