Kinetic depth effect examined under conditions of unimodal versus bimodal sensory input

To perceive the three-dimensional rotation of a shadow figure, displacement and line length change are required. Without displacement, persons perceive a line lengthening and shortening on a two-dimensional plane. The present investigation attempted to create the kinetic depth effect without displacement by including auditory input. 48 persons were randomly assigned to two groups (line-length change with tone or line-length change without tone). The tone group received sound through headphones which oscillated in amplitude in synchrony with the shadow of a rotating "T" figure. The tone group perceived a three-dimensional figure in rotation significantly more often than did the non-tone group. These results suggest that the kinetic depth effect may be created by more than one combination of sensory input.