[转贴]记忆简介

Introduction

fficeffice" /> 

ENDEL TULVING

 

Memory is the capacity of nervous systems to benefit

from experience. It is a ubiquitous presence in all higher

life forms. It takes many shapes, from simple to complex,

from highly specific to most general, from trifling

to fundamentally important. In its manifold expressions

it is being observed, investigated, and measured in numerous

organisms, at many different levels of analysis,

from a variety of vantage points, and relying on many

different approaches and techniques. It reaches its evolutionary

culmination in human beings.

The study of memory has occupied the center stage of

cognitive neuroscience since its inception. It continues

to fascinate and frustrate large numbers of capable scientists.

Novel findings are reported almost daily, yet the

major insight gained from more than one hundred years

of scientific study of memory may be the realization that

the complexity of memory far exceeds anyone’s imagination.

It is clear that memory did not evolve for the

convenience of the neuroscientist.

The nine chapters in the memory section of the second

edition of The Cognitive Neurosciences provide summaries

of and glimpses into some of the more active foci of

contemporary cognitive neuroscience of memory. Six

chapters deal solely or primarily with human memory,

whereas three others focus on work done with nonhuman

primates. Collectively, they illustrate the variety of

methods and procedures used. These include electrical

recording from single neurons in monkeys (chapters 50

and 51) and from multiple scalp sites in normal human

subjects (chapter 56); the study of the effects of experimentally

created lesions in monkeys (chapter 52) and

the mnemonic consequences of brain damage resulting

from disease or accident (chapters 53, 54, and 58); effects

of psychoactive drugs (chapter 55); and functional

728 MEMORY

neuroimaging of memory-related processes in healthy

volunteers (chapters 57 and 58). The overarching concern

in all these chapters is to gain insight into the neuronal

substrates of behavioral and cognitive manifestations of

learning and memory and into the nature of the relation

between neural mechanisms and memory processes.

Because of the vast size and diversity of the domain, it

simply is not possible to deal with memory as a whole.

Nor is it possible to make any intelligent generalizations

about it. Any claim about “memory” or “memory impairment”

immediately requires clarification: About which

kind of memory, memory task, memory process, or

memory system are we talking? These terms define the

major fault lines along which the whole of memory can

be fractionated into more manageable components

within which generalizability of factual statements and

theoretical claims are more likely to be valid. The concepts

represented by these terms have evolved from the

observations made about memory at the level of observable

behavior and reportable experience. Directly or indirectly,

they provide the backdrop against which we

seek to understand the relation between brain and behavior

or between brain and mind.

This introduction to the section on memory describes

the outlines of the conceptual framework within which

much research on human memory is conducted and attempts

to clarify some of the arcane terms that, although

useful to insiders, frequently mystify outsiders. It touches

on topics such as memory systems, memory tasks, memory

processes, and conscious awareness in memory.

Memory systems

The concept of memory systems is one answer to the

need to specify different “kinds” of memory. Different

systems share certain basic features, such as some device

or means of retaining the consequences of a current act

of behavior or cognition, and they differ with respect to

others, such as the functions they serve, their behavioral

or cognitive manifestations, the principles of their operations,

and the brain mechanisms involved in the operations.

The most fundamental division in memory deals with

the distinction between behavior and thought. Many

forms of learning and memory are expressed in behavior

(doing something, carrying out a procedure),

whereas others are expressed in thought (contemplating

something, being cognizant of some mental contents).

The behavioral kinds collectively are referred to

as “procedural” memory; the ones expressed in thought

are referred to as “cognitive” memory. Although the

distinction is not a simple one, a rule of thumb that can

be used for deciding how to classify any particular act

of memory consists in the answer to the question—can

one hold in mind the product of the act of memory? An

affirmative answer suggests that memory is cognitive;

the negative answer means that it is procedural.

The distinction between procedural and cognitive

holds very broadly for learning and memory in many

species. Other terms have been used to designate them.

