Involuntary attentional capture is determined by task set: evidence from event-related brain potentials

Abstract

To find out whether attentional capture by irrelevant but salient visual objects is an exogenous bottom-up 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 top-down intention, and demonstrate the central role of task set in involuntary attentional orienting.

Figure 1

Illustration of the different task conditions used in Experiments 1 and 2. In all tasks, a colour singleton cue array was presented for 50 ms and was followed after a blank interval of 150 ms by a target array (50 ms duration), and participants had to report the orientation of the unique stimulus in the target array. This target stimulus was a red bar among grey bars in the colour task, a single grey bar in the onset task, and a small grey bar among larger grey bars in the size task. In the inverted colour task, the cue singleton was grey among red items, and the unique target stimulus was a grey bar presented among red bars. Red stimuli are shown in dark grey, grey stimuli in white.

Figure 2

Response times (line graphs) and error rates (bar graphs) in the colour and onset tasks of Experiment 1 for trials where colour singleton cues and subsequent targets were presented at the same location or at different locations.

Figure 3

ERPs elicited in the 600 ms interval after cue onset in the colour task of Experiment 1, collapsed across lateral posterior electrodes PO7/PO8, and across all cue and target locations. P1, N1, and N2 components triggered by the cue array are followed by P1 and N1 components elicited in response to the target array - P1(t) and N1(t). ‘T’ marks the onset of the target array.

Figure 4

ERPs elicited in the 300 ms interval after cue onset in the colour task (top left) and in the onset task (top right) of Experiment 1 at posterior electrode sites PO7/8 contralateral (solid lines) and ipsilateral (dashed lines) to the visual hemifield where the colour singleton cue was presented. The bottom panel shows difference waves obtained by subtracting ipsilateral from contralateral ERPs in the colour task (solid line) and onset task (dashed line).

Figure 5

Response times (line graphs) and error rates (bar graphs) in the colour, size, and inverted colour tasks of Experiment 2 for trials where colour singleton cues and subsequent targets were presented at the same location or at different locations.

Figure 6

ERPs elicited in the 300 ms interval after cue onset in the colour task, size task, and inverted colour tasks of Experiment 2 at posterior electrode sites PO7/8 contralateral (solid lines) and ipsilateral (dashed lines) to the visual hemifield where the colour singleton cue was presented. The bottom panel shows difference waves obtained by subtracting ipsilateral from contralateral ERPs in the colour task (solid black line), size task (dashed line), and inverted colour task (solid grey line).

Figure 7

Topographical maps of cue-induced N2pc scalp distributions obtained during the 180-235 ms time interval after cue onset. These maps were constructed by spherical spline interpolation (see Perrin, Pernier, Bertrand, & Echallier, 1989) after mirroring the ipsilateral-contralateral difference waveforms to obtain symmetrical voltage values for both hemispheres. As a result of the mirroring procedure, the N2pc appears as negative voltage (-) over the left hemisphere and as positive voltage (+) over the right hemisphere. Note the different scale used for the size task of Experiment 2 (bottom left panel), and the inverted polarity of the N2pc effect in this task, representing an enhanced negativity ipsilateral to the side of the colour singleton cue.