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Clara Casco, Alba Grieco, Enrico Giora; Saliency from orthogonal velocity component in texture segregation. Journal of Vision 2006;6(6):582. doi: https://doi.org/10.1167/6.6.582.
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We show that a moving target line, more-vertical than 45°-oriented background lines, pops-out (d'=1.2) although it moves at the same speed of background elements and although it is invisible in static presentation (d'=. 5).
We suggest that the moving more-vertical target is more salient because the motion system responds to the orthogonal-velocity-component (V⊥= Δd/Δt sinθ) that is larger for the more-vertical target than for distracters.
However, motion does not produce high d' when the target is more horizontal than background (d'= .6). This result is not expected if saliency resulted from the sum of saliency of orientation and motion independently coded but is instead predicted.
A line length effect on the moving target saliency also suggests that V⊥ is extracted on the whole line and this operation is facilitated by line length in the same way for more-vertical and more-horizontal targets.
Altogether, these results demonstrate that speed-based segmentation operating on V⊥ not only affects speed and direction of motion discrimination, as previously demonstrated, but accounts for high saliency of image features that would otherwise prove undetectable of the basis of orientation-contrast.
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