How loss of meaning with preservation of phonological word form affects immediate serial recall performance: a linguistic account

We present HP, a patient who following the occurrence of herpes simplex encephalitis, lost the ability to understand a subset of words while others remained preserved. Of particular interest is the fact that the meaningless items retained their lexical status. HP's immediate serial recall of meaningless words was thus compared with that of meaningful words to assess the unique contribution of semantic knowledge without the confounding influence of phonological word (lexical) form. The results revealed a clear recall advantage for meaningful over meaningless words, indicating a specific contribution to recall from the semantic level of representation. Furthermore, an error analysis showed that phonemic errors were most common when semantic information was lacking. Interestingly, the same error pattern was found for pseudo-words that shared phonological elements with meaningless words. These findings support a linguistic and interactive activation account of short-term serial recall, which assumes that all levels of representation, including semantic knowledge about words, contribute to recall performance. In addition, the findings provide preliminary evidence that this view may be extended to the recall of pseudo-words, as there appear to be some influences of semantic representation on pseudo-word recall.     

How Loss of Meaning with Preservation of Phonological Word Form Affects Immediate Serial Recall Performance: A Linguistic Account

We present HP, a patient who following the occurrence of herpes simplex encephalitis, lost the ability to understand a subset of words while others remained preserved. Of particular interest is the fact that the meaningless items retained their lexical status. HP’s immediate serial recall of meaningless words was thus compared with that of meaningful words to assess the unique contribution of semantic knowledge without the confounding influence of phonological word (lexical) form. The results revealed a clear recall advantage for meaningful over meaningless words, indicating a specific contribution to recall from the semantic level of representation. Furthermore, an error analysis showed that phonemic errors were most common when semantic information was lacking. Interestingly, the same error pattern was found for pseudo-words that shared phonological elements with meaningless words. These findings support a linguistic and interactive activation account of short-term serial recall, which assumes that all levels of representation, including semantic knowledge about words, contribute to recall performance. In addition, the findings provide preliminary evidence that this view may be extended to the recall of pseudo-words, as there appear to be some influences of semantic representation on pseudo-word recall.     

Semantic memory is key to binding phonology: Converging evidence from immediate serial recall in semantic dementia and healthy participants

Patients with semantic dementia (SD) make numerous phoneme migration errors when recalling lists of words they no longer fully understand, suggesting that word meaning makes a critical contribution to phoneme binding in verbal short-term memory. Healthy individuals make errors that appear similar when recalling lists of nonwords, which also lack semantic support. Although previous studies have assumed that the errors in these two groups stem from the same underlying cause, they have never been directly compared. We tackled this issue by examining immediate serial recall for SD patients and controls on “pure” word lists and “mixed” lists that contained a mixture of words and nonwords. SD patients were equally poor at pure and mixed lists and made numerous phoneme migration errors in both conditions. In contrast, controls recalled pure lists better than mixed lists and only produced phoneme migrations for mixed lists. We also examined the claim that semantic activation is critical for words in the primacy portion of the list. In fact, the effect of mixed lists was greatest for later serial positions in the control group and in the SD group recall was poorest towards the ends of lists. These results suggest that mixing nonwords with words in healthy participants closely mimics the impact of semantic degradation in SD on word list recall. The study provides converging evidence for the idea that lexical/semantic knowledge is an important source of constraint on phonological coherence, ensuring that phonemes in familiar words are bound to each other and emerge together in recall.     

The impact of phonological or semantic impairment on delayed auditory repetition: Evidence from stroke aphasia and semantic dementia

