Abstract
Studies of selective attention during perception have revealed modulation of the pupillary response according to the brightness of task-relevant (attended) vs. -irrelevant (unattended) stimuli within a visual display. As a strong test of top-down modulation of the pupil response by selective attention, we asked whether changes in pupil diameter follow internal shifts of attention to memoranda of visual stimuli of different brightness maintained in working memory, in the absence of any visual stimulation. Across 3 studies, we reveal dilation of the pupil when participants orient attention to the memorandum of a dark grating relative to that of a bright grating. The effect occurs even when the attention-orienting cue is independent of stimulus brightness, and even when stimulus brightness is merely incidental and not required for the working-memory task of judging stimulus orientation. Furthermore, relative dilation and constriction of the pupil occurred dynamically and followed the changing temporal expectation that 1 or the other stimulus would be probed across the retention delay. The results provide surprising and consistent evidence that pupil responses are under top-down control by cognitive factors, even when there is no direct adaptive gain for such modulation, since no visual stimuli were presented or anticipated. The results also strengthen the view of sensory recruitment during working memory, suggesting even activation of sensory receptors. The thought-provoking corollary to our findings is that the pupils provide a reliable measure of what is in the focus of mind, thus giving a different meaning to old proverbs about the eyes being a window to the mind.
Highlights
Studies of selective attention during perception have revealed modulation of the pupillary response according to the brightness of task-relevant vs. -irrelevant stimuli within a visual display
The probe stimulus had a constant, intermediate level of brightness, and could not itself induce any differential preparatory pupillary response according to cueing condition
Responses for grating orientations were more precise in trials with valid compared to neutral retrocues (Fig. 1B) [main effect of validity, F(1, 21) = 5.8, P = 0.025, η2p = 0.22]
Summary
Studies of selective attention during perception have revealed modulation of the pupillary response according to the brightness of task-relevant (attended) vs. -irrelevant (unattended) stimuli within a visual display. Attention in working memory modulates sensory cortical responses to the prioritized memoranda in a way that is decodable during the working-memory retention period from the sensory regions and susceptible to disruptive transcranial magnetic stimulation [8, 19,20,21]. Based on these findings, it has been proposed that attention can prioritize the sensory content of these mnemonic representations [5, 6]. Such a finding is interesting, but is entirely explainable by the effects of spatial selective attention on the perceptual stimuli relevant for encoding [17, 18]
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