title: A new perceptual bias reveals suboptimal population decoding of sensory responses.
abstract: Several studies have reported optimal population decoding of sensory responses in two-alternative visual discrimination tasks. Such decoding involves integrating noisy neural responses into a more reliable representation of the likelihood that the stimuli under consideration evoked the observed responses. Importantly, an ideal observer must be able to evaluate likelihood with high precision and only consider the likelihood of the two relevant stimuli involved in the discrimination task. We report a new perceptual bias suggesting that observers read out the likelihood representation with remarkably low precision when discriminating grating spatial frequencies. Using spectrally filtered noise, we induced an asymmetry in the likelihood function of spatial frequency. This manipulation mainly affects the likelihood of spatial frequencies that are irrelevant to the task at hand. Nevertheless, we find a significant shift in perceived grating frequency, indicating that observers evaluate likelihoods of a broad range of irrelevant frequencies and discard prior knowledge of stimulus alternatives when performing two-alternative discrimination.
authors.affiliation: Laboratory of Experimental Psychology, University of Leuven, Leuven, Belgium. tom.putzeys@psy.kuleuven.be
authors.forename: Tom
authors.initials: T
authors.lastname: Putzeys
authors.forename: Matthias
authors.initials: M
authors.lastname: Bethge
authors.forename: Felix
authors.initials: F
authors.lastname: Wichmann
authors.forename: Johan
authors.initials: J
authors.lastname: Wagemans
authors.forename: Robbe
authors.initials: R
authors.lastname: Goris
mesh_terms: D003198:Computer Simulation; D003463:Cues; D003657:Decision Making / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D010470:Perceptual Masking / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*