The evidence overwhelmingly indicates that people can learn
a lot without intending to; incidental learning is usually
closer to intentional learning than to chance. The intention
to learn seems to have little effect beyond focusing attention
on the items to be learned (Hyde & Jenkins, 1969; Mandler,
1967). However, the assumption of obligatory encoding does
not imply that all items will be encoded equally well. Attention
to an item may be sufficient to encode it into memory, but
the quality of the encoding will depend on the quality and
quantity of attention. As the levelsofprocessing literature
has shown, subjects remember the same items better when they
attend to their semantic features rather than their physical
features (Craik & Tulving, 1975). Dualtask studies show that
subjects remember less under dualtask conditions than under
singletask conditions (NavehBenjamin & Jonides, 1984; Nissen
& Bullemer, 1987).
The assumption of obligatory retrieval is supported by studies
of Stroop and priming effects, in which attention to an item
activates associations in memory that facilitate performance
in some situations and interfere with it in others (for a
review, see Logan, 1980). The most convincing evidence comes
from studies of episodic priming that show facilitation from
newly learned associates (McKoon & Ratcliff, 1980; Ratcliff&
Mc Koon, 1978, 1981). The assumption of obligatory retrieval
does not imply that retrieval will always be successful or
that it will be easy. Many factors affect retrieval time (Ratcliff,
1978), including practice on the task (Pirolli & Anderson,
1985). The prevailing conditions in studies of automaticity
are generally good for retrieval: The same items have been
presented many times and so should be easy to retrieve. The
algorithm, if used in parallel with retrieval, will screen
out any slow or difficult retrievals by finishing first and
providing a solution to the task. The assumption of an instance
representation for learning contrasts with the modal view.
Many theories assume a strength representation (e.g., LaBerge
& Samuels, 1974; MacKay, 1982; Schneider, 1985), and others
include strength as one of several learning mechanisms (e.g.,
Anderson, 1982), In instance theories, memory becomes stronger
because each experience lays down a separate trace that may
be recruited at the time of retrieval; in strength theories,
memory becomes stronger by strengthening a connection between
a generic representation of a stimulus and a generic representation
of its interpretation or its response.
Instance theories have been pitted against strength theories
in studies of memory and studies of categorization. In memory,
strength is not enough; the evidence is consistent with pure
instance theories or strength theories supplemented by instances
(for a review, see Hintzman, 1976). In categorization, abstraction
is the analog of strength. Separate exposures are combined
into a single generic, prototypic representation, which is
compared with incoming stimuli. The evidence suggests that
prototypes by themselves are not enough; instances are important
in categorization (for a review, see Medin & Smith, 1984).
