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Patrick Monnier; The bandwidth of chromatic mechanisms mediating visual search. Journal of Vision 2007;7(9):680. doi: https://doi.org/10.1167/7.9.680.
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© ARVO (1962-2015); The Authors (2016-present)
BACKGROUND: The nature of suprathreshold color representation still is unclear. In addition to determining the number of mechanisms, measuring the mechanisms' bandwidth is important in characterizing color vision. Broad (narrow) bandwidths indicate linear (non-linear) combinations of cone signals. In this study, the bandwidth of chromatic mechanisms was assessed by systematically varying distractor color heterogeneity in a latency visual search task.
METHODS: Reaction time was measured for chromatic targets presented with 48 distractors. The chromatic composition of the distractors was determined by selecting colors on an equal-performance sector in color space. E.g., a 360 deg sector would consist of colors from an equal-performance circle centered at the target chromaticity. A 0 deg sector would consist of distractors of a single chromaticity (homogeneous) complementary from that of the target chromaticity. Reaction time was measured for the same chromatic target presented with distractors of various color heterogeneity (the sector angle was systematically varied).
RESULTS: Distractor color heterogeneity had a profound effect on search performance, often increasing reaction time by a factor of five. The ratio of reaction time for the heterogeneous and homogeneous conditions was taken as an indicator of the effect of color heterogeneity. Ratios smaller than one indicated worse search performance for the heterogeneous compared to the homogeneous condition. Plotting these ratios as a function of the size of the chromatic sector was used to estimate the bandwidth of chromatic mechanisms mediating search. Across three observers and two different target chromaticities, the bandwidths were generally broad showing a doubling of reaction time between sector sizes of 90–135 deg.
CONCLUSIONS: Distractor color heterogeneity, selected from equal-performance sectors in color space, is a viable approach to estimate the bandwidth of chromatic mechanisms mediating search. Bandwidth estimates were similarly broad across observers and target chromaticities.
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