Semantics and semantic errors: implicit access to semantic information from words and nonwords in deep dyslexia

In this paper we describe dissociations of implicit versus explicit access to semantic information in a patient with deep dyslexia. This acquired reading disorder is characterized by the production of morphological (e.g., SLEEP read as SLEEPING) and semantic errors (e.g., HEART read as BLOOD) and consequently provides a potential window into the operation of both aspects of the language system. The deep dyslexic patient in this study (JO) demonstrated implicit semantic access to items in a number of tasks despite the fact that she was unable to correctly read these items aloud. The findings from this study are consistent with a model of lexical deficits that distinguishes between explicit and implicit access to lexical representations on the basis of inhibitory processes.     

Semantic ambiguity and the failure of inhibition hypothesis as an explanation for reading errors in deep dyslexia

We report evidence for dissociation between explicit and implicit access to word representations in a deep dyslexic patient (JO). JO read aloud a series of ambiguous (e.g., bank) and unambiguous (e.g., food) words and performed a lexical decision task using these same items. When required to explicitly access the items (i.e., naming), JO showed relative impairment for ambiguous compared with unambiguous words. In contrast, the same stimuli produced an advantage for ambiguous words in lexical decision. The results are discussed within a framework of deep dyslexia that considers errors in production to arise through a failure to inhibit spuriously activated candidate representations.     

Word associations in deep dyslexia

Deep dyslexia is an acquired reading disorder resulting in the production of semantic errors during oral reading and an inability to read aloud nonwords. Several researchers have postulated that patients with deep dyslexia have both phonological and semantic access impairments but the data supporting these claims are not convincing. In fact, the hallmark feature of deep dyslexia--the semantic errors--strongly implies that these patients can access semantic information from printed words. We test the integrity of the semantic system in two such patients through auditory and visual word association tasks. The data support the notion that semantics remains intact and that the disorder and associated errors arise through a selection impairment related to failure of inhibitory connections in the phonological lexicon.     

Deep dyslexia and semantic errors: a test of the failure of inhibition hypothesis using a semantic blocking paradigm

Deep dyslexia is an acquired reading disorder that involves the production of semantic errors and the inability to read aloud nonwords successfully. Several explanations for this reading impairment posit multiple loci of damage to account for the various error types produced in deep dyslexia. In contrast, the failure of inhibition hypothesis suggests that damage in the phonological output lexicon alone can explain these errors. Specifically, this hypothesis proposes normal processing via orthographic and phonological reading routes, as well as an intact semantic system. However, slowed or reduced inhibitory connections result in the failure to suppress spuriously activated neighbours in the phonological output lexicon, where neighbourhood can be defined in terms of phonology, orthography, or semantics. Given a failure to inhibit semantically related candidates, semantic reading errors occur. Important to the test of this hypothesis is that it evolves several predictions that are contrary to performance observed in the normal population. In particular, semantic errors are predicted to be greater in conditions where words are blocked according to semantic category than in random presentations. In addition, a semantic interference effect is expected. The results of semantic blocking were consistent with these predictions and lend support to the failure of inhibition hypothesis.     

Effects of depth-of-processing and ageing on word-stem and word-fragment implicit memory tasks: Test of the lexical-processing hypothesis

The joint effects of depth-of-processing and age on repetition priming in implicit memory tests of word-fragment completion (WFC) and word-stem completion (WSC) were investigated. The experiment consisted of three study tasks (perceptual, lexical, and semantic) and four memory conditions: implicit (WSC and WFC) and explicit (WS cued recall and WF cued recall). In the WSC condition, semantic and lexical study processing produced equal priming, both superior to the perceptual study processing, whereas the WFC test showed equal priming for these three study conditions. This finding provides clear evidence, consistent with the lexical-processing hypothesis, that depth-of-processing in WSC priming reflects a lexical rather than a semantic process. It also provides support for the view that WSC and WFC involve different processes. However, there was no evidence of an age effect on either of these two implicit tasks. The data also revealed an overall significant effect of age and depth-of-processing, and an interaction between these variables on explicit cued recall tasks, indicating that older adults benefited less than younger ones from a deep encoding condition.     

Deficient implicit phonological representations in children with dyslexia

This study tested the segmentation hypothesis of dyslexia by measuring implicit phonological representations in reading-disabled 11- to 13-year-olds. Implicit measures included lexical gating, priming, and syllable similarity tasks designed to reduce metalinguistic demands. Children with dyslexia performed consistently worse than CA and RA controls when more segmental representations were required across all three tasks. Implicit phonological representations were correlated with measures of speech perception, phoneme awareness, and phonological short-term memory, but not rapid automatized naming, and accounted for unique variance in predicting reading ability. Results provide strong support for less mature implicit phonological representations in children with dyslexia.     

