Starting from Marr's ideas about levels of explanation, a theory of the data structures and access processes in human memory is demonstrated on 10 tasks. Functional characteristics of human memory are captured implementation-independently. Our theory generates a multidimensional task classification subsuming existing classifications such as the distinction between tasks that are implicit versus explicit, data driven versus conceptually driven, and simple associative (two-way bindings) versus higher order (threeway bindings), providing a broad basis for new experiments. The formal language clarifies the (...) binding problem in episodic memory, the role of input pathways in both episodic and semantic (lexical) memory, the importance of the input set in episodic memory, and the ubiquitous calculation of an intersection in theories of episodic and lexical access. (shrink)

In contrast to the views put forth by Stein & Glasier, we support the use of inbred strains of rodents in studies of the immunobiology of neural transplants. Inbred strains demonstrate homology of the major histocompatibility complex (MHC). Virtually all experimental work in transplantation immunology is performed using inbred strains, yet very few published studies of immune rejection in intracerebral grafts have used inbred animals.

The research guided by the correspondence metaphor is lauded for its emphasis on functional analysis, but the term “correspondence” itself needs clarification. Of the two terms in the relationship, only one is well defined. It is suggested that behavior at acquisition needs to be analyzed and that molecular principles from the learning laboratory might be useful in doing so.

Parallel to Koriat & Goldsmith's accounting of human memory, there are two distinct approaches in animal learning. Behaviorist approaches focus on quantitative aspects of conditioned response probability, whereas cognitive and ethological approaches focus on qualitative aspects of how memory is used in real life. Moreover, in animal research these distinguishable measures of memory are dissociated in experimental amnesia.

It is accepted that “primary awareness” may emerge from the integration of two classes of information. It is unclear, however, why this cannot take place within the comparator rather than in conjunction with feedback to the perceptual systems. The model has plausibility in relation to the continuity of conscious experience in the normal waking state and may be extended to encompass certain aspects of the “sense of self” which are frequently disrupted in psychotic patients.

The novel correspondence metaphor outlined by Koriat & Goldsmith offers important advantages for studying critical issues of memory-accuracy. It also fits well with the current emphasis on the reconstructive nature of memory and on the role of cognitive, metacognitive, and motivational factors in memory performance. These positive features notwithstanding, the storehouse/correspondence framework faces potential perils having to do with its implied linkage to the laboratory/real-life controversy and its proposal of studying correspondence issues in isolation from memory phenomena captured by the (...) storehouse paradigm. (shrink)

This commentary deals with criteria for assigning truth values to memory contents. A parallel with perception shows how truth values can be assigned by considering subjects' beliefs about the truth state of the memory content. This topic is also relevant to the study of processes of control over retrieval.

The study of memory is witnessing a spirited clash between proponents of traditional laboratory research and those advocating a more naturalistic approach to the study of “real-life” or “everyday” memory. The debate has generally centered on the “what” (content), “where” (context), and “how” (methods) of memory research. In this target article, we argue that the controversy discloses a further, more fundamental breach between two underlying memory metaphors, each having distinct implications for memory theory and assessment: Whereas traditional memory research has (...) been dominated by thestorehousemetaphor, leading to a focus on thenumberof items remaining in store and accessible to memory, the recent wave of everyday memory research has shifted toward acorrespondencemetaphor, focusing on theaccuracyof memory in representing past events. The correspondence metaphor calls for a research approach that differs from the traditional one in important respects: in emphasizing the intentional –representational function of memory, in addressing the wholistic and graded aspects of memory correspondence, in taking an output-bound assessment perspective, and in allowing more room for the operation of subject-controlled metamemory processes and motivational factors. This analysis can help tie together soine of the what, where, and how aspects of the “real-life/laboratory” controversy. More important, however, by explicating the unique metatheoretical foundation of the accuracy-oriented approach to memory we aim to promote a more effective exploitation of the correspondence metaphor inbothnaturalistic and laboratory research contexts. (shrink)

Quantitative losses of memory content imply replicative processing; correspondence losses imply reconstructive processing. Research should focus on the relationship between these processes by obtaining accuracy- and quantity-based indicators of memory within the same framework. This approach will also yield information about the effects of task and individual-difference variables on loss and distortion, as well as the time course of each process.

A major problem in developing an effective gene therapy for the nervous system lies in understanding the principles that maintain or turn off the expression of genes following their transfer into the CNS.

