The effect of divided attention on global judgment of learning accuracy

This study examined the effect of divided attention (DA) on global judgment of learning (JOL) accuracy in a multitrial list learning paradigm. A word monitoring task was used to divide attention. Participants were assigned to an attention condition (DA at encoding, DA at judgment, DA at retrieval, or focused attention) and completed 4 learning trials, each comprising a study, judgment, and recall phase. Participants showed greater overconfidence in the DA at encoding (Trial 2) and DA at retrieval (Trials 1 and 2) conditions than in the focused attention condition. DA atjudgment did not affect JOL accuracy, and there was no effect of DA in Trials 3 and 4 on JOL accuracy across all attention conditions. Results indicate that participants consider conditions of encoding and retrieval but do not engage in recall when forming global JOLs. These findings suggest that people rely on extrinsic cues when making repeated, global metamemoryjudgments.     

Critical reading of words and phrases in aphasia

To assess ability to read critically at the word and phrase level, four tests were administered to aphasic patients blocked on site of lesion and severity of auditory comprehension defect. Overall, site of lesion did not affect the quantitative scores or the patterns of errors in the four tests; this result suggests that there is a fixed order of difficulty in reading comprehension irrespective of the locus of the aphasic deficit. In contrast, profiles of performance differed significantly, depending on severity of comprehension difficulty. Patients with significant comprehension defect proved relatively superior at recognizing misspelled words; relatively poor at matching written nouns with their depicted referents; less likely to display improved comprehension when an additional substantive was included in a written phrase; relatively better at recognizing which words were the same parts of speech than at recognizing which words share salient semantic features; and relatively better at matching words which belonged together than at choosing the word which does not belong to a set. Taken together, the results suggest that strategies of reading may change in the presence of a severe aphasia, with such impaired patients relying less on semantic considerations and consequently more on orthographic information and on the distributional and sequential properties of words in sentences.     

Aphasic performance on a lexical decision task: multiple meanings and word frequency

The lexical access of words varying in the number of meanings and frequency of occurrence was examined in fluent and nonfluent aphasic individuals and a control group of non-brain-damaged adults, using a lexical decision task. Fluent aphasic subjects performed similarly to nonfluent aphasic and normal subjects, showing that words with a high number of meanings and with a high frequency of occurrence were recognized as real words faster than words with few meanings or a low frequency of occurrence. While previous research has demonstrated that the number of meanings associated with a word exerts a powerful influence on the internal lexicon of normals, the results of this study suggest that brain damage resulting in aphasia does not disrupt this semantic organization.     

Lexical and Prosodic Effects on Syntactic Ambiguity Resolution in Aphasia

The purpose of this study was to determine whether and when individuals with aphasia and healthy controls use lexical and prosodic information during on-line sentence comprehension. Individuals with aphasia and controls (n = 12 per group) participated in a self-paced listening experiment. The stimuli were early closure sentences, such as "While the parents watched(,) the child sang a song." Both lexical and prosodic cues were manipulated. The cues were biased toward the subject- or object- of the ambiguous noun phrase (the child). Thus, there were two congruous conditions (in which both lexical cues and prosodic cues were consistent) and two incongruous conditions (in which lexical and prosodic cues conflicted). The results showed that the people with aphasia had longer listening times for the ambiguous noun phrase (the child) when the cues were conflicting, rather than consistent. The controls showed effects earlier in the sentence, at the subordinate verb (watched or danced). Both groups showed evidence of reanalysis at the main verb (sang). These effects demonstrate that the aphasic group was sensitive to the lexical and prosodic cues, but used them on a delayed time course relative to the control group.     

The effects of slowed speech on auditory comprehension in aphasia

The present study investigates the effects of slowed speech on auditory comprehension in aphasia. Specifically, an attempt was made to isolate the effects of added time on comprehension at the language processing stages of auditory perception, by increasing the duration of the vowel segments in each word; word recognition and semantic analysis, by adding silences between words; and syntactic analysis, by adding silences at constituent phrase boundaries. Sentences were also read at a slow rate to see the effects of naturally slowed speech on sentence comprehension. Test sentences consisted of simple active and passive declarative sentences, and complex sentences with embedded medial and final relative clauses. Sentences were either semantically reversible or nonreversible. Thirty-four aphasic patients who varied in both severity and type of aphasia were tested on a picture verification task. Results indicated that slowing facilitated language comprehension significantly only in the syntactic condition. Neither syntactic complexity nor semantic reversibility interacted with slowed speech to facilitate auditory language comprehension. Further, it was only the Wernicke's aphasics who showed significant improvement with time added at constituent boundaries. These results suggest that time alone does not facilitate language comprehension in aphasia, but that rather it is the interaction of time with syntactic processing which improves comprehension.     

