Brian White, Karl Gegenfurtner & Dirk KerzelEmail: brian.j.white@psychol.uni-giessen.de

www.allpsych.uni-giessen.de

Remote distractors and an extended fixation zoneWalker et al. (1997)

~10°

amplitude modulated

latency increased target axis

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). The significance of non-target onsets in this central region has been suggested earlier by the notion of a “dead-zone” for express saccades (Weber & Fischer, 1994). Recent research has also suggested that an inhibited saccadic response from a large transient onset (e.g., a display change) is also believed to have a basis in the superior colliculus (SC) (Reingold & Stampe, 2002).

IntroductionOur aim was to investigate the nature of non-target effects on saccadic latency, in particular its relation to both small, localized non-target stimuli (as employed in a typical remote distractor paradigm), and global non-target onsets (e.g., a display change, Reingold & Stampe, 2002). We tested the effect of a background texture known to have similar statistical properties as natural images, pink noise. In this case, a saccade target (Gabor patch, 4c/deg, SD=0.7deg²) was embedded in the 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

Distractors and express saccadesWeber & Fischer (1994)

Express saccades eliminated in either case

These results have 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 latency typically found with remote distractors. Our data suggest that only a localized element (i.e. potential object) can drive collicular fixation neurons.

• Because the SC can receive direct retinal input in ~40ms, the SC has been implicated as the mechanism behind apparently reflexive effects due to a large transient onset (e.g., “Saccadic Inhibition Effect”, Reingold & Stampe, 2002). If both the remote distractor effect and saccadic inhibition have a basis in the SC, our results suggest further inquiry into the nature of this difference. These effects appear to be temporally separate, and may involve different mechanisms.

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, 93, 3214-3223.

Funding by the Bundesministerium für Bildung und Forschung (Project MODKOG). D. Kerzel supported by the Deutsche Forschungs-gemeinschaft (DFG 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

e.g. Possible target, distractor locations

36 x 36 deg patch

2.3 x 2.3 deg patch

(2.3 X 2.3 deg patch36 x 36 deg patch or

No-Distractor Control)

Non-target onset, fixation offset

0-T SOA +T SOA

EXP 1: We first tested whether a small (2.3X2.3deg) patch of the texture would result in a typical remote distractor effect (e.g., Walker et al. 1997).

Results show a sharp latency increase with centrally displayed distractors only (no differences in saccadic error across conditions).

EXP 3: Here we examined the time-course of the effect in Exp2:

At SOAs <= 0 latencies were consistently elevated for the small patch only (no effect of full background during this period).

At SOAs > 0, the pattern reverses as a background facilitates latency.

Results

EXP 4: Finally, we varied the size of the centrally displayed texture from 1.6°X1.6° to 4.5°X4.5° (included are data in which the edges of the patches were filtered out).

The results show a steady decrease in latency as the size of the texture increased.

References

EXP 2: The key experiment compared the small (2.3X2.3deg) centrally displayed patch to a large (36X36 deg) background of the same texture.

Only the small patch caused a significant increase in latency. No effect of the full background on latency or accuracy.

Conclusion

Dot T4Dash T7Solid T10

Effects of structured backgrounds on saccadic latency

1.6 x 1.6 deg patch

4.5 x 4.5 deg patch