Consequences of a phonological coding deficit on sentence processing

The role of verbal short-term memory in complex sentence comprehension: An observational study on aphasia

BACKGROUND

The comprehension profile of people with agrammatism is a debated topic. Syntactic complexity and cognitive resources, in particular phonological short-term memory (pSTM), are considered as crucial components by different interpretative accounts.

AIM

To investigate the interaction of syntactic complexity and of pSTM in sentence comprehension in a group of persons with aphasia with and without agrammatism.

METHODS & PROCEDURES

A cohort of 30 participants presenting with aphasia was assessed for syntactic comprehension and for pSTM. A total of 15 presented with agrammatism and 15 had fluent aphasia.

OUTCOMES & RESULTS

Linear nested mixed-model analyses revealed a significant interaction between sentence type and pSTM. In particular, participants with lower pSTM scores showed a reduced comprehension of centre-embedded object relatives and long coordinated sentences. Moreover, a significant interaction was found between sentence type and agrammatism, with a lower performance for passives within the agrammatic group.

CONCLUSIONS & IMPLICATIONS

These results confirm that pSTM is involved in the comprehension of complex structures with an important computational load, in particular coordinated sentences, and long-distance filler gap dependencies. On the contrary, the specific deficit of the agrammatic group with passives is a pure syntactic deficit, with no involvement of pSTM.

Sentence Recall in Latent and Anomic Aphasia: An Exploratory Study of Semantics and Syntax

We investigated whether semantic plausibility and syntactic complexity affect immediate sentence recall in people with latent and anomic aphasia. To date, these factors have not been explored in these types of aphasia. As with previous studies of sentence recall, we measured accuracy of verbatim recall and uniquely real-time speech measures. The results showed that accuracy did not distinguish performance between latent aphasia and neurotypical controls. However, some of the real-time speech measures distinguished performance between people with latent aphasia and neurotypical controls. There was some evidence, though not pervasive, that semantic plausibility and syntactic complexity influenced recall performance. There were no interactions between semantic plausibility and syntactic complexity. The speed of preparation of responses was slower in latent aphasia than controls; it was also slower in anomic aphasia than both latent and control groups. It appears that processing speed as indexed by temporal speech measures may be differentially compromised in latent and anomic aphasia. However, semantic plausibility and syntactic complexity did not show clear patterns of performance among the groups. Notwithstanding the absence of interactions, we advance an explanation based on conceptual short-term memory as to why semantically implausible sentences are typically more erroneous and possibly also slower in recall.

Verbal memory and sentence comprehension in aphasia: A case series

This case series explores the relationship between verbal memory capacity and sentence comprehension in four patients with aphasia. Two sentence comprehension tasks showed that two patients, P1 and P2, had impaired syntactic comprehension, whereas P3 and P4's sentence comprehension was intact. The memory assessment tasks showed that P1 and P2 had severely impaired short-term memory, whereas P3 and P4 performed within the normal range in the short-term memory tasks. This finding suggests an association between short-term memory deficit and sentence comprehension difficulties. P1 and P3 exhibited impaired comparable working memory deficits, suggesting a dissociation between working memory and sentence comprehension.

Neural processing critical for distinguishing between speech sounds

We aimed to identify neural regions where ischemia acutely after stroke is associated with impairment in phoneme discrimination, and to determine whether such deficits are associated with impairment of spoken word comprehension. We evaluated 33 patients within 48 h of left hemisphere ischemic stroke onset with tests of phoneme discrimination and word-picture matching. We identified Pearson correlations between accuracy in phoneme discrimination and accuracy of word comprehension and identified areas where the percentage of infarcted tissue was associated with severity of phoneme discrimination deficit. We found that 54% had deficits in phoneme discrimination relative to healthy controls. Accuracy in phoneme discrimination correlated with accuracy on word comprehension tests. Damage to left intraparietal sulcus and hypoperfusion and/or infarct of left superior temporal gyrus were associated with phoneme discrimination deficits acutely, although patients with these lesions showed improvement or resolution of the deficit by six months.