The relation between oral movement control and speech

A large series of neurological patients, selected solely on the basis that they had damage restricted to one hemisphere of the brain, was given a variety of tests of basic speech and praxic function. Within the left-damaged group, patients were further identified as aphasic or nonaphasic, based on preexisting standard tests of aphasia. Subgroups of aphasics were studied on the basis of lesion location, rather than on the basis of aphasia type. The focus of the study was the relation between the production of speech and nonspeech oral movements, particularly across anterior and posterior lesions. Reproduction of single nonverbal oral movements and of single isolated speech sounds was found to be very highly correlated, and both depended selectively on the left anterior region of the brain. This same region was critically important for rapid repeated articulation of a syllable, suggesting that it mediates control at some "unit" level of movement, in a phenomenological sense, for both speech and nonspeech movements. Other "speech" regions in the left hemisphere appeared to be dispensable for the production of single oral movements, whether these were verbal or nonverbal movements. However, for most aphasic patients, an area in the left posterior region was inferred to be essential for production of multiple oral movements, whether nonverbal or verbal, suggesting a critical role in the accurate selection of movements. Within the posterior region, there was further differentiation for multisyllabic speech into a parietal system, which appeared to mediate primarily praxic function, and a temporal system, which appeared to mediate verbal-echolalic function. Aphasias from anterior and posterior lesions resembled "Broca's" and "Wernicke's" aphasia only insofar as they differed in fluency, with anterior aphasics clearly less fluent. Tests of speech comprehension did not differentiate the groups. It is suggested that classifying aphasic patients via lesion location rather than aphasic typology might yield a view of functional subsystems different from those commonly accepted.     

Sensitivity to local sentence context information in lexical ambiguity resolution: evidence from left- and right-hemisphere-damaged individuals

Using a cross-modal semantic priming paradigm, the present study investigated the ability of left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects to use local sentence context information to resolve lexically ambiguous words. Critical sentences were manipulated such that they were either unbiased, or biased toward one of two meanings of sentence-final equibiased ambiguous words. Sentence primes were presented auditorily, followed after a short (0 ms) or long (750 ms) interstimulus interval (ISI) by the presentation of a first- or second-meaning related visual target, on which subjects made a lexical decision. At the short ISI, neither patient group appeared to be influenced by context, in sharp contrast to the performance of the NBD control subjects. LHD nonfluent aphasic subjects activated both meanings of ambiguous words regardless of context, whereas RHD subjects activated only the first meaning in unbiased and second-meaning biased contexts. At the long ISI, LHD nonfluent aphasic subjects failed to show evidence of activation of either meaning, while RHD individuals activated first meanings in unbiased contexts and contextually appropriate meanings in second-meaning biased contexts. These findings suggest that both left (LH) and right hemisphere (RH) damage lead to deficits in using local contextual information to complete the process of ambiguity resolution. LH damage seems to spare initial access to word meanings, but initially impairs the ability to use context and results in a faster than normal decay of lexical activation. RH damage appears to initially disrupt access to context, resulting in an over-reliance on frequency in the activation of ambiguous word meanings.     

Comprehension of Idioms in Turkish Aphasic Participants

Brain damaged participants offer an opportunity to evaluate the cognitive and linguistic processes and make assumptions about how the brain works. Cognitive linguists have been investigating the underlying mechanisms of idiom comprehension to unravel the ongoing debate on hemispheric specialization in figurative language comprehension. The aim of this study is to evaluate and compare the comprehension of idiomatic expressions in left brain damaged (LBD) aphasic, right brain damaged (RBD) and healthy control participants. Idiom comprehension in eleven LBD aphasic participants, ten RBD participants and eleven healthy control participants were assessed with three tasks: String to Picture Matching Task, Literal Sentence Comprehension Task and Oral Idiom Definition Task. The results of the tasks showed that in overall idiom comprehension category, the left brain-damaged aphasic participants interpret idioms more literally compared to right brain-damaged participants. What is more, there is a significant difference in opaque idiom comprehension implying that left brain-damaged aphasic participants perform worse compared to right brain-damaged participants. On the other hand, there is no statistically significant difference in scores of transparent idiom comprehension between the left brain-damaged aphasic and right brain-damaged participants. This result also contribute to the idea that while figurative processing system is damaged in LBD aphasics, the literal comprehension mechanism is spared to some extent. The results of this study support the view that idiom comprehension sites are mainly left lateralized. Furthermore, the results of this study are in consistence with the Giora’s Graded Salience Hypothesis.     

