Effects of task- and switch-predictability on task-switching during scene viewing.
Mills M., Bahle B., Dalmaijer E., Van der Stigchel S., Dodd M.
Previous examinations of task-set and visual behavior indicate that viewing task influences saccade- and fixation-relevant parameters such as the rate of change in saccade amplitudes and fixation durations over time (Mills et al., 2011). Such demonstrations invite the possibility that gaze control parameters are task-relevant and potentially affected by task-switching. In support, recent work has demonstrated a general effect of task-switching on sequential dependencies between saccades (Dodd et al., VSS, 2014). Here, we investigate the possibility that gaze control settings may be represented and switched as part of a task-set. Participants viewed scenes while either searching for a target 'N' or 'Z', memorizing the scene in preparation for a memory test, or evaluating scene pleasantness. The critical manipulations were task-predictability (fixed or random task-order) and switch-predictability (fixed or random switch-schedule), yielding four conditions. In the Task-Predictable condition (fixed task-order, random switch-schedule), participants knew what task to switch to but not when to switch. In the Switch-Predictable condition (random task-order, fixed switch-schedule), participants knew on which trial to switch tasks but not which task they would be switching to. In the Both-Predictable condition (fixed task-order, fixed switch-schedule), participants knew what task to switch to and when to switch. Finally, in the Neither-Predictable condition (random task-order, random switch-schedule), participants did not know the task-order or switch-schedule. In each condition, gaze parameters showed stereotypic non-linear change whereby durations increased and amplitudes decreased, with change in both parameters reaching asymptote ~2-4 seconds into viewing. Importantly, in the Switch-Predictable condition there was no effect of task-switching on change in these parameters over time. This is in contrast to the Neither-Predictable and Task-Predictable conditions in which rates of change tended to be shallower on task-switch versus task-repeat trials. Thus, the effect of task-switching on gaze control parameters appears to depend on unpredictable task-switches. Meeting abstract presented at VSS 2015.