Background/Aims: This study aimed to evaluate the interactive account of repetition by examining the influence of factors that differentially tapped semantic and phonological processing in a case series of patients with semantic or phonological impairment. Methods & Procedures: We compared two patient groups: predominantly phonologically impaired cases with aphasia following cerebrovascular accident, and patients with semantic dementia. Immediate repetition was contrasted with repetition after a 5-second filled delay, and lexicality, frequency, and imageability were manipulated—therefore both the task and the neuropsychological impairment biased processing in favour of either lexical-semantic or phonological capacities. Outcomes & Results: Substantial interactivity was observed between phonological/semantic impairment and variables largely tapping these processes. The phonologically impaired patients showed substantial effects of lexicality and imageability that were larger in delayed than immediate repetition. The semantically impaired patients exhibited the complementary pattern, showing reduced effects of these lexical-semantic variables and a delay effect that was larger for more poorly comprehended, low-frequency items. Semantic errors were related to phonological deficits whereas semantic impairment led to an increase in phonological errors. The phonologically impaired stroke cases also made more perseverative responses. Conclusions: These findings support the view that repetition is underpinned by interaction between semantics and phonology within a single route and not by distinct lexical and sub-lexical pathways. The results also provide evidence of a continuum between phonological and deep dysphasia.     

Phonological learning in semantic dementia

Patients with semantic dementia (SD) have anterior temporal lobe (ATL) atrophy that gives rise to a highly selective deterioration of semantic knowledge. Despite pronounced anomia and poor comprehension of words and pictures, SD patients have well-formed, fluent speech and normal digit span. Given the intimate connection between phonological STM and word learning revealed by both neuropsychological and developmental studies, SD patients might be expected to show good acquisition of new phonological forms, even though their ability to map these onto meanings is impaired. In contradiction of these predictions, a limited amount of previous research has found poor learning of new phonological forms in SD. In a series of experiments, we examined whether SD patient, GE, could learn novel phonological sequences and, if so, under which circumstances. GE showed normal benefits of phonological knowledge in STM (i.e., normal phonotactic frequency and phonological similarity effects) but reduced support from semantic memory (i.e., poor immediate serial recall for semantically degraded words, characterised by frequent item errors). Next, we demonstrated normal learning of serial order information for repeated lists of single-digit number words using the Hebb paradigm: these items were well-understood allowing them to be repeated without frequent item errors. In contrast, patient GE showed little learning of nonsense syllable sequences using the same Hebb paradigm. Detailed analysis revealed that both GE and the controls showed a tendency to learn their own errors as opposed to the target items. Finally, we showed normal learning of phonological sequences for GE when he was prevented from repeating his errors. These findings confirm that the ATL atrophy in SD disrupts phonological processing for semantically degraded words but leaves the phonological architecture intact. Consequently, when item errors are minimised, phonological STM can support the acquisition of new phoneme sequences in patients with SD.     

Proactive interference in a semantic short-term memory deficit: role of semantic and phonological relatedness

Previous research has indicated that patients with semantic short-term memory (STM) deficits demonstrate unusual intrusions of previously presented material during serial recall tasks (Martin and Lesch, 1996). These intrusions suggest excessive proactive interference (PI) from previous lists. Here, we explore one such patient's susceptibility to PI. Experiment 1 demonstrated patient M.L.'s extreme susceptibility to PI using a probe recognition task that manipulates the recency of negative probes (the recent negatives task). When stimuli consisted of letters, M.L. showed greatly exaggerated effects of PI, well outside of the range of healthy control participants. Experiment 2 used a variation of the recent negatives task to examine the relative contribution of semantic and phonological relatedness in PI. This task manipulated semantic and phonological relatedness of probes and recently presented list items. Relative to healthy control participants, patient M.L. showed exaggerated interference effects for both phonological and semantically related probes, both for probes related to the current list and for probes related to the previous list. These data have important implications for theories of semantic STM deficits. Specifically, these data suggest that it is not the rapid decay of semantic representations that is responsible for difficulties in short-term recall, but rather the abnormal persistence of previously presented material. We propose that this susceptibility to PI is the result of a deficit in control processes acting on STM.     

A Third Route for Reading? Implications from a Case of Phonological Dyslexia

Models of reading in the neuropsychological literature sometimes only include two routes from print to sound, a lexical semantic route and a sublexical phonological route. Other researchers hypothesize an additional route that involves a direct connection between lexical orthographic representations and lexical phonological representations. This so-called ‘third route’ has been invoked to account for the preserved oral reading of some patients who show severe semantic impairments and a disruption of the sublexical phonological route. In their summation hypothesis, Hillis and Caramazza proposed that reading in these cases could result from a combination of partial lexical semantic information and partial sublexical phonological information, thus obviating the need for the third route. The present study examined the case of a phonological dyslexic patient (ML) who exhibited preserved word reading, even for items he could not name, along with a non-word reading impairment. The relationship between ML’s naming and reading, and the influence of semantic variables on his reading were examined. The results of this examination are interpreted as supporting the existence of the third route.     

