Hypnosis Delayed Recall

Hypnosis, Delayed Recall,
and the Principles of Memory
John F. Kihlstrom
University of Arizona
This paper reviews seven principles of memory function that set limits on the
degree to which any attempt to recover a long-forgotten memory can succeed:
encoding, organization, time-dependency, cue-dependency, encoding specificity,
schematic processing, and reconstruction. In the absence of independent
corroboration, there is no "litmus test" that can reliably distinguish
true from false memories, or memories that are based on perception from those
that are based on imagination. Practicing clinicians should use great caution
when using hypnosis or any other technique to facilitate delayed recall.
Hypnosis, Delayed Recall, and the Principles of Memory
Clinical interest in memory processes has been revived by the claim that a
whole host of problems, including anxiety, depression, and eating disorders,
have their origins in childhood experiences of incest and other sexual trauma,
abuse, neglect, and deprivation -- memories of which have been repressed by the
patient. Therefore, many therapists seek to recover these memories, and bring
them into conscious awareness, so that the patient can deal with them more
adaptively. Sometimes, hypnosis plays a role in this process. However, the very
nature of memory places strict limitations on the degree to which any attempt to
recover memories from the distant past will succeed. In this paper, I wish to
discuss some of these principles and their clinical implications (for fuller
explication of these principles, and documentation of their sources in the
experimental literature, see Kihlstrom & Barnhardt, 1993; for a further
discussion of ostensibly repressed memory, see Kihlstrom, 1993).
Seven Principles of Remembering
In analyzing the causes of remembering and forgetting, it is common to
characterize memory processing as consisting of three stages (Crowder, 1976):
encoding, the process by which a trace of current experience is laid down in
memory; storage, by which an encoded memory trace remains available over time;
and retrieval, the process by which information is recovered from storage and
used in ongoing cognitive activity. Logically, a memory cannot be retrieved from
storage unless it was encoded in the first place, or if it has been lost from
storage. But even the encoding of a memory, and its availability in storage,
does not guarantee that a veridical memory of the original event will be
retrieved. In order to understand how this is so, it is important to consider
the manner in which memory operates.
The Elaboration Principle: The memorability of an event increases
when that event is related to pre-existing knowledge at the time of
encoding.
The Organization Principle: The memorability of an event increases
when that event is related to other events at the time of encoding.
The point here is that events can be remembered to the extent that they were
encoded at the time they occurred, and that proper encoding does not occur
automatically, but rather requires active, cognitive effort. This fact accounts,
in large part, for the familiar phenomena of infantile and childhood amnesia:
most adults remember so little of childhood because children lack both the
knowledge base and the information-processing capacity to encode such memories
in retrievable form. There are also other factors involved, such as whether the
event in question is the topic of conversation between the child and other
people; see Fivush & Hudson, 1990; Nelson, 1993); of course, such social
interactions are likely to facilitate elaborative and organizational processes.
Elaboration and organization, are highly relevant in the case of ostensibly
repressed memories, most of which appear to be for events occurring in early
childhood, and cover events which by their very nature are not shared with other
people.
Assuming that a memory has been encoded, it remains available for subsequent
retrieval and use -- at least in principle. But in practice, memories seem to
fade over time, an observation that has been enshrined in another principle (Ebbinghaus,
1885):
The Time-Dependency Principle: The memorability of an event declines
as the length of the storage interval (i.e., between encoding and retrieval)
increases.
Of course, there are instances in which knowledge appears to be preserved in
rich detail over long periods of time, as in so-called "flashbulb"
memories for emotionally arousing events (Winograd & Neisser, 1992), and the
"permastore" of factual knowledge (Bahrick, 1984). But these are the
exceptions that test the rule, and in any event careful studies have shown that
many flashbulb memories are highly inaccurate, and the notion of a permastore
generally refers to factual knowledge rather than memory for particular events.
Again, the principle of time-dependency is clearly relevant when we are talking
about the adult recollection of childhood events.
The experimental literature does contain a number of studies of so-called hypermnesia,
in which memory appears to grow rather than fade with time (Erdelyi, 1984;
Kihlstrom & Barnhardt, 1993; Payne, 1987). This phenomenon is potentially
relevant to the problem of repressed memories, but does not contradict the
principles governing encoding and storage. Hypermnesia occurs when items were
subject to elaborative and organizational activity at the time of encoding, and
most hypermnesia is accomplished on the first few attempts at retrieval,
relatively soon after encoding has taken place.
The retrieval process itself is governed by a large set of principles. One of
these relates to the fact that, by and large, recognition tests produce more
memory than recall tests, and cued recall produces more memory than free recall
(Tulving, 1974):
The Cue-Dependency Principle: The memorability of an event increases
with the amount of information supplied by the retrieval cue.
