title: Superior size-weight illusion performance in patients with schizophrenia: evidence for deficits in forward models.
abstract: When non-psychiatric individuals compare the weights of two similar objects of identical mass, but of different sizes, the smaller object is often perceived as substantially heavier. This size-weight illusion (SWI) is thought to be generated by a violation of the common expectation that the large object will be heavier, possibly via a mismatch between an efference copy of the movement and the actual sensory feedback received. As previous research suggests that patients with schizophrenia have deficits in forward model/efference copy mechanisms, we hypothesized that schizophrenic patients would show a reduced SWI. The current study compared the strength of the SWI in schizophrenic patients to matched non-psychiatric participants; weight discrimination for same-sized objects was also assessed. We found a reduced SWI for schizophrenic patients, which resulted in better (more veridical) weight discrimination performance on illusion trials compared to non-psychiatric individuals. This difference in the strength of the SWI persisted when groups were matched for weight discrimination performance. The current findings are consistent with a dysfunctional forward model mechanism in this population. Future studies to elucidate the locus of this impairment using variations on the current study are also proposed.
authors.affiliation: Department of Psychology, University of California San Diego, 9500 Gilman Drive #0109, La Jolla, CA 92093-0109, USA. lewilliams1@gmail.com
authors.forename: Lisa E
authors.initials: LE
authors.lastname: Williams
authors.forename: Vilayanur S
authors.initials: VS
authors.lastname: Ramachandran
authors.forename: Edward M
authors.initials: EM
authors.lastname: Hubbard
authors.forename: David L
authors.initials: DL
authors.lastname: Braff
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Light
mesh_terms: D000328:Adult; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D008960:Models, Psychological; D009483:Neuropsychological Tests; D010468:Perceptual Disorders / Q000209:etiology*; D011601:Psychophysics; D012559:Schizophrenia / Q000150:complications; D012858:Size Perception / Q000502:physiology*; D014892:Weight Perception / Q000502:physiology*