Richard Godijn

Programming of endogenous and exogenous saccades: Evidence for a competitive integration model

Participants were required to make a saccade to a uniquely colored target while ignoring the presentation of an onset distractor. The results provide evidence for a competitive integration model of saccade programming that assumes endogenous and exogenous saccades are programmed in a common saccade map. The model incorporates a lateral interaction structure in which saccade-related activation at a specific location spreads to neighboring locations but inhibits distant locations. In addition, there is top-down, location-specific inhibition of locations to which the saccade should not go. The time course of exogenous and endogenous activation in the saccade map can explain a variety of eye movement data, including endpoints, latencies, and trajectories of saccades and the well-known global effect.

Symbolic Control of Visual Attention

The present study reports four pairs of experiments that examined the role of nonpredictive (i.e., task-irrelevant) symbolic stimuli on attentional orienting. The experiments involved a simple detection task, an inhibition of return (IOR) task, and choice decision tasks both with and without attentional bias. Each pair of experiments included one experiment in which nonpredictive arrows were presented at the central fixation location and another experiment in which non-predictive direction words (e.g., “up,” “down,” “left,” “right”) were presented. The nonpredictive symbolic stimuli affected responses in all experiments, with the words producing greater effects in the detection task and the arrows producing greater effects in the IOR and choice decision tasks. Overall, the present findings indicate that there is a strong connection between the overlearned representations of the meaning of communicative symbols and the reflexive orienting of visual attention.

Parallel allocation of attention prior to the execution of saccade sequences.

In a series of 5 experiments, the allocation of attention prior to the execution of saccade sequences was examined by using a dual-task paradigm. In the primary task, participants were required to execute a sequence of 2 endogenous saccades. The secondary task was a forced-choice letter identification task. During the programming of the saccade sequences, letters were briefly presented at the saccade goals and at no-saccade locations. The results showed that performance was better for letters presented at any of the saccade goals than for letters presented at any of the no-saccade locations. The results support a spatial model that assumes that prior to the execution of a saccade sequence, attention is allocated in parallel to all saccade goals. ((c) 2003 APA, all rights reserved)

Irrelevant singletons capture attention: evidence from inhibition of return.

Previous research has shown that a salient feature singleton may capture attention in a stimulus-driven, bottom-up fashion (e.g., Theeuwes, 1992, 1994b). This conclusion has been challenged by others claiming that the observed attentional capture by irrelevant singletons may not be stimulus driven but due to top-down attentional control settings and/or nonspatial filtering costs. In the present study, we show that inhibition of return (IOR) occurs at the location of an irrelevant singleton. Participants were slower to detect a target presented at the location of the irrelevant singleton, relative to other locations. Since IOR can be observed only as a result of anexogenous, stimulus-driven shift ofspatial attention, it is unlikely that top-down control settings and/or nonspatial filtering costs played a role. In line with earlier claims, the present findings provide strong evidence that salient singletons capture spatial attention in a purely bottom-up way.

The relationship between inhibition of return and saccade trajectory deviations.

After presentation of a peripheral cue, a subsequent saccade to the cued location is delayed (inhibition of return: IOR). Furthermore, saccades typically deviate away from the cued location. The present study examined the relationship between these inhibitory effects. IOR and saccade trajectory deviations were found after central (endogenous) and peripheral (exogenous) cuing of attention, and both effects were larger with an onset cue than with a color singleton cue. However, a dissociation in time course was found between IOR and saccade trajectory deviations. Saccade trajectory deviations occurred at short delays between the cue and the saccade, but IOR was found at longer delays. A model is proposed in which IOR is caused by inhibition applied to a preoculomotor attentional map, whereas saccade trajectory deviations are caused by inhibition applied to the saccade map, in which the final stage of oculomotor programming takes place.

Attentional and oculomotor capture with static singletons

Previous research has shown that in visual search static singletons have the ability to capture attention (Theeuwes, 1991a, 1992). The present study investigated whether these singletons also have the ability to capture the eyes. Participants had to make an eye movement and respond manually to a shape singleton while a color singleton was present. When participants searched for a unique shape while a unique color singleton was present there was strong attentional and oculomotor capture (Experiment 1). However, when participants searched for a specific-shape singleton (a green circle) when a specific-color singleton (a red element) had to be ignored, there was attentional capture but no oculomotor capture (Experiment 2). The results suggest that an attentional set for a specific feature value defining both the target and the distractor (as in Experiment 2) allows such a fast disengagement of attention from the location of the distractor that a saccade execution to that location is prevented.

A new estimation of the duration of attentional dwell time

How rapidly can attention move from one object to the next? Previous studies in which the dwell time paradigm was used have estimated attentional switch times of 200–500 msec, results incompatible with the search rate estimates of 25–50 msec shown in numerous visual search studies. It has been argued that dwell times are so long in the dwell time paradigm because the attentional shifts measured are unlike those used in visual search. In the present experiment, a variation of a visual search task was used, in which serial endogenous (volitional) deployments of attention were measured directly by means of a probe reaction time task. The experiment revealed a dwell time of about 250 msec, consistent with the faster estimates from other dwell time studies. This result suggests that endogenous shifts of attention may be relatively slow and that the faster attentional shifts estimated from visual search tasks may be due to the involvement of bottom-up processes.

Inhibition-of-return and oculomotor interference

The present study shows that inhibition-of-return reduces competition for selection within the oculomotor system. We examined the effect of a distractor when it was presented at an inhibited location (IOR). The results show that due to IOR distractors cause less interference. This was evident in all three measures. First, there was less oculomotor capture when a distractor was presented at an inhibited location. Second, the saccade latency to the target was shorter when a distractor appeared at an inhibited location than when it appeared at a non-inhibited location. Third, there was less curvature towards the distractor when it was presented at inhibited location relative to a non-inhibited location. The observation that there is less interference for a distractor presented at an inhibited location suggests that IOR reduces the exogenous activation of the distractor within the saccade map.

Endogenous saccades are preceded by shifts of visual attention: Evidence from cross-saccadic priming effects

The present study examines whether endogenous saccades are preceded by shifts of attention. Three experiments are reported in which participants were required to execute a saccadic eye movement to a certain location and to subsequently identify the orientation of a target triangle. Prior to the execution of the saccade a prime was presented, which was compatible or incompatible with the target. A priming effect (faster responses in the compatible condition than in the incompatible condition) occurred only when the prime was presented at the saccade destination, and this effect was larger when the prime was presented during oculomotor programming than when it was presented prior to oculomotor programming. The results indicate that an endogenous shift of attention precedes endogenous saccades, providing further support for theories of visual selection that assume a tight coupling between attention and saccades.

The relationship between exogenous and endogenous saccades and attention.

Publisher Summary This chapter reviews the evidence regarding the relationship between endogenous and exogenous attention and saccades. Over the past 20 years, a great deal of research has been conducted to determine the relationship between (endogenous and exogenous) shifts of attention and saccades. Because both attention and saccades have the goal of selecting relevant portions of a visual scene, the idea that attention and saccades are, to a certain extent, related is intuitively appealing. In this view, attention and saccades are related on the basis of their common function. To further process and respond to an object, both orienting systems are typically directed to the same object, although in principle, their focus may be dissociated. An alternative view that assumes a tighter relationship between attention and saccades is the efference view. According to this view, attention is required at the saccade destination to program a saccade. Attention shifts are accomplished by preparing an eye movement to that location. However, this does not imply that whenever attention moves, the eyes must follow. It is assumed that attention and saccade programing are causally related, but a separate go-signal is required to trigger the saccade that has been programed. Therefore, attention may move, while the eyes remain fixated.