Figure 1
Task design. The task uses four different types of stimuli (uppermost panel), each of which is composed of two features (a color, C, and a form, F). Three levels of processing are envisaged, i.e. the feature-level, the motor-level, and behavior. The target, C+F+, demands a response, whereas all non-targets require not to respond. When the target object is the red ellipse, C+F+, the red rectangle is the color-overlap distractor, C+F- (composed of the target-compatible color feature, C+, and the target-incompatible form feature, F-), the blue ellipse is the form-overlap distractor, C-F+ (composed of the target-incompatible color feature, C-, and the target-compatible form feature, F+), and the blue rectangle serves as standard distractor, C-F- (composed of the target-incompatible color feature, C-, and the target-incompatible form feature, F-). Attentional modulation by target color (C+) can be analyzed by comparing the ERP over the parieto-occipital scalp in response to the color-overlap distractor and the standard distractor, i.e. ERPC+F- vs. ERPC-F-. Attentional modulation by target form (F+) can be analyzed by comparing the ERP over the parieto-occipital scalp in response to the form-overlap distractor and the standard distractor, i.e. ERPC-F+ vs. ERPC-F-. R = response.