  Some studies of unconscious cognition rely on judgments of participants
stating that they have "not seen" the critical stimulus (e.g., in a
masked-priming experiment). Trials in which participants gave "not-seen"
judgments are then treated as those where the critical stimulus was
"subliminal" or "unconscious", as opposed to trials with higher visibility
ratings. Sometimes, only these trials are further analyzed, for instance, for
unconscious priming effects. Here I argue that this practice requires implicit
assumptions about subjective measures of awareness incompatible with basic
models of categorization under uncertainty (e.g., modern signal-detection and
threshold theories). Most importantly, it ignores the potential effects of
response bias. Instead of taking "not-seen" judgments literally, they would
better be employed in parametric experiments where stimulus visibility is
manipulated systematically, not accidentally. This would allow studying
qualitative and double dissociations between measures of awareness and of
stimulus processing per se.