Phonology, Lexical Access in Reading, and Articulatory Suppression: A Critical Review

Considerable confusion exists in the literature on visual word recognition and reading with respect to the effects of articulatory suppression upon phonological recoding. The authors of a large number of journal articles, chapters, cognitive psychology textbooks, and books devoted to reading processes have concluded that suppression interferes with phonological receding of print and have used this supposed fact as a basis for determining when phonology is involved in various reading tasks. Others have concluded that suppression need not interfere with phonological recoding (e.g. Besner, Davies and Daniels, 1981; Besner and Davelaar, 1982). The present review concludes that a phonological code can be derived from printed English and used for lexical access without interference from suppression. However, operations performed upon a phonological code—e.g. post-assembly phonemic segmentation and deletion, maintenance in working memory—are disrupted by suppression. A review of the literature supports this distinction; some implications of these views are noted.

Role for Memory Capacity in Sentence Comprehension: Evidence from Acute Stroke

BACKGROUND

Previous research has suggested that short-term and working memory resources play a critical role in sentence comprehension, especially when comprehension mechanisms cannot rely on semantics alone. However, few studies have examined this association in participants in acute stroke, before the opportunity for therapy and reorganization of cognitive functions.

AIMS

The present study examined the hypothesis that severity of short-term memory deficit due to acute stroke predicts the severity of impairment in the comprehension of syntactically complex sentences. Furthermore, we examined the association between damage to the short-term and working memory network and impaired sentence comprehension, as an association would be predicted by the previous hypothesis.

METHODS & PROCEDURES

47 participants with acute stroke and 14 participants with a transient ischemic attack (TIA; the control group) were included in the present study. Participants received a language battery and clinical or research scans within 48 hours of hospital admittance. The present study focused on the behavioral data from the short-term memory and working memory span tasks and a sentence-picture matching comprehension task included in this battery. Using regression analyses, we examined whether short-term and working memory measures explained significant variance in sentence comprehension performance.

OUTCOMES & RESULTS

Consistent with prior research, short-term memory explained significant variance in sentence comprehension performance in acute stroke; in contrast, working memory accounted for little variance beyond that which was already explained by short-term memory. Furthermore, ischemia that included the short-term/working memory network was sufficient to cause sentence comprehension impairments for syntactically complex sentences.

CONCLUSIONS

The present study suggests that short-term memory resources are an important source of sentence comprehension impairments.

The Role of Broca's Area in Sentence Comprehension

The role of Broca's area in sentence processing has been debated for the last 30 years. A central and still unresolved issue is whether Broca's area plays a specific role in some aspect of syntactic processing (e.g., syntactic movement, hierarchical structure building) or whether it serves a more general function on which sentence processing relies (e.g., working memory). This review examines the functional organization of Broca's area in regard to its contributions to sentence comprehension, verbal working memory, and other multimodal cognitive processes. We suggest that the data are consistent with the view that at least a portion of the contribution of Broca's area to sentence comprehension can be attributed to its role as a phonological short-term memory resource. Furthermore, our review leads us to conclude that there is no compelling evidence that there are sentence-specific processing regions within Broca's area.

Short-term and working memory impairments in aphasia

The aim of the present study is to investigate short-term memory and working memory deficits in aphasics in relation to the severity of their language impairment. Fifty-eight aphasic patients participated in this study. Based on language assessment, an aphasia score was calculated for each patient. Memory was assessed in two modalities, verbal and spatial. Mean scores for all memory tasks were lower than normal. Aphasia score was significantly correlated with performance on all memory tasks. Correlation coefficients for short-term memory and working memory were approximately of the same magnitude. According to our findings, severity of aphasia is related with both verbal and spatial memory deficits. Moreover, while aphasia score correlated with lower scores in both short-term memory and working memory tasks, the lack of substantial difference between corresponding correlation coefficients suggests a possible primary deficit in information retention rather than impairment in working memory.

Phonological short-term memory contributions to sentence processing in young children

Two experiments investigated the contribution of phonological short-term memory to the processing of spoken sentences by 4- and 5-year-old children. In Experiment 1, sentences contained either short or longer words, and varied in syntactic structure. Overall, repetition but not comprehension of the sentences was significantly influenced by word length. In Experiment 2, children selected on the basis of their high phonological short-term memory ability were founded to be superior at repeating sentences to children of lower phonological short-term memory ability, although the two groups did not differ in their comprehension accuracy for the same sentences. In both experiments, comprehension and repetition performance were differently influenced by particular sentence structures. It is proposed that sentence repetition in children is constrained by phonological memory capacity, and is therefore directly influenced by memory-related factors that include the length and number of words in sentences, and individual differences in memory skills.