Deep dyslexia in the two languages of an Arabic/French bilingual patient.

We present a single case study of an Arabic/French bilingual patient, ZT, who, at the age of 32, suffered a cerebral vascular accident that resulted in a massive infarct in the left peri-sylvian region. ZT's reading displays the characteristics of the deep dyslexia syndrome in both languages, that is, production of semantic, visual, and morphological errors, and concreteness effect in reading aloud and impossibility of reading nonwords. In the first part of this paper, using a three-route model of reading, we account for the patient's performance by positing functional lesions, which affect the non-lexical, the semantic lexical and the non-semantic lexical routes of reading. Phonological priming observed in a cross-language visual lexical decision task indicates that implicit assembled phonological recoding is possible. The above lesions and implicit nonword reading characterize the output form of deep dyslexia. However, error distribution reveals dissociations across languages (e.g. the semantic error rate is higher in French whereas translations are more frequent in the Arabic testing) that cannot be accounted for within a three-route model. In the second part, extensions to Plaut and Shallice's connectionist model (Cognitive Neuropsychology, 10 (5) (1993) 377) are proposed to account for the translinguistic errors observed. ZT's error distribution is compared to that obtained by Plaut and Shallice after lesions had been applied at different locations through the 40-60 network. The overall syndrome of deep dyslexia found in both languages is explained as resulting from lesions along the direct (O-->I) and output (S-->Ip, Ip-->P) pathways of reading. Lesions along the output pathway mostly affecting S-->Ip connections in French and Ip-->P connections in Arabic account for discrepancies in ZT's error pattern across tasks and languages. This case study demonstrates the superiority of a connectionist approach for predicting the error pattern in deep dyslexia.     

An investigation of false memory in perceptual implicit tasks

Reports of critical lure priming in perceptual implicit tasks [e.g., McKone, E., & Murphy, B. (2000). Implicit false memory: Effects of modality and multiple study presentations on long-lived semantic priming. Journal of Memory and Language, 43, 89-109] using the Deese-Roediger-McDermott [Roediger, H. L., III, & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory, and Cognition, 21, 803-814] procedure have suggested availability of the lexical form of lure items at study. Three experiments were conducted to further explore "false" implicit priming in perceptual tests. In Experiments 1 and 3, implicit and explicit stem completion tests were given in the DRM procedure with semantic lists; in Experiment 2, a graphemic response test was used in a similar design. For all experiments, explicit instructions resulted in reliable false memory, while implicit instructions resulted in priming for list items and no priming for lure items. Priming for lure items was evident for "test-aware" subjects only in Experiment 1 and in a combined analysis for all three experiments. These results establish boundary conditions for priming for critical lures and indicate that access to the lexical form of critical lures may not occur under incidental learning conditions when strong controls against explicit retrieval are implemented.     

The effect of midazolam on implicit and explicit memory in category exemplar production and category cued recall

Transfer-appropriate processing theory (Roediger, Weldon, & Challis, 1989) proposes that dissociations between performance on explicit and implicit memory tests arise because these tests often rely on different types of information processing (e.g., perceptual processing vs conceptual processing). This perspective predicts that implicit and explicit memory tasks that rely primarily on conceptual processing should show comparable results, not dissociations. Numerous studies have demonstrated such similarities. It is, however, possible that these results arise from explicit memory contamination of performance on implicit memory tasks. To address this issue, an experiment was conducted in which participants were administered the sedative midazolam prior to study. Midazolam is known to create a temporary, but dense, period of anterograde amnesia. The effects of blocking stimulus materials by semantic category at study and generation at study were investigated on category exemplar production and category-cued recall. The results of this study demonstrated a dissociation of the effects of midazolam on category exemplar production and category-cued recall. Specifically, midazolam reduced the effect of blocking stimulus materials in category-cued recall, but not in category exemplar production. The differential effect of midazolam on explicit and implicit memory is at odds with transfer-appropriate processing theory and suggests that theories of memory must distinguish the roles of different types of conceptual processing on implicit and explicit memory tests.     

The role of phonological and orthographic information in lexical selection

We report the performance of two patients with lexico-semantic deficits following left MCA CVA. Both patients produce similar numbers of semantic paraphasias in naming tasks, but presented one crucial difference: grapheme-to-phoneme and phoneme-to-grapheme conversion procedures were available only to one of them. We investigated the impact of this availability on the process of lexical selection during word production. The patient for whom conversion procedures were not operational produced semantic errors in transcoding tasks such as reading and writing to dictation; furthermore, when asked to name a given picture in multiple output modalities--e.g., to say the name of a picture and immediately after to write it down--he produced lexically inconsistent responses. By contrast, the patient for whom conversion procedures were available did not produce semantic errors in transcoding tasks and did not produce lexically inconsistent responses in multiple picture-naming tasks. These observations are interpreted in the context of the summation hypothesis (Hillis & Caramazza, 1991), according to which the activation of lexical entries for production would be made on the basis of semantic information and, when available, on the basis of form-specific information. The implementation of this hypothesis in models of lexical access is discussed in detail.     