In addition to the scientific and medical issues surrounding the use of fetal tissue transplants, the ethical implications should be considered. Two major ethical issues are relevant. The first of these is whether this experimental procedure can be justified on the basis of potential benefit to the patient. The second is whether the use of tissue obtained from intentionally aborted fetuses can be justified in the context of historical and existing guidelines for the protection of human subjects. The separation of (...) ethical decisions from medical practice and scientific research is necessary to prevent the exploitation of innocent human life. (shrink)

The spinal cord provides an alternative model for nerve tissue grafting experiments. Anatomo-functional correlations are easier to make here than in any other region of the CNS because of a direct implication of spinal cord neurons in sensorimotor activities. Lesions can be easily performed to isolate spinal cord neurons from descending inputs. The anatomy of descending monoaminergic systems is well defined and these systems offer a favourable paradigm for lesion-graft experiments.

Grafts of embryonic neural tissue into the brains of adult patients are currently being used to treat Parkinson's disease and are under serious consideration as therapy for a variety of other degenerative and traumatic disorders. This target article evaluates the use of transplants to promote recovery from brain injury and highlights the kinds of questions and problems that must be addressed before this form of therapy is routinely applied. It has been argued that neural transplantation can promote functional recovery through (...) the replacement of damaged nerve cells, the reestablishment of specific nerve pathways lost as a result of injury, the release of specific neurotransmitters, or the production of factors that promote neuronal growth. The latter two mechanisms, which need not rely on anatomical connections to the host brain, are open to examination for nonsurgical, less intrusive therapeutic use. Certain subjective judgments used to select patients who will receive grafts and in assessment of the outcome of graft therapy make it difficult to evaluate the procedure. In addition, little long-term assessment of transplant efficacy and effect has been done in nonhuman primates. Carefully controlled human studies, with multiple testing paradigms, are also needed to establish the efficacy of transplant therapy. (shrink)

By utilizing new information from both clinical and experimental (lesion, electrophysiological, and gene-activation) studies with animals, the anatomy underlying anterograde amnesia has been reformulated. The distinction between temporal lobe and diencephalic amnesia is of limited value in that a common feature of anterograde amnesia is damage to part of an comprising the hippocampus, the fornix, the mamillary bodies, and the anterior thalamic nuclei. This view, which can be traced back to Delay and Brion (1969), differs from other recent models in (...) placing critical importance on the efferents from the hippocampus via the fornix to the diencephalon. These are necessary for the encoding and, hence, the effective subsequent recall of episodic memory. An additional feature of this hippocampalanterior thalamic and the perirhinal–medial dorsal thalamic systems are compromised, leading to severe deficits in both recall and recognition. (shrink)

This commentary elaborates on Gray's conclusion that his neurophysiological model of consciousness might explain how consciousness arises from the brain, but does not address how consciousness evolved, affects behaviour or confers survival value. The commentary argues that such limitations apply to all neurophysiological or other third-person perspective models. To approach such questions the first-person nature of consciousness needs to be taken seriously in combination with third-person models of the brain.

A lesion to the brain is not necessary for a successful neural transplantation. Embryonic Purkinje cells placed on the surface of an uninjured adult cerebellum can develop and migrate into the host molecular layer. Both the Purkinje cells that migrated into the host cerebellum and those that remained in the graft were innervated by collateral sprouting of adult intact climbing fibers.

The correspondence view is consistent with a theory of direct remembering that assumes continuity between perception and memory. Two implications of direct remembering for correspondence are suggested. It is assumed that forgetting is exponential, and that remembering at one time is independent of factors influencing remembering at another. Elaboration of the correspondence view in the same terms as perception offers a novel approach to the study of memory.

In Gray's conjecture, mismatches in the subicular comparator and matches have equal prominence in consciousness. In rival cognitive views novelty and difficulty especially elicit more conscious modes of cognition and higher levels of self-regulation. The mismatch between Gray's conjecture and these views is discussed.

This commentary is divided into two parts. The first considers a possible role for Gray's predictor plus comparator mechanism in human episodic recognition memory. It draws on the computational specifications of recognition outlined in Humphreys et al. to demonstrate how the logically necessary components of recognition tasks might be mapped onto the mechanism. The second part demonstrates how the mechanism outlined by Gray might be implicated in a form of imitative learning suitable for the acquisition of complex tasks.

Everyday memory tasks often require that researchers focus on output-bound measures of memory. As a result, nonmemorial processes (e.g., report option and grain size) may influence recall accuracy. These nonmemorial processes, usually eliminated by laboratory researchers, have the potential to explain some anomalous results and may even be useful to enhance everyday recollection.

