title: Pupil size reflects the focus of feature-based attention.
abstract: We measured pupil size in adult human subjects while they selectively attended to one of two surfaces, bright and dark, defined by coherently moving dots. The two surfaces were presented at the same location; therefore, subjects could select the cued surface only on the basis of its features. With no luminance change in the stimulus, we find that pupil size was smaller when the bright surface was attended and larger when the dark surface was attended: an effect of feature-based (or surface-based) attention. With the same surfaces at nonoverlapping locations, we find a similar effect of spatial attention. The pupil size modulation cannot be accounted for by differences in eye position and by other variables known to affect pupil size such as task difficulty, accommodation, or the mere anticipation (imagery) of bright/dark stimuli. We conclude that pupil size reflects not just luminance or cognitive state, but the interaction between the two: it reflects which luminance level in the visual scene is relevant for the task at hand.
authors.affiliation: Department of Psychology, University of Washington, Seattle, Washington; and Department of Translational Research on New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy p.binda1@in.cnr.it.
authors.forename: Paola
authors.initials: P
authors.lastname: Binda
authors.affiliation: Department of Psychology, University of Washington, Seattle, Washington; and.
authors.forename: Maria
authors.initials: M
authors.lastname: Pereverzeva
authors.affiliation: Department of Psychology, University of Washington, Seattle, Washington; and.
authors.forename: Scott O
authors.initials: SO
authors.lastname: Murray
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D005133:Eye Movements; D005260:Female; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology; D010775:Photic Stimulation; D011680:Pupil / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: attentional modulation of visual responses; feature-based attention; motion-defined surfaces; spatial attention