Search

The connectionist triangle model of reading aloud proposes that semantic activation of phonology is particularly important for correct pronunciation of low-frequency exception words. Our consideration of this issue (Woollams, Lambon Ralph, Plant, & Patterson, 2007) reported computational simulations demonstrating that reduction and disruption of this semantic activation resulted in the marked deficit in low-frequency exception word reading that is characteristic of surface dyslexia. We then presented 100 observations of reading aloud from 51 patients with semantic dementia (SD) demonstrating a universal decline into surface dyslexia, a phenomenon we termed 'SD-squared.' Coltheart, Tree, and Saunders (2010) have more recently provided a simulation of the SD-squared data within the dual route cascaded (DRC) model, achieved by varying the amount of damage to components of the lexical and nonlexical pathways. Although they suggested that these simulations provide a closer fit to the SD patients' reading data than our own, we demonstrate here that this is not the case. Moreover, we argue that the connectionist triangle model account has substantially greater explanatory and predictive power than the DRC account. Keywords: surface dyslexia, semantic memory, reading aloud, frequency, regularity DOI: 10.1037/a0017641

Semantic short-term memory (STM) patients have a reduced ability to retain semantic information over brief delays but perform well on other semantic tasks; this pattern suggests damage to a dedicated buffer for semantic information. Alternatively, these difficulties may arise from mild disruption to domain-general semantic processes that have their greatest impact on demanding STM tasks. In this study, mild semantic processing impairments were demonstrated in 2 semantic STM patients. They performed well on untimed semantic tasks but were deficient in accuracy and reaction times on speeded tasks. Demanding semantic production tasks were also affected. These patients were compared with a case series of individuals with semantic aphasia whose multimodal semantic difficulties stemmed from poor cognitive control. STM and semantic performance were more impaired in this group, but there were qualitative similarities to the semantic STM patients. The difference between the 2 patient types may be a matter of degree. In semantic aphasia, severe disruption to semantic control leads to global semantic impairments, whereas in semantic STM milder disruption might impact mainly on STM tests because of the high control demands of these tasks. Keywords: short-term memory, stroke aphasia, semantic control

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jml.2007.06.004 Byline: Elizabeth Jefferies (a), Paul Hoffman (a), Roy Jones (b), Matthew A. Lambon Ralph (a) Keywords: Verbal short-term memory; Semantic dementia; Aphasia; Stroke; Semantic memory Abstract: This study presents the first direct comparison of immediate serial recall in semantic dementia (SD) and transcortical sensory aphasia (TSA). Previous studies of the effect of semantic impairment on verbal short-term memory (STM) have led to important theoretical advances. However, different conclusions have been drawn from these two groups. This research aimed to explain these inconsistencies. We observed (a) qualitative differences between SD and TSA in the nature of the verbal STM impairment and (b) considerable variation within the TSA group. The SD and TSA patients all had poor semantic processing and good phonology. Reflecting this, both groups remained sensitive to phonological similarity and showed a reduced effect of lexicality in immediate serial recall. The SD patients showed normal serial position effects; in contrast, the TSA patients had poor recall of the initial list items and exhibited large recency effects on longer lists. The error patterns of the two groups differed: the SD patients made numerous phoneme migration errors whereas the TSA group were more likely to produce entire words in the wrong order, often initiating recall with terminal list items. The SD cases also showed somewhat larger effects of word frequency and imageability. We propose that these contrasting performance patterns are explicable in terms of the nature of the underlying semantic impairment. SD is associated with anterior lobe atrophy and produces degradation of semantic knowledge -- this is more striking for less frequent/imageable items, accentuating the effects of these lexical/semantic variables in STM. SD patients frequently recombine the phonemes of different list items due to the reduced semantic constraint upon phonology (semantic binding: Patterson, K., Graham, N., & Hodges, J. R. (1994). The impact of semantic memory loss on phonological representations. Journal of Cognitive Neuroscience, 6, 57-69). In contrast, the semantic impairment in TSA follows frontal or temporoparietal lesions and is associated with poor executive control of semantic processing (deregulated semantic cognition: Jefferies, E., & Lambon Ralph, M. A. (2006). Semantic impairment in stroke aphasia vs. semantic dementia: a case-series comparison. Brain, 129, 2132-2147), explaining why these patients are liable to recall entire words out of serial order. Author Affiliation: (a) Neuroscience and Aphasia Research Unit (NARU), Zochonis Building, School of Psychological Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK (b) Research Institute for the Care of the Elderly, Bath, UK Article History: Received 16 May 2006; Revised 5 June 2007

Within the connectionist triangle model of reading aloud, interaction between semantic and phonological representations occurs for all words but is particularly important for correct pronunciation of lower frequency exception words. This framework therefore predicts that (a) semantic dementia, which compromises semantic knowledge, should be accompanied by surface dyslexia, a frequency-modulated deficit in exception word reading, and (b) there should be a significant relationship between the severity of semantic degradation and the severity of surface dyslexia. The authors evaluated these claims with reference to 100 observations of reading data from 51 cases of semantic dementia. Surface dyslexia was rampant, and a simple composite semantic measure accounted for half of the variance in low-frequency exception word reading. Although in 3 cases initial testing revealed a moderate semantic impairment but normal exception word reading, all of these became surface dyslexic as their semantic knowledge deteriorated further. The connectionist account attributes such cases to premorbid individual variation in semantic reliance for accurate exception word reading. These results provide a striking demonstration of the association between semantic dementia and surface dyslexia, a phenomenon that the authors have dubbed SD-squared. Keywords: surface dyslexia, semantic memory, reading aloud, frequency, regularity

