Bischof, W. F., Seiffert, A., and Di Lollo, V. (1996). Psychophysical evidence for sustained-transient input to directionally-selective motion mechanisms. Perception, 25, 1263-1280.

Three human psychophysical studies on directional-motion discrimination examined the characteristics of the sustained input to directionally-selective motion sensors. Apparent motion was produced by displaying a group of dots in two frames (F1 and F2), where F2 was a translated version of F1. All stimuli included parts that contained both F1 and F2 (combined images) and parts containing only F1 or F2 (single images). The first of three experiments was carried out in photopic conditions. All displays began with a single image (F1), continued with the combined image, and ended with F2. Six durations of single and of combined images (10, 20, 40, 80, 160, or 320 ms) were crossed factorially. As the duration of the single image was increased, perception of directional motion first improved, and then declined at longer durations. This outcome contrasted with the monotonic increment obtained in earlier studies under low-luminance conditions. To account for the entire pattern of results, we modified earlier models of the Reichardt motion sensor so as to include a mixed transient-sustained input to one of the sensor's filters. Predictions from the new model were tested and confirmed in two experiments carried out under both low-luminance and high-luminance viewing conditions.

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