The Mechanisms Underlying The Modulation Of Object Manipulability On Visual Size Perception

Visual perception and action have a close relationship as demonstrated by action being guided by perception and perception being influenced by action.According to an f MRI study,the connections between the left lateral occipital lobe(LOC)and superior parietal lobule(SPL)are involved in the modulation of object manipulability on visual size perception.The present study used a two-alternative forced choice(2AFC)experimental paradigm to further investigate the causal role of LOC and SPL and the connections between them in object manipulability modulation of size perception by using the Ebbinghaus illusion effect as an index of size perception in conjunction with noninvasive brain stimulation techniques(transcranial magnetic stimulation and transcranial electrical stimulation,i.e.,TMS and t DCS).The present study manipulate object manipulability by replacing the target circle in the Ebbinghaus configuration with a watermelon(low manipulability)and a basketball(high manipulability)picture with the same physical size.Experiment 1 aimed to investigate whether the effect of object manipulability on size illusion is mediated by the response modes(keypress and pointing).The results showed that the magnitude of the illusion was significantly greater for the watermelon than the basketball target in both keypress and pointing tasks,and there was no significant difference between the two response modes.Experiment 2 was conducted by applying inhibitory TMS to the LOC in order to examine the causal role of the left LOC in the modulation of visual size illusion by object manipulability.The results showed that the magnitude of the illusion was significantly greater for the watermelon than the basketball target in both sham and true stimulation conditions,and there was no significant difference between the two stimulation conditions.Experiment 3 was designed to examine the causal role of the left SPL in the object manipulability modulation of the size illusion by applying inhibitory TMS to the SPL.The results showed that the magnitude of the illusion was significantly greater for the watermelon than the basketball target in both sham and true stimulation conditions.In addition,for the watermelon target,the illusion magnitude in the sham stimulation condition was significantly larger than that in the true stimulation condition;however,for the basketball target,there was no significant difference between the two stimulation conditions.Experiment 4 explored the causal role of the left LOC to SPL connection in the object manipulability modulation of the size illusion using the t DCS technique.It was found that when anodal stimulation was applied to the LOC and cathodal stimulation was applied to the SPL,the magnitude of the illusion was significantly greater for the basketball target in the true stimulation condition than in the sham stimulation condition,but the illusion magnitude for the watermelon target was not significantly different between the two stimulation conditions.The above findings suggest that the effect of object manipulability on size illusion is not modulated by response modality and that the left LOC to SPL connection plays a causal role in it.