A third route for reading? Implications from a case of phonological dyslexia

Models of reading in the neuropsychological literature sometimes only include two routes from print to sound, a lexical semantic route and a sublexical phonological route. Other researchers hypothesize an additional route that involves a direct connection between lexical orthographic representations and lexical phonological representations. This so-called 'third route' has been invoked to account for the preserved oral reading of some patients who show severe semantic impairments and a disruption of the sublexical phonological route. In their summation hypothesis, Hillis and Caramazza proposed that reading in these cases could result from a combination of partial lexical semantic information and partial sublexical phonological information, thus obviating the need for the third route. The present study examined the case of a phonological dyslexic patient (ML) who exhibited preserved word reading, even for items he could not name, along with a non-word reading impairment. The relationship between ML's naming and reading, and the influence of semantic variables on his reading were examined. The results of this examination are interpreted as supporting the existence of the third route.     

Lesion-site affects grammatical gender assignment in German: perception and production data

Two experiments investigated phonological, derivational-morphological and semantic aspects of grammatical gender assignment in a perception and a production task in German aphasic patients and age-matched controls. The agreement of a gender indicating adjective (feminine, masculine or neuter) and a noun was evaluated during perception in Experiment 1 (grammaticality judgment). In Experiment 2 the same participants had to produce the matching definite article to a noun. In the perception task patients with left frontal lesions (LF) made more errors during phonological gender assignment as compared to derivational-morphological and semantic gender assignment, while patients with lesions of the posterior superior temporal gyrus (pSTG) made more errors in derivational-morphological gender assignment as compared to phonological and semantic gender assignment. In the production task no differences between patient groups were found. These data support previous evidence that left frontal brain areas are critically involved in phonological processing. The pSTG on the other hand may be critically engaged in the integration of phonological and lexical information essential for phonological and derivational-morphological gender assignment.     

Lexicality effects in word and nonword recall of semantic dementia and progressive nonfluent aphasia

Background: Verbal working memory is an essential component of many language functions, including sentence comprehension and word learning. As such, working memory has emerged as a domain of intense research interest both in aphasiology and in the broader field of cognitive neuroscience. The integrity of verbal working memory encoding relies on a fluid interaction between semantic and phonological processes. That is, we encode verbal detail using many cues related to both the sound and meaning of words. Lesion models can provide an effective means of parsing the contributions of phonological or semantic impairment to recall performance.

Methods & Procedures: We employed the lesion model approach here by contrasting the nature of lexicality errors incurred during recall of word and nonword sequences by three individuals with progressive nonfluent aphasia (a phonological dominant impairment) compared to that of two individuals with semantic dementia (a semantic dominant impairment). We focused on psycholinguistic attributes of correctly recalled stimuli relative to those that elicited a lexicality error (i.e., nonword → word OR word → nonword).

Outcomes & Results: Patients with semantic dementia showed greater sensitivity to phonological attributes (e.g., phoneme length, wordlikeness) of the target items relative to semantic attributes (e.g., familiarity). Patients with PNFA showed the opposite pattern, marked by sensitivity to word frequency, age of acquisition, familiarity, and imageability.

Conclusions: We interpret these results in favour of a processing strategy such that in the context of a focal phonological impairment patients revert to an over-reliance on preserved semantic processing abilities. In contrast, a focal semantic impairment forces both reliance on and hypersensitivity to phonological attributes of target words. We relate this interpretation to previous hypotheses about the nature of verbal short-term memory in progressive aphasia.     

Verbal short‐term memory in Down's syndrome: An articulatory loop deficit?

