Repetition Priming 465explicit memory. The results of the experiments by Gabrieli
and colleagues provide strong evidence that the processes
supporting repetition priming do not necessarily contribute to
explicit memory performance. Thus, repetition-priming ef-
fects should not be interpreted in terms of degraded explicit
memory performance. In addition, it should be noted that
these patients’ ability to perform a perceptual identification
task without eliciting repetition priming presents difficulties
for models such as the counter model, which assumes that
repetition priming occurs as a by-product of performing this
task.
On the basis of observed functional and stochastic dis-
sociations between implicit and explicit memory, as well as
the evidence from amnesics and other patients with brain
damage, theorists have proposed a multiple systems view
of memory (e.g., Schacter, 1992; Squire, 1992; Tulving &
Schacter, 1990), which holds that neurologically distinct sys-
tems subserve different types of memory. The patterns of data
have suggested to many that implicit memory is supported by
systems distinct from those required for the formation of
explicit memories.
The multiple systems view also divides implicit memory
into subsystems. Perhaps the best elaborated multiple sys-
tems account is that of Tulving and Schacter (1990), who
propose a set of neurologically distinct perceptual representa-
tion systems (PRS), each of which is designed to encode a
particular type of information. Each PRS is presemantic—
encoding perceptual information without the necessity for the
stimulus to be processed semantically—and supports repeti-
tion priming on tasks that use that information. Schacter and
his colleagues postulate at least three such systems: a system
that encodes information about object parts and their relations
in the form of structural descriptions (e.g., Humphreys &
Quinlan, 1987; Riddoch & Humphreys, 1987) and supports
repetition priming for objects (e.g., Schacter, Cooper, &
Delaney, 1990a, 1990b); a visual word-form system that
encodes graphemic word information and supports repeti-
tion priming for visually presented words (e.g., Marsolek,
Kosslyn, & Squire, 1992); and a similar auditory word-form
system (e.g., Church & Schacter, 1994). Other systems pre-
sumably support repetition priming in more conceptual tasks,
although the focus of the multiple systems view has thus far
been on perceptual tasks. However, whether implicit and
explicit memory are subserved by separate systems at all is a
heavily debated issue (cf. Blaxton, 1989; Roediger, 1990;
Shimamura, 1990).
Processing Theories. Many researchers have chosen to
distinguish memory phenomena on the basis of the different
cognitive processes required by the memory tests (e.g., Graf
& Mandler, 1984; Roediger & Blaxton, 1987; Roediger,
Weldon, & Challis, 1989). Rather than assuming that implicit
and explicit tests access separate memory systems, processing
theories assume that memory tests are composed of various
component processes, and dissociations between performance
on memory tests reflect the operation of different processes.
Perhaps the most commonly stated processing account of
memory is embodied in the principle of transfer appropriate
processing (TAP; e.g., Morris, Bransford, & Franks, 1977;
Franks, Bilbrey, Lien, & McNamara, 2000). A primary as-
sumption of TAP is that performance on a memory test bene-
fits to the extent that the cognitive operations at test overlap
with those engaged during initial learning. In general, disso-
ciations between performance on explicit and implicit mem-
ory tests are characterized in terms of a distinction between
conceptually driven processes and data-driven processes
(Roediger et al., 1989). Explicit memory tasks typically (but
not always) depend on conceptual processing that is assumed
to be sensitive to delay and depth of processing manipula-
tions, whereas implicit memory tests usually depend on data-
driven processing that is assumed to be insensitive to these
factors. Along the same lines as TAP, Jacoby (1991) has pro-
posed that implicit memory involves automatic processes,
whereas explicit memory requires consciously controlled
processes. Although Jacoby argues against equating specific
memory tests with proposed cognitive processes, he suggests
the possibility that special populations, such as amnesics,
may show a deficit in intentional processing but preserve au-
tomatic or unconscious forms of memory. Jacoby argues that
both automatic and controlled processes are always operat-
ing, and he has postulated a framework called process disso-
ciationthat is designed to parse out the relative contributions
of each process to performance on a given task.
There has been much debate in recent years concerning
the issue of whether memory should be characterized in
terms of memory systems or in terms of cognitive processes
(e.g., Graf & Ryan, 1990; Mitchell, 1993; Roediger, 1990;
Roediger et al., 1989). It is not uncommon for multiple
memory systems and processing views to be represented in
the implicit memory literature as rival hypotheses. Several
researchers, however, have pointed out that these two per-
spectives are not necessarily incompatible (Schacter, 1990;
Shimamura, 1989, 1993). Shimamura (1993) argues that the
debate between multiple-systems and TAP views appears to
be the result of scientists’ working from two different per-
spectives. Processing views, such as TAP, for instance, are
typically championed by researchers in cognitive psychol-
ogy, whereas multiple-systems views are often forwarded by
researchers in neuroscience. The argument for a processing
view—in contrast to a multiple-systems view—is often