Monika Kiss

Involuntary Attentional Capture is Determined by Task Set: Evidence from Event-related Brain Potentials

To find out whether attentional capture by irrelevant but salient visual objects is an exogenous bottomup phenomenon, or can be modulated by current task set, two experiments were conducted where the N2pc component was measured as an electrophysiological marker of attentional selection in response to spatially uninformative color singleton cues that preceded target arrays. When observers had to report the orientation of a uniquely colored target bar among distractor bars (color task), behavioral spatial cueing effects were accompanied by an early cue-induced N2pc, indicative of rapid attentional capture by color singleton cues. In contrast, when they reported the orientation of target bars presented without distractors (onset task), no behavioral cueing effects were found and no early N2pc was triggered to physically identical cue arrays. Experiment 2 ruled out an alternative interpretation of these N2pc differences in terms of distractor inhibition. These results do not support previous claims that attentional capture is initially unaffected by topdown intention, and demonstrate the central role of task set in involuntary attentional orienting.

Reward Priority of Visual Target Singletons Modulates Event-Related Potential Signatures of Attentional Selection

We examined visual search for color singleton targets, whose shape was discriminated. Critically, we varied the reward priority of singleton colors (correct fast performance was worth more bonus points for red singletons than for green singletons, or vice versa) to test whether event-related potential signatures of visual selection can be affected by distinct reward priorities for different target types, even when every target has to be selected for report. The N2pc component was earlier and larger for high- than for low-reward targets. This influence of reward on the N2pc correlated with the subject-by-subject impact of reward level on efficiency of behavioral performance. Later postselection processing was also affected by reward level. These results demonstrate that visual selection of task-relevant items is rapidly modulated by reward-related priorities, even when every target has to be selected for response.

Electrophysiological markers of visual dimension changes and response changes

In cross-dimensional visual search tasks, target discrimination is faster when the previous trial contained a target defined in the same visual dimension as the current trial. The dimension-weighting account (DWA; A. Found & H. J. Müller, 1996) explains this intertrial facilitation by assuming that visual dimensions are weighted at an early perceptual stage of processing. Recently, this view has been challenged by models claiming that intertrial facilitation effects are generated at later stages that follow attentional target selection (K. Mortier, J. Theeuwes, & P. A. Starreveld, 2005). To determine whether intertrial facilitation is generated at a perceptual stage, at the response selection stage, or both, the authors focused on specific event-related brain potential components (directly linkable to perceptual and response-related processing) during a compound search task. Visual dimension repetitions were mirrored by shorter latencies and enhanced amplitudes of the N2-posterior- contralateral, suggesting a facilitated allocation of attentional resources to the target. Response repetitions and changes systematically modulated the lateralized readiness potential amplitude, suggesting a benefit from residual activations of the previous trial biasing the correct response. Overall, the present findings strengthen the DWA by indicating a perceptual origin of dimension change costs in visual search.

Response Profile of the Face-Sensitive N170 Component: A Rapid Adaptation Study

To study the response profile of the face-selective N170 component, an adaptation procedure was employed where adaptor and test stimuli were presented in rapid succession. Test stimuli came from 4 different face categories (upright, inverted, and eyeless faces and eyes-only images). The same face stimuli, as well as upright and inverted houses, served as adaptors. Strong N170 amplitude reductions indicative of adaptation were found for all types of face test stimuli preceded by face adaptors relative to house adaptors, demonstrating that at a generic level, the N170 reflects the activation of face-selective neurons by full faces and by face parts. The highly specific pattern of N170 adaptation effects for different combinations of adaptor and test stimulus categories suggests additional distinct contributions of eye-selective neurons and of face-sensitive neurons that are tuned to deviations from canonical stimulus orientations to the N170 component. Results demonstrate that the N170 is generated by multiple neural sources at both early and later stages of configural face processing and that rapid adaptation techniques provide a powerful tool to dissociate these sources.

The Roles of Feature-Specific Task Set and Bottom-Up Salience in Attentional Capture: An ERP Study.

We investigated the roles of top-down task set and bottom-up stimulus salience for feature-specific attentional capture. Spatially nonpredictive cues preceded search arrays that included a color-defined target. For target-color singleton cues, behavioral spatial cueing effects were accompanied by cue-induced N2pc components, indicative of attentional capture. These effects were only minimally attenuated for nonsingleton target-color cues, underlining the dominance of top-down task set over salience in attentional capture. Nontarget-color singleton cues triggered no N2pc, but instead an anterior N2 component indicative of top-down inhibition. In Experiment 2, inverted behavioral cueing effects of these cues were accompanied by a delayed N2pc to targets at cued locations, suggesting that perceptually salient but task-irrelevant visual events trigger location-specific inhibition mechanisms that can delay subsequent target selection.

