Abstract
Size constancy is one of the well-known visual phenomena that demonstrates perceptual stability to account for the effect of viewing distance on retinal image size. Although theories involving distance scaling to achieve size constancy have flourished based on psychophysical studies, its underlying neural mechanisms remain unknown. Single cell recordings show that distance-dependent size tuned cells are common along the ventral stream, originating from V1, V2, and V4 leading to IT. In addition, recent research employing fMRI demonstrates that an object’s perceived size, associated with its perceived egocentric distance, modulates its retinotopic representation in V1. These results suggest that V1 contributes to size constancy, and its activity is possibly regulated by feedback of distance information from other brain areas. Here, we propose a neural model based on these findings. First, we construct an egocentric distance map in LIP by integrating horizontal disparity and vergence through gain-modulated MT neurons. Second, LIP neurons send modulatory feedback of distance information to size tuned cells in V1, resulting in a spread of V1 cortical activity. This process provides V1 with distance-dependent size representations. The model supports that size constancy is preserved by scaling retinal image size to compensate for changes in perceived distance, and suggests a possible neural circuit capable of implementing this process.
Highlights
Humans make stable judgments about an object’s actual size despite changes in its retinal size with distance, which is known as size constancy phenomenon
This distance information output from the model’s lateral intraparietal cortex (LIP) feeds back to MT and to V1 to modulate the activity of size tuned cells
Distance and angle of gaze modulate neural responses in parietal cortex as well as on the dorsal pathway from V1 to parietal cortex [16]. These results suggest that spatial modulation exists in both the dorsal and ventral visual cortical streams, and appears to be a fundamental attribute of the visual cortex
Summary
Humans make stable judgments about an object’s actual size despite changes in its retinal size with distance, which is known as size constancy phenomenon. Previous research proposed a size-distance invariance hypothesis (SDIH) to explain the size constancy. It states that some function of retinal size combines multiplicatively with perceived distance to obtain the perceived size of an object [1,2,3,4] Many size illusions, such as the Ponzo and moon illusions, are suggested to be based on this size–distance relationship [5,6,7,8,9]. The SDIH has long been proposed, its underlying neural mechanisms remain unclear. Single cell recordings in awake and anesthetized monkeys confirm the existence of distancedependent size tuned cells along the ventral pathway from visual cortical area V1, V2 and V4
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