Abstract
In the hallway illusion, the perceived size of the two objects with the same retinal size is affected by the three-dimensional spatial context in the image. Previous studies have shown that neural activity of V1 correlates with perceived size, not the physical angular size of objects. However, it is not clear whether there is a relationship between the individual magnitude of illusion and cortical activity related to the visual-spatial resolution. To answer this question, we used psychophysical tasks to measure the magnitude of illusion, size discrimination threshold, and vernier acuity threshold. Experiment 1 (n = 6) showed that the magnitude of illusion did not change across different stimulus durations (100 ms versus 300 ms). Critically, even when the stimuli were masked after a brief stimulus presentation (100 ms), the magnitude of illusion was equivalent to the condition of the long stimulus duration without masking. In experiment 2 (n = 52), we measured the individual magnitude of size illusion, physical size discrimination threshold, and vernier acuity threshold. We found that the vernier acuity threshold correlated with the size discrimination threshold and the magnitude of size illusion. The smaller the vernier acuity threshold, the smaller the size discrimination threshold and the greater the magnitude of the size illusion. However, the size discrimination threshold did not correlate with the magnitude of the size illusion. Our results demonstrate that the size illusion is mediated by rapid visual processing such as V1 neural activity when the spatial context is presented, in which feedback signals might be already in place. Furthermore, our findings suggest that although physical size judgments and illusory size judgments are related to the cortical activity for hyperacuity, they might reflect different cortical mechanisms.