![]() ![]() 14–16 Therefore, it is possible that perceptual differences stem from dissimilar weighting of sensory evidence and prior knowledge. There is good reason to believe that perceptual experience results from inferential processes whereby sensory evidence is weighted by prior knowledge about the world. 12, 13 We investigated schizophrenia patients and synesthetes because for low-level, degraded visual stimuli involving letters, their perceptual experiences differ despite receiving the same input-impaired perception in schizophrenia patients and additional color experiences for grapheme-color synesthetes. 11 Reports for low-level visual processing are limited, including both enhanced and reduced sensitivity. Perception can be altered in synesthetes. 9, 10 Synesthetes are aware their synesthetic experiences are not real, contrary to hallucinations or delusions in schizophrenia. 8 Synesthetic experiences are associated with activation of cortical areas (eg, color-sensitive) known to process stimulus qualities of the synesthetic concurrent experience. Another condition is synesthesia, a form of altered perception in which specific stimuli (eg, letters) consistently and automatically trigger vivid additional conscious experiences (eg, color), described as being percept-like. Schizophrenia is a neuropsychiatric disorder that is not only characterized by positive symptoms like hallucinations and delusions, and disorganized thought, but also by perceptual deficits such as impaired perceptual grouping, 1 multisensory integration, 2 object recognition deficits, 3–5 and impaired low-level visual processing (eg, refs. Perceptual closure, predictive coding, precision weighting, inter-individual variability, synaesthesia, schizo- phrenia Introduction Our results imply that perceptual variability might result from differences in the precision afforded to prior beliefs and sensory evidence, respectively. Additionally, in both synesthetes and schizophrenia patients explicit, short-term priors-introduced during the hysteresis experiment-lowered thresholds but did not normalize perception. In contrast, synesthetes exhibited lowered thresholds exclusively for synesthesia-inducing stimuli suggesting high-precision long-term priors. Schizophrenia patients showed increased visibility thresholds, consistent with overreliance on sensory evidence. Additionally, precise long-term priors in synesthetes were leveraged by presenting either synesthesia-inducing or neutral stimuli. Participants rated the subjective visibility of stimuli embedded in noise while we parametrically manipulated the availability of sensory evidence. We tested this hypothesis by comparing visibility thresholds in a perceptual hysteresis task across medicated schizophrenia patients ( N = 20), synesthetes ( N = 20), and controls ( N = 26). Perceptual variability may result from different precision weighting of sensory evidence and prior knowledge. Is there a unifying principle explaining inter-individual variability in perception? There is good reason to believe perceptual experience results from inferential processes whereby sensory evidence is weighted by prior knowledge about the world. Considering inter-individual variability, synesthetes experience stable additional sensations schizophrenia patients suffer perceptual deficits in, eg, perceptual organization (alongside hallucinations and delusions). ![]() Individual differences in perception are widespread. ![]()
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