Awareness of "Invisible" Arrows in a Metacontrast Masking Paradigm

A common strategy in unconscious perception research is to use either pattern masking or metacontrast masking to render prime stimuli "invisible" to consciousness. However, several recent studies have questioned whether the identities of prime stimuli (typically arrows or diamonds and squares) in metacontrast masking studies are impossible to consciously perceive. In a series of studies, we concurrently related prime awareness, target response time priming, and prime identification across 3 prime-mask stimulus onset asynchronies (27, 40, and 67 ms). We found that increases in prime awareness ratings were accompanied by better prime identification performance. Significant prime identification in the 27-ms condition was obtained only at the highest awareness rating; for the other 2 stimulus onset asynchronies most awareness ratings were associated with above-chance prime identification. The priming effects obtained in these paradigms occur, to some degree, when participants are likely to be aware of the prime stimuli. Our results, collectively, suggest that metacontrast masking of primes does not necessarily preclude their awareness. Priming effects may depend on at least partial awareness of the prime stimuli.