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Nikolaus F. Troje, Cord Westhoff; Detection of direction in scrambled motion: a simple “life detector”?. Journal of Vision 2005;5(8):1058. doi: 10.1167/5.8.1058.
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© ARVO (1962-2015); The Authors (2016-present)
Spatially scrambled point-light displays of humans or animals in locomotion contain unambiguous information about the direction in which the agent is facing. Observers are well able to retrieve this information, but only if the displays are presented right-side up. Even though spatial integrity is not required for direction discrimination the temporal relations between dots may still be important. Here, we report the results of an experiment in which we manipulated the temporal integrity of spatially scrambled point-light displays in two different ways. In the first condition we apply random offsets to the phase of the single dots. Whereas this manipulation changes the “beat” of the pattern which defines the particular gait of the agent, it leaves it's general rhythmicity intact. In a second condition, we also changed the playback speed individually for each dot, which results in completely uncorrelated dot movements.
The results show a small but consistent effect of the temporal integrity on the strength of the inversion effect. As the degree of temporal scrambling increases the inversion effect decreases. Even though temporal integrity apparently plays a role, observers can still determine the direction of the upright, fully scrambled point-light agent with an accuracy that is still much higher than the spatially and temporally intact, but inverted walker.
The results can be modeled by means of a simple linear model and they are discussed in terms of a basic, yet reliable and form invariant visual filter designed for the general detection of animate motion in the visual environment.
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