Procedural memory has been called habit memory, nondeclarative

memory, and even implicit memory, although

for many students of memory, implicit memory

means something rather different than the broad category

of learning and memory that is not cognitive. Cognitive

memory has been called declarative memory,

propositional memory, and also explicit memory, although,

again, explicit memory does not really correspond

to all forms of learning and memory that are not

cognitive. The extensive, and sometimes undisciplined,

use of different terms to designate the same underlying

concepts is a continuing problem in the field.

Cognitive memory, which constitutes the lion’s share

of memory research with human subjects, can be further

subdivided into four major categories, or “systems.” They

are (1) working memory, whose function is to hold information

的确介绍得不错，顺便把另一帖的记忆分类问题也解决了。

Downloaded. I will read it later.

Thank you so much!

 “on line” over short intervals of time while cognitivefficeffice" />

operations are performed on it; (2) the perceptual

representation system, whose function is to mediate

memory-based facilitation of perceptual identification of

objects; (3) semantic memory, whose function is to mediate

the acquisition and use of individuals’ general knowledge

of the world; and (4) episodic memory, whose

function is to mediate conscious access to the personally

experienced past.

The separability of the four systems from one another

is widely if not universally accepted. The distinctions

among them receive support from sharp dissociation

between task performances that depend heavily on the

different underlying systems in normal subjects and

brain-damaged individuals, as well as from functional

neuroimaging and psychopharmacological studies. Relevant

evidence is discussed in many chapters in this section.

Much of the research effort currently is directed at

the refinement and elaboration of the taxonomic

scheme, and at the identification and characterization of

the many subdivisions of the major categories.

Tasks and processes

Cognitive memory in the laboratory is studied in segments

of reality called tasks. A typical cognitive memory

task consists of three stages: (1) presentation of some material

to the subject, usually with instructions to “remember”

it; (2) a retention interval during which the subject

may engage in other (mental) activities; and (3) a test of

TULVING: INTRODUCTION 729

the subject’s knowledge of the originally presented material.

The outcome of the test is expressed in terms of

some measure of the subject’s performance on the test. It

is frequently but not necessarily a measure of how well

the subject can reproduce originally presented material.

A great variety of cognitive memory tasks exists, defined

in terms of a large number of possible variations in

the specific features of the three stages of the task. Tasks

can vary in the kinds and units of the material presented

for learning and the specific parameters of the presentation,

the length of the retention interval (which can

range from seconds to years), the nature of the “interpolated”

activities, and many other independent variables.

An especially important feature of the task is the nature

of the test. Tests also can vary widely with respect to the

instructions that specify the subject’s mission and the nature

and type of cue information provided to guide and

aid its execution.

Given this thumbnail sketch of the memory task, how

are we to think about and describe, in general abstract

terms, what happens when the subject is engaged in a

cognitive memory task? For a long time in the history of

learning and memory the dominant theoretical concept

that provided the answer to this question was “association.”

During learning, associations were assumed to be

formed, maintained in force, sometimes interfered with,

and then expressed in behavior. The concept of association

still is used in special situations, especially in studies

of learning and memory with nonverbal subjects. In the

mainstream cognitive psychology, however, some 30 to

40 years ago the associative paradigm was replaced by

information processing as the general pretheoretical framework.

This framework currently determines how most

students of memory think and talk about the workings of

memory.

The three sequential stages of the standard memory

task correspond to three major memory processes of encoding,

storage, and retrieval. The presentation of the

to-be-remembered material is an event about which

“information” is “encoded” into the memory “store.”

Usually, the material consists of discrete items (words,

pictures, objects, faces, and simple sentences), and the

presentation of each is a “miniature event” about which

information is encoded into the store. During the retention

interval, this information is maintained in the store

as an “engram,” and it may be “consolidated” or “recoded.”