Cathodal transcranial direct current stimulation of the right Wernicke's area improves comprehension in subacute stroke patients

Previous studies have shown the appearance of right-sided language-related brain activity in right-handed patients after a stroke. Non-invasive brain stimulation such as transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) have been shown to modulate excitability in the brain. Moreover, rTMS and tDCS have been found to improve naming in non-fluent post-stroke aphasic patients. Here, we investigated the effect of tDCS on the comprehension of aphasic patients with subacute stroke. We hypothesized that tDCS applied to the left superior temporal gyrus (Wernicke’s area) or the right Wernicke’s area might be associated with recovery of comprehension ability in aphasic patients with subacute stroke. Participants included right-handed subacute stroke patients with global aphasia due to ischemic infarct of the left M1 or M2 middle cerebral artery. Patients were randomly divided into three groups: patients who received anodal tDCS applied to the left superior temporal gyrus, patients who received cathodal tDCS applied to the right superior temporal gyrus, and patients who received sham tDCS. All patients received conventional speech and language therapy during each period of tDCS application. The Korean-Western Aphasia Battery (K-WAB) was used to assess all patients before and after tDCS sessions. After intervention, all patients had significant improvements in aphasia quotients, spontaneous speech, and auditory verbal comprehension. However, auditory verbal comprehension improved significantly more in patients treated with a cathode, as compared to patients in the other groups. These results are consistent with the role of Wernicke’s area in language comprehension and the therapeutic effect that cathodal tDCS has on aphasia patients with subacute stroke, suggesting that tDCS may be an adjuvant treatment approach for aphasia rehabilitation therapy in patients in an early stage of stroke.     

Noun and verb processing in Greek-English bilingual individuals with anomic aphasia and the effect of instrumentality and verb-noun name relation

Noun and verb comprehension and production was investigated in two groups of late bilingual, Greek-English speakers: individuals with anomic aphasia and a control group of non-brain injured individuals matched for age and gender. There were no significant differences in verb or noun comprehension between the two groups in either language. However, verb and noun production during picture naming was significantly worse in the bilingual individuals with anomic aphasia in both languages, who also showed a specific verb impairment in Greek and English. The potential underlying level of breakdown of the specific verb impairment was further investigation with reference to two specific features of verbs: instrumentality and verb-noun relationship. Additional results revealed a facilitatory effect of Instrumentality in both languages. However, there was no effect of verb-noun name relation in Greek, and a negative effect of verb-noun name relation was observed in English. Lemma retrieval seemed to be intact in this group of bilingual individuals whose main problem seemed to arise during the retrieval of the phonological representation of the target word. This impairment was greater in English. The findings are discussed in terms of three current models of word production.     

Divided attention and memory: evidence of substantial interference effects at retrieval and encoding

In 5 divided attention (DA) experiments, students (24 in each experiment) performed visual distracting tasks (e.g., recognition of words, word and digit monitoring) while either simultaneously encoding an auditory word list or engaging in oral free recall of the target word list. DA during retrieval, using either of the word-based distracting tasks, produced relatively larger interference effects than the digit-monitoring task. DA during encoding produced uniformly large interference effects, regardless of the type of distracting task. Results suggest that when attention is divided at retrieval, interference is created only when the memory and concurrent task compete for access to word-specific representational systems; no such specificity is necessary to create interference at encoding. During encoding, memory and concurrent tasks compete primarily for general resources, whereas during retrieval, they compete primarily for representational systems.     

A linguistic analysis of fluent aphasia

Fluent aphasia is a general term for those posterior aphasic syndromes which involve little or no motor difficulties and which exhibit rather normal rates of speech output. This paper is a comparative neurolinguistic study of three types of fluent aphasia. Differences as well as similarities regarding language behavior both within and across groups are analyzed. Much attention is given to anomia and to how it is confronted by each group. Various possible paraphasic processes which may be involved in the genesis of neologisms are discussed. Localization information is provided for the patients in the study, and special attention is drawn to prerequisite neuroanatomical involvement for neologistic jargon.     

