S.M. Dornhoefer

The omnipresent prolongation of visual fixations: saccades are inhibited by changes in situation and in subject's activity

Presenting a distractor prolongs not only saccadic reaction times in paced tasks but also fixation durations in unpaced tasks. To investigate whether the effect of a distractor is a pure optomotor reflex, we used both visual and auditory distractors in an unpaced picture-viewing paradigm. Results show a distractor effect for both modalities. Analysis of data from previous studies showed similar effects, even in amodal shifts of attention. These findings challenge the hypothesis that the effect is modality-specific and suggest that the distractor effect may be another expression of the orienting reflex.

Change detection and occlusion modes in road-traffic scenarios

Abstract Change blindness phenomena are widely known in cognitive science, but their relation to driving is not quite clear. We report a study where subjects viewed colour video stills of natural traffic while eye movements were recorded. A change could occur randomly in three different occlusion modes—blinks, blanks and saccades—or during a fixation (as control condition). These changes could be either relevant or irrelevant with respect to the traffic safety. We used deletions as well as insertions of objects. All occlusion modes were equivalent concerning detection rate and reaction time, deviating from the control condition only. The detection of relevant changes was both more likely and faster than that of irrelevant ones, particularly for relevant insertions, which approached the base line level. Even in this case, it took about 180 ms longer to react to changes when they occurred during a saccade, blink or blank. In a second study, relevant insertions and the blank occlusion were used in a driving simulator environment. We found a surprising effect in the dynamic setting: an advantage in change detection rate and time with blanks compared to the control condition. Change detection was also good during blinks, but not in saccades. Possible explanation of these effects and their practical implications are discussed.

Blinks, blanks and saccades: How blind we really are for relevant visual events

We report on a study in which subjects viewed color video stills of natural traffic situations while eye movements were recorded. A display change could occur randomly during three different occlusion modes--blinks, blanks and saccades--or during a fixation. These changes could be either relevant or irrelevant with respect to the traffic safety situation. Furthermore we contrasted insertions and deletions. All occlusion modes appeared equivalent concerning detection rate and detection time, and only differed from the fixation condition. The results also show that the detection of relevant changes was more likely and faster than that of irrelevant ones. However, even relevant insertions, which were almost always detected, were around 180 ms longer to report when they occurred during an occlusion. Furthermore, the detection of relevant changes was fairly stable across a wide range of the visual field, whereas irrelevant changes were less well detected, the further away from the fovea they occurred. We close with an outlook on a follow-up study where only relevant insertions and the blank occlusion were used in a driving simulator environment. Surprisingly, we found an advantage in change detection rate and time with blanks compared to the control condition. Change detection was also good during blinks, but not in saccades.