Consolidation is thought of as a biologically determined

autonomous process that runs its course

independently of the interpolated activity, whereas recoding

is an active psychological process that is shaped

by the particulars of the interpolated activity. At the time

of the test, the information “available” in the engram is

“retrieved,” or rendered “accessible.” Retrieval means

use of stored information, and because stored information

can be used in many different ways, the term retrieval

is very broad and usually needs to be specified

more precisely.

The concept of information runs through this pretheoretical

processing framework like a red thread. It is

useful to keep in mind, therefore, that neither information

nor process can be defined readily. Information simply

is the intangible, ineffable, unknown “stuff” that is

somehow created, transferred, transformed, preserved

(“processed”) in the mind/brain, which, when appropriately

“converted,” determines behavior and conscious

thought. Both information and process are “placeholder”

concepts in contemporary cognitive sciences.

They will be used until a better paradigm comes along.

Even though they are not readily definable, the terms

make abstract thought about the workings of the brain/

mind possible and the doubts about how to best study it

tolerable.

Conscious awareness in memory

The products of retrieval in all cognitive memory tasks

are, in the first instance, expressed as mental experiences.

They can be contemplated internally, in the absence

of any overt behavior, and they can be “held in

mind.” It would be normal to expect, therefore, that the

efforts to understand cognitive memory be directed at

the study of the retrieval experience. For a long time in

the history of the science of memory, however, this was

not done. Subjects’ memory performance invariably was

measured in terms of behavioral indices of variousfficeffice" />

kinds. The tacit assumption, seldom explicitly formulated,

was that behavioral output in the memory test

faithfully reflects the mental contents of what the individual

has retrieved from memory. We now know that

this assumption does not always hold.

Recently, the issue of individuals’ conscious experiences

that accompany the act of retrieval from the memory

store has been shifted into a sharp focus, in two

different ways. One distinguishes between “conscious”

and “nonconscious” retrieval; the other, concerned

solely with conscious retrieval, distinguishes between

two forms of it. The first issue is dealt with under the

heading of explicit versus implicit memory, the second under

the heading of remembering and knowing, or recollection

and familiarity. We consider them in turn.

Explicit and implicit memory

The first issue of consciousness in memory has to with

the rememberer’s awareness, at the time of the test, of

the relation between the current experience (and activity)

730 MEMORY

on the one hand, and the original learning or encoding

episode on the other. In ordinary everyday-type of remembering,

the relation is clearly felt: when the individual

recollects a previous event, such as the study of some

specific material in the first stage of the experiment, he or

she also is fully aware that what he or she is experiencing

has its origin in the earlier episode. The technical term

that is used currently to refer to this kind of awareness at

retrieval is explicit memory.

Explicit memory contrasts with implicit memory: retrieval

of stored information in the absence of the awareness

that the current behavior and experience have been

influenced by a particular earlier happening. It is in this

sense, and this sense only, that explicit memory is said

to be “conscious,” whereas implicit memory is “nonconscious.”

Consciousness refers to the awareness of the relation

between the present thought (and action) and a

specific previous thought (or action).

An important point to note is that the distinction between

explicit and implicit memory is that between explicit

and implicit retrieval—that is, the distinction applies

only the final stage of our typical memory task. This is

because there is no difference between explicit and implicit

encoding, and there is, as yet, no known way to

distinguish between explicit and implicit storage. For

this reason among others, explicit and implicit memories

do not qualify as memory “systems.”

In memory experiments, explicit retrieval is effected

by the instructions given to the subject at test: “Remember

what you saw, or what you did, or what happened to

you at some earlier time, in some place (such as the first

stage of the experiment)?” Implicit retrieval, too, is experimentally

effected by the instructions given to the

subjects at the time of retrieval as to what they are to do.

Many different forms of implicit memory tests exist and

have been used, but they all have in common the fact

that the subject need not think back to the first stage of the

task, or to any other specific episode, to perform the task

at a level that has benefited from the first stage. Thus,

implicit memory satisfies the definition of memory—the

individual benefits from experience, but he or she is unaware

that he or she has done so.

