Previous work (Ringer et al., 2013, VSS) showed that blur detection in natural scenes was unaffected by cognitive load in a gaze-contingent blur detection task, suggesting that blur may be detected preattentively. However, cognitive load was manipulated by the N-back task with a maximum of 3-back, which may have been insufficient load to affect attention. That study used both auditory and visual n-back tasks (from single-task to dual-task with 0- to 3-back) in two experiments, while participants completed gaze-contingent blur detection. The current study analyzed the eye movement data from the previous study to directly measure the effects of cognitive load on overt attention. Specifically, cognitive load has been shown to reduce attentional breadth as measured by a tighter distribution of fixations within an image (Miura, 1986; Reimer et al., 2012). Furthermore, the previous study had used a simple new/old picture memory task to encourage eye-movements, thus we measured recognition memory as another proxy for the effects of cognitive load on attention. Specifically, the encoding of visual information into long-term memory has been shown to be affected by attentional selection (Cowan, 1993; Matsukura et al., 2011). Finding effects of the N-back task on attention as measured by both eye movements and visual recognition memory would rule out the argument that the N-back load was insufficient to affect visual attention. Results: Fixation distributions showed increased density at the center of the image for the 3-back dual task over single-task blur detection (i.e., a significantly smaller Bivariate Contour Ellipse). Furthermore, recognition memory accuracy was significantly impaired with increasing N-back. Together these results provide compelling evidence that the cognitive load manipulation would have been powerful enough to evoke an attentional effect on blur sensitivity if blur thresholds were amenable to attentional manipulations.
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