Resolving controversies: effects of endogenous attention on conscious perception

Endogenous and exogenous attention produce well-known effects on supra-threshold information. However, when information is presented near the threshold of conscious perception, some studies report that endogenous attention only produces weak effects on perceptual sensitivity (Chica et al., 2011), while others suggest that endogenous attention does, in fact, increase perceptual sensitivity (Vernet et al., 2019). In comparing Chica and Vernet’s conflicting findings, several methodological differences stand out, with the most relevant being the method used to titrate the stimulus at the threshold of consciousness. While Chica titrated the stimuli to be detected in 50% of the trials (seen-unseen reports), Vernet titrated the stimuli to be discriminated in 50% of the trials (correct-incorrect discrimination responses). We therefore hypothesized that Chica may have used less contrasted stimuli than Vernet, which might explain the discrepancy in their findings: endogenous attention might produce larger effects as stimulus contrast increases. To test this hypothesis, we conducted a study in which stimuli were titrated either for detection or for discrimination in 50% of the trials (as in Chica and Vernet, respectively) and compared the effects of endogenous attention under these conditions. Results demonstrated that, in both conditions, endogenous attention increased the proportion of consciously reported targets. However, the attentional effect was driven by changes in response criterion rather than changes in perceptual sensitivity. Diffusion Drift Modeling revealed no modulations in drift rate (speed for accumulating information) and a significant modulation in non-decision time (changes in reaction time that occur independently of the decision-making process) when targets were titrated for detection and not for discrimination. These results indicate that different perceptual processes underlie the modulation of endogenous attention under different titration conditions, highlighting that endogenous attention does not improve perceptual sensitivity or information accumulation but response criterion and non-decisional processes under this experimental conditions.