Previously, using a face vs car categorization task and single-trial EEG analysis, we reported the existence of two discriminating EEG components which resulted in neurometric functions that can account for psychophysical performance (Philiastides and Sajda, SFN 2004). Though the earliest component was shown to be consistent with the well-known N170, the later component (~300ms) was the best match to the psychophysical data. We proposed that the early component is linked to early visual perception whereas the late component is likely to reflect post-sensory processing (i.e. decision) stages. In order to characterize the neural correlates of task difficulty and possibly describe the decision uncertainty, we repeat these experiments and use our single-trial linear discriminator to compare trials at different levels of stimulus evidence (i.e. different % phase coherence levels). We observe a maximally discriminating component that is situated between the early and late components (i.e. it occurs at ~250 ms po...