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Cristiano Cellini, Alexander C. Schütz, Karl R. Gegenfurtner; Saccadic eye movements to Gaussian luminance and color blobs. Journal of Vision 2009;9(8):438. doi: 10.1167/9.8.438.
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In the past several paradigms were used to investigate the influence of an additional target on saccade latencies and end points. If a second target is presented far away of the actual saccade target, latencies are increased, which is called the remote distractor effect. If the second target is presented closer to the actual target, saccade amplitudes are directed to the center-of gravity of both targets, the global effect. In all of these paradigms two distinct targets are clearly visible. Here we investigated how saccades are influenced if two overlapping targets are present.
To this end we measured saccades to pairs of Gaussian blobs of luminance or DKL color contrast, which were presented on a uniform gray background. The blobs were presented at an eccentricity of 10 deg at a randomized angle, their standard deviation was 0.5 deg of visual angle and they were separated by 0.5 deg. This way two largely overlapping blobs were visible. One blob (reference) always had a fixed contrast of 20%, the contrast of the other blob (comparison) took values of 8, 10, 40 and 50%. The subjects were instructed to move their gaze toward the blobs, as soon as the fixation point vanished.
We observed that saccades land closer to the blob with higher color or luminance contrast. Moreover the latency decreased with increasing contrast of the comparison blob. In general latencies in the color condition were larger than in the luminance condition.
The results indicate that even when the spatial layout is constant, the visual system puts a larger weight on features with a higher contrast.
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