The Effect of Color on Letter Discrimination Can Be Modulated by the Global/Local Processing and Attention Level

This study explored whether the color of letters could influence letter discrimination task performances and whether this effect of color could be modulated by processing level (global vs. local) and attention level of color (color-attended vs. color-unattended). We used the Navon letters in red, green, or white as stimuli at a relatively small (Experiment 1) or large visual angle (Experiments 2, 3, and 4). Each experiment included two tasks: color-attended task in which participants were told to respond only to target letters in a designated color; color-unattended task in which color was task-irrelevant. Experiment 1 found that the responses to red stimuli were significantly faster than those to the other color stimuli in the color-attended task. In Experiment 2, the same pattern occurred only at the local level in the color-attended task. Experiments 3 and 4 further controlled the brightness and chroma of stimuli and the results replicated the enhancement effect of red at the local level in the color-attended task and demonstrated an interference effect of red and green in the color-unattended task. These results suggested that red facilitated letter discrimination at the local processing level, reflecting the effect of avoidance motivation evoked by red on cognition and behavior which was consistent with color-in-context model. Moreover, this study found that the effect of color was modulated by attention level of color, and the interference effect of color in the color-unattended task confirmed that the color effect might mainly arise from controlled processes but not automatic processes.