Induced movement-in-depth and induced changing-size elicited by a luminous rotating spiral

Induced movement-in-depth and induced changing-size are infrequently investigated forms of a phenomenon whereby movement is ascribed to a stationary stimulus. The present note concerns qualitative responses to a display designed to elicit both forms. The inducer was a two-arm luminous rotating linear-function spiral, and the stationary stimulus was an annulus concentric with the spiral; it was patterned with concentric luminous circles. Viewing was monocular. Among the findings, induced movement-in-depth was more frequently reported than induced changing-size, despite the lack of veridical movement-in-depth in the display. Possible lines of explanation are suggested.