So we can make sense of place reidentification in terms either of the

features
Points of View 173
holding at places. This in turn opens the way to the thought that we can
understand some forms of place reidentification in terms of feature
reidentification.
So we can make sense of place reidentification in terms either of the
notion of an object* or that of feature reidentification, or of course in
terms of both. This answers the worry that place reidentification depends
on object reidentification by showing that at least a primitive form of
place recognition can be prior to object identification.3 But there is an
important dimension not yet discussed. We can draw a broad distinction
between two types of memory. There are, on the one hand, instances
of memory in which past experiences influence present experience but
without any sense on the part of the subject of having had the relevant
past experiences and, on the other, instances in which past experiences
not only influence present experience but also the subject is in some
sense aware of having had those past experiences. In the former case
what licenses talk of memory is the fact that a subject (or an animal or
even a plant) can respond differentially to a stimulus as a function of
prior exposure to that stimulus or to similar stimuli. This is not to deny
that such a memory can be extremely complex. Quite the contrary, it
seems to be central to the acquisition of any skill, even the most developed.
The “differential response” does not have to be simple or repetitive.
Nonetheless, we can draw a contrast between memory at this level and
the various forms of memory that do involve an awareness of having had
the relevant past experiences, as, for example, when a memory image
comes into one’s mind or one successfully recalls what one did the previous
day. Clearly, there are many levels of such memory (which I shall term
‘conscious memory’), of which autobiographical memory is probably the
most sophisticated. One thing that these forms of conscious or explicit
memory all have in common, however, is that previous experience is consciously
registered, rather than unconsciously influencing present
experience.4
This distinction of forms of memories is a crude one, not least because
such terms as ‘conscious’ and ‘explicit’ are so hazy, but it can be illustrated
through some striking experimental work carried out with amnesic
patients (Schacter, McAndrews, and Moscovitch 1988). As is well
known, amnesia is an inability to remember recent experiences (even from
174 Chapter 7
the very recent past) and to learn various types of information, and it
results from selective brain damage that leaves perceptual, linguistic, and
intellectual skills untouched. Memory deficits in amnesic patients have
traditionally been studied using techniques designed to elicit explicit
memories. So, for example, amnesic patients might be instructed to think
back to a learning episode and either recall information from that episode
or say whether a presented item had previously been encountered in the
learning episode. On tests like these, amnesic patients perform very badly.
What is interesting, though, is that the very same patients who perform
badly on these tests of recall and recognition can perform successfully
(sometimes as successfully as normal subjects) on tests that do not require
thinking back to specific episodes or consciously bringing to mind earlier
experiences. The acquisition of skills is a case in point, and there is considerable
experimental evidence showing that amnesic patients can acquire
both motor and intellectual skills over a series of learning episodes
even though they cannot explicitly remember any of the learning episodes.
A striking example is the densely amnesic patient who learned how
to use a personal computer over numerous sessions, despite declaring at
the beginning of each session that he had never used a computer before
(Glisky, Schacter, and Tulving 1986). In addition to this sort of capacity
to learn over a succession of episodes, amnesics have performed well on
single-episode learning tasks (such as completing previously shown words
when given 3-letter cues). Experiments like these in amnesic patients
clearly reveal the difference between conscious and nonconscious memory,
but similar dissociations can be observed in normal subjects, as when
performance on indirect tasks reveals the effects of prior events that are
not remembered.
Nonetheless, the distinction of forms of memories is not yet as clear as
it needs to be, since the distinguishing feature of conscious memories, as
so far defined, is that they issue in verbal reports, which is of limited use
at the nonconceptual level. To sharpen the distinction further it is helpful
to recall that memory is a causal notion (Martin and Deutscher 1966).
This holds both of conscious and unconscious memory, although, of
course, in different ways. At a very general level, the notion of memory
has the following core role to play in the explanation of behavior: we need
to appeal to the operations of memory to explain a creature’s current
Points of View 175
behavior where we cannot fully explain that behavior without assuming
that it is being being causally affected by previous experiences and/or
thoughts (henceforth, ‘experiences/thoughts’). But the satisfaction of this
core condition counts as an instance of conscious memory if and only
if the previous experiences/thoughts are causally efficacious through the
medium of occurrent experiences/thoughts that refer back to those previous
experiences/thoughts. In the case of unconscious memory, in contrast,
this further requirement is not satisfied.
Note that there are two ways in which the further requirement for conscious
memory could fail to be satisfied. First, it could be the case that
there are no distinctive occurrent experiences/thoughts. Of course, this
would not mean that there are no occurrent experiences/thoughts at all.
Rather, this case arises when a creature’s occurrent experiences/thoughts
are precisely those that it would have had if the previous experiences/
thoughts had not been causally efficacious. As an example, consider
Glisky’s amnesic patient encountering his computer at the beginning of
his tenth lesson (which, of course, he thinks is his first). Despite the effects
of the previous nine lessons, the patient has more or less the same experiences/
thoughts that he had when he first encountered the computer. No
distinctive experiences/thoughts are caused by his previous encounters
with the computer. Nonetheless, those previous encounters could be causally
efficacious if, for example, the patient’s first action was to switch on
the computer and take hold of the mouse. A second way of failing the
further requirement would occur if, although the subject in question did
have distinctive occurrent experiences/thoughts caused in the appropriate
way, those experiences/thoughts do not refer back to the previous experiences
and/or thoughts that caused them. One common way in which this
occurs is when perceptual discriminative capacities have been sharpened
through long experience. Here a creature’s occurrent perceptions could
be significantly altered by previous experiences/thoughts without there
being any reference back to the experiences/thoughts that are causally
responsible for the increased discrimination manifest in its occurrent
perceptions.
It is important to recognize that neither form of potential failure can be
present if we are plausibly to maintain the presence of conscious memory.
Conscious memory requires more than that past experience/thoughts