The selective impairment of phonological processing in speech production

We report the naming performance of a patient (DM) with a fluent progressive aphasia who made phonological errors in all language production tasks. The pattern of errors in naming was strikingly clear: DM made very many phonological errors that resulted almost always in nonword responses. The complete absence of semantic errors and the very low ratio of formal errors relative to nonword errors (1.6:30.3) in DM's performance are discussed in the context of recent claims about the nature of naming deficits in fluent aphasics. We argue that DM's performance makes highly improbable the claim that fluent aphasia results from global lesions affecting all levels of the lexical access system equally.     

The interaction of multiple routes in oral reading: evidence from dissociations in naming and oral reading in phonological dyslexia

During oral reading we hypothesized that lexical representations are activated and selected for output by the simultaneous activation of the semantic, the direct lexical orthography to phonology, and the sublexical grapheme-to-phoneme conversion (GPC) routes (Southwood & Chatterjee, 1999). Serial models of reading argue that the semantic route governs oral reading with minimal influence from the nonlexical direct route and the sublexical GPC route. These models predict that semantic errors should occur in reading when the semantic route and GPC are both impaired. The Simultaneous Activation Hypothesis predicts few semantic errors in oral reading but many during picture naming. Semantic errors are infrequent in reading because information from all three reading routes constrains activation of a phonological entry. By contrast phonological selection in picture naming is constrained primarily by the semantic route and if damaged additional information is unavailable to select the appropriate phonological code. In agreement with the Simultaneous Activation Hypothesis five phonological dyslexics produced semantic errors during picture naming but not when reading aloud. Phonological errors were present during oral reading and minimal during picture naming.     

Contrasting effects of phonological priming in aphasic word production

Two fluent aphasics, IG and GL, performed a phonological priming task in which they repeated an auditory prime then named a target picture. The two patients both had selective deficits in word production: they were at or near ceiling on lexical comprehension tasks, but were significantly impaired in picture naming. IG's naming errors included both semantic and phonemic paraphasias, as well as failures to respond, whereas GL's errors were mainly phonemic and formal paraphasias. The two patients responded very differently to phonological priming: IG's naming was facilitated (both accuracy and speed) only by begin-related primes (e.g. ferry-feather), whereas GL benefited significantly only from end-related primes (e.g. brother-feather), showing no more than a facilitatory trend with begin-related primes. We interpret these results within a two-stage model of word production, in which begin-related and end-related primes are said to operate at different stages. We then discuss implications for models of normal and aphasic word production in general and particularly with respect to sequential aspects of the phonological encoding process.     

A computational account of deep dysphasia: evidence from a single case study.

We present a case study of a patient, NC, who demonstrates the defining characteristics of deep dysphasia including semantic errors in repetition and an inability to repeat nonwords. In addition, NC's single word repetition and lexical decision performances are influenced by the imageability of the word input. NC also demonstrates a severely restricted phonological short-term memory (one digit, one word). Although his phonological discrimination is good in a minimal pairs judgment task, it becomes impaired when a delay is imposed or rehearsal is prevented between presentation of each member of a pair. NC's output is fluent but contains many formal paraphasias and neologisms. NC's total language profile is evaluated within the framework of Dell's (1986) interactive spreading activation model of language production. Adapting this output model to input processes, we account for all of NC's deep dysphasic symptoms as well as his pattern of production in a way that is more parsimonious than other attempts to model this disorder. In particular, we suggest that the semantic and formal paraphasias in naming and repetition result from a pathological increase in the rate of decay of primed nodes in the semantic-lexical-phonological network. This rapid decay increases the probability that phonologically and/or semantically related lexical nodes primed by top-down and bottom-up feedback during the operation of lexical activation and retrieval will be activated and selected instead of the lexical target. The advantages of using this model to account for aphasic symptoms and the implications for other lexical theories are discussed.     

Fluent versus nonfluent primary progressive aphasia: a comparison of clinical and functional neuroimaging features

To better characterize fluent and nonfluent variants of primary progressive aphasia (PPA). Although investigators have recognized both fluent and nonfluent patients with PPA, the clinical and neuroimaging features of these variants have not been fully defined. We present clinical and neuropsychological data on 47 PPA patients comparing the fluent (n=21) and nonfluent (n=26) subjects. We further compared language features with PET/SPECT data available on 39 of these patients. Compared to the nonfluent PPA patients, those with fluent PPA had greater impairment of confrontational naming and loss of single word comprehension. They also exhibited semantic paraphasic errors and loss of single word comprehension. Patients with nonfluent PPA were more likely to be female, were more often dysarthric, and exhibited phonological speech errors in the absence of semantic errors. No significant differences were seen with regard to left hemisphere abnormalities, suggesting that both variants result from mechanisms that overlap frontal, temporal, and parietal regions. Of the language measures, only semantic paraphasias were strongly localized, in this case to the left temporal lobe. Fluent and nonfluent forms of PPA are clinically distinguishable by letter fluency, single word comprehension, object naming, and types of paraphasic errors. Nevertheless, there is a large amount of overlap between dysfunctional anatomic regions associated with these syndromes.     