Background Verbal short‐term memory, as measured by digit or word span, is generally impaired in individuals with Down's syndrome (DS) compared to mental age‐matched controls. Moving from the working memory model, the present authors investigated the hypothesis that impairment in some of the articulatory loop sub‐components is at the base of the deficient maintenance and recall of phonological representations in individuals with DS. Methods Two experiments were carried out in a group of adolescents with DS and in typically developing children matched for mental age. In the first experiment, the authors explored the reliance of these subjects on the subvocal rehearsal mechanism during a word‐span task and the effects produced by varying the frequency of occurrence of the words on the extension of the word span. In the second experiment, they investigated the functioning of the phonological store component of the articulatory loop in more detail. Results A reduced verbal span in DS was confirmed. Neither individuals with DS nor controls engaged in spontaneous subvocal rehearsal. Moreover, the data provide little support for defective functioning of the phonological store in DS. Conclusions No evidence was found suggesting that a dysfunction of the articulatory loop and lexical‐semantic competence significantly contributed to verbal span reduction in subjects with DS. Alternative explanations of defective verbal short‐term memory in DS, such as a central executive system impairment, must be considered.     

Phonological working memory in children with phonological impairment

Phonological working memory was examined in a group of children with phonological impairment and a group of normal age-matched controls. Based on the Baddeley and Hitch model of working memory, traditional serial recall tasks of word length and phonological similarity were used to examine the efficiency of subvocal rehearsal and short-term storage, respectively. Analysis of recall performance for lists of four and six words revealed that, in comparison to agematched controls, children with phonological impairment are similarly sensitive to the effects of word length and phonological similarity, but demonstrate poorer overall recall for word lists of unrelated items. Theoretically, these findings suggest that the subvocal rehearsal mechanism and the phonological short-term store appear to be operating efficiently in this group of children with phonological impairment. Therefore their poorer recall performance may be attributable to interactions between short-term memory processes and aspects of phonological knowledge stored in long-term memory rather than to specific components of a phonological loop.     

The natural history of late-stage "pure" semantic dementia

Relatively little is known about the neuropsychological profile of late-stage semantic dementia. This article provides a detailed assessment of patient MK who, despite her very severe semantic impairments, remained cooperative to testing and, unusually, did not show additional behavioral/personality changes. Although MK's initial presentation was typical of semantic dementia (SD), her performance began to deviate from the normal pattern. She developed impairments of single word repetition and regular word reading, and began to produce phonological errors in picture naming and spontaneous speech. These deficits might suggest that late-stage SD includes an independent disorder of phonology. An alternative possibility, however, is that phonological processing cannot proceed normally in the face of profound semantic degradation. A series of experiments supported the latter explanation of MK's deficits. In picture naming, MK showed little effect of progressive phonological cueing, did not reveal an increased sensitivity to word length or phonological complexity and continued to show a high degree of item-specific consistency in both accuracy and errors: she tended to produce the same erroneous phonemes for each item. She remained sensitive to the effects of phonological similarity in immediate serial recall. Letter substitution errors in regular word reading were more common for lower frequency letters (e.g., Q, Z). These letters also produced more item errors in immediate serial recall, suggesting that a frequency-graded loss of letter knowledge, rather than separate orthographic and phonological deficits, accounted for the deficits in both of these tasks. These findings are discussed in terms of theories that posit strong interactivity between phonology and semantics.     

Case Study Impairment to phonological processes in a Cantonese‐speaking brain‐damaged patient

