Why Is the Size of an Object Unchanged Regardless of Changes in Viewing Distance?

Material below summarizes the article Computation of Object Size in Visual Cortical Area V4 as a Neural Basis for Size Constancy, published on August 26, 2015, in JNeurosci and authored by Shingo Tanaka and Ichiro Fujita.

Perceiving the sizes of visual objects appears to be a simple perceptual experience in which no big scientific conundrum exists. Contrary to this intuitive impression, size perception involves complex neural processes and is not determined solely by the size of object images projected onto the retina.

A notable example is that we perceive the size of an object to be relatively stable despite changes in the size of its retinal image that accompany changes in viewing distance. For example, when a car is moving away from us, we perceive this car as getting gradually further away, not gradually shrinking in size, although the retinal image size of the car changes in a similar way between the two cases. This phenomenon, called size constancy, is accomplished by combining retinal image size and distance information in our brain.

About the Contributors

Ichiro Fujita, PhD

Ichiro Fujita is a professor at Osaka University Graduate School of Frontier Biosciences.

Shingo Tanaka, PhD

Shingo Tanaka is a postdoctoral researcher at the Brain Science Institute, Tamagawa University. His research started in molecular biology and switched to cognitive neuroscience. His ongoing research explores the neural mechanism of the value-based decision making in the prefrontal cortex.