Verb retrieval in brain-damaged subjects: 2. Analysis of errors

Verb retrieval for action naming was assessed in 53 brain-damaged subjects by administering a standardized test with 100 items. In a companion paper (Kemmerer & Tranel, 2000), it was shown that impaired and unimpaired subjects did not differ as groups in their sensitivity to a variety of stimulus, lexical, and conceptual factors relevant to the test. For this reason, the main goal of the present study was to determine whether the two groups of subjects manifested theoretically interesting differences in the kinds of errors that they made. All of the subjects' errors were classified according to an error coding system that contains 27 distinct types of errors belonging to five broad categories-verbs, phrases, nouns, adpositional words, and "other" responses. Errors involving the production of verbs that are semantically related to the target were especially prevalent for the unimpaired group, which is similar to the performance of normal control subjects. By contrast, the impaired group had a significantly smaller proportion of errors in the verb category and a significantly larger proportion of errors in each of the nonverb categories. This relationship between error rate and error type is consistent with previous research on both object and action naming errors, and it suggests that subjects with only mild damage to putative lexical systems retain an appreciation of most of the semantic, phonological, and grammatical category features of words, whereas subjects with more severe damage retain a much smaller set of features. At the level of individual subjects, a wide range of "predominant error types" were found, especially among the impaired subjects, which may reflect either different action naming strategies or perhaps different patterns of preservation and impairment of various lexical components. Overall, this study provides a novel addition to the existing literature on the analysis of naming errors made by brain-damaged subjects. Not only does the study advance our knowledge of the relatively under investigated topic of action naming errors, but it also approaches the analysis from the point of view of a detailed, theoretically motivated, and reliable error coding system.     

Mechanisms for accessing lexical representations for output: evidence from a category-specific semantic deficit

We report the performance of a neurologically impaired patient, JJ, whose oral reading of words exceeded his naming and comprehension performance for the same words--a pattern of performance that has been previously presented as evidence for "direct, nonsemantic, lexical" routes to output in reading. However, detailed analyses of JJ's reading and comprehension revealed two results that do not follow directly from the "direct route" hypothesis: (1) He accurately read aloud all orthophonologically regular words and just those irregular words for which he demonstrated some comprehension (as indicated by correct responses or within-category semantic errors in naming and comprehension tasks); and (2) his reading errors on words that were not comprehended at all (but were recognized as words) were phonologically plausible (e.g., soot read as "suit"). We account for these results by proposing that preserved sublexical mechanisms for converting print to sound, together with partially preserved semantic information, serve to mediate the activation of representations in the phonological output lexicon in the task of reading aloud. We present similar arguments for postulating an interaction between sublexical mechanisms and lexical output components of the spelling process.     

Lexical Anomia: Or the Case of the Missing Lexical Entries

This paper reports the case of an aphasic patient, EE, with a problem in word retrieval. He is consistently unable to produce specific lexical items, which tend to be items of low rated familiarity. His retrieval of these words is not aided by the provision of phonemic cues or extra time for word retrieval. His errors consist primarily of failures to respond, and the provision of semantic information without any attempt at the target. It is argued that this pattern of performance is consistent with the loss of specific lexical items from a phonological lexicon for speech production.

EE is shown to have no impairment in auditory recognition and comprehension of the lexical items that are unavailable for naming. This dissociation is problematic for theories that propose a single phonological lexicon for both word recognition and production, but is easily accounted for by separate input and output lexicons.     

语音在维——汉双语者汉字识别中的作用

采用语音启动技术,以第二语言为汉语的46名维吾尔族大学生为研究对象,考查了语音在维-汉双语者汉字识别中的作用.结果发现,维吾尔族被试在命名任务和词汇判断任务中都获得了语音启动效应,语义启动效应只出现在词汇判断任务中.结论:语音在维吾尔族大学生汉字识别中是自动激活的,而且语音的自动激活参与了语义通达.     

Lexical Retrieval Deficit in Picture Naming: Implications for Word Production Models

In models of word retrieval, it is common to differentiate lexical-semantic (word meaning) and lexical-phonological (word form) levels. There has been considerable interest in the relationship between these two levels. The so-called discrete two-stage model claims that phonological activation follows selection at the lexical-semantic level and is limited only to the selected item. In contrast, nondiscrete (interactive and cascade) models assume that all activated lexical-semantic candidates are also phonologically activated to some extent. We addressed this issue by studying an anomic patient who suffered from a partial functional disconnection between lexical-semantic and lexical-phonological levels. A multitarget repeated naming task with phonological training was employed. Systematic manipulation of semantic and phonological relatedness between the to-be-named items indicated that our patient's word error patterns were sensitive to both types of lexical relatedness. A delayed repetition task employing the same items failed to show similar effects, suggesting that they were specific to naming. The discrete two-stage model is unable to explain the observed effects of semantic and phonological relatedness. However, they are consistent with assumptions of nondiscrete models of lexical retrieval. In addition to the theoretical implications of this study, the observed effects of lexical context on word retrieval have implications for treatment of anomia.     