Background: Previous studies have shown that brain‐damaged patients with selective deficits to phonological processes produced frequent phonological errors and similar error patterns in all spoken tasks, exhibited the effects of word frequency, grammatical class, and imageability, and were unable to make rhyming judgements, due to impaired lexical retrieval and/or phonological representations. Aims: This paper describes a Cantonese‐speaking brain‐damaged patient, LKK, whose performance patterns in spoken tasks indicate impairment to both the lexically mediated non‐semantic and semantic pathways of oral production, as well as the phonological output buffer. Methods & Procedures: A range of tasks was conducted including repetition, reading aloud, oral naming, written/spoken word–picture matching, non‐verbal semantic tests, written lexical decision, and homophone judgements. Outcomes & Results: LKK performed normally on written lexical decision, word–picture matching, and non‐verbal semantic tests, but he was unable to make homophone judgements and showed impaired production in all oral tasks. He was better able to read aloud names of objects than to name them. He also made more semantic errors in naming than reading. His accuracy in reading single words was affected by word frequency and form class. Further observations of his oral production included better (but nevertheless impaired) performance on repetition than reading and naming, a consistent effect of word length across tasks, and a tendency for phonological errors to occur on the coda compared with the onset. Conclusions: There was sufficient evidence for deficits of the phonological lexicon and/or the access to it along the non‐semantic route and the semantic pathway at the post‐semantic level in LKK. The effect of word length and comparable patterns of error distribution across spoken tasks suggested additional impairment to the phonological output buffer. The different levels of accuracy in repetition, reading, and naming, as well as the differential rates of semantic errors in these tasks were consistent with predictions of the summation hypothesis.     

Exploring the dynamics of aphasic word production using the picture-word interference task: a case study

In this study, we use an auditory picture-word interference task to examine an anomic individual, NP. NP produced semantic errors in picture naming, but his comprehension was relatively well preserved. In the task, pictures to be named were accompanied by semantically, phonologically or unrelated distractors, presented at onsets ranging from -200ms (before target) to +400ms (after target). Naming latencies were measured. A group of 12 older controls showed semantic interference (slower latencies with semantic than with unrelated distractors), which was significant at -200ms, and steadily diminished across later onsets. In contrast, at 0ms, NP showed powerful semantic facilitation. There were no significant semantic effects at other onsets, but the trends, particularly at later onsets, were towards interference. Phonological effects for NP were in the same direction as for controls (facilitation) but were of greater magnitude. Indeed, NP showed a reliable facilitatory effect at 0ms (and trends at -200ms and +200ms), but a similar trend in controls failed to reach significance. Within recent models of this task, in which semantic facilitation effects are attributed to an early, pre-lexical semantic processing stage, NP's pattern indicates that semantic processing is abnormally prolonged. The phonological facilitation effects are also consistent with this interpretation. We discuss their implications and future applications of the task to aphasia.     

Hemisphere differences in accessing lexical knowledge of Chinese characters

The lateralisation of lexical knowledge of Chinese characters is investigated in this study. Three experiments were conducted in which stimuli were presented unilaterally to a visual field for recognition tests. The orthographic similarity of two alternative items for choice in Experiment 1 was manipulated, and the results showed an LVF advantage effect for legal characters in the visually similar condition and a more prominent LVF than RVF character-superiority effect. The phonological similarity of two alternative items for choice was manipulated in Experiment 2. The results showed a prominent RVF advantage effect and a significant phonological similarity effect in the RVF. In Experiment 3, the semantic similarity was manipulated, and the semantic similarity effect was observed in the RVF. These results suggest hemisphere asymmetries in accessing lexical knowledge of Chinese characters.     

Verbal learning in semantic dementia: Is repetition priming a useful strategy?

Background: Semantic dementia (SD) is a neurodegenerative disease that impacts long-term conceptual and lexical knowledge (Hodges & Patterson, 1996). Severe naming difficulties are prevalent in SD, yet little is known about the potential for word learning in this population.Aims: We assessed patterns of repetition and implicit learning in patients with moderate to advanced SD via repeated exposure to word lists varied by frequency and imageability. We propose a tentative framework for the language loss incurred in SD and open a dialogue for treatment approaches targeted towards progressive semantic anomia.Methods and Procedures: In two experiments, we examined immediate serial recall and short-term learning in five patients with SD. We predicted reduced semantic effects (imageability), preservation of lexical effects (frequency), and diminished primacy effects in serial recall, consistent with other semantically impaired populations (Martin & Saffran, 1997). We also predicted that severity of semantic impairment would modulate the facilitative effects of repeated exposure (i.e., repetition priming) on word list recall.Outcomes and Results: In immediate serial recall, all participants showed reduced imageability effects, but only one patient showed a significant word frequency advantage. Two patterns of serial position effects emerged: (1) poor recall of initial list items and (2) better recall of initial and final items. All participants showed minimal gains across repeated trials; however, patients who poorly recalled initial items showed the least benefit from repeated exposure.Conclusions: We discuss the usefulness of repetition-based interventions for SD and advocate maintenance of known vocabulary over reacquisition of forgotten words. We provide a theoretical framework for progressive language loss associated with SD; this model reflects an ordered reduction of lexical-semantic support coinciding with dementia severity.     