It is important to note a complication: Explicit retrieval

instructions do not necessarily guarantee that the

responses made by the subject are accompanied by a

sense of recollection, as they ideally would. Subjects’ explicit

memory performance may be influenced processes

that support implicit retrieval. Nor do implicit

instructions guarantee that retrieval occurs in the absence

of recollection of the relevant encoding experience,

as it ideally should. Purification of research designs

aimed at reducing or eliminating such unwanted “contamination”

of the desired type of retrieval by extraneous

factors is an important part of research on explicit

and implicit memory. Some of these issues are discussed

in chapters 55, 56, and especially 58.

Many experiments, of many different kinds, have

convincingly demonstrated the reality of the distinction

between explicit and implicit memory. The major theoretical

import of the discovery of these two forms of retrieval

lies in the sharp distinction that they draw

between overt behavior and the mental experience that

accompanies such behavior. The subject’s ability to produce

a particular over-response, whose likelihood has

been enhanced by a particular earlier event, may be

identical in two tests. However, the mental experiences

may be altogether different.

Remembering and knowing

The second issue of consciousness emerges in situations

in which the awareness of the relation between the

present experience and an earlier specific event is in fact

present. It has to do with two different kinds of awareness

that may accompany explicit memory retrieval. One is

referred to as remembering or recollection, the other as

knowing or familiarity. In explicit tests of recognition and

recall, the subject may make a correct response not because

he or she actually remembers or recollects the

event of the item’s earlier presentation, but rather because

the recognition test item “looks familiar,” or because

he or she “simply knows” that the word he or she

has just recalled was in the presented list. Because the

subject is fully aware of the previous presentation episode

of the material, he or she—usually correctly—attributes

the feeling of familiarity or “knowing” to the

episode.

The remembering/knowing or recollection/familiarity

distinctions currently are subjects of lively interest to

many memory researchers. Rugg and Allan (chapter 56)

discusses the electrophysiological evidence for the distinction,

and Squire and Knowlton (chapter 53) deal

with the issue of how remembering and knowing are relatedfficeffice" />

to the amnesic syndrome and whether they are

both dependent on the medial temporal lobes. Schacter

and Curran (chapter 58) and Curran (chapter 55) also

touch on the distinction. The major theoretical point,

however, is that here, finally, we have an active area of

research aimed at the essence of cognition: Conscious

mental experiences that have been changed as a result

of earlier experience-induced physical changes in the

brain.

Other levels and species

Concepts such as encoding and retrieval, explicit and

implicit memory, or remembering and knowing make

TULVING: INTRODUCTION 731

good sense at the level of behavior and cognition of the

whole individual, or the whole brain. They are less

readily applicable to the study of memory-related events

at the level of single neurons, in analyses of the kind described

by Goldman-Rakic and associates and Erickson

and colleagues in chapters 50 and 51, respectively. Although

encoding and retrieval ultimately are rooted in

neuronal activity, a single neuron cannot encode or retrieve

anything. A neuron may “fire” differentially during

the interval between the presentation of the target

and the signal for the saccade in the oculomotor working-

memory task used by Goldman-Rakic and colleagues,

thus providing for a neat neuronal mechanism

for holding information “on line” in the short-term

memory “store.” But although it is possible to think of

this “on-line holding” mechanism as comparable in principle

to “holding” information in the long-term “store,”

the parallel probably would not work. Retrieval—use of

the “stored” information—has different meanings to the

organism and is based on rather different operations, in

the two situations. Similarly, a neuron may respond differentially

to a stimulus when presented for the first time

versus the second, as shown by the studies of Erickson

and colleagues (chapter 51), and it is tempting to think of

the difference as in some sense paralleling novelty versus

familiarity detection, or even encoding and retrieval,

at the level of the whole brain, but the two levels of analyses

are too far apart to allow one to feel confident about

such thoughts. A challenging task for neuroscience of

memory is to determine to what extent such high-level

phenomena as conscious recollection of the occurrence

of an event depend on the differential activity of individual

units, and to what extent they represent networklevel

happenings, or as yet unknown mechanisms, in the

brain.

