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N. E. Scott-Samuel, R. F. Hess; What does the Ternus display tell us about motion processing in human vision?. Journal of Vision 2001;1(3):156. doi: 10.1167/1.3.156.
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The Ternus display is a moving visual stimulus that elicits two very different percepts, according to the length of the interstimulus interval (ISI) between each frame of the motion sequence. These two percepts, referred to as element and group motion, have previously been analysed in terms of the operation of a low-level, dedicated short-range motion process (in the case of element motion), and of a higher-level, attentional long-range motion process (in the case of group motion). We used a Ternus display to examine a more recent dichotomy, the division of stimuli into 1st-order and 2nd-order. Recent research suggests that moving 2nd-order stimuli are analysed only via long-range motion processing. We showed that Ternus displays comprised of elements defined by either 1st-order or 2nd-order characteristics exhibit both element and group motion, implying that 2nd-order stimuli are amenable to analysis by both the short-range and long-range processes. However, a second experiment demonstrated that both element and group motion are, in fact, mediated solely by a process sensitive to changes in the spatial appearance of the Ternus elements. In light of this, it appears that Ternus displays tell us nothing about specific low-level motion processing, implying that previous studies using Ternus displays require reinterpretation. A third experiment revealed that the orientation and spatial frequency discrimination of the process underlying the analysis of Ternus displays was far worse than thresholds for spatial vision. We conclude that Ternus displays are analysed via a long-range motion, or feature-tracking, process, and that this process is distinct from spatial vision.
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