Paced reading in semantic dementia: word knowledge contributes to phoneme binding in rapid speech production

Patients with semantic dementia (SD) show deficits in phoneme binding in immediate serial recall: when attempting to reproduce a sequence of words that they no longer fully understand, they show frequent migrations of phonemes between items (e.g., cap, frog recalled as "frap, cog"). This suggests that verbal short-term memory emerges directly from interactions between semantic and phonological systems, allowing semantic knowledge to make a critical contribution to the stability of phonological sequences. According to this standpoint, SD patients should show phoneme binding deficits in additional language tasks beyond standard assessments of verbal short-term memory: for example, these errors should emerge in paced reading, which also requires the rapid production of semantically degraded words in order. To test this hypothesis, we examined a cyclical paced reading task in three SD patients for the first time. Every patient showed deficits in phoneme binding: they were more vulnerable than a set of age-matched controls to phoneme competition effects following the repetition of a small set of words across several cycles. They also showed substantially elevated numbers of phoneme migration, substitution and omission errors, despite being able to read the individual words almost without error. These findings confirm that the semantic contribution to phoneme binding is disrupted in SD patients across tasks. In line with the view that verbal short-term memory emerges from interactions between basic phonological and semantic components, these effects occur both within classic short-term memory paradigms, such as immediate serial recall, and tasks without explicit memory demands, such as paced reading.     

Effects of Task Structure on Category Priming in Patients With Parkinson's Disease and in Healthy Individuals

Lexical decision tasks have been used to study both shifts of attention and semantic processing in Parkinson's Disease (PD). Whereas other laboratories have reported normal levels of semantic priming among PD patients, our laboratory has reported abnormally large levels. In this study, two experiments were performed to determine the influence of task structure on the extent of semantic priming during lexical decision-making and pronunciation tasks among PD patients and neurologically healthy controls. In Experiment 1, the effect of Prime Dominance (the ratio of category to neutral trials) on lexical decision-making was studied. Although equal numbers of word and nonword trials were presented, half of the PD patients and controls were studied under Category Prime Dominance (category : neutral prime ratio of 2:1) and half were studied under Neutral Prime Dominance (category : neutral prime ratio of 1:2). In Experiment 2, PD and control participants were studied on lexical decision-making and pronunciation tasks where twice as many words as nonword trials were presented, consistent with other studies from our laboratory. In Experiment 1, we found no group differences in the magnitude of priming and no effect of Prime Dominance. Moreover, the findings were similar in pattern and magnitude to results published by Neely (1977). In Experiment 2, we observed larger priming effects among PD patients than among controls, but only on the lexical decision (LD) task. These results support the hypothesis that abnormally large category-priming effects appear in LD studies of PD patients when the number of word trials exceeds the number of nonword trials. Furthermore, increased lexical priming in PD appears to be due to processes operating during the decision-making period that follows presentation of the lexical target.     

The role of noun syntax in spoken word production: Evidence from aphasia

We describe MH who presents with agrammatic aphasia and anomia, and who produces semantic errors in the absence of a central semantic impairment. This pattern of performance implies damage to syntactic processes operating between semantics and phonological output. Damage here may lead to lexical selection errors and a deficit in combining words to form phrases.We investigated MH's knowledge and processing of noun syntax in mass and count nouns. She produced more count nouns than mass nouns. She showed impaired knowledge of noun syntax in judgement tasks and production tasks, with mass noun syntax being more impaired than count.We interpret these results in terms of a two-stage model of lexical retrieval. We propose that syntactic information represented at the lemma level is activated even in bare noun production, and can be differentially impaired across noun categories. That same damage can lead to semantic errors in production. For MH limited syntactic options are available to support production, and these favour count noun production. The data provide a new account of output semantic errors.