|The masked priming paradigm developed by Forster and Davis (1984)
is sometimes referred to as a 'sandwich' technique, because the prime
is sandwiched between a forward pattern mask and the target stimulus,
which acts as a backward mask.
mask (500 ms) #####
What makes the paradigm interesting is that the prime is, for most subjects, virtually invisible. Since information about the prime never reaches consciousness, it seems clear that any observed priming effects cannot be a result of any conscious appreciation of the relationship between the prime and the target stimulus. Yet strong effects of the prime on the processing of the target stimulus are readily obtained (Forster & Davis, 1984; Forster, Davis, Schoknecht & Carter, 1987). Our hypothesis is that we are observing a 'purer' form of priming, one in which, so to speak, the contribution of the frontal lobes to priming has been largely, if not entirely eliminated.
Given this hypothesis, it is obviously of interest that certain forms of priming that are normally very difficult to obtain with visible primes are clearly revealed with masked primes (Forster et al., 1987). The most interesting example is form-priming, where the prime is similar to, but not identical to the target (e.g., nature-mature). And the converse is also probably true also.
It is obviously important to address the question of whether subjects are 'really' unaware of the prime or not. This is a vexed question. Attempts to deal with this question rapidly become bogged down in methodological disputes (the psychologist's first love), or in a debate about the nature of consciousness (e.g., if we forget what we have experienced within 100 ms, were we ever aware of it?).
In an attempt to avoid some of these problems, we are providing an on-line demonstration of what the display actually looks like. This way you can actually experience the same thing as our subjects experience. We find that there is usually not a lot of discussion about whether subjects were really aware once the display has been viewed.
However, not everyone will share your experience. In our experience, about one person in fifty can actually see the prime quite plainly, and can report it. We have no idea why this should be the case.
Forster, K.I., & Davis, C. (1984). Repetition priming and frequency attenuation in lexical access. Journal of Experimental Psychology: Learning, Memory, and Cognition, 10, 680-698.
Forster, K.I., & Davis, C. (1991). The density constraint on form-priming
in the naming task: Interference effects from a masked prime. Journal
of Memory and Language, 30, 1-25.
For an excellent survey of the field, one cannot go past the following book:
Kinoshita, S. & Lupker, S.J. (2003). Masked Priming: State of the Art. New York: Psychology Press.