B. Zenger et M. Fahle, Performance asymmetries in visual search demonstrate failure of independent-processing models, VISION RES, 40(19), 2000, pp. 2677-2696
We report psychophysical data from orientation-popout experiments that are
inconsistent with a rather general decision model. Stimuli consisted of 121
line segments arranged on an 11 x 11 grid. There were two tasks: in the 1-
Singleton Task all lines except one had the same orientation, and observers
had to report which quadrant contained the singleton. In the 3-Singleton T
ask three quadrants contained orientation singletons and observers had to i
dentify the quadrant without singleton. These tasks can be Viewed as asymme
tric search tasks, in which either a singleton-quadrant has to be found amo
ng three homogeneous quadrants, or a homogeneous quadrant has to be found a
mong three singleton-quadrants. Using tools from signal-detection theory we
show that the large performance asymmetries between 1-Singleton and 3-Sing
leton Tasks are inconsistent with any model that makes two (Very basic and
common) assumptions: (1) independent processing of the four quadrants and (
2) an ideal-observer decision. We conclude that at least one of the two ass
umptions is inadequate. As a plausible reason for the model failure we sugg
est a global competition between salient elements that reduces popout stren
gth when more than one singleton is present. (C) 2000 Elsevier Science Ltd.
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