Abstract
Visual attention studies have demonstrated that the shape of space-based selection can be governed by salient object contours: when a portion of an enclosed space is cued, the selected region extends to the full enclosure. Although this form of object-based attention (OBA) is well established, one continuing investigation focuses on whether this selection is obligatory or under voluntary control. We attempt to dissociate between these alternatives by interrogating the locus coeruleus-norepinephrine (LC-NE) system – known to fluctuate with top-down attention – during a classic two-rectangle paradigm in a sample of healthy human participants (N = 36). An endogenous spatial pre-cue directed voluntary space-based attention (SBA) to one end of a rectangular frame. We manipulated the reliability of the cue, such that targets appearing at an uncued location within the frame occurred at low or moderate frequencies. Phasic pupillary responses time-locked to the cue display served to noninvasively measure LC-NE activity, reflecting top-down processing of the spatial cue. If OBA is controlled analogously to SBA, then object selection should emerge only when it is behaviorally expedient and when LC-NE activity reflects a high degree of top-down attention to the cue display. Our results bore this out. Thus, we conclude that OBA was voluntarily controlled, and furthermore show that phasic norepinephrine may modulate attentional strategy.
Highlights
Egly et al (1994) introduced to the visual attention literature the ubiquitous two-rectangle paradigm, which commonly elicits a selection of space governed by object contours
We verified that the observed results described below were not the product of a speed-accuracy trade-off: Pearson correlations between reaction time (RT) and accuracy were negative and significant on average, suggesting that correct responses were associated with faster RTs in our data, r = -0.04, 95% confidence interval (CI) [-0.06, -0.02], t (35) = -4.80, p < 0.001
Given the variable interstimulus interval (ISI) in our design, it is possible trials with the longer delays were associated with larger peak pupil diameters at target onset due to temporal lag in the pupillary response. In light of this expected relationship, we examined the number of trials drawn from early (300–575 ms), intermediate (600–875 ms), and late (900–1,175 ms) delays to establish that the proportion of trials at each ISI sorted into large and small pupil diameter groups were matched across the two spatial-validity groups
Summary
Egly et al (1994) introduced to the visual attention literature the ubiquitous two-rectangle paradigm, which commonly elicits a selection of space governed by object contours. Using an endogenous spatial cue in conjunction with a two-rectangle paradigm, Shomstein and Behrmann (2006) found that left posterior parietal cortex (PPC) showed greater activation following a cue to shift attention within an object than a between-object shift cue Together, these studies suggest that OBA is directed by a similar, if not common, topdown control mechanism to SBA (Scolari et al, 2014; Scolari et al, 2015). We conducted a between-subjects manipulation of the reliability of a central, endogenous precue in an otherwise identical two-rectangle display (Egly et al, 1994; Shomstein & Yantis, 2004) in an attempt to find support for either the attentional prioritization or attentional spreading accounts This approach enables us to hold stimulus display parameters constant while stringently testing how target location uncertainty might modulate selection in the presence of object contours. If OBA is driven solely by properties of the stimulus display, we would expect any relationship between this physiological response and the presence or magnitude of OBA effects to remain constant across cue reliability manipulations
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