Short-term memory and sentence processing: Evidence from neuropsychology

Traditional models of memory assume that short-term memory, as measured by memory span, plays an important role in linguistic processing and the learning ofverbal information. Contradicting this view are findings from a brain-damaged patient, E.A., who, despite a verbal memory span of about two items, demonstrated normal sentence comprehension in a variety oftasks. She was, however, impaired whenever verbatim phonological information had to be maintained or learned. These results and those from other patients with reduced span suggest that the phonological storage capacity that is critical to memory span plays only a limited role in language processing, specifically in the maintenance and learning of phonological forms. Implications for models of short-term memory are discussed. It is argued that short-termmemory should be seen as deriving from the processing and retentive capacities of language processing modules, with span tasks drawing on only a subset of these modules.     

Autonomic and behavioral evidence of "implicit" memory in amnesia

A profoundly amnesic patient with a left retrosplenial-fornix lesion was tested on a recognition task that evaluated both verbal and electrodermal aspects of new learning. In addition, "implicit memory" tasks (mirror reading and perceptual identification) were given. The patient displayed strong evidence of learning on all tasks although the results of this learning were not represented in explicit recall or recognition. These findings suggest that autonomic as well as behavioral evidence can index spared memory functions in amnesia. The specific meaning of electrodermal recognition and its possible place in the distinction between implicit and explicit memory is discussed.     

Focus identification during sentence comprehension: evidence from eye movements

Three eye movement experiments investigated focus identification during sentence comprehension. Participants read dative or double-object sentences (i.e., either the direct or indirect object occurred first), and a replacive continuation supplied a contrast that was congruous with either the direct or the indirect object. Experiments 1 and 2 manipulated focus by locating only adjacent to either the direct or indirect object of dative (Experiment 1) or double-object (Experiment 2) sentences. Reading-time effects indicated that the surface position of the focus particle influenced processing. In addition, Experiment 1 reading times were longer when the replacive was incongruous with the constituent that only adjoined, and particle position modulated a similar effect in Experiment 2. Experiment 3 showed that this effect was absent when only was omitted. We conclude that the surface position of a focus particle modulates focus identification during on-line sentence comprehension.     

Midazolam amnesia and retrieval from semantic memory: Developing methods to test theories of implicit memory

Studies of organic anterograde amnesia have been central to the development of theories of implicit memory. Pharmacological amnesia provides an additional method for exploring implicit memory, allowing for the experimental manipulation of amnesia and the testing of more participants. A significant concern with pharmacological amnesia is whether its cognitive effects are specific to explicit memory. The current research examines the effects of the benzodiazepine, midazolam, on retrieval from semantic memory and encoding in explicit memory. We focus on midazolam because it holds significant advantages over other benzodiazepines in inducing pharmacological amnesia and prior research suggests it may be useful for testing theories of implicit memory. Our results demonstrate that midazolam does not impair accuracy of retrieval from semantic categories, even when it produces anterograde amnesia for retrieved category items on a later recall test. These results suggest ways midazolam can be used to help test theories of implicit memory.     

Distinguishing states of awareness from confidence during retrieval: evidence from amnesia

Two experiments were conducted to determine whether recollective experience is distinguishable from confidence. In Experiment 1, we tested college participants in a within-subjects design and replicated Gardiner and Java's (1990) findings from a between-subjects design. We observed higher remember judgments for words than for nonwords, but higher know judgments for nonwords than for words. For confidence judgments, we obtained greater sure than unsure responses for both words and nonwords. In Experiment 2, we tested amnesic participants and matched control participants. Control participants produced the same pattern of results as college participants, but the results of amnesic participants diverged in an important way. For confidence judgments, the amnesic participants, like the control and college participants, made more sure than unsure judgments to both words and nonwords. But for recollective judgments, amnesic participants did not produce the crossover interaction for words and nonwords. This striking difference between the performance of memory-intact and amnesic participants demonstrates that recollective judgments and confidence that accompany retrieval are not isomorphic psychological experiences.     

Verbal working memory and sentence comprehension

This target article discusses the verbal working memory system used in sentence comprehension. We review the concept of working memory as a short-duration system in which small amounts of information are simultaneously stored and manipulated in the service of accomplishing a task. We summarize the argument that syntactic processing in sentence comprehension requires such a storage and computational system. We then ask whether the working memory system used in syntactic processing is the same as that used in verbally mediated tasks that involve conscious controlled processing. Evidence is brought to bear from various sources: the relationship between individual differences in working memory and individual differences in the efficiency of syntactic processing; the effect of concurrent verbal memory load on syntactic processing; and syntactic processing in patients with poor short-term memory, patients with poor working memory, and patients with aphasia. Experimental results from these normal subjects and patients with various brain lesions converge on the conclusion that there is a specialization in the verbal working memory system for assigning the syntactic structure of a sentence and using that structure in determining sentence meaning that is separate from the working memory system underlying the use of sentence meaning to accomplish other functions. We present a theory of the divisions of the verbal working memory system and suggestions regarding its neural basis.     

