1. Brian White, Karl Gegenfurtner & Dirk Kerzel Email: brian.j.white@psychol.uni-giessen.de www.allpsych.uni-giessen.de Random noise textures as visual distractors for saccadic eye movements Remote distractors and an extended fixation zone Walker et al. (1997) ~10° Amplitude modulated Latency increased Target axis What qualifies as a distractor for saccadic eye movements? It’s been suggested that the remote distractor effect is caused by non-target stimulation of a collicular fixation zone. The distributed network of the cells responsible for the effect is believed to extend over a large area, responding to distractors up to 10 deg in the periphery (Walker et al., 1997). A large transient onset (e.g., a display change) has also been shown to produce an inhibited saccadic response (Reingold & Stampe, 2002), an effect also believed to have a basis in the superior colliculus (SC). Introduction We asked whether large onsets should necessarily inhibit a saccadic response. We were primarily interested in the effect of backgrounds on saccadic eye movements, in particular we wanted to test the effect of a visual texture known to have similar statistical properties as natural images, pink noise (A). We then compared this to a condition similar to a typical remote distractor paradigm by using a small localized patch of the texture as a distractor (B). A similar comparison was made by Weber & Fischer (1994). Purpose and Design Results Distractors and express saccades Weber & Fischer (1994) Express saccades eliminated in either case Conclusion To return to our initial question, it’s clear that the visual system does not interpret a background of pink noise as a form of distraction. Only a small localized patch increased saccadic latency. This has important implications for the mechanisms proposed to underlie the effect of distractors on a saccadic response, in particular the SC. While the SC is thought to play an important role in reflexive oculomotor responses, raw visual stimulation of the region representing the fixation zone is not in itself sufficient to produce an increase in saccadic latency typically found with remote distractors. The foveal region is particularly sensitive to a distractor, but our data suggest that only a localized element (i.e. potential object) can drive collicular fixation neurons. This is inconsistent with several studies suggesting the SC as the mechanism behind an inhibited saccadic response following a large transient flash (e.g., Reingold & Stampe, 2002). It is questionable then whether a background change without the presence of obviously salient elements should drive collicular fixation cells. This research has also led us to ask whether the statistical structure of pink noise might contribute to rapid saccadic target selection. Reingold & Stampe (2002) Saccadic inhibition in voluntary and reflexive saccades. JOCN, 14, 371-388. Walker, Deubel, Schneider & Findlay (1997) Effect of remote distractors on saccade programming: Evidence for an extended fixation zone. J Neurophysiol, 78, 1108-1119. Weber & Fischer (1994) Differential effects of non-target stimuli on the occurrence of express saccades in man. Vision Research, 34, 1883-1891. White, Gegenfurtner & Kerzel (2005) Effects of structured non-target stimuli on saccadic latency. J Neurophysiol, (in press). References Acknowledgements This research was funded by the Bundesministerium für Bildung und Forschung (Project MODKOG). D. Kerzel was supported by the Deutsche Forschungs-gemeinschaft (DFK KE 825/3-1 and 825/4-1, 2). Target Gabor(4c/deg) Always 4, 7 or 10° left or right of central fixation, and always simultaneous with distractor onset, except for Exp 3 Random noise texture as a “distractor” A B No-distractor 2.3 x 2.3 deg patch 36 x 36 deg patch EXP 3: Here we varied target onset relative to the other events which remained simultaneous. For the small patch, latencies were consistently elevated at target SOAs 0, the pattern reverses as a background of pink noise actually facilitates saccadic latency. EXP 1: We first tested whether a small (2.3X2.3deg) patch of our texture would in fact increase saccade latency similar to typical remote distractors. The patch could appear centrally or 4, 7 or 10° directly above or below fixation. Our results show a sharp latency increase for centrally displayed distractors only. T4° dotted T7° dashed T10° solid Distractor No-distractor control EXP 2: We then compared the small centrally displayed patch to a large (36X36 deg) background of the same texture. Only the small patch caused a significant increase in latency. The onset of the large texture did not at all hinder saccadic latency or accuracy. EXP 4: Finally, when we varied patch size from 1.6°X1.6° to 4.5°X4.5°, the results revealed a steady decrease in saccadic latency.