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Kit Wolf, Anya Hurlbert; Attentional modulation of simultaneous chromatic contrast. Journal of Vision 2003;3(9):707. doi: 10.1167/3.9.707.
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© ARVO (1962-2015); The Authors (2016-present)
The colour of a surface is, under certain conditions, largely determined by its chromatic contrast with surrounding surfaces. Evidence suggests that the neural mechanisms underlying simultaneous chromatic contrast occur early in visual processing. On the other hand, chromatic contrast may be linked to colour constancy and other perceptual phenomena integral to our conscious experience of surface properties; if so, it may be perpetrated or strongly influenced by higher-level processing. Here we investigate whether attentional modulation affects the strength of simultaneous chromatic contrast, in a dual-task paradigm (similar to Li et al. PNAS, 99:9596–9601).
Our paradigm combines a serial search task that modulates attention with a concurrent 2afc task that measures the strength of simultaneous contrast. In the search task, five jumbled Ls or Ts are presented centrally for a brief time. The observer must indicate whether all five letters are the same (LLLLL, TTTTT) or different (LLLLT, TTTTL), whilst simultaneously performing the second task, which is to report the colour (‘reddish’ or ‘greenish’) of a very briefly flashed peripheral square against a red background. The colour of the square varies in constant steps along a red-green axis passing through the fixed background chromaticity and the neutral point. Contrast strength is measured as the chromatic distance between the square colour that appears neutral, and the neutral point itself. A neutral screen is displayed for a short time between trials to maintain long-term DC adaptation. In the control experiment, the background remains neutral throughout.
Our results show that simultaneous chromatic contrast influences colour appearance even when attention is diverted to the central search task. Yet, preliminary findings indicate that contrast is weaker in the dual-task than in the single-task condition, suggesting that simultaneous contrast is modulated by neural mechanisms beyond the pre-attentive level.
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