Superior size-weight illusion performance in patients with schizophrenia: evidence for deficits in forward models.
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.
Williams
Lisa E
LE
Department of Psychology, University of California San Diego, 9500 Gilman Drive #0109, La Jolla, CA 92093-0109, USA. lewilliams1@gmail.com
Ramachandran
Vilayanur S
VS
Hubbard
Edward M
EM
Braff
David L
DL
Light
Gregory A
GA
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*