Better performance when recalling speed from object motion compared to texture motion.

Our daily visual environment abounds with motion. Accurately perceiving object speed is essential when avoiding collisions or intercepting moving objects. Accurately remembering object speed is equally essential, as moving objects may become temporarily occluded. Most studies of speed use texture motion stimuli (e.g., dot motion), which minimize spatial cues but do not reflect the natural spatiotemporal dynamics of moving objects. In contrast, object motion contains rich spatial cues that better capture real-world motion. Neural mechanisms underlying texture and object motion processing differ across the visual hierarchy. Might memory for speed also differ between texture and object motion? To explore this question, we tested human participants on speed recall for both texture and object motion stimuli across different speeds (2-32°/s) and delays (1-8 s). Both types of target stimuli moved along a circular trajectory (for 4-6 s) and were recalled via the method of adjustment. Replicating previous work, we found a strong decrease in speed recall performance with increasing target speed. Importantly, we also observed that recall was significantly worse for texture stimuli than for object motion stimuli, implying an advantage for spatiotemporally bound objects. For object motion, longer target and delay durations led to better and worse speed recall, respectively. Gaze was subtly biased toward the location of the object moving along its trajectory. For both types of stimuli, responses were biased toward the recall probe, and congruency between target and probe direction improved speed recall. Together, our findings provide a solid psychophysical basis for understanding human short-term memory for speed.