Theories of spoken word recognition deficits in aphasia: evidence from eye-tracking and computational modeling

We used eye-tracking to investigate lexical processing in aphasic participants by examining the fixation time course for rhyme (e.g., carrot-parrot) and cohort (e.g., beaker-beetle) competitors. Broca’s aphasic participants exhibited larger rhyme competition effects than age-matched controls. A re-analysis of previously reported data (Yee, Blumstein, & Sedivy, 2008) confirmed that Wernicke’s aphasic participants exhibited larger cohort competition effects. Individual-level analyses revealed a negative correlation between rhyme and cohort competition effect size across both groups of aphasic participants. Computational model simulations were performed to examine which of several accounts of lexical processing deficits in aphasia might account for the observed effects. Simulation results revealed that slower deactivation of lexical competitors could account for increased cohort competition in Wernicke’s aphasic participants; auditory perceptual impairment could account for increased rhyme competition in Broca’s aphasic participants; and a perturbation of a parameter controlling selection among competing alternatives could account for both patterns, as well as the correlation between the effects. In light of these simulation results, we discuss theoretical accounts that have the potential to explain the dynamics of spoken word recognition in aphasia and the possible roles of anterior and posterior brain regions in lexical processing and cognitive control.     

PET activation studies comparing two speech tasks widely used in surgical mapping

"Automatic" speech, especially counting, is frequently preserved in aphasia, even when word production is severely impaired. Although brain sites and processes for automatic speech are not well understood, counting is frequently used to elicit fluent speech during preoperative and intraoperative cortical mapping for language. Obtaining both behavioral and functional brain imaging measures, this study compared counting with a word production task (generation of animal names), including non-verbal vocalizations and quiet rest as control states, in normal and aphasic subjects. Behavioral data indicated that normal and aphasic groups did not differ in counting or non-verbal vocalizations, but did differ significantly in word production ("naming" animals). Functional brain imaging results on normal subjects using partial least squares analysis of PET rCBF images revealed three significant latent variables (LVs): one for naming and vocalizing, identifying bilateral anterior areas, with left predominating over right; a second LV for naming, identifying left and right frontal and temporal areas. For the third, only marginally significant LV, which was associated with automatic speech alone (counting), right and subcortical sites predominated. For patients, two LVs emerged, identified with naming and vocalization, and corresponding to a variety of cerebral sites; the analysis failed to find a specific latent variable for counting. A comparison between group data for normal subjects and patients suggested that the naming, counting, and vocalization tasks were performed differently by the two groups. These results suggest that word generation as a verbal task is more likely to elicit activity in classical language areas than counting. Further studies are suggested to better understand differences between neurological substrates for non-propositional and automatic speech.     

The classifier problem in Chinese aphasia

In recent years, research on the relationship between brain organization and language processing has benefited tremendously from cross-linguistic comparisons of language disorders among different types of aphasic patients. Results from these cross-linguistic studies have shown that the same aphasic syndromes often look very different from one language to another, suggesting that language-specific knowledge is largely preserved in Broca's and Wernicke's aphasics. In this paper, Chinese aphasic patients were examined with respect to their (in)ability to use classifiers in a noun phrase. The Chinese language, in addition to its lack of verb conjugation and an absence of noun declension, is exceptional in yet another respect: articles, numerals, and other such modifiers cannot directly precede their associated nouns, there has to be an intervening morpheme called a classifier. The appropriate usage of nominal classifiers is considered to be one of the most difficult aspects of Chinese grammar. Our examination of Chinese aphasic patients revealed two essential points. First, Chinese aphasic patients experience difficulty in the production of nominal classifiers, committing a significant number of errors of omission and/or substitution. Second, two different kinds of substitution errors are observed in Broca's and Wernicke's patients, and the detailed analysis of the difference demands a rethinking of the distinction between agrammatism and paragrammatism. The result adds to a growing body of evidence suggesting that grammar is impaired in fluent as well as nonfluent aphasia.     

