Abstract
Pre-saccadic attention is known to selectively enhance performance at saccadic target location prior to saccade execution, but this phenomenon has mostly been investigated during experimentally-dictated saccade-related instructions which may have modulated performance enhancement. Here 67 participants performed center-periphery discrimination of faces in foveal to parafoveal locations (≤4°, appearing for 200ms). Despite being instructed to keep fixation throughout the experiment, 2/3 of the participants performed internally-driven saccades towards parafoveal targets that could appear in 1 of 13 random locations. The rest of the participants kept fixation. These two different individual eye-movement behaviours (hoppers, fixators) were also substantiated by unsupervised k-means clustering algorithm, and were consistent across visual categories (inverted faces: 31/32, houses: 21/23). As expected, hoppers’ performance significantly improved when their saccades landed before target disappeared (relative to when landing after target disappeared). However, given the expected pre-saccadic attention performance improvement, it was surprising that hoppers’ performance (when landing after target disappeared) was not significantly better than that of fixators. To examine whether instructed pre-saccadic attention is required to improve performance, participants underwent another session. First, their characteristic saccadic behavior was verified (in 30/33). Fixators were then asked to perform a saccade towards the target immediately after it disappeared, assuming this will result in typical pre-saccadic attention improvement, and hoppers were asked to refrain from hopping, to examine if this will decrease performance. The results confirmed our assumptions with fixators showing significant improvements following the instructed post-stimulus saccades, corresponding to typical pre-saccadic attention results, while hoppers performance did not change. Our results of improved performance for instructed but not for spontaneous pre-saccadic attention suggest that pre-saccadic attention during naturalistic behavior may in fact span a much broader range of influences on behavior than are currently known, and may also support a dissociation between saccade planning and peripheral enhancement.