Attentional capture by auto- and allo-cues

LIP responses to a popout stimulus are reduced if it is overtly ignored

Bright objects capture our attention by virtue of 'popping out' from their surroundings. This correlates with strong responses in cortical areas thought to be important in attentional allocation. Previous studies have suggested that with the right mindset or training, humans can ignore popout stimuli. We studied the activity of neurons in monkey lateral intraparietal area while monkeys performed a visual search task. The monkeys were free to move their eyes, and a distractor, but never the search target, popped out. On trials in which the monkeys made a saccade directly to the search target, the popout distractor evoked a smaller response than the non-popout distractors. The intensity of the response to the popout correlated inversely with the monkeys' ability to ignore it. We suggest that this modulation corresponds to a top-down mechanism that the brain uses to adjust the parietal representation of salience.

Electrophysiological Evidence of the Capture of Visual Attention

We investigated the ability of salient yet task-irrelevant stimuli to capture attention in two visual search experiments. Participants were presented with circular search arrays that contained a highly salient distractor singleton defined by color and a less salient target singleton defined by form. A component of the event-related potential called the N2pc was used to track the allocation of attention to lateralized positions in the arrays. In Experiment 1, a lateralized distractor elicited an N2pc when a concurrent target was presented on the vertical meridian and thus could not elicit lateralized components such as the N2pc. A similar distractor-elicited N2pc was found in Experiment 2, which was conducted to rule out certain voluntary search strategies. Additionally, in Experiment 2 both the distractor and the target elicited the N2pc component when the two stimuli were presented on opposite sides of the search array. Critically, the distractor-elicited N2pc preceded the target-elicited N2pc on these trials. These results demonstrate that participants shifted attention to the target only after shifting attention to the more salient but task-irrelevant distractor. This pattern of results is in line with theories of attention in which stimulus-driven control plays an integral role.

Just like new: Newly segregated old objects capture attention

Subjects searched for target letters that were either contained in or segregated from a group of distracting letters and were either moving or stationary. Subjects were faster to identify targets that had recently become segregated from the group regardless of whether the segregation was accomplished by (1) the element itself moving away from the group or (2) the group moving away from the segregated element. The results show that attention can be captured by newly apparent objects that are produced by a new grouping of an existing scene.

Temporal expectations modulate attentional capture

Subjects' ability to override attentional capture by salient distractors during singleton search has been attributed to the adoption of an attentional set for the type of discontinuity characterizing the target (Folk, Remington, & Johnston, 1992) or to fast disengagement of attention from the salient distractor's location (Theeuwes, Atchley, & Kramer, 2000). The present results support an alternative account by showing that temporal expectancies modulate attentional capture. In a color singleton search, an irrelevant onset preceding the target by a given time interval produced capture when the distractor-to-target interval varied unpredictably but failed to do so when this interval was predictable. Moreover, with unpredictable intervals and moderately salient stimuli, capture was overridden at the expected average interval. These findings invite caution when stimulus onset asynchrony manipulations are used to study the temporal deployment of attention, since they demonstrate that such manipulations introduce powerful temporal expectations.

Unique Temporal Change Is the Key to Attentional Capture

Attentional capture refers to the observation that some events break through and attract one's attention even when one is engaged in a task for which these events are irrelevant. Previous research, focusing primarily on spatial factors, has shown that a new object is more salient in this regard than an abrupt change in an object's features. Here we show that feature changes can be as effective as new objects in capturing attention, provided that they occur during a period of temporal calm. Conversely, both feature changes and new objects are far less effective in capturing attention when they occur simultaneously with other display changes, such as coincident with the initial onset of the display or with small visual transients that occur during a display transition. These results highlight the importance of considering both space and time in studies of attentional capture; the most effective stimulus is unique in both dimensions.

Effects of target and distractor heterogeneity on search for a color target

Experiments were designed to investigate the effects of target and distractor heterogeneity on the threshold for detection of a color target in a search task. In the first two experiments stimuli were chosen so that the target and distractor stimuli varied along one Cardinal axis in color space, while the target differed from distractors along another Cardinal axis. The Cardinal axis signaling the relevant target-distractor difference was consistent from trial to trial within an experiment. When observers searched for a color target among homogeneous distractors but the color of the target and distractors changed from trial to trial there was a small increase in threshold. When the distractors within a display were heterogeneous, and the target color varied from trial to trial there was a larger and more consistent increase in threshold. Varying stimuli along a Cardinal axis other than the Cardinal axis that differentiates target and distractors can impair performance in visual search tasks. Further experiments showed that the presence of heterogeneous distractors had little or no effect on thresholds when location or color cues indicated that these stimuli were irrelevant to the task. Results suggest that the effect of heterogeneity in these experiments is attentional in nature rather than sensory.

Taking control of reflexive social attention

Attention is shifted reflexively to where other people are looking. It has been argued by a number of investigators that this social attention effect reflects the obligatory bottom-up activation of domain-specific modules within the inferior temporal (IT) cortex that are specialized for processing face and gaze information. However, it is also the case that top-down factors may modulate the activation of IT cells. Here we examined behaviorally whether reflexive social orienting is purely automatic or sensitive to top-down modulation. Participants were shown an ambiguous stimulus that could be perceived either as representing EYES or a CAR. In we demonstrated between groups that an automatic shift of attention, equivalent to that triggered by a schematic FACE, occurred only when the stimulus was referred to as possessing EYES. In all participants received the EYES and CAR conditions. When the stimulus was first referred to as a CAR and then as EYES, an attentional shift was only present for the EYES condition. However, when the stimulus was first referred to as possessing EYES, and then later as a CAR, attentional shifts were observed for both conditions. These data indicate that the emergence of a reflexive social attention effect is influenced by top-down mechanisms but in an asymmetrical manner. Top-down processes appear to be effective for triggering IT involvement, that is, for perceiving a stimulus as a face, which produces the social attention effect. But top-down mechanisms are ineffective once IT involvement has been triggered. That is, once a stimulus has been seen as having eyes, it continues to be seen that way, and accordingly, the social attention effect persists.

Attention: Reaction Time and Accuracy Reveal Different Mechanisms

The authors propose that there are 2 different mechanisms whereby spatial cues capture attention. The voluntary mechanism is the strategic allocation of perceptual resources to the location most likely to contain the target. The involuntary mechanism is a reflexive orienting response that occurs even when the spatial cue does not indicate the probable target location. Voluntary attention enhances the perceptual representation of the stimulus in the cued location relative to other locations. Hence, voluntary attention affects performance in experiments designed around both accuracy and reaction time. Involuntary attention affects a decision as to which location should be responded to. Because involuntary attention does not change the perceptual representation, it affects performance in reaction time experiments but not accuracy experiments. The authors obtained this pattern of results in 4 different versions of the spatial cuing paradigm.