Masked Priming in a Semantic Selection Task Reveals 'Feeling of Knowing' Experiences but No Subliminal Perception

In a masked priming experimental paradigm, we studied a possible subliminal perception effect on a semantic selection task (SST). To gauge the degree to which subjects solved the SST consciously, they subsequently reported their level of confidence of having made a correct response. This was done on each trial, and the subjects used individually constructed category rating scales to do so, in order to achieve a more sensitive measurement of which trials were influenced by conscious processes. During the construction of these individual rating scales, subjects verbally reported their experiences after each trial. The present study failed to find evidence of performance above chance level when subjects themselves reported to be at chance level. In fact, performance closely covaried with subjects' confidence ratings. About half of the subjects reported they would sometimes experience a 'feeling of knowing' (FOK) the correct response to the SST, despite being unaware of the specific identity of the prime. From this, we observe the methodological point that in order to demonstrate subliminal perception in a masked priming paradigm with a semantic selection task it is not enough to demonstrate a lack of conscious visual perception of the prime, since a vague, yet conscious, FOK experience can be used by subjects to solve the task.