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Abstract:
Among homogeneous non-targets, the reaction time (RT) for finding a target unique in orientation (O) is shortened when this target is also unique in color (C). RT(CO) for finding this double-feature target CO, unique in both C and O, is shorter than predicted by a statistical facilitation (Raab 1962) between RT(C) and RT(O) for the singlefeature targets C and O (Krummenacher et al 2001, Koene & Zhaoping 2007), implicating contributions by neurons conjunctively tuned to C and O. The RT for a target unique in O is also shortened by making the target also unique in eye of origin (E), e.g., the target/non-targets shown to the left/right eye, implicating the primary visual cortex (V1, Zhaoping 2008). However, the RT(E) for a target unique only in E is unmeasurable directly, since E is perceptually non-distinctive (Wolfe & Franzel 1988). Confirming and extending the previous findings, we show that the RT for a target C, O, or CO becomes shorter by making the target unique in E additionally. Furthermore, using the V1 saliency hypothesis, we derive RT(E) (if E singletons were perceptually distinctive for our task) from the measurable RTs for targets unique in C, O, CO, CE, EO, and CEO.Additionally, we infer the contribution by V1 neurons conjunctively tuned to both of the unique target features, e.g., C and E, to saliency by examining whether, e.g., RT(CE) is shorter than predicted by the statistical facilitation. The significance of this contribution depends on the colors of both the target and non-targets.
