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

On the control of visual fixation durations in free viewing of complex images

“…In order to reconcile this distinction with our view of the modes of visual attention, the focal attention mode should require ventral network activity, whereas ambient processing would be related to activity of the dorsal network. Regarding the present study, this implies that an interruption by the appearance of a distractor should have a stronger influence when the focal-processing mode is active, a claim that has been partly supported by previous experimental data (Pannasch & Velichkovsky, 2009). …”

“…Additionally, distractor fixations were classified as either ambient or focal on the basis of the preceding saccade amplitude (Pannasch & Velichkovsky, 2009).…”

“…This presentation interval was selected in accordance with previous work (cf. Graupner et al, 2007;Pannasch & Velichkovsky, 2009) in order to ensure that distractors did not become predictable and to acquire enough unaffected fixations to create a baseline. Distractors were triggered by the fixation onset, with an onset latency of either 100 or 200 ms; they remained visible for 100, 200, or 300 ms and were centered on the coordinates of the actual fixation.…”

“…This allows for classifying fixations on the basis of the prior saccadic amplitude: If the preceding amplitude is larger than 5°, this fixation is presumably in the service of the ambient attention mode, whereas for preceding saccadic amplitudes smaller than 5°, the fixation is assumed to belong to the focal attention mode (cf. Pannasch & Velichkovsky, 2009). …”

Examining the influence of task set on eye movements and fixations

“…According to the two visual systems hypothesis, the relationship between fixation durations and saccade amplitudes over time is systematic and indicative of two qualitatively distinct modes of scanning: global and local scanning (Frost & Poppel, 1976;Pannasch et al, 2008;Pannasch & Velichkovsky, 2009;Unema et al, 2005;Velichkovsky, Joos, Helmer, & Pannasch, 2005;Velichkovsky, Rothert, Kopf, Dornhoefer, & Joos, 2002;Velichkovsky et al, 2003). Accordingly, global processing can be seen as an orienting phase, during which shorter fixations and larger amplitudes dominate, presumably to capture the gist of a scene and establish regions of interest.…”