The effect of midazolam on implicit and explicit memory in category exemplar production and category cued recall

Transfer‐appropriate processing theory (Roediger, Weldon, & Challis, 1989) proposes that dissociations between performance on explicit and implicit memory tests arise because these tests often rely on different types of information processing (e.g., perceptual processing vs conceptual processing). This perspective predicts that implicit and explicit memory tasks that rely primarily on conceptual processing should show comparable results, not dissociations. Numerous studies have demonstrated such similarities. It is, however, possible that these results arise from explicit memory contamination of performance on implicit memory tasks. To address this issue, an experiment was conducted in which participants were administered the sedative midazolam prior to study. Midazolam is known to create a temporary, but dense, period of anterograde amnesia. The effects of blocking stimulus materials by semantic category at study and generation at study were investigated on category exemplar production and category‐cued recall. The results of this study demonstrated a dissociation of the effects of midazolam on category exemplar production and category‐cued recall. Specifically, midazolam reduced the effect of blocking stimulus materials in category‐cued recall, but not in category exemplar production. The differential effect of midazolam on explicit and implicit memory is at odds with transfer‐appropriate processing theory and suggests that theories of memory must distinguish the roles of different types of conceptual processing on implicit and explicit memory tests.     

Semantic priming in visual word recognition: Activation blocking and domains of processing

The fact that letter search on a prime eliminates the typically robust semantic priming effect in lexical decision is often attributed to the “shallowness” of the prime-processing task. In three experiments we investigated this claim by using two different “shallow” prime-processing tasks: letter search and color identification. Consistent with previous reports, lexical decisions to semantically related targets were not facilitated when subjects searched the prime for a probe letter. In contrast, semantic priming was observed following a color discrimination task on the prime. We suggest that a levels-of-processing interpretation is not an adequate framework for understanding these data. Instead, a domain-specific processing account is offered in which explicit processing at the letter level (as in letter search) makes demands on resources (e.g., activation) that drives processing at the semantic level. This competition is resolved by establishing a temporary activation block at the lexical-semantic interface, which results in the elimination or attenuation of semantic priming. In contrast, global judgment of color is viewed as a domain that does not make demands on the resources that drive the visual word recognition machinery. There is therefore no need for an activation block, and semantic priming is not prevented.     

Influence du contexte sémantique sur la performance d'identification d'odeurs

Our olfactory knowledge is mainly implicit and the last step for cognitive processing of odors — naming — is not always performed. To facilitate naming, odor identification by forced choice between alternatives is used. However, presenting names induces semantic priming. To assess which level of spontaneous odor processing is influenced by semantic context, we compared three priming conditions. Our results indicate that the identification process is based mainly on the rejection of semantic categories that are most remote from the target, and firstly of those with a different hedonic valence. The analysis of identification errors supports the hypothesis that odor naming rests more on global semantic discriminations than on what is called lexical access in other sensory modes.     

Recruitment of anterior and posterior structures in lexical-semantic processing: an fMRI study comparing implicit and explicit tasks

Previous studies examining explicit semantic processing have consistently shown activation of the left inferior frontal gyrus (IFG). In contrast, implicit semantic processing tasks have shown activation in posterior areas including the superior temporal gyrus (STG) and the middle temporal gyrus (MTG) with less consistent activation in the IFG. These results raise the question whether the functional role of the IFG is related to those processes needed to make a semantic decision or to processes involved in the extraction and analysis of meaning. This study examined neural activation patterns during a semantic judgment task requiring overt semantic analysis, and then compared these activation patterns to previously obtained results using the same semantically related and unrelated word pairs in a lexical decision task which required only implicit semantic processing (Rissman, J., Eliassen, J. C., & Blumstein, S. E. (2003). An event-related fMRI investigation of implicit semantic priming. Journal of Cognitive Neuroscience, 15, 1160-1175). The behavioral results demonstrated that the tasks were equivalent in difficulty. fMRI results indicated that the IFG and STG bilaterally showed greater activation for semantically unrelated than related word pairs across the two tasks. Comparison of the two task types across conditions revealed greater activation for the semantic judgment task only in the STG bilaterally and not in the IFG. These results suggest that the pre-frontal cortex is recruited similarly in the service of both the lexical decision and semantic judgment tasks. The increased activation in the STG in the semantic judgment task reflects the greater depth of semantic processing required in this task and indicates that the STG is not simply a passive store of lexical-semantic information but is involved in the active retrieval of this information.     

