The size-weight illusion in visual form agnosic patient DF

Eleanor Hassan, Anna Sedda, Gavin Buckingham, Robert McIntosh

Research output: Contribution to journalArticlepeer-review


The size-weight illusion is a perceptual illusion in which smaller objects are judged as heavier than larger objects of equal weight. A previous informal report suggests that patient DF, who has visual form agnosia, does not experience the size-weight illusion when vision is the only available cue to object size. We tested this experimentally by comparing the magnitudes of DF’s visual, kinaesthetic and visual-kinaesthetic size-weight illusions to those of 28 similarly-aged controls. A modified t-test found that DF’s visual size-weight illusion was significantly smaller than that of controls (zcc= -1.7). A test of simple dissociation based on the Revised Standardised Difference Test found that the discrepancy between the magnitude of DF’s visual and kinaesthetic size-weight illusions was not significantly different from that of the controls (zdcc = -1.054), thereby failing to establish a dissociation between the visual and kinaesthetic conditions. These results are consistent with previous suggestions that visual form agnosia, following ventral visual stream damage, is associated with an abnormally reduced size-weight illusion. The results, however, do not confirm that this reduction is specific to the use of visual size cues to predict object weight, rather than reflecting more general changes in the processing of object size cues or the use of predictive strategies for lifting.
Original languageEnglish
Pages (from-to)277-284
JournalNeurocase: The Neural Basis of Cognition
Early online date17 Aug 2020
Publication statusE-pub ahead of print - 17 Aug 2020


  • size-weight illusion
  • visual agnosia
  • multisensory integration
  • ageing
  • perception


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