Remembering usually begins with some kind of cue that provides some
information about the event which is to be remembered. Cues that are highly
informative are more likely to contact available memory traces than those that
are not. In some respects, encoding and retrieval are in a complementary
relationship: access to well encoded memories generally requires fewer retrieval
cues, and lots of retrieval cues can gain access even to very poorly encoded
memories. But the success of recognition testing comes with a price: false
alarms. Subjects may remember more correct information on a recognition test
than on a recall test, but they also remember more incorrect information.
In the laboratory, we can tell which is which. But in real life, corroborating
evidence may be entirely lacking -- which is why the problem of false
identification in police lineups is so difficult (Malpass & Devine, 1984).
Cues are important, but they must also supply the right kind of information,
not just the right amount (Tulving & Thomson, 1973):
The Encoding Specificity Principle: The memorability of an event
increases when the information processed at the time of retrieval was also
processed at the time of encoding.
The manner in which an event is encoded -- the meaning of the event, how it
is perceived and interpreted and categorized -- determines which retrieval cues
will be successful in gaining access to that event. Encoding specificity appears
to underlie the phenomenon of state-dependent memory -- whether
"state" is defined in physiological, emotional, or environmental
terms. It is certainly relevant in the case of ostensibly repressed memories.
For example, memories that have been processed during states of high emotional
arousal may only be accessible if the same affect is reinstated at the time of
retrieval (Bower, 1981; Eich & Metcalfe, 1989).
Moreover, it turns out that memory is determined by the degree to which an
event conforms to our expectations and beliefs (Hastie, 1981):
The Schematic Processing Principle: The memorability of an event
increases when that event is relevant to expectations and beliefs about that
event.
The general principle is straightforward enough, but the details may be a
little surprising. If memory is plotted as a function of the degree to which the
target events can be predicted on the basis of pre-existing knowledge,
represented in the form of organized knowledge structures known as schemata, it
turns out that events that are highly congruent with expectations are highly
memorable; but events that are highly incongruent with active schemata
are even more memorable. The U-shaped function apparently reflects the operation
of two different principles: events that are inconsistent with preexisting
schemata are surprising and draw more attention, and receive more elaborative
and organizational activity at the time of encoding; and at the time of
retrieval, the schema provides additional cue information that can facilitate
access to relevant memories. Events that are irrelevant to the schema get
neither advantage, and so are poorly remembered.
The role of cognitive schemata is also underscored by another principle
(Bartlett, 1932):
The Reconstruction Principle: The memory of an event reflects a blend
of information retrieved from specific traces encoded at the time of that
event with knowledge, expectations, and beliefs derived from other sources.
In describing how memory works, we often resort to the metaphor of a library:
memory traces are books that must be purchased and catalogued; the prospective
user must look up the book in the catalog in order to know where to find it; and
in order for the search to succeed, the book must not have been eaten by worms,
or displaced by a careless user. The library metaphor will take us a long way,
but the notion of memory retrieval obscures the fact that memories can be
distorted, biased, and otherwise changed by changes in perspective and other
events that occur after the time of encoding. In the final analysis, memory is
not so much like reading a book as it is like writing one from
fragmentary notes. The reconstruction principle is of utmost importance in the
present context, because it means that any particular memory is only partly
derived from trace information encoded at the time of the event: in the process
of remembering, trace information combined with knowledge, beliefs, and
inferences derived from other sources.
Validating Memories
Is there any way in which we can determine the source of the information
contained in memory? And, in the absence of independent corroboration, is there
any way in which we can determine which memories are valid representations of
past experience and which are not? Some data in this respect come from studies
on source memory and on reality monitoring. Source memory refers to the person's
ability to remember the circumstances under which he or she acquired certain
items of information. Anecdotal evidence strongly indicates that source memory
is not perfect: we have all wondered whether something really happened, or
whether we dreamed or imagined it; we have all confused what we did with what we
intended to do, or wish that we had done. Sometimes we don't know whether we saw
a movie in the cinema or on television. And we have all forgotten who told us a
particular joke, or let us in on a particularly juicy rumor.
Johnson and her colleagues have studied this problem extensively. In a
representative experiment (Johnson & Raye, 1981), subjects viewed a set of
words and pictures representing familiar objects. For half the words, the
subjects are asked to count the number of vowels; for the other half, they are
asked how long it would take to draw a picture of the object represented by the
word. Similar questions were asked about the pictures: how long it would take to
draw, and how many vowels are in the word corresponding to the picture. Later,
the subjects were read the words, and asked whether they saw the item as a
picture or as a word. Johnson observed a number of confusions, especially for
those words for which the subjects made a visual judgment, and those pictures
for which they made a lexical one.
Do we have any way of telling which memories are products of perception, and
which are the products of imagination? Johnson and her colleagues have proposed
a number of attributes which tend to distinguish between the two types of
memories (Johnson, Foley, Suengas, & Ray, 1988). For example, memories of
percepts contain more sensory detail, are less complex, more realistic, and more
likely to contain information about the spatial and temporal context in which
the remembered event occurred. But it should be understood that these
distinctions are entirely probabilistic: that is, the presence of one or more of
these attributes only increases the likelihood that the memory is a product of
real experience, rather than of imagination. Moreover, the list of attributes
distinguishing between memories of perceived and imagined events from
childhood was very short. Thus, there is no litmus test that is 100%
reliable, or even close to it.
