Sensitivity vs. awareness curve: a novel model-based analysis to uncover the processes underlying nonconscious perception

We present a novel model-based analysis of the association between awareness and perceptual processing based on a multidimensional version of signal detection theory (general recognition theory, or GRT). The analysis fits a GRT model to behavioral data and uses the estimated model to construct a sensitivity vs. awareness (SvA) curve, representing sensitivity in the discrimination task at each value of relative likelihood of awareness. This approach treats awareness as a continuum rather than a dichotomy, but also provides an objective benchmark for low likelihood of awareness. In two experiments, we assessed nonconscious facial expression recognition using SvA curves in a condition in which emotional faces (fearful vs. neutral) were rendered invisible using continuous flash suppression (CFS) for 500 (Experiment 1) and 700 (Experiment 2) milliseconds. Participants had to provide subjective awareness reports, expression discrimination responses, and metacognitive judgements of confidence on those discrimination responses. We predicted and found evidence for the nonconscious processing of facial expression, in the form of higher than chance-level sensitivity in the area of low likelihood of awareness. We also found evidence for metacognitive sensitivity in the absence of awareness. The similarity between the pattern of results from perceptual discrimination and metacognitive judgements is in line with the detection-theoretic assumption that both processes are based on the same perceptual evidence variable. To the best of our knowledge, this is the first objective and bias-free demonstration of nonconscious perceptual processing of facial expression.