Mediated and convergent lexical priming in language production: a comment on Levelt et al. (1991)

Levelt et al. (1991) argued that modular semantic and phonological stage theories of lexical access in language production are to be preferred over interactive spreading-activation theories (e.g., Dell, 1986). As evidence, they show no mediated semantic-phonological priming during picture naming: Retrieval of sheep primes goat, but the activation of goat is not transmitted to its phonological relative, goal. This research reconciles this result with spreading-activation theories and shows how the absence of mediated priming coexists with the convergent priming necessary to account for mixed semantic-phonological speech errors. The analysis leads to the proposal that the language-production system may best be characterized as globally modular but locally interactive.     

The relative time course of semantic and phonological activation in reading Chinese

The relative time course of semantic and phonological activation was investigated in the context of whether phonology mediates access to lexical representations in reading Chinese. Compound words (Experiment 1) and single-character words (Experiments 2 and 3) were preceded by semantic and phonological primes. Strong semantic priming effects were found at both short (57 ms) and long (200 ms) stimulus onset asynchrony (SOA), but phonological effects were either absent in lexical decision (Experiment 1), were present only at the longer SOA in character decision (Experiment 2) or were equally strong as semantic effects in naming (Experiment 3). Experiment 4 revealed facilitatory or inhibitory effects, depending on SOA, in phonological judgments to character pairs that were not phonologically but semantically related. It was concluded that, in reading Chinese, semantic information in the lexicon is activated at least as early and just as strongly as phonological information.     

Semantic and phonological information flow in the production lexicon

When speakers produce words, lexical access proceeds through semantic and phonological levels of processing. If phonological processing begins based on partial semantic information, processing is cascaded; otherwise, it is discrete. In standard models of lexical access, semantically processed words exert phonological effects only if processing is cascaded. In 3 experiments, speakers named pictures of objects with homophone names (ball), while auditory distractor words were heard beginning 150 ms prior to picture onset. Distractors speeded picture naming (compared with controls) only when related to the nondepicted meaning of the picture (e.g., dance), exhibiting an early phonological effect, thereby supporting the cascaded prediction. Distractors slowed picture naming when categorically (e.g., frisbee) related to the depicted picture meaning, but not when associatively (e.g., game) related to it. An interactive activation model is presented.     

Processing lexical ambiguity and visual word recognition in a deep orthography

We investigated the effect of semantic and phonemic ambiguity on lexical decision and naming performance in the deep Hebrew orthography. Experiment 1 revealed that lexical decisions for ambiguous consonant strings are faster than those for any of the high- or low-frequency voweled alternative meanings of the same strings. These results suggested that lexical decisions for phonemically and semantically ambiguous Hebrew consonant strings are based on the ambiguous orthographic information. However, a significant frequency effect for both ambiguous and unambiguous words suggested that if vowels are present, subjects do not ignore them completely while making lexical decisions. Experiment 2 revealed that naming low-frequency voweled alternatives of ambiguous strings took significantly longer than naming the high-frequency alternatives or the unvoweled strings without a significant difference between the latter two string types. Voweled and unvoweled unambiguous strings, however, were named equally fast. We propose that semantic and phonological disambiguation of unvoweled words in Hebrew is achieved in parallel to the lexical decision, but is not required by it. Naming Hebrew words usually requires a readout of phonemic information from the lexicon.     

Naming consistency in Alzheimer''s disease

Although lexical semantic deficits are postulated to play a prominent role in the anomia of Alzheimer's disease, it is unclear whether the primary disturbance is one of lexical access or one of lexical semantic loss. Response consistency on a naming task is one means of evaluating the underlying source of naming impairment. Access dysfunction usually implies variable word-finding difficulty, while a theory of lexical loss predicts that many word names would be consistently unavailable. Nineteen Alzheimer's disease patients were administered a visual confrontation naming task (the Boston Naming Test) on two occasions 6 months apart. Eighty percent of errors occurred consistently at both times; only 20% of errors occurred on only one occasion. Response consistency occurred significantly more often than expected under the assumption of no response consistency. Findings support the hypothesis that anomia in Alzheimer's disease is in part due to a loss of lexical semantic information.     

