Cowan assumes that chunk-based capacity limits are synonymous with the essence of a “specialized STM mechanism.” In a single experiment, we measured the capacity, or span, of long-term memory and found that it, too, corresponds roughly to the magical number 4. The results imply that a chunk-based capacity limit is not a signature characteristic of remembering over the short-term.

Ruchkin et al. make a strong claim about the neural substrates of active information. Some qualifications on that conclusion are: (1) Long-term memories and neural substrates activated for perception of information are not the same thing; (2) humans are capable of retaining novel information in working memory, which is not long-term memory; (3) the content of working memory, a dynamically bound representation, is a quantity above and beyond the long-term memories activated, (...) or the activity in perceptual substrates. (shrink)

Moderate physiological or emotional arousal induced after learning modulates memory consolidation, helping to distinguish important memories from trivial ones. Yet, the contribution of subjective awareness or interpretation of arousal to this effect is uncertain. Alexithymia, which is an inability to describe or identify one’s emotional and arousal states even though physiological responses to arousal are intact, provides a tool to evaluate the role of arousal interpretation. Participants scoring high and low on alexithymia learned a list of 30 words, followed (...) by immediate recall. Participants then saw either an arousing or neutral video . Memory was tested 24-h later. Physiological response to arousal was comparable between groups, but subjective response to arousal was impaired in high alexithymia. Yet, delayed word recognition was enhanced by arousal regardless of alexithymia status. Thus, subjective response to arousal, i.e., cognitive appraisal, was not necessary for memory modulation to occur. (shrink)

Retrieval practice, relative to further study, leads to long-term memory enhancement known as the “testing effect.” The neurobiological correlates of the testing effect at retrieval, when the learning benefits of testing are expressed, have not been fully characterized. Participants learned Swahili-English word-pairs and were assigned randomly to either the Study-Group or the Test-Group. After a week delay, all participants completed a cued-recall test while undergoing functional magnetic resonance imaging. The Test-Group had superior memory for the word-pairs (...) compared to the Study-Group. While both groups exhibited largely overlapping activations for remembered word-pairs, following an interaction analysis the Test-Group exhibited differential performance-related effects in the left putamen and left inferior parietal cortex near the supramarginal gyrus. The same analysis showed the Study-Group exhibited greater activations in the dorsal MPFC/pre-SMA and bilateral frontal operculum for remembered vs. forgotten word-pairs, whereas the Test-Group showed the opposite pattern of activation in the same regions. Thus, retrieval practice during training establishes a unique striatal-supramarginal network at retrieval that promotes enhanced memory performance. In contrast, study alone yields poorer memory but greater activations in frontal regions. (shrink)

Ruchkin et al. ascribe a pivotal role to long-term memory representations and binding within working memory. Here we focus on the interaction of working memory and long-term memory in supporting on-line representations of experience available to guide on-going processing, and we distinguish the role of frontal-lobe systems from what the hippocampus contributes to relational long-term memory binding.

Neural models have proposed how short-term memory (STM) storage in working memory and long-term memory (LTM) storage and recall are linked and interact, but are realized by different mechanisms that obey different laws. The authors' data can be understood in the light of these models, which suggest that the authors may have gone too far in obscuring the differences between these processes.

We focus on the functional specificity of theta and alpha oscillations and show that theta is related to working memory, whereas alpha is related to semantic long-term memory. Recent studies, however, indicate that alpha oscillations also play an important role during short-term memory retention and retrieval. This latter finding provides support for the basic hypothesis suggested by Ruchkin et al.

The view that short-term memory should be conceived of as being a process based on the activation of long-term memory is inconsistent with neuropsychological evidence. Data from brain-damaged patients, showing specific patterns of impairment, are compatible with a vision of memory as a multiple-component system, whose different aspects, in neurologically unimpaired subjects, show a high degree of interaction.

Subjects classified visible 2-digit numbers as larger or smaller than 55. Target numbers were preceded by masked 2-digit primes that were either congruent (same relation to 55) or incongruent. Experiments 1 and 2 showed prime congruency effects for stimuli never included in the set of classified visible targets, indicating subliminal priming based on long-term semantic memory. Experiments 2 and 3 went further to demonstrate paradoxical unconscious priming effects resulting from task context. For example, after repeated practice classifying (...) 73 as larger than 55, the novel masked prime 37 paradoxically facilitated the “larger” response. In these experiments task context could induce subjects to unconsciously process only the leftmost masked prime digit, only the rightmost digit, or both independently. Across 3 experiments, subliminal priming was governed by both task context and long-term semantic memory. (shrink)

High temporal resolution event-related brain potential and electroencephalographic coherence studies of the neural substrate of short-term storage in working memory indicate that the sustained coactivation of both prefrontal cortex and the posterior cortical systems that participate in the initial perception and comprehension of the retained information are involved in its storage. These studies further show that short-term storage mechanisms involve an increase in neural synchrony between prefrontal cortex and posterior cortex and the enhanced activation of long- (...) class='Hi'>term memory representations of material held in short-term memory. This activation begins during the encoding/comprehension phase and evidently is prolonged into the retention phase by attentional drive from prefrontal cortex control systems. A parsimonious interpretation of these findings is that the long-term memory systems associated with the posterior cortical processors provide the necessary representational basis for working memory, with the property of short-term memory decay being primarily due to the posterior system. In this view, there is no reason to posit specialized neural systems whose functions are limited to those of short-term storage buffers. Prefrontal cortex provides the attentional pointer system for maintaining activation in the appropriate posterior processing systems. Short-term memory capacity and phenomena such as displacement of information in short-term memory are determined by limitations on the number of pointers that can be sustained by the prefrontal control systems. Key Words: coherence; event-related potentials; imaging; long-term memory; memory; short-term memory; working memory. (shrink)