The relation of phoneme discrimination, lexical access, and short-term memory: A case study and interactive activation account

A brain-damaged patient (AP) is reported who had a strong tendency to identify nonwords as words on auditory lexical decision and to lexicalize nonwords in repetition, yet who showed a normal ability to perceive individual phonemes. It was initially hypothesized that these findings could be accounted for in terms of disrupted lexical phonological representations. This hypothesis was rejected on the basis of an interactive activation model of word recognition which revealed that modifications at the lexical level did not mimic the patient's pattern of results. Instead, it was found that increasing the rate of decay of activation at the phoneme level produced output that was consistent with the phoneme discrimination, lexical decision, and repetition results. This hypothesis of increased phoneme level decay led to the prediction that speech discrimination would decline with increased interstimulus interval and that short-term memory performance would be impaired. Both predictions were confirmed. The results of this study provide support for an interactive activation model of word recognition with feedback from the lexical to the phonemic level and for a close connection between the processes involved in word recognition and short-term memory.

Why is short-term sentence recall verbatim? An evaluation of the role of lexical priming

By showing that short-term sentence recall can be significantly affected by words encountered in an intervening distractor task, Potter and Lombardi (1990, Journal of Memory and Language, 29, 633-654) argue that short-term sentence recall is often verbatim because of the availability of recently activated lexical entries during the regeneration of the sentence from its conceptual representation. We show that similar effects can be obtained even when bilinguals perform an intervening task in a different language from that of sentence recall, or when monolinguals perform an intervening task upon pictures. Furthermore, we show that the presentation of a word in P&L's distractor task does not, in any case, affect subsequent retrieval of a semantically related word as measured in a picture-naming task. We suggest that the effects on recall reported here and by P&L should be explained in terms of conceptual level interference at the time of recall. We also discuss the implications of our suggestion for the issue of the verbatimness of short-term sentence recall.

Sentence imitation by adolescents and young adults with Down's syndrome and other intellectual disabilities

Sentence imitation performance was evaluated longitudinally in 26 adolescents and young adults with Down's syndrome (DS), and 26 age- and IQ-matched non-DS individuals with other causes of intellectual disability (ID). In each of three annual assessments, the DS group began sentence repetitions more slowly and imitated sentences less accurately than the ID group. DS sentence repetition accuracy was equivalent to the ID group only for two-word sentences and was poorer for every other sentence length. Comparisons of sentence imitation and auditory digit span scores suggested that only ID subjects benefitted from the additional meaning and structure provided by sentences. Correlational analyses performed between each year's sentence imitation score and a set of language, memory and hearing measures revealed that sentence imitation was related to grammatical comprehension, auditory short-term memory and IQ in both groups, and to expressive language ability, speed of spoken word processing, speech discrimination and acoustic reflexes in the DS group only. A significant relationship between sentence imitation and middle-ear functioning was further supported by a categorical analysis in which DS subjects with bilateral abnormal tympanograms tended to perform more poorly on sentence imitation tasks than DS subjects with at least one normal tympanogram. It was concluded that sentence imitation is a task that is sensitive to the auditory-perceptual, cognitive and expressive difficulties evidenced by individuals with DS.

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 of verbal 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 of tasks. 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-term memory 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.

Phonology, working memory, and foreign-language learning

Three tasks were used to predict English learning by Finnish children over a three-year period. In the pseudoword repetition task the pupils had to repeat aloud tape-recorded pseudowords sounding like Finnish or English. In the pseudoword copying task the pupils saw strings of letters resembling Finnish or English words and copied them when they had disappeared from view. When comparing syntactic-semantic structures, the pupils had to find the syntactically matching pairs from two sets of Finnish sentences. Repetition and copying accuracy and the ability to compare syntactic-semantic structures predicted English learning. Intercorrelations between test scores and English and mathematics grades suggest that repetition and copying accuracy were specifically related to language learning. It is concluded that the ability to represent unfamiliar phonological material in working memory underlies the acquisition of new vocabulary items in foreign-language learning.