On the preservation of word order in aphasia: cross-linguistic evidence

Studies of language production in English-speaking aphasics (both fluent and nonfluent) generally lead to the conclusion that word order is preserved to a much greater degree than grammatical morphology and/or lexical retrieval. However, because word order is rigidly preserved even in normal English speech, this pattern might reflect nothing more than "the weak link in the chain." Using a constrained production paradigm, we provide evidence showing that canonical sentence order is well preserved in both fluent and nonfluent patients, in Italian and German (languages that permit much more pragmatic word-order variation) as well as English. Patients also retain the ability to order nouns around a preposition, and among Italian patients, access to a high-frequency form of pragmatic word-order variation is also retained. Syntactic difficulties seem to revolve not around loss of ordering principles, but (1) reduction in syntactic complexity, (2) overuse of canonical word order as a "safe harbor," (3) blend errors in which a form appears in legal but semantically incorrect position, and (4) abandonment of the effort to produce a complete sentence under stressful conditions. We offer a redefinition of syntactic impairment as a problem in the access of phrase structure types, resulting in a preference for higher frequency forms. Parallels between lexical retrieval and phrase structure retrieval suggest that similar mechanisms may be at work in both cases.     

The role of attention at retrieval on the false recognition of negative emotional DRM lists

This study examined the role of attention at retrieval on the false recognition of emotional items using the Deese–Roediger–McDermott (DRM) paradigm. Previous research has shown that divided attention at test increases false remember judgements for neutral critical lures. However, no research has yet directly assessed emotional false memories when attention is manipulated at retrieval. To examine this, participants studied negative (low in valence and high in arousal) and neutral DRM lists and completed recognition tests under conditions of full and divided attention. Results revealed that divided attention at retrieval increased false remember judgements for all critical lures compared to retrieval under full attention, but in both retrieval conditions, false memories were greater for negative compared to neutral stimuli. We believe that this is due to reliance on a more easily accessible (meaning of the word) but less diagnostic form of source monitoring, amplified under conditions of divided attention.     

Defects of immediate memory in Broca's and conduction aphasia

It has been suggested that the repetition defect seen in conduction aphasia is caused by an auditory immediate memory defect. The purposes of this study were the following: to ascertain whether the finding of an auditory immediate memory defect in conduction aphasia could be replicated, to ascertain whether Broca's aphasics have a similar type of immediate memory defect, and to ascertain whether a relationship exists between immediate memory and comprehension of spoken language. Digits were either spoken or presented visually to Broca's and conduction aphasics. An analysis of span scores reveals that within each group there were no significant differences between the modes of presentation or the response modes. There were no significant differences between the aphasic groups. Comprehension of spoken language significantly correlated with digit span scores.     

The role of number words: the phonological length effect in multidigit addition

We explored the role of phonological representations of number words in exact calculation. The reaction times and accuracy of responses in multidigit addition problems were compared across three groups of participants (young healthy, older healthy, and 3 patients with severe aphasia) and two types of addition problems: phonologically long in English (containing the bisyllabic number word ??seven??) and short in English (monosyllabic number words??e.g., ??six??). Older healthy participants were significantly faster and more accurate in calculation than younger healthy participants. The older participants showed no evidence of a phonological length effect. However this effect was apparent in the younger adults, with longer reaction times on phonologically long problems. Furthermore, there was an association between the presence of a phonological length effect and the overall speed of response, suggesting that less proficient calculators were more reliant on phonological mediation of performance. The aphasic participants retained the ability to complete multidigit additions and were as accurate as the younger healthy group, although the response times of two of the 3 patients were slow. The aphasic participants varied with regard to the presence of a phonological length effect. Two participants showed no evidence of phonological mediation, while 1 displayed a phonological length effect. The results suggest that language resources are not mandatory for exact addition, although they may be used to scaffold math performance in less competent calculators. Evidence of phonological mediation of performance in aphasic participants may provide insight into the integrity or otherwise of inner speech in severe aphasia.     

Prosody, linguistic demands, and auditory comprehension in aphasia.

Prosody plays a clear role in the auditory comprehension of narratives by aphasic listeners. Previous research, however, has pointed to questions regarding variables which increase task complexity (e.g., memory, reading level) and the influence of the severity of aphasia. This study examined the role of the severity of aphasia and linguistic complexity in narrative comprehension by aphasic listeners. Findings indicate that while all subject groups improved their auditory comprehension when emphasis was present, people with severe aphasia improved significantly more, but only in a low linguistic complexity condition. However, subjects had additional opportunity for improved performance in both low and high linguistic complexity conditions. These results pose additional questions about perceived task difficulty (and performance) and resource allocation strategies.