Biased competition for visual selective attention: Endo- and exo-genous processes integrate at the perceptual level Damien N. FERNANDEZ*, George A. MICHAEL, Laboratoire EMC, U.M.R. 5596, Université Lyon2 5 avenue Pierre Mendès France, 69676 Bron cedex *e-mail:
[email protected]
Competition can be resolved bottom-up (salience), top-down (relevance) or both. According to the Biased Competition theory (Desimone and Duncan, 1995), attention is an emergent property of the visual processing. Endo- and Exo-genous processus are only distinct modes of biasing the same perceptual processes. Salience and Relevance interactions should be: • Integrative when they trigger the same perceptual dimension, • At max, additive when they trigger a different perceptual dimension. A visual search task was proposed to participants (n = 16). The target color was (validly) cued in half of the trials, not cued in the remainder (Relevance). This relevance signal was not salient per se, as distractors were heterogenous (3 different colors, see fig. 1). One item could be made salient in either the same (color) or an other dimension (size) that the one used for relevance. This Salience signal was not relevant: it was absent in ½ trials and, when present, concerned the target in ¼ and a distractor in ¾ of trials. •Orthogonal manipulation of Salience vs Relevance. •Interaction at the perceptual level: same vs diff. Dimension between Salience (color & Size) and Relevance (Color).
Cue (Color vs Neutral) Inter-stimulus interval Search display
Orange
C: Size Salience (here: distractor) +
Neutre
B: Color Salience (here: target)
800 ms
1200 ms
A: No Salience
Time course Until Response
Thus, trials were separated in two groups, depending on whether the preceding trial was color cued or not cued.
Figure 1
500
Target Color Target Size
Cue benefits (ms)
If dimension weighting occured when color was cued, and if the effects endured from one trial to the next (Muller et al., 2003): They probably masked interaction effects.
400 300 200 100
Not Cued
Cued
Preceding trial
Synopsis of the search task. Color saturation was exagerated. The color of the target to come was cued, or not. After an 1200 ms ISI, the display appeared until the response. The target (e.g. B) or a distractor (C) might be salient in either color (B) or size (C). A: neutral condition.
Results Anova with only Salience Type (No salience, Target Color, Target Size) and Relevance (Cued, Uncued) as withinsubject factors : • Main effects of Relevance (F(1,15)=82; p