Gray's integration of the different levels of description and explanation in his theory is problematic: The introduction of consciousness into his theorising consists of the mind-brain identity assumption, which tells us nothing new. There need not be correlations between levels of description. Gray's account does not extend beyond “brute” correlation. Integration must be achieved in a principled, mutually constraining way.

The comparator model is insufficient for three reasons. First, consciousness is involved in the process of comparison as well as in the output. Second, we still do not have enough neurophysiological information to match the events of consciousness, although such knowledge is growing. Third, the anatomical localisation proposed can be damaged bilaterally but consciousness will persist.

Koriat & Goldsmith propose that the correspondence metaphor captures the essence of everyday memory research. We suggest that correspondence is often not at issue because objective assessments of everyday events are frequently lacking. In these cases, other questions arise, such as how individuals evaluate the validity of memories and the significance they attach to those evaluations.

The function of memory is to allow past experience to subserve present goal-oriented thought and action. The defining characteristic of goal-oriented approach/avoidance is value. Value lies beyond the reproductive conception of memory that is basic to both metaphors discussed in Koriat & Goldsmith's target article. Functional memory requires a quite different metaphor, for which a grounded theory is available.

Koriat & Goldsmith's distinction between encoding processes and metamnemonic decision processes is theoretically and practically important, as is their methodology for separating the two. However, their accuracy measure is a conditional statistic, subject to the unfathomable selection effects that have hindered analogous measures in the past. We also find their arguments concerning basic and applied research mostly beside the point.

Gene therapy approaches have great promise in the treatment of neurodegenerative disorders and malignant brain tumors. Neuwelt et al. review available viral-mediated gene therapy methods and their blood-brain-barrier (BBB) disruption delivery technique, briefly mentioning nonviral mediated gene therapy methods. This commentary discussed the BBB disruption delivery technique, viral and nonviral mediated gene therapy approaches to Parkinson's disease, and the potential use of antisense oligo to suppress malignant brain tumors.

The neural transplantation research described by Sinden and colleagues provides part of the rationale for the clinical application of neural transplantation. The authors are asked to clarify their view of the role of the cholinergic system in cognition, to address extrahippocampal damage caused by transient forebrain ischemia, and to consider the effects of delayed neural degeneration in their structure-function analysis.

This commentary reviews data supporting circuitry reconstruction, replacement neurotransmitters, and trophic action as mechanisms whereby transplants promote recovery of function. Issue is taken with the thesis of Sinden et al. that adequate data exist to indicate that reconstruction of hippocampal circuitry damaged by hypoxia with CA1 transplants is a confirmed mechanism whereby these transplants produce recovery. Sinden et al.'s and Stein & Glasier's proposal that there is definitive evidence showing that all transplants produce trophic effects is also questioned.

It is well established that neural grafts can exert functional effects on the host animal by a multiplicity of different mechanisms – by diffuse release of trophic molecules, neurohormones, and deficient neurotransmitters, as well as by growth and reformation of neural circuits. Our challenge is to understand how these different mechanisms complement each other.

To explore the mechanism of sensation correlations between EP component amplitude and signal detection indices were studied. The time of sensation coincided with the peak latency of those EP components that showed a correlation with both indices. The components presumably reflected information synthesis in projection cortical neurons. A mechanism providing the synthesis process is proposed.

The value of accuracy and quantity as memory measures is assessed. It is argued that (1) accuracy does not measure correspondence (monitoring) because it ignores omissions and correct rejections, (2) quantity is confounded with monitoring in recall, and (3) in recognition, if targets and foils are unequal, both measures, even together, still ignore correct rejections.

Gray's comparator model fails to provide an adequate explanation of consciousness for two reasons. First, it is based on a narrow definition of consciousness that excludes basic phenomenology and active functions of consciousness. Second, match/mismatch decisions can be made without producing an experience of consciousness. The model thus violates the sufficiency criterion.

On the basis of neuropsychological evidence, it is clear that attention should be given a role in any model of consciousness. What is known about the many instances of dissociation between explicit and implicit knowledge after brain damage suggests that conscious experience might not be linked to a restricted area of the brain. Even if it were true that there is a single brain area devoted to consciousness, the subicular area would seem to be an unlikely possibility.

The work of Sinden et al. suggests that it may be possible to produce improvement in the areas of brain function by transplanting brain tissue. What appears to be the limiting factor is not the complexity of the mental process under consideration but the discreteness of the lesion which causes the impairment and the appropriateness and accuracy of placement of the grafted tissue.

