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

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, B. M., Joos, M., Helmert, J. R. and Pannasch, S. 2005. “Two visual systems and their eye movements: Evidence from static and dynamic scene perception”. In Proceedings of the XXVII conference of the Cognitive Science Society, Edited by: Bara, B. G., Barsalou, L. and Bucciarelli, M. 2283–2288. Mahwah, NJ: Lawrence Erlbaum Associates, Inc. [Google Scholar]; Velichkovsky, Rothert, Kopf, Dornhoefer, & Joos, 2002 Velichkovsky, B. M., Rothert, A., Kopf, M., Dornhoefer, S. M. and Joos, M. 2002. Towards an express diagnostics for level of processing and hazard perception. Transportation Research, 5F(2): 145–156. [Google Scholar]). 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 Pannasch, S., Dornhoefer, S. M., Unema, P. J. A. and Velichkovsky, B. M. 2001. The omnipresent prolongation of visual fixations: Saccades are inhibited by changes in situation and in subject's activity. Vision Research, 41(25–26): 3345–3351. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) 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.