The role of motion streaks in human visual motion perception

For many years, artists and photographers have used blurred lines or ‘motion streaks’ along an object’s trajectory of motion to indicate fast motion. As it turns out, these streaks must occur in vision, because the visual system integrates information over time, around 100 120 ms. Generally streaks are not seen, but they could prove a useful cue to direction of motion, as suggested in an influential model proposed by Geisler (1999). In experiments exploting the tilt aftereffect and illusion paradigms, we found that strong motion streaks produced robust tilt aftereffects and illusions, similar in magnitude and orientation tuning to those induced by tilted lines. These effects were weak or absent in weak streak conditions, and when motion was too slow to form streaks. We also investigated binocular rivalry suppression of static stimuli by fast and slow motion, and found that grating stimuli oriented parallel to the direction of fast, rivalling motions were more deeply suppressed than those orthogonal to the motion direction, but only for fast, ‘streaky’ motion, not slow motion. We attributed this deeper suppression to within-channel masking by motion streaks, as there was clear orientation tuning of this effect, both during suppression and dominance phases. We further explored masking by motion streaks in two further studies addressing the orientation and spatial frequency tuning of dichoptic and monoptic masking by motion streaks. Finally, we used functional magnetic resonance imaging to explore the neural correlates of these streaks, and found similar patterns of activity for fast motion and static, oriented patterns, which could successfully be used by a classifier algorithm to decode whether a participant was viewing one of two directions of motion (45◦ or 135◦) after training on orientation sessions alone. Together, these results indicate that motion streaks produced by temporal integration of fast translating features effectively adapt orientation-selective cells, that they cause masking similar to that caused by static stimuli, that they can cause tuned suppression of oriented stimuli even when not seen, and that they are present in early visual cortex. Thus, motion streaks are present in the visual system, and would be available to perform the function ascribed to them by Geisler. This is dicussed in terms of traditional models of motion perception, and some novel predictions and future experiments are proposed.