AN ENERGY-MODEL OF INTERFRAME INTERVAL EFFECTS IN SINGLE-STEP APPARENT MOTION

A computational model was developed to explain the effects of an inter frame interval (IFI) in single-step apparent motion experiments. In th ese experiments a stimulus appears in one position, disappears, and th en reappears in a shifted position after a short or long IFI. If the l uminance during the IFI matches the mean luminance of the stimulus fra mes, long IFTs result in perceived motion opposite the short-IFI condi tions. Brighter or darker IFIs, however, do not support the reversed m otion effect. The model possesses the following defining characteristi cs: (1) a biphasic (''transient'') channel whose signalled direction o f motion reverses with changes of IFI duration; (2) a combined directi on-opponent output which is the sum of directional responses developed in two channels-biphasic (''transient'') and monophasic (''sustained' '); (3) a signal/noise weighting of the contributions of the two chann els to the final directional output of the system. Predictions of the model about the effects of IFI intensity and viewing eccentricity were tested and confirmed in two new psychophysical experiments. The inter pretations of past studies which included a role for second-order moti on mechanisms in explaining IFI duration effects were reexamined. Furt her empirical tests of the model were outlined.