Abstract
In contrast to the short-duration and quick reversibility of attention, a long-term sensitization to color based on attention in a visual search task was reported by Tseng et al. (Nature, 2004). When subjects are trained for a few days to search for a red object among colored distracters, sensitivity to red is altered for weeks. This sensitization is quantified using ambiguous motion displays containing isoluminant red-green and texture-contrast gratings, in which the perceived motion direction depends both on the attended color and on the relative red-green saturation. Thus, sensitization can be measured by the additional color saturation required to balance the motion sequence.
Such long-term effects could result from either sensitization of the attended color, or suppression of unattended colors, or a combination of the two. Here we tried to unconfound these effects by eliminating one of the paired colors of the motion display from the search task. The other paired color in the motion display can then be either a target or distracter in the search task. Thereby, we can separately measure the effect of attention on sensitizing the target color or suppressing distracter colors.
The results in the motion test indicated both effects, sensitization of the target color in the search task and suppression of the distracter colors: · When red was the attended color and blue was the distracter color, salience to red increased at the expense of green for 4/5 subjects. · When blue was the target color and red was the distracter color, suppression of red in favor of green occurred in 3/4 observers. The magnitudes of sensitization and suppression were positively correlated with search performance. Conclusion: Selective attention to a color in visual search causes long-term sensitization to the attended color and long-term suppression of the unattended color. Our findings imply that the facilitatory and inhibitory effects of attention might be mediated separately.