title: Pupil size directly modulates the feedforward response in human primary visual cortex independently of attention.
abstract: Controversy revolves around the question of whether psychological factors like attention and emotion can influence the initial feedforward response in primary visual cortex (V1). Although traditionally, the electrophysiological correlate of this response in humans (the C1 component) has been found to be unaltered by psychological influences, a number of recent studies have described attentional and emotional modulations. Yet, research into psychological effects on the feedforward V1 response has neglected possible direct contributions of concomitant pupil-size modulations, which are known to also occur under various conditions of attentional load and emotional state. Here we tested the hypothesis that such pupil-size differences themselves directly affect the feedforward V1 response. We report data from two complementary experiments, in which we used procedures that modulate pupil size without differences in attentional load or emotion while simultaneously recording pupil-size and EEG data. Our results confirm that pupil size indeed directly influences the feedforward V1 response, showing an inverse relationship between pupil size and early V1 activity. While it is unclear in how far this effect represents a functionally-relevant adaptation, it identifies pupil-size differences as an important modulating factor of the feedforward response of V1 and could hence represent a confounding variable in research investigating the neural influence of psychological factors on early visual processing.
authors.affiliation: Dept. of Experimental Psychology, Ghent University, 9000 Ghent, Belgium. Electronic address: klaas.bombeke@ugent.be.
authors.forename: Klaas
authors.initials: K
authors.lastname: Bombeke
authors.affiliation: Dept. of Experimental Psychology, Ghent University, 9000 Ghent, Belgium.
authors.forename: Wout
authors.initials: W
authors.lastname: Duthoo
authors.affiliation: Dept. of Experimental Clinical and Health Psychology, Ghent University, 9000 Ghent, Belgium.
authors.forename: Sven C
authors.initials: SC
authors.lastname: Mueller
authors.affiliation: Otto-von-Guericke University Magdeburg, 39120 Magdeburg, Germany; Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany.
authors.forename: Jens-Max
authors.initials: JM
authors.lastname: Hopf
authors.affiliation: Dept. of Experimental Psychology, Ghent University, 9000 Ghent, Belgium.
authors.forename: C Nico
authors.initials: CN
authors.lastname: Boehler
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D004569:Electroencephalography; D004644:Emotions / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D011680:Pupil; D012815:Signal Processing, Computer-Assisted; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology; D055815:Young Adult
keywords: Attention; Emotion; Primary visual cortex; Pupil size