Distractor effect and saccade amplitudes: Further evidence on different modes of processing in free exploration of visual images

Abstract

In view of a variety of everyday tasks, it is highly implausible that all visual fixations fulfil the same role. Earlier we demonstrated that a combination of fixation duration and amplitude of related saccades strongly correlates with the probability of correct recognition of objects and events both in static and in dynamic scenes (Velichkovsky, Joos, Helmert, & Pannasch, 2005; Velichkovsky, Rothert, Kopf, Dornhoefer, & Joos, 2002). In the present study, this observation is extended by measuring the amount of the distractor effect (characterized as a prolongation of visual fixation after a sudden change in stimulation; see Pannasch, Dornhoefer, Unema, & Velichkovsky, 2001) in relation to amplitudes of the preceding saccade. In Experiment 1, it is shown that retinotopically identical visual events occurring 100 ms after the onset of a fixation have significantly less influence on fixation duration if the amplitude of the previous saccade exceeds the parafoveal range (set on 5° of arc). Experiment 2 demonstrates that this difference diminishes for distractors of obvious biological value such as looming motion patterns. In Experiment 3, we show that saccade amplitudes influence visual but not acoustic or haptic distractor effects. These results suggest an explanation in terms of a shifting balance of at least two modes of visual processing in free viewing of complex visual images.

Keywords:

• Ambient processing
• Distractor effect
• Fixation duration
• Focal processing
• Intermodal processing
• Saccade amplitude
• Scene perception
• Two visual systems

Acknowledgements

We thank Marina Danilova, Sven-Thomas Graupner, Sonja Gruen, Jens Helmert, Junji Ito, Andrei Nikolaev, Ben Tatler, Tim Smith, and one anonymous reviewer for their helpful suggestions and comments on the manuscript. This research was supported by grants from the European Commission to BMV (Network of Excellence COGAIN 511598 and NEST-Pathfinder projects MINET 043297 and PERCEPT 043261).