Two modality effects in verbal short-term memory: Evidence from sentence recall

This paper investigates the mechanisms underlying the standard modality effect (i.e., better recall performance for auditorily presented than for visually presented materials), and the modality congruency effect (i.e., better memory performance if the mode of recall and presentation are congruent rather than incongruent). We tested the assumption that the standard modality effect is restricted to the most recent word(s) of the sentences but occurs in both verbatim and gist recall (Experiments 1 and 2), whereas the modality congruency effect should be evident for the rest of the sentence when using verbatim recall (Experiment 3) but not when using gist recall (Experiment 4). All experiments used the Potter-Lombardi intrusion paradigm. When the target word was the most recent word of the sentence, a standard modality effect was found with both verbatim recall and gist recall. When the target word was included in the middle of the sentences, a modality congruency effect was found with verbatim recall but not with gist recall.     

Recovery of memory from infantile amnesia is developmentally constrained

Episodic memories formed during infancy are rapidly forgotten, a phenomenon associated with infantile amnesia, the inability of adults to recall early-life memories. In both rats and mice, infantile memories, although not expressed, are actually stored long term in a latent form. These latent memories can be reinstated later in life by certain behavioral reminders or by artificial reactivations of neuronal ensembles activated at training. Whether the recovery of infantile memories is limited by developmental age, maternal presence, or contingency of stimuli presentation remains to be determined. Here, we show that the return of inhibitory avoidance memory in rats following a behavioral reactivation consisting of an exposure to the context (conditioned stimuli [CS]) and footshock (unconditioned stimuli [US]) given in a temporally unpaired fashion, is evident immediately after US and is limited by the developmental age at which the reactivations are presented; however, it is not influenced by maternal presence or the time interval between training and reactivation. We conclude that one limiting factor for infantile memory reinstatement is developmental age, suggesting that a brain maturation process is necessary to allow the recovery of a “lost” infantile memory.

Hippocampus-dependent episodic memories formed early in life are rapidly forgotten. This process of forgetting is evolutionarily conserved and is associated with infantile amnesia, the inability of adults to recall early-life memories (Campbell and Spear 1972; Rovee-Collier 1999; Hayne 2004; Josselyn and Frankland 2012; Callaghan et al. 2014; Madsen and Kim 2016; Alberini and Travaglia 2017).Although they are rapidly forgotten, early-life experiences influence brain functions throughout life (Jacobs and Nadel 1985; Meaney et al. 1988; Sroufe et al. 1990; Brunson et al. 2005; Pryce et al. 2005; Mineka and Zinbarg 2006; Bale et al. 2010; Poulos et al. 2014; Perry and Sullivan 2014) and produce long-lasting biological changes in the brain. For example, aversive early-life experiences regulate the expression of hippocampal glucocorticoid receptor and hypothalamic–pituitary–adrenal (HPA) functions in a persistent fashion (Champagne and Curley 2009). Moreover, threatening experiences in early life can predispose individuals to psychopathologies such as post-traumatic stress disorder (PTSD) and mood and anxiety disorders (Heim and Nemeroff 2001). Consistent with this long-lasting influence on behavior, studies in rodent models have shown that, in contrast to what was previously believed, memories formed in infancy (at postnatal days 16–18 [PN16–PN18]) although not expressed, are not lost. Rather, they are stored over the longer term in a latent form and can reemerge at later times, up to adulthood, following behavioral reactivations or artificial stimulation of the neuronal ensembles activated at learning (Travaglia et al. 2016; Guskjolen et al. 2018; Bessières et al. 2020).In our previous studies based on rat inhibitory avoidance (IA), a paradigm in which the animal learns to avoid a context previously paired with a footshock, we confirmed that an infantile episodic learning event given at PN17 resulted in the typical rapid forgetting. We then found that, however, this memory was stored long term in a latent form, as demonstrated by the observation that it could reemerge following a behavioral reactivation consisting of exposure to the training context (conditioned stimulus [CS]) and a later time footshock of the same intensity that was used during training (unconditioned stimulus [US]) but now given in a distinct context. Reexperiencing either the context or the footshock alone failed to reinstate the infantile memory (Travaglia et al. 2016), suggesting that the return of infantile memory is limited by certain boundaries.Several questions about the conditions for the recovery of latent, infantile episodic memories remain to be addressed. First, is infantile memory reinstatement following the unpaired US presentation temporally regulated? Second, is there an age limit for memory reinstatement? Third, given that other types of learning, such as non-hippocampus-dependent cued conditioning, are regulated by the maternal presence during infancy (Moriceau and Sullivan 2006), is infantile episodic memory reinstatement limited or regulated by the presence of the mother? In this study, we set out to address these questions using IA in infant rats.     

Multiple memory systems: evidence from stroke

In this report, we describe the "fractionation of memory systems" in a 62-yr.-old woman following a left anterior stroke. Despite the presence of a significant, persistent declarative memory (verbal learning) deficit, this patient exhibited relatively intact procedural learning. The latter was manifested over a 4-day period by improved performance on a maze task executed under "mirror-tracing" conditions. By the final set of trials, the patient's performance approximated that of a normal control subject with respect to speed, although not errors. The selective preservation of particular learning abilities in brain-damaged patients has implications for rehabilitative interventions.     