Attentional Capture by Salient Distractors during Visual Search Is Determined by Temporal Task Demands

The question whether attentional capture by salient but task-irrelevant visual stimuli is triggered in a bottom–up fashion or depends on top–down task settings is still unresolved. Strong support for bottom–up capture was obtained in the additional singleton task, in which search arrays were visible until response onset. Equally strong evidence for top–down control of attentional capture was obtained in spatial cueing experiments in which display durations were very brief. To demonstrate the critical role of temporal task demands on salience-driven attentional capture, we measured ERP indicators of capture by task-irrelevant color singletons in search arrays that could also contain a shape target. In Experiment 1, all displays were visible until response onset. In Experiment 2, display duration was limited to 200 msec. With long display durations, color singleton distractors elicited an N2pc component that was followed by a late Pd component, suggesting that they triggered attentional capture, which was later replaced by location-specific inhibition. When search arrays were visible for only 200 msec, the distractor-elicited N2pc was eliminated and was replaced by a Pd component in the same time range, indicative of rapid suppression of capture. Results show that attentional capture by salient distractors can be inhibited for short-duration search displays, in which it would interfere with target processing. They demonstrate that salience-driven capture is not a purely bottom–up phenomenon but is subject to top–down control.

Attentional capture by task-irrelevant fearful faces is revealed by the N2pc component.

We measured the N2pc component as an electrophysiological indicator of attentional selection to investigate whether fearful faces can attract attention even when they are entirely task-irrelevant and attention is focused on another demanding visual monitoring task. Participants had to detect infrequent luminance changes of the fixation cross, while ignoring stimulus arrays containing a face singleton (a fearful face among neutral faces, or neutral face among fearful faces) to the left or right of fixation. On trials without a target luminance change, an N2pc was elicited by fearful faces presented next to fixation, irrespective of whether they were singletons or not, demonstrating that irrelevant fearful faces can bias the spatial distribution of attention. The N2pc to fearful faces was attenuated when face arrays were presented simultaneously with a target luminance change, suggesting that concurrent target processing reduces attentional capture by emotional salient events.

Attention modulates the processing of emotional expression triggered by foveal faces

To investigate whether the processing of emotional expression for faces presented within foveal vision is modulated by spatial attention, event-related potentials (ERPs) were recorded in response to stimulus arrays containing one fearful or neutral face at fixation, which was flanked by a pair of peripheral bilateral lines. When attention was focused on the central face, an enhanced positivity was elicited by fearful as compared to neutral faces. This effect started at 160 ms post-stimulus, and remained present for the remainder of the 700 ms analysis interval. When attention was directed away from the face towards the line pair, the initial phase of this emotional positivity remained present, but emotional expression effects beyond 220 ms post-stimulus were completely eliminated. These results demonstrate that when faces are presented foveally, the initial rapid stage of emotional expression processing is unaffected by attention. In contrast, attentional task instructions are effective in inhibiting later, more controlled stages of expression analysis.

Attentional capture by visual singletons is mediated by top-down task set: New evidence from the N2pc component

To investigate whether attentional capture by salient visual stimuli is mediated by current task sets, we measured the N2pc component as a marker of the spatial locus of visual attention during visual search. In each trial, a singleton stimulus that could either be a target (color task: red circle; shape task: green diamond) or a nontarget (blue circle or green square) was presented among uniform distractors (green circles). As predicted by the view that attentional capture is contingent on task set, the N2pc was strongly affected by task instructions. It was maximal for targets, attenuated but still reliably present for nontarget singletons defined in the target dimension (even when these were accompanied by an irrelevant-dimension singleton), and small or absent for equally salient irrelevant-dimension singletons. Results demonstrate that attentional capture is not a purely bottom-up phenomenon, but is strongly determined by top-down task set.

Influence of attentional demands on the processing of emotional facial expressions in the amygdala

Recent studies have cast doubts on the appealing idea that the processing of threat-related stimuli in the amygdala is unconstrained by the availability of attentional resources. However, these studies exclusively used face stimuli presented at fixation and it is unclear whether their conclusion can apply to peripheral face stimuli. Thus, we designed an experiment in which we manipulated the perceptual attentional load of the task used to divert attention from peripheral face stimuli: participants were presented simultaneously with four peripheral pictures (two faces, either both neutral or both fearful, and two houses) that were slightly tilted, and had to match two of these pictures (defined by their position on the screen) either for orientation of the tilt or for identity. The identity task was confirmed to involve greater attentional load than the orientation task by differences in accuracy, reaction times, subsequent face recognition performance, and patterns of activation in several cortical regions. In the orientation task, ignored fearful faces led to stronger activation in the right amygdala than ignored neutral faces. However, this differential response was abolished when participants performed the difficult identity-matching task. Thus, emotional processing of peripheral faces in the amygdala also appears to depend on the available perceptual attentional resources.