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Garry Kong, David Alais, Erik Van der Burg; Investigating Linear Separability in Visual Search for Orientation. Journal of Vision 2016;16(12):1280. doi: 10.1167/16.12.1280.
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© 2017 Association for Research in Vision and Ophthalmology.
Visual search for orientation is often thought of in terms of the angular difference between the target and distractors and modelling typically use four reference orientations: 0°, 45°, 90° and 135°. However orientation is a dimension which wraps around after 180° and studies on orientation in visual search often run into problems with linear separability, a phenomenon in visual search where the presence of distractors that flank the target along a given dimension makes search for that target difficult. We investigated the limits of linear separability in orientation by systematically varying both the target orientation (0°, 15°, 45°, 75° and 90° from vertical) and the angular difference between target and distractors (7.5° to 75°). Displays were presented for one second and we measured participants' accuracy at detecting the presence of a gap on the target. Psychometric curves were fitted to the accuracy data, which showed the lowest thresholds for 0 and 90° targets, followed by 45°. The highest thresholds were found for 15° and 75°. However, the lapse rate for 45° targets was much greater than for the other target orientations. We suspect that participants are creating an on-line representation of 45° using their internal representations of vertical and horizontal, allowing for a higher threshold than 15° and 75°, which do not have accessible representations. However, the on-line nature of this representation results in slower processing times, leading to a higher lapse rate. Search for the 15° and 75° targets are likely treated as search for a slightly off 0° and 90° target respectively, leading to greatly increased thresholds.
Meeting abstract presented at VSS 2016
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