In another line of research, Raskin, Steller, and their colleagues have been
promoting a technique called criteria-based statement analysis (Raskin
& Steller, 1989; Steller & Koehnken, 1989, originally developed in
Germany by Undeutsch (1984). These investigators have proposed a number of
criteria by which the veracity of a witness's statement might be assessed. For
example, they assert that factual statements contain a large number of details,
especially those that are unusual or superfluous, make reference to unexpected
complications, portray the witness's own mental state, and spontaneous
corrections, admissions of lack of memory, and expressions of self-doubt. Many
of these criteria make intuitive sense, and some of them overlap with those
developed by Johnson; but it should be said that the empirical basis of these
criteria is rather thin at present. Undeutsch and his colleagues have found that
attributes such as these make statements appear credible, but their surface
credibility is uninformative as to their actual truth-value. There is little or
no evidence that these characteristics actually distinguish between accurate and
inaccurate memories.
In the final analysis, then, there do not appear to be any internal criteria
-- that is, standards that can be applied to the statements themselves -- that
can serve to reliably distinguish between accurate recollections and
fabrications and confabulations. Nothing substitutes for external criteria --
that is, the verification of individual statements by objective evidence. In the
absence of such independent corroboration, we have no means of reliably
distinguishing between fact and fantasy.
Implications for Clinical Practice
The success of any attempt to exhume a memory will depend on why that memory
was forgotten. Of the all the principles of remembering and forgetting
summarized above, perhaps the broadest is the encoding specificity principle (Tulving
& Thomson, 1973), which may be restated as follows: what is encoded depends
on what was perceived, and what is encoded determines what subsequently will be
retrieved. A variety of factors may conspire against elaborative and
organizational processing, but the consequence is always the same: if an event
is poorly encoded in the first instance, the prospects for its subsequent
retrieval and conscious recollection, especially after a long retention
interval, are very poor as well.
To some extent, an extremely rich retrieval environment may compensate for
poor encoding received by a memory. However, there are limits to this
compensation: even recognition testing, in which the person is cued by a copy of
the event in question, often fails. Moreover, attempts to enrich the retrieval
environment by providing extra cues increase the risk that the subject will
incorporate that information into his or her memory, or at least become confused
about whether the source of particular details is in the trace or the query. The
result may well be a distortion of memory. In the absence of independent
corroboration (which is so often the case in delayed recall), such distortions
are arguably worse than no memory at all, because neither the subject nor the
questionner know where truth lies.
Nothing about hypnosis changes the rules by which memories are encoded,
stored, and retrieved; accordingly, these rules constrain the utility of
hypnosis (or any other procedure) as a technique for the enhancement of memory.
There is no scientific evidence that hypnosis can improve the retrieval of
poorly encoded memories, or those that have been degraded by interference
accumulated over long retention intervals. It is possible, at least in
principle, that hypnosis could be used to provide an extremely rich set of
retrieval cues, overcoming encoding and storage conditions. For example, age
regression could be used to structure an hallucinated environment that returns
the person to the circumstances, both environmental and emotional, of the
forgotten episode: if accurate, this would be the richest retrieval cue
imaginable.
Unfortunately, the clinical and forensic circumstances in which hypnosis is
used to enhance recall are those in which such information is rarely available.
In any event, the suggestions used to reconstruct such a mental representation
of the past may also promote confabulation, and in such a manner that neither
the therapist nor the patient will be able to determine, with accuracy, whether
the recollection is accurate. For this reason, hypnosis should be used, if
indeed it is to be used at all in forensic and therapeutic situations, only in
the generation of hypotheses to be corroborated by independent evidence.
Hypnotically refreshed memories should never be allowed to stand alone.
Author Notes
Paper prepared for a special issue of the International Journal of
Clinical & Experimental Hypnosis on "Hypnosis and Delayed
Recall". The point of view taken in this paper is based on research
supported in part by Grant #MH-35856 from the National Institute of Mental
Health. I thank Terrence Barnhardt, Lawrence Couture, Jennifer Dorfman,
Elizabeth Glisky, Martha Glisky, Victor Shames, Michael Valdisseri, Susan
Valdisseri, and James Wood for their comments.
Kihlstrom, J.F. (1993, April). The recovery of memory in laboratory and
clinic. Invited address presented at the joint annual meeting of the Rocky
Mountain Psychological Association and Western Psychological Association,
Phoenix.
Kihlstrom, J.F., & Barnhardt, T.M. (1993). The self-regulation of memory:
For better and for worse, with and without hypnosis. In D.M. Wegner & J.W.
Pennebaker (Eds.), Handbook of mental control (pp. 88-125). Englewood
Cliffs, N.J.: Prentice-Hall.