Retinotopic temporal integration of motion across saccadic eye movements

Perceptual judgments of motion require information to be integrated over time. During integration, however, the visual input may be temporarily interrupted by occlusion from other objects, or suppressed during saccadic eye movements. We examined whether motion integration continued across saccades, or whether eye movements halted or otherwise interfered with the integration of motion across separate fixations. Observers viewed a motion 'patch' (8 deg) containing two motion intervals (translation, 10 deg/sec, limited lifetime dots) embedded in a stream of random noise, and made a directional discrimination judgment. Signal-to-noise sensitivity was measured for the two separate motion signals and compared to presentations of a single motion signal. The results indicated that the signal and noise periods were integrated over a period of hundreds of milliseconds up to one second. When a saccadic eye movement (2 deg) within the boundaries of the patch was made during a period of random noise, or during a blank background, there was still integration of the motion signals (and noise) from before and after the saccade. Saccades were always orthogonal to the direction of motion. In a further test, the entire motion patch (8 × 4 deg) was displaced immediately to the new fixation position before the saccade (4.1 deg). There was no spatial overlap of the two motion patches. Nonetheless, the motion signals from the two patches were integrated when the patches were in identical retinotopic positions. These results suggest that motion signals, unlike many other forms of visual information, can be retinotopically combined across fixations. Trans-saccadic motion integration, combined with the suppression of motion perception during saccades, may play an important role in the perceived stability of the world across eye movements.