The binding of motion to form is not direct but mediated by location signals

Form and motion are processed along parallel neural streams. Unified visual perception of form and motion requires interaction between these streams of information. How this interaction occurs is an unsolved problem, known as the binding problem. Here we present a stimulus that demonstrates that motion is not directly bound to form. The stimulus consists of the sequential presentation of two patterns (53 × 67 deg). The two patterns contain identical distributions of easily visible random dots (0.5 deg). One pattern is displaced relative to the other by a few dots in a certain direction, except for an area in the shape of a square (12 × 12 deg) of which the dots are displaced in the opposite direction. When the patterns are generated on a CRT monitor running at 75 Hz, they are perceived as a single, static, random-dot pattern, containing white, black and grey dots, in which the square is not visible. The square becomes clearly visible if the presentation of each pair of patterns is interleaved with a grey field of uniform brightness. Furthermore, the texture inside the square is perceived to move in one direction and the texture of the pattern outside the square seems to move in the opposite direction. The motion is induced by the displacements of the dots of one pattern relative to those of the other pattern, whereas the perceived texture results from the stationary, mean, brightness distribution of the two patterns. Thus motion is perceived of textures that are not displaced. This finding suggests that motion is not directly bound to form, but that the binding is mediated by signals which indicate specific locations.