Previous studies have reported that, in contrast to the effect on immediate serial recall, lexical/semantic factors have little effect on immediate serial recognition. This has been taken as evidence that linguistic knowledge contributes to verbal short-term memory in a redintegrative process at recall. Contrary to this view, we found that lexicality, frequency, and imageability all influenced matching span. The standard matching span task, requiring changes in item order to be detected, was less susceptible to lexical/semantic factors than was a novel task involving the detection of phoneme order and hence item identity changes. Therefore, in both immediate recognition and immediate serial recall, lexical/semantic knowledge makes a greater contribution to item identity than to item order memory. Task sensitivity, and not the absence of overt recall, may have underpinned previous failures to show effects of these variables in immediate recognition. We also compared matching span for pure and unpredictable mixed lists of words and nonwords. Lexicality had a larger impact on immediate recognition for pure than for mixed lists, in line with findings for immediate serial recall. List composition affected the detection of phoneme but not item order changes in matching span; similarly, in recall, mixed lists produce more frequent word phoneme migrations but not migrations of entire items. These results point to strong similarities between immediate serial recall and recognition. Lexical/semantic knowledge may contribute to phonological stability in both tasks.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jml.2005.08.001 Byline: Elizabeth Jefferies (a), Clive R. Frankish (b), Matthew A. Lambon Ralph (a) Keywords: Redintegration; Semantic binding; Semantic dementia; Verbal short-term memory; Immediate serial recall Abstract: Semantic dementia patients make numerous phoneme migration errors in their immediate serial recall of poorly comprehended words. In this study, similar errors were induced in the word recall of healthy participants by presenting unpredictable mixed lists of words and nonwords. This technique revealed that lexicality, word frequency, imageability, and the ratio of words to nonwords all influence the stability of the phonological trace. These factors affected phoneme migrations and phoneme identity errors for both the words themselves and the nonwords they were presented with. Therefore, lexical/semantic knowledge encourages the phonological segments of familiar words to emerge together in immediate serial recall. In the absence of such knowledge, the elements of a particular item are more likely to recombine with the phonemes of other list items. These findings demonstrate the importance of lexical and semantic binding in verbal short-term memory. Author Affiliation: (a) University of Manchester, UK (b) University of Bristol, UK Article History: Received 8 February 2005; Revised 30 August 2005

Wernicke (1900, as cited in G. H. Eggert, 1977) suggested that semantic knowledge arises from the interaction of perceptual representations of objects and words. The authors present a parallel distributed processing implementation of this theory, in which semantic representations emerge from mechanisms that acquire the mappings between visual representations of objects and their verbal descriptions. To test the theory, they trained the model to associate names, verbal descriptions, and visual representations of objects. When its inputs and outputs are constructed to capture aspects of structure apparent in attribute-norming experiments, the model provides an intuitive account of semantic task performance. The authors then used the model to understand the structure of impaired performance in patients with selective and progressive impairments of conceptual knowledge. Data from 4 well-known semantic tasks revealed consistent patterns that find a ready explanation in the model. The relationship between the model and related theories of semantic representation is discussed.

Native speakers of Japanese were shown single-character Kanji words which they read aloud as quickly as possible. Simultaneous multiple regression was used to investigate which of a set of nine variables predicted reading speed. Two factors exerted strong independent effects upon reading speed - the age at which the words enter a Japanese child's spoken vocabulary and the age at which Japanese children learn the characters that are used to write those words. Of three measures of word frequency, only rated familiarity made a significant independent contribution. There were no significant effects of word imageability, the number of alternative pronunciations of a Kanji character, the visual complexity of a character, or the length of the spoken word. We suggest that the quality of lexical representations is affected by the age at which they are learned, and that the effects of age of spoken and written acquisition reflect the influence of those variables upon the speech output lexicon and the visual input lexicon respectively., When instructed to read single words aloud as fast and as accurately as possible, skilled readers of English consistently pronounce some words faster than others. Exploration of the factors which [...]

The role of long-term and working memory in automatic and controlled processing in sentence recall is examined. The results indicate that the contributions from both automatic linguistic processes and attentionally limited working memory are reflected by sentence recall.

The mechanisms that underlie the neuropsychological dissociations between regular and irregular past tense verb processing were studied in nonfluent aphasic patients. The results indicated a central phonological deficit under which distinctions lacking phonological salience are particularly vulnerable.

Recent investigations and theorising about category-specific deficits have begun to focus upon patients with progressive brain disease such as semantic dementia and Alzheimer's disease. In this commentary we briefly review what insights have been gained from studying patients of this type. We concentrate on four specific issues: the sensory/functional distinction, correlation between features, neuroanatomical considerations, and confounding factors.