提取干扰对知觉和概念启动的影响

通过学习—测验范式,分别以词汇判断、语义分类任务为测验,探讨提取干扰对不同识别式记忆的影响差异。结果发现,实验1验证了识别式知觉内隐记忆的提取干扰效应,实验2发现识别式概念内隐记忆在提取干扰下也明显降低;两个实验启动量联合分析发现,相比无干扰条件,概念启动比知觉启动受到提取干扰的破坏更大。上述结果说明识别式内隐记忆的提取干扰具有普遍性,提取干扰产生了不同识别式内隐记忆之间的分离,识别式概念内隐记忆更容易受到提取干扰的影响。     

The locus of the frequency effect in picture naming: When recognizing is not enough

The lexical frequency effect in picture naming is generally assumed to constitute a signature of lexical access. Lexical frequency, however, is correlated with other variables, like concept familiarity, that can produce effects similar to those of lexical frequency in picture naming tasks. In this study, a delayed picture naming task was employed to address the hypothesis that the frequency effect in picture naming is due to variables that affect processing in the perceptual and semantic identification stages (i.e., input stages). Despite the fact that all the input processing stages were completed prior to the presentation of the naming cue, a strong frequency effect was still obtained in this task. These results establish that the lexical frequency effect is independent of variables affecting the input stages of picture naming, and, hence, confirm the lexical frequency effect as a signature effect of lexical access.     

Parkinson’s disease disrupts both automatic and controlled processing of action verbs

The problem of how word meaning is processed in the brain has been a topic of intense investigation in cognitive neuroscience. While considerable correlational evidence exists for the involvement of sensory-motor systems in conceptual processing, it is still unclear whether they play a causal role. We investigated this issue by comparing the performance of patients with Parkinson’s disease (PD) with that of age-matched controls when processing action and abstract verbs. To examine the effects of task demands, we used tasks in which semantic demands were either implicit (lexical decision and priming) or explicit (semantic similarity judgment). In both tasks, PD patients’ performance was selectively impaired for action verbs (relative to controls), indicating that the motor system plays a more central role in the processing of action verbs than in the processing of abstract verbs. These results argue for a causal role of sensory-motor systems in semantic processing.     

Semantic errors in a deep dyslexic

A case of a Swedish-speaking deep dyslexic is reported whose semantic paralexias appeared to result mainly from a lexical retrieval failure in oral reading. He was able to draw correct pictures of the written words for which he had simultaneously produced a semantically erroneous oral reading response. Repeated attempts to correct paralexic responses were common, indicating that the patient was often aware of the errors. His lexical retrieval problems and semantic errors extended to naming as well, and the results support Nolan and Caramazza's (1982, Brain and Language, 16, 237-264), dual-deficit model of deep dyslexia.     

Speculation about behavior, brain damage, and self-organization: the other way to herd a cat

This article contrasts aphasic patients' performance of word naming and lexical decision with that of intact college-aged readers. We discuss this contrast within a framework of self-organization; word recognition by aphasic patients is destabilized relative to intact performance. Less stable performance shows itself as an increase in the dispersion of patients' response times compared to college students'. Dispersion is also more pronounced for low-frequency words than for high frequency words. We speculate, that increased dispersion originates in a reduction of constraints that support naming and lexical decision performances. A sufficient reduction of constraints yields qualitative changes in performance such as the production of semantic errors in deep dyslexia. These hypotheses are offered as alternatives to postulating distinct modules.     

Gender and lexical access in Italian

Two new procedures were employed to investigate the effects of semantic and grammatical gender on lexical access in Italian and to investigate the interaction of gender with other factors that are known to influence lexical access in other languages. The gender-monitoring task requires a conscious decision about the gender of each noun, whereas the word repetition task does not require explicit attention to gender. In both tasks, single words are presented out of context, under speeded conditions. Both procedures proved to be sensitive indices of word recognition, with reaction times that are closely tied to the point at which words can be uniquely identified (although some processing before and after the uniqueness point was seen). In both tasks, reaction times were strongly affected by phonological factors (e.g., length, number of syllables, and presence of frication on the initial consonant). Phonological transparency of gender marking had a reliable effect on gender monitoring but had no effect on word repetition, suggesting that explicit attention to gender may be a factor affecting utilization of this phonological cue. Semantic factors (including semantic gender) had no effect on performance. Frequency and age of acquisition had very small effects when other factors were controlled. Implications for current models of lexical access are discussed, with special reference to the role of gender.