In this paper, we propose a new mathematical model of retrieval of intentions from long-term memory. We model retrieval as a stochastic race between a plurality of potentially relevant intentions stored in long-term memory. Psychological theories are dominated by two opposing conceptions of the role of memory in temporally extended agency – as when a person has to remember to make a phone call in the afternoon because, in the morning, she promised she (...) would do so. According to the Working Memory conception, remembering to make the phone call is explained in terms of the construction and maintenance of intentions in working-memory. According to the Long-Term Memory conception, we should explain the episode in terms of an ability to store intentions in long-term memory. The two conceptions predict different processing profiles. The aim of this paper is to present a new mathematical model of the type of memory mechanism that could realise the long-term memory representations of intentions necessary for the Long-Term Memory conception. We present and illustrate the formal model and propose a new type of experimental paradigm that could allow us to test which of the two conceptions provides the best explanation of the role of memory in temporally extended agency. (shrink)

Episodic memory often is conceptualized as a uniquely human system of long-term memory that makes available knowledge accompanied by the temporal and spatial context in which that knowledge was acquired. Retrieval from episodic memory entails a form of first–person subjectivity called autonoetic consciousness that provides a sense that a recollection was something that took place in the experiencer’s personal past. In this paper I expand on this definition of episodic memory. Specifically, I suggest that (...) (a) the core features assumed unique to episodic memory are shared by semantic memory, (b) episodic memory cannot be fully understood unless one appreciates that episodic recollection requires the coordinated function of a number of distinct, yet interacting, “enabling” systems. Although these systems – ownership, self, subjective temporality, and agency – are not traditionally viewed as memorial in nature, each is necessary for episodic recollection and jointly they may be sufficient, and (c) the type of subjective awareness provided by episodic recollection (autonoetic) is relational rather than intrinsic – i.e., it can be lost in certain patient populations, thus rendering episodic memory content indistinguishable from the content of semantic long-term memory. (shrink)

Recent evidence from our lab indicates that LTP shares an important property with memory consolidation: it is consolidated by natural reinforcement. Nevertheless, the hypothesis, that LTP-like mechanisms or other forms of enhanced synaptic efficacy are basic elements in learning is not unequivocally supported. Skepticism aside, LTP is an accessible experimental model that is optimally equipped for the investigation of the cellular and molecular machinery involved in synaptic weight changes.

As an explicit organizing metaphor, memory aid, and conceptual framework, the prefrontal cortex may be viewed as a five-member ‘Executive Committee,’ as the prefrontal-control extensions of five sub-and-posterior-cortical systems: the ‘Perceiver’ is the frontal extension of the ventral perceptual stream which represents the world and self in object coordinates; the ‘Verbalizer’ is the frontal extension of the language stream which represents the world and self in language coordinates; the ‘Motivator’ is the frontal cortical extension of a subcortical extended-amygdala stream (...) which represents the world and self in motivational/emotional coordinates; the ‘Attender’ is the frontal cortical extension of a subcortical extended-hippocampal stream which represents the world and self in spatiotemporal coordinates and directs attention to internal and external events; and the ‘Coordinator’ is the frontal extension of the dorsal perceptual stream which represents the world and self in body- and eye-coordinates and controls willed action and working memory. This tutorial review examines the interacting roles of these five systems in perception, working memory, attention, long - term memory, motor control, and thinking. (shrink)

With reference to Ruchkins et al.'s framework, this commentary briefly considers the history of working memory, and whether, heuristically, this is a useful concept. A neuropsychologically motivated critique is offered, specifically with regard to the recent trend for working-memory researchers to conceptualise this capacity more as a process than as a set of distinct task-specific stores.

This study examined the effect of an interference task on the consolidation of duration in long-term memory. In a temporal generalization task, the participants performed a learning phase with a reference duration that either was, or was not, followed 30 minutes later by a 15-min interference task. They were then given a memory test, 24h later. Using different participant groups, several reference durations were examined, from several hundred milliseconds (600ms) to several seconds (2.5, 4 and 8s). (...) The results showed that the scalar timing property (i.e. precision proportional to judged duration) was preserved despite the interference task given during the memory consolidation process. However, the interference task increased the variability of time judgment and tended to produce a lengthening effect in all reference duration conditions. The modeling of individual data with parameters derived from scalar expectancy theory suggests that disrupting the memory consolidation of learned reference durations introduces noise in their representation in memory, with time being specifically distorted towards a lengthened duration. (shrink)

How much information from experience does a normal adult remember? The “functional information content” of human memory was estimated in several ways. The methods depend on measured rates of input and loss from very long‐ term memory and on analyses of the informational demands of human memory‐based performance. Estimates ranged around 109 bits. It is speculated that the flexible and creative retrieval of facts by humans is a function of a large ratio of “hardware” capacity (...) to functional storage requirements. (shrink)

Phenomenal reports were obtained immediately after participants retrieved information from long-term memory. Data were gathered for six basic forms of memory and for three forms of memory that asked for declarative information about procedural tasks . The data show consistent reports of mental imagery during retrieval of information from the generic perceptual, recollective, motor—declarative, rote—declarative, and cognitive—declarative categories; much less imagery was reported for the semantic, motor, rote, and cognitive categories. Overall, the data provide support (...) for the theoretical framework outlined in Brewer and Pani. (shrink)