Erkelens C J, 2003, "Averaging of motion across short-interval displacements" Perception 32 ECVP Abstract Supplement
Averaging of motion across short-interval displacements
C J Erkelens
Apparent motion enables us to see motion in movies and on electronic displays such as televisions and computer monitors. The alleged explanation for apparent motion is that neurons early in the visual cortex act as spatiotemporal filters that smooth out discrete displacements, rendering apparent motion indistinguishable from natural motion. Recently, I presented a novel apparent-motion stimulus showing that, at temporal frequencies higher than 30 Hz, human observers perceive motion in directions opposite to those predicted by spatiotemporal filtering (Erkelens, 2002 Journal of Vision 2 705a). To clarify the counterintuitive observation I measured motion detection in response to short-interval displacements in two-frame and three-frame kinematograms (random-dot patterns of 36 deg × 36 deg), in which displacement (up to 18 min of arc) and SOA (between 13 and 52 ms) were the independent variables. The results show that motion detection thresholds are related to stimulus velocities (ratios of displacement and SOA), averaged across direction and across time within a window of about 40 ms. Temporal and directional averaging explains the motion perceived at high temporal frequencies. These properties of motion detection are incompatible with those of cortical motion-selective cells reported in the literature. The hypothesis is put forward that high-frequency detection of motion results from a low-level process, which may already start in the eyes.
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