Nissen and Bullemer's serial reaction time task has proven to be a useful model task for exploring implicit sequence learning. Neuropsychological research indicates that SRT learning may depend on the integrity of the basal ganglia, but not on medial temporal and diencephalic structures that are crucial for explicit learning. Recent neuroimaging research demonstrates that motor cortical areas , prefrontal, and parietal cortex also may be involved. This paper reviews this neuropsychological and neuroimaging research, but finds it lacking specific links between (...) structure and function. In order to promote better functional hypotheses, the second part of the paper examines the function of these brain areas from a broader perspective. Neuroimaging and neuropsychological research with human subjects, as well as neurophysiological and lesion research with animals, suggests a number component operations that these brain mechanisms may contribute to learning in the SRT task. (shrink)

Drawing on previous models of anxiety, intermediate memory, the positive symptoms of schizophrenia, and goal-directed behaviour, a neuropsychological hypothesis is proposed for the generation of the contents of consciousness. It is suggested that these correspond to the outputs of a comparator that, on a moment-by-moment basis, compares the current state of the organism's perceptual world with a predicted state. An outline is given of the information-processing functions of the comparator system and of the neural systems which mediate them. The hypothesis (...) appears to be able to account for a number of key features of the contents of consciousness. However, it is argued that neitherthis nor any existing comparable hypothesis is yet able to explain why the brain should generate conscious experience of any kind at all. (shrink)

Compositionality has been a central concept in linguistics and philosophy for decades, and it is increasingly prominent in many other areas of cognitive science. Its status, however, remains contentious. Here, I reassess the nature and scope of the principle of compositionality (Partee, 1995) from the perspective of psycholinguistics and cognitive neuroscience. First, I review classic arguments for compositionality and conclude that they fail to establish compositionality as a property of human language. Next, I state a new competence argument, acknowledging the (...) fact that any competent user of a language L can assign to most expressions in L at least one meaning which is a functiononlyof the meanings of the expression's parts and of its syntactic structure. I then discuss selected results from cognitive neuroscience, indicating that the human brain possesses the processing capacities presupposed by the competence argument. Finally, I outline a language processing architecture consistent with the neuroscience results, where semantic representations may be generated by a syntax‐driven streamandby an “asyntactic” processing stream, jointly or independently. Compositionality is viewed as a constraint on computation in the former stream only. (shrink)

The transplantation of cholinergic neurons into the hippocampal formation has been well characterized. We describe our studies on the effects of cholinergic transplants in the retrosplenial cortex. These transplants were capable of ameliorating spatial navigation deficits in rats with septohippocampal lesions. In addition, we provide evidence for the modulation of transplanted neurons by the host brain.

Various apparently incompatible theories of hippocampal function have been proposed but integration is now needed. It is argued that the involvement of the hippocampus is most clearly seen when the animal needs to extrapolate beyond current sensory information. Such control can involve both the initiation of behaviour in the absence of appropriate sensory input and the inhibition of behaviour that might otherwise be triggered by current sensory input.

Classical antiquity provides not just the storehouse metaphor, which postdates Plato, but also parts of the correspondence metaphor. In the fifth century B.C., Thucydides (1.22) considered the role of gist and accuracy in writing history, and Aristotle (Poetics1451b, 1460b 8–11) offered an explanation. Finally, the Greek for truth (alêtheia) means “that which is not forgotten.”.

Koriat & Goldsmith's distinction between the correspondence and storehouse metaphors is valuable for both memory theory and methodology. It is questionable, however, whether this distinction underlies the heated debate about so called “everyday memory” research. The distinction between experimental and naturalistic methodologies better characterizes this debate. I compare these distinctions and discuss how the methodological distinction, between experimental and naturalistic designs, could give rise to different theoretical approaches.

The correspondence view of memory is not a metaphor. However, correspondence is the essential feature of the archaeology metaphor, which harks back to Freud and Neisser. A modern version of this metaphor and some of its implications are briefly described. The archaeology metaphor integrates the idea of stored traces in a nonmechanistic framework.

Koriat & Goldsmith are right in their claim that the “ecological” and “traditional” approaches to memory rely on different metaphors. But the underlying ecological metaphor is notcorrespondence(which in any case is not a metaphorical notion): it isaction. Remembering is a kind of doing; like most other forms of action it is purposive, personal, and particular.

Investigations of metacognition – and also the application of the storehouse and correspondence metaphors – seem as appropriate for laboratory research as for naturalistic research. In terms of measurement, the only quantitative difference between the “input-bound percent correct” and “output-bound percent correct” is the inclusion versus exclusion (respectively) of omission errors in the denominator of the percentages.