Effect of spatial distance on perceptual motion grouping

Biological motion perception is the perceptual phenomenon that induces human moving form as the sum of coherent local motions. A part such as an arm is organized by the motion grouping of coherently moving dots. To clarify the spatial mechanism of the local motion integration process for motion grouping, we studied the influence of distance between coherently moving dots and the amount of background noise on the perceptual strength of motion grouping. The perception of motion grouping was strong when the coherently moving dots were close to each other, and was attenuated by increasing the distance between the coherently moving dots. The perception of motion grouping was also strong when the number of noise dots was small, and weak when it was large. We used various combinations of the distance between coherent moving dots and the number of the noise dots, and when the ratio of the distance between coherently moving dots to the average distance of the noise dots was the same, the performance was almost the same. Our results show that the perceptual strength of motion grouping has scale invariant properties with respect to the relationship between the distance between the coherently moving dots and that of the noise dots.