Scharff, L.V. (2000). Serial Visual Searches Processed More Efficiently Across Multiple Depth Planes. Investigative Ophthalmology and Visual Science, 41, S424.


Purpose.  Previous work indicated that search for a simple conjunctive (color/size) target was more efficient when the distractors were spread across three depth planes (at or in front of the plane of fixation) rather than when all distractors were in the same depth plane (Scharff, 1998).  The current series of experiments investigated whether this conclusion would be supported if a more complex conjunctive target was used, one of the depth planes was behind the plane of fixation, and if the distractors were given random disparities (within two ranges) versus disparities fixed within in one of three planes of disparity.  Method. Reaction times were measured for five participants for an L-conjunction search task (the targets and distractors were all the same shape but varied in orientation).  The number of distractors in the same depth plane (or range) as the target varied between 5 and 30, with the remainder of the distractors randomly placed in the other two depth planes (or ranges).  Depth conditions were again repeated so that the target could be in the front, middle (plane of fixation) or back depth position.  Results.  The single depth plane conditions resulted in a serial search pattern.  When distractors were spread across different depths, searches were faster but there was a stronger effect of number of distractors when the target and distractors were placed in a depth range rather than when placed in one of the disparity planes.  However, regardless of depth configuration, searches including depth were faster than single depth searches including the same number of distractors.  Overall, target location (front, middle, back) did not affect search times for any of the experiments, and prior knowledge of the target depth plane did not systematically affect search times.  Conclusions.  Serial searches are more efficient when the distractors are placed across multiple depth planes.  This suggests that multiple depth planes (or disparity channels) may be processed simultaneously during visual search.  Because prior knowledge of target depth had an inconsistent effect, it is suggested that we are not efficient at limiting searches to one specific depth plane.

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