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James Pomerantz, Curtiss Chapman, Jon Flynn, Colin Noe, Tian Yingxue; Parallelism is an emergent feature not derived from the detection of individual line slopes. Journal of Vision 2017;17(10):166. doi: https://doi.org/10.1167/17.10.166.
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© ARVO (1962-2015); The Authors (2016-present)
Visual systems are quite sensitive to parallelism between two or more line segments, but how do they detect this feature? Many methods are possible, one of which includes computing and then comparing the slopes of the lines in a feedforward manner. If the visual system employs this method, it should be harder for us to perceive parallelism between two lines when they are oriented obliquely, compared with being horizontal or vertical, because of the oblique effect (OE; Appelle, 1972). Our experiment confirmed the expected OE for processing individual line segments, but we found a greatly reduced OE for processing pairs of parallel vs. nonparallel lines. We also demonstrated a sizeable configural superiority effect (CSE; Pomerantz, Sager, and Stoever, 1977) for line pairs over individual line segments. This CSE means it is easier to determine which of four line segments has a different slope from the other three identical segments when the same, non-informative line segment is added next to all four segments to create four pairs of segments, three pairs of which are parallel and one non-parallel (or vice versa). Our findings differed largely in expected ways when the stimuli were presented inside a diamond-shaped frame (sharing parallelism within the frame) rather than square: performance with oblique lines improved. In summary, our results suggest that parallelism is a salient emergent feature in vision, more salient to us than the slopes of the individual lines from which it arises. Parallelism appears to be detected through some method other than computing and comparing the slopes of the two line segments, perhaps by being detected directly. Parallelism thus joins other emergent features arising from line segments, including collinearity, intersection, closure, and symmetry, as an extremely salient higher-order property of wholes that is more perceptible are than the component parts from which it derives.
Meeting abstract presented at VSS 2017
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