Similar thoughts apply to memory in nonhuman animals.

A good deal of knowledge about memory, and

especially about the neural basis of memory-based behavior,

has been derived from work with other animals—

nonhuman primates, rodents, birds, and others,

all the way to insects, worms, and sea slugs. A major

advantage of this work lies in the possibility of a greater

range of surgical, chemical, and other material interventions

in the normal brain activity.

Because memory capabilities, functions, and processes

of any two species are always not only similar in

some ways but also different in others, some of the

methods, findings, and theoretical ideas about human

memory have no direct parallels and no direct applicability

to nonhuman animals. Thus, there are as yet no

known means that could be used to separate implicit

from explicit retrieval, or to distinguish between what

animals remember and what they know, or what they

recollect and what they find merely familiar. Therefore,

the important distinctions that shape thought about human

memory cannot be transferred forthwith into the

study of learning and memory in nonhuman animals.

This simple fact also imposes certain limitations on the

extent to which the findings from animal studies can be

generalized to humans. When these limitations are kept

in mind, however, and flat generalizations are avoided,

study of memory in one species can be invaluable in

providing useful information and offering inspiration to

the study of memory in others. The basic structural similarity

among the brains of all mammals, especially primates,

cannot be gainsaid, and this structural similarity

clearly implies some functional similarity as well. The

challenging task is to identify exactly wherein the similarities

lie.

Conclusion

This, then, is a brief description of the framework within

which much of the neurocognitive research takes place.

In one way or another, more or less directly, many empirical

findings and most major theoretical ideas and

debates involve memory processes, retrieval-related

awareness, and memory systems. Study of amnesia and

other forms of memory impairments, and theoretical

disputes about it, revolve around issues of memory processes,

memory awareness, and memory systems. Studies

of functional neuroanatomy of memory, made

possible by novel techniques such as positron emission

tomography (PET) and functional magnetic resonance

imaging (fMRI) are focused on memory processes, their

interactions with the type of remembered material, and

on differences between implicit and explicit retrieval.

The outsider who is not familiar with the field should

gain some idea from this section about where cognitive

neuroscience of memory stands at the turn of the millennium.

The insider who knows what the situation was like

only 5 years ago, when the first edition of The Cognitive

Neurosciences appeared, should find that great changes

have occurred since then. New techniques, such as the

use of excitotoxic lesions, described by Murray (chapter

52), have produced data that, by past standards, can be

regarded as revolutionary. New phenomena, such as

“false remembering” discussed and dissected by Schacter

and Curran (chapter 58), were not only unknown but

also even largely unimaginable 5 years ago. Moreover,

most everything that functional neuroimaging techniques

(PET and fMRI) have revealed about human

memory, as described and analyzed by Buckner (chapter

57), has been discovered in the last 5 years. Stress-related

memory impairments and the real possibility that what

were thought of as “psychogenic amnesias” have as real a

732 MEMORY

physiological basis as “organic amnesias,” discussed by

Markowitsch (chapter 54), are newcomers on the memory

scene. Even approaches that have been in use for a

while, such as psychopharmacology (chapter 55), eventrelated

potentials (chapter 56), single-unit recording

(chapter 51), and the study of amnesic patients (chapter

53) have yielded new discoveries and fresh insights of a

kind that attest genuine progress in the field.

These are exciting times in neurocognitive memory

research. Happenings at the horizon point to the next 5

years being even more so.

 

[系统提示]:
  .::本帖子因为[奖励]值得推荐的转帖文章被神经科学论坛管理员a2s2d3实行了：+10金钱 +10经验 的奖惩::.

转自《new cognitive neuroscience》（2000），累死我了，没想到这么长。

这部分我还没看到，不过可能有人有兴趣，所以贴上来了。

［此帖子已被 remind_me 在 2005-10-19 13:09:04 编辑过］