Recent studies have suggested that visual attention affects responses in the early visual pathways such as chromatic and achromatic channels. In our previous study, chromatic and achromatic detection sensitivities were examined using a dual task paradigm (Uchikawa et al., JOSAA, 2014). Threshold elevations for peripheral chromatic targets, due to the central attention task performed simultaneously, were found much larger than those for achromatic targets, suggesting that detection of chromatic targets requires more attentional resources than that of achromatic ones. In the present study we further examined how visual attention influenced on chromatic and achromatic discrimination sensitivities. The peripheral test stimulus consisted of two discs of 1.2 deg diameter presented for 100 ms to the right and the left field at 4 deg eccentricity. The increment threshold of the test stimulus was obtained both in the dual task and the single task condition. The peripheral test stimulus had the pedestal contrast, which was fixed at four times of detection thresholds. The observer's task was to indicate which disc, right or left, appeared higher in contrast. The central attention task was to find the gaps in two-concentric low-contrast rings presented on the central field. The results showed that threshold elevation for achromatic targets was higher than that for chromatic targets, as opposed to our previous detection thresholds. This discrepancy may be explained by luminance transient existing in the targets. The present results, as well as the previous ones, indicate that the visual attention influences chromatic and achromatic sensitivities in a different way.
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