Cued recall from image and sentence memory: a shift from episodic to identical elements representation

The applicability of the identical elements (IE) model of arithmetic fact retrieval (T. C. Rickard, A. F. Healy, & L. E. Bourne, 1994) to cued recall from episodic (image and sentence) memory was explored in 3 transfer experiments. In agreement with results from arithmetic, speedup following even minimal practice recalling a missing word from an episodically bound word triplet did not transfer positively to other cued recall items involving the same triplet. The shape of the learning curve further supported a shift from episode-based to IE-based recall, extending some models of skill learning to cued recall practice. In contrast with previous findings, these results indicate that a form of representation that is independent of the original episodic memory underlies cued-recall performance following minimal practice.     

The allocation of memory resources during sentence comprehension: Evidence from the elderly

Two experiments were carried out to examine the ability of elderly subjects to establish syntactically governed dependency relations during the course of sentence comprehension. The findings reveal the manner in which memory constraints operate during syntactic processing.     

Episodic representations support early semantic learning: evidence from midazolam induced amnesia

Current controversy exists regarding the role of episodic representations in the formation of long-term semantic memories. Using the drug midazolam to induce temporary amnesia we tested participants' memories for newly learned facts in a semantic cue condition or an episodic and semantic cue condition. Following midazolam administration, memory performance was superior in the episodic and semantic condition, suggesting early semantic learning is supported by episodic representations.     

Kinetic and static imagery in sentence memory

This experiment investigates the possibility that two different kinds of imagery codes are used in sentence memory, one involving moving images (kinetic imagery) and the other involving stationary images (static imagery). Using a modality-specific interference task it was shown that only sentences involving kinetic imagery were affected by the visual interference task; neither static nor low imagery sentences were so affected. The results are interpreted as showing that some kind of imaginal code is used in memory, but that there are different kinds of code available. It is claimed that this result is inconsistent both with Paivio's (1971) ‘dual-coding’ hypothesis and with propositional accounts of sentence memory.     

Working memory and planning during sentence production

Speakers retrieve conceptual, syntactic and lexical information in advance of articulation during sentence production. What type of working memory (WM) store is used to hold the planned information before speaking? To address this question, we measured onset latencies when subjects produced sentences that began with either a complex or a simple initial noun phrase, while holding semantic, phonological or spatial information in WM. Although we found that subjects had longer onset latencies for sentences beginning with a complex noun phrase, showing a phrasal scope of planning, the magnitude of this complexity effect was not affected by any type of WM load. However, subjects made more syntactic errors (but not lexical errors) for sentences beginning with a complex noun phrase, suggesting that advance planning for these phrases occurs at a syntactic rather than lexical–semantic level, which may account for the lack of effect with various types of WM load in the current study.     

Storage and retrieval processes in sentence memory

Two experiments investigated how much time Ss take to verify a sentence with respect to a set of subject-verb-object (SVO) propositions they had learned. Three triplets of SVOs provided differing degrees of equivocation, including (1) unique SVOs, (2) a V with 3 SOs, and (3) an SV with 3 Os. A general class of models was proposed regarding the representation of prepositional trees in memory and an algorithm by which a probe tree might be verified against a set of trees in memory. In Expt I, verification times were least for Condition (1), slower and equal for Conditions (2) and (3). In Expt II, a fourth condition, an SO with 3 Vs, produced verification times as slow as those in Condition (3). Of several models considered, the closest-fitting one assumed parallel search processes proceeding simultaneously from S, V, and O positions of the probe, scanning through memory trees structered according to the HAM (Human Associative Memory) theory of Anderson and Bower.     

Working memory and the control of action: evidence from task switching.

A series of 7 experiments used dual-task methodology to investigate the role of working memory in the operation of a simple action-control plan or program involving regular switching between addition and subtraction. Lists requiring switching were slower than blocked lists and showed 2 concurrent task effects. Demanding executive tasks impaired performance on both blocked and switched lists, whereas articulatory suppression impaired principally the switched condition. Implications for models of task switching and working memory and for the Vygotskian concept of verbal control of action are discussed.     

Long-term memory in amnesia: cued recall, recognition memory, and confidence ratings

We explored what kind of information is acquired when amnesic patients are able to exhibit significant retention on tests of cued recall and recognition memory. Amnesic patients and control subjects attempted to learn sets of sentences. Memory for the last word in each sentence was tested after 1 hr in the case of the amnesic patients, or after 1 to 2 weeks in the case of (delayed) control subjects. Amnesic patients and (delayed) control subjects performed at similar levels on tests of cued recall and recognition memory. Amnesic patients were just as confident of their correct answers as were control subjects. However, amnesic patients were no more disadvantaged than control subjects when they were cued indirectly by presenting paraphrases of the original sentences. These findings demonstrate that the residual knowledge retained by amnesic patients can be as flexible, as accessible to indirect cues, and as available to awareness as the knowledge retained by (delayed) control subjects.