Temporal image fusion in human vision

We studied temporal integration by presenting sequences of orthogonal high-contrast sinusoidal gratings. In rapid alternation (38 Hz) gratings appear fused whereas at lower rates they appear segregated. To test whether afterimages are the source of the fused and segregated appearance, we probed the decay characteristics of a vertical grating’s afterimage by flashing an otherwise identical horizontal grating at varying times after the grating’s offset. The results show a rapid decay function for a negative afterimage with a 50-ms time constant, much shorter than expected from other paradigms. From dichoptic presentations we conclude that the site of the interaction is before that of binocular integration.