The nature of the global effect beyond the first eye movement.

When two or more visual objects appear in close proximity, the initial oculomotor response is systematically aimed at a location in between the objects, a phenomenon named the global effect. The global effect is known to arise when saccades are initiated relatively quickly, immediately after the presentation of a display, but it has also been shown that a global effect may occur much later in time, even for eye movements beyond the first. That is, when participants are searching for a complex target among complex distractor objects, it can take several eye movements to hit the target, and these eye movements mainly land at intermediate locations. It is debatable whether these findings are caused by the same mechanisms as those involved in the more typical global effect studies, studies in which much simpler search tasks are employed. In the current two experiments, we examined whether and under which circumstances a global effect can be found for a second oculomotor response in a search display containing two simple objects. Experiment 1 showed that the global effect only occurs when the presentation of the target and distractor objects is delayed, until after the first oculomotor response is initiated. Experiment 2 demonstrated that identity information, rather than spatial information, is crucial for the occurrence of the global effect. These results suggest that the global effect is not due to a failure to dissociate between the locations of multiple objects, but a failure to determine which one is the target

Pupil Dilation Reflects Task Relevance Prior to Search

When observers search for a specific target, it is assumed that they activate a representation of the task relevant object in visual working memory (VWM). This representation – often referred to as the template – guides attention towards matching visual input. In two experiments we tested whether the pupil response can be used to differentiate stimuli that match the task-relevant template from irrelevant input. Observers memorized a target color to be searched for in a multi-color visual search display, presented after a delay period. In Experiment 1, one color appeared at the start of the trial, which was then automatically the search template. In Experiments 2, two colors were presented, and a retro-cue indicated which of these was relevant for the upcoming search task. Crucially, before the search display appeared, we briefly presented one colored probe stimulus. The probe could match either the relevant-template color, the non-cued color (irrelevant), or be a new color not presented in the trial. We measured the pupil response to the probe as a signature of task relevance. Experiment 1 showed significantly smaller pupil size in response to probes matching the search template than for irrelevant colors. Experiment 2 replicated the template matching effect and allowed us to rule out that it was solely due to repetition priming. Taken together, we show that the pupil responds selectively to participants’ target template prior to search