Averaging saccades are repelled by prior uninformative cues at both short and long intervals

Abstract

When two spatially proximal stimuli are presented simultaneously, a first saccade is often directed to an intermediate location between the stimuli (averaging saccade). In an earlier study, Watanabe (2001) showed that, at a long cue–target onset asynchrony (CTOA; 600 ms), uninformative cues not only slowed saccadic response times (SRTs) to targets presented at the cued location in single target trials (inhibition of return, IOR), but also biased averaging saccades away from the cue in double target trials. The present study replicated Watanabe's experimental task with a short CTOA (50 ms), as well as with mixed short (50 ms) and long (600 ms) CTOAs. In all conditions on double target trials, uninformative cues robustly biased averaging saccades away from cued locations. Although SRTs on single target trials were delayed at previously cued locations at both CTOAs when they were mixed, this delay was not observed in the blocked, short CTOA condition. We suggest that top-down factors, such as expectation and attentional control settings, may have asymmetric effects on the temporal and spatial dynamics of oculomotor processing.

Keywords:

• Attention
• Inhibition of return
• Saccade averaging

Acknowledgments

We are grateful to three anonymous reviewers for their constructive suggestions on an earlier version of this paper. This project was supported by a grant from Natural Sciences and Engineering Research Council of Canada (NSERC) to RMK.

Notes

¹One may suggest that target expectancy should be input to the network before target onset. Such an implementation is unjustified for the following reasons. First of all, if target expectancy reaches the SC long before target onset, in a spatial cueing task, one would expect a slow build-up of neuronal activity following cue onset when the CTOA is relatively long. However, this is not the case (for recordings, see Fecteau & Munoz, 2005; Dorris et al., 2002). Second, it has been shown that fixation offset can serve as a warning signal and raise the activation level in the SC (Dorris, Pare, & Munoz, 1997), starting from about 150 ms after fixation offset (Marino et al., 2011). However, because no temporal gap was included in the present behavioural experiments, fixation offset could not possibly be used as a warning signal by the participant. Thus, in the present experiments, it is most like that target expectancy boosted the top-down decision about where the eyes should go, rather than the baseline activation level in the SC.