Visual word recognition of single-syllable words

Speeded visual word naming and lexical decision performance are reported for 2428 words for young adults and healthy older adults. Hierarchical regression techniques were used to investigate the unique predictive variance of phonological features in the onsets, lexical variables (e.g., measures of consistency, frequency, familiarity, neighborhood size, and length), and semantic variables (e.g. imageahility and semantic connectivity). The influence of most variables was highly task dependent, with the results shedding light on recent empirical controversies in the available word recognition literature. Semantic-level variables accounted for unique variance in both speeded naming and lexical decision performance, level with the latter task producing the largest semantic-level effects. Discussion focuses on the utility of large-scale regression studies in providing a complementary approach to the standard factorial designs to investigate visual word recognition.     

Are semantic errors actually semantic?: Evidence from alzheimer's disease

Patients with Alzheimer's disease (AD) produce a high rate of semantic errors when naming to confrontation. This is considered to be one of the many consequences of their semantic memory deficit. However, it has been shown, in aphasic patients with focal lesions, that semantic errors could arise from impairment to any one of the levels in the naming process. To check this hypothesis in AD, we assessed in 15 patients the capacity to name and access semantic knowledge (by multiple-choice probe questions) about 14 objects presented successively in the visual, tactile, auditory, and verbal modalities. In the visual naming task, 33 errors were recorded: 26 (78.8%) were semantic and 7 (21.2%) were unrelated errors. Of the 26 semantic errors, 8 were related to a deficit of the semantic knowledge related to the item and 17 to a deficit in the retrieval of the phonological form of the word. One was associated with a deficit of access to semantic knowledge in the visual modality. The 7 unrelated errors were associated with a loss of semantic knowledge for 4 and deficit of access to the phonological form for 3. In conclusion, this study shows that semantic errors do not systematically reflect a deficit of semantic knowledge in Alzheimer's disease. It also seems that unrelated errors are more frequently related to semantic deficits than semantic errors in this population.     

Simultaneous activation of reading mechanisms: evidence from a case of deep dyslexia

We report the performance of LC, a deep dyslexic. We investigated extensively her errors according to serial cognitive neuropsychological models of oral reading. Initial evaluation of her reading suggested impaired access to the phonological output lexicon (POL). Impaired grapheme-to-phoneme conversion (GPC) and semantic errors in reading suggested that LC read via an impoverished semantic route. However, a serial model of oral reading could not explain error differences in reading, picture naming, spontaneous speech, and repetition. Neologisms occurred in oral reading but not in spontaneous speech and repetition. Semantic errors in naming exceeded those in oral reading. To account for these different error patterns we propose that the semantic route, the direct route from the orthographic input lexicon to the POL, and GPC activate simultaneously during reading, converging at the POL to constrain phonological selection. These routes are modular but not functionally encapsulated. For LC, the POL receives ambiguous information due to degradation of all routes, causing reading errors.     

The simultaneous activation hypothesis: explaining recovery from deep to phonological dyslexia

Deep dyslexia evolved into phonological dyslexia in one patient. Semantic errors resolved while phonological and derivational errors persisted in reading. Nonword reading improved but remained inferior to word reading. Despite a residual semantic deficit naming improved. The Simultaneous Activation Hypothesis explains recovery from deep to phonological dyslexia and the continued dissociation between reading and naming errors. Partial recovery to all three reading routes increased constraints for word selection at the phonological output lexicon (POL) improving word reading. With recovery, the POL receives additional supportive information from the partially recovered direct oral reading route and grapheme-to-phoneme conversion (GPC) eliminating semantic errors in oral reading. Nonword reading also improved because of partial recovery to all three routes. Semantic errors in naming persisted because additional constraints were unavailable at the POL to activate a phonological entry. Phonological and derivational errors were more frequent in reading than in naming the result of incomplete GPC recovery. Residual nonword reading deficits resulted from incomplete GPC recovery, indicated by the persistence of neologisms in nonwords. The Simultaneous Activation Hypothesis readily accounts for the evolution from deep to phonological dyslexia.     

Orthographic and phonological activation in recognizing Chinese characters

This paper is a contribution to the study of whether visual contact with lexical units in any writing system necessarily arouses their corresponding phonological information. In two experiments it was investigated whether phonological information is automatically activated during the semantic processing of Chinese characters. In these experiments, both using a semantic-categorization task, subjects produced the same proportion of false positive categorization errors and showed the same decision latencies on homophone foils and their non-homophonic controls, thus indicating that phonological information does not seem to affect the semantic task. Experiment 2 further revealed that subjects made more errors and produced longer response times on graphemically similar foils than on the corresponding controls. The absence of phonological effects and the presence of clear effects of visual similarity for Chinese characters in semantic tasks can be taken to indicate that phonological information may not be automatically activated during the processing of meanings of Chinese characters. The present results also cast serious doubts on the hypothesis that phonological activation is a universal principle of lexical processing.