title: Prestimulus alpha-band power biases visual discrimination confidence, but not accuracy.
abstract: The magnitude of power in the alpha-band (8-13Hz) of the electroencephalogram (EEG) prior to the onset of a near threshold visual stimulus predicts performance. Together with other findings, this has been interpreted as evidence that alpha-band dynamics reflect cortical excitability. We reasoned, however, that non-specific changes in excitability would be expected to influence signal and noise in the same way, leaving actual discriminability unchanged. Indeed, using a two-choice orientation discrimination task, we found that discrimination accuracy was unaffected by fluctuations in prestimulus alpha power. Decision confidence, on the other hand, was strongly negatively correlated with prestimulus alpha power. This finding constitutes a clear dissociation between objective and subjective measures of visual perception as a function of prestimulus cortical excitability. This dissociation is predicted by a model where the balance of evidence supporting each choice drives objective performance but only the magnitude of evidence supporting the selected choice drives subjective reports, suggesting that human perceptual confidence can be suboptimal with respect to tracking objective accuracy.
authors.affiliation: Department of Psychology, The University of Wisconsin-Madison, Madison, WI, USA. Electronic address: jsamaha@wisc.edu.
authors.forename: Jason
authors.initials: J
authors.lastname: Samaha
authors.affiliation: Berlin School of Mind and Brain, Humboldt-Universität zu Berlin, Germany.
authors.forename: Luca
authors.initials: L
authors.lastname: Iemi
authors.affiliation: Department of Psychology, The University of Wisconsin-Madison, Madison, WI, USA; Department of Psychiatry, The University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Postle
mesh_terms: D000328:Adult; D000513:Alpha Rhythm / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D055815:Young Adult