Abstract
The context in which a saccadic eye movement is made is known to influence saccadic latency and error rate. Much less is known about contextual effects on saccadic metrics. We previously showed that both expectancy (prior probability) and trial history may bias the actual endpoint of an antisaccade (Rodriguez et al, Previous saccades to other locations affect the programming of current antisaccade coordinates, but not those of prosaccades. VSS 2008). In this report we studied the temporal parameters of the historical bias.
Subjects performed antisaccades to a stimulus randomly located either on the horizontal meridian, 40° below, or 40° above the horizontal meridian, with all three locations equally likely and equally frequent in each block, and all locations within the same horizontal hemifield. We analyzed the endpoint of antisaccades to the location on the horizontal meridian, contrasting the effects of preceding trials in which the target was above the meridian with trials in which the target was below the meridian. We analyzed several historical effects: not just that from the immediately preceding trial (n-1), but also the penultimate (n-2) and (n-3) trials. We also compared the historical effects on short-latency versus long-latency antisaccades, using 250ms as a latency criterion.
We found that antisaccades were significantly displaced towards the preceding saccadic endpoint at all three levels (n-1, n-2, n-3). The historical effect was present only in short-latency and not in long-latency antisaccades. We conclude that the location of prior antisaccades can bias the spatial programming of upcoming antisaccades, that this historical effect persists over many seconds, and that it influences mainly rapidly programmed eye movements.
Funding was provided by CIHR MOP-81270, an AAN SIGN scholarship award (TR), Schweizerische Stiftung für medizinisch-biologische Stipendien (MA), a Canada Research Chair and Michael Smith Foundation for Health Research Senior Scholarship (JB).