Effects of spacing and repetition on amnesic patients' performance during perceptual identification, stem completin, and category exemplar production.

The effects of repetition and spacing of repetitions on amnesic patients' implicit task performance was studied. Amnesic patients and control participants performed a perceptual identification task, a word-stem completion task, and a category exemplar production task after the presentation of target words repeated within a list. Repetition proved to have no effect on perceptual identification or on word-stem completion, but it did play a role in category exemplar production. As expected, the amnesic patients demonstrated normal performance on the perceptual identification and word-stem completion tasks. However, on category exemplar production, the amnesic patients' performance was significantly below that of the control participants, and the 2 groups differentially responded to repetition. The normal control participants' spontaneous ability to analyze semantic features of words led to unconscious priming of the category and its links to the exemplars after only one presentation of a word. Amnesic patients. on the other hand, seemed to rely more on the fluency produced by multiple presentations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of a molecular clone of HIV type 2 infectious for Macaca nemestrina

The effects of repetition and spacing of repetitions on amnesic patients' implicit task performance was studied. Amnesic patients and control participants performed a perceptual identification task, a word-stem completion task, and a category exemplar production task after the presentation of target words repeated within a list. Repetition proved to have no effect on perceptual identification or on word-stem completion, but it did play a role in category exemplar production. As expected, the amnesic patients demonstrated normal performance on the perceptual identification and word-stem completion tasks. However, on category exemplar production, the amnesic patients' performance was significantly below that of the control participants, and the 2 groups differentially responded to repetition. The normal control participants' spontaneous ability to analyze semantic features of words led to unconscious priming of the category and its links to the exemplars after only one presentation of a word. Amnesic patients, on the other hand, seemed to rely more on the fluency produced by multiple presentations.     

Serotonin levels influence patterns of repetition priming.

Repetition priming in a word-stem completion task was examined in a group of control subjects and in a group of experimental subjects under conditions of acute tryptophan depletion (T-) and tryptophan augmentation (T+). Experimental subjects ingested amino acid compounds that depleted or loaded the body with tryptophan, and word-stem completion priming performance was measured. Results indicate differential effects of T- and T+ manipulations on word-stem completion priming. In the control group, both specific-visual and amodal priming were observed. Conversely, in the T+ condition, specific-visual priming, but no amodal priming, was observed, whereas in the T- condition, amodal priming, but no specific-visual priming, was observed. The authors conclude that serotonin (5-hydroxytryptamine) plays a critical role in repetition priming by helping to modulate which neural systems contribute to priming effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Affective valence of words, explicit and implicit memory in clinical depression

Explicit and implicit memory for affectively valenced words (positive, negative or neutral) were investigated in 30 patients suffering from a major depressive episode (DSM-III-R criteria) and 30 normal control subjects. Explicit memory was assessed with a free-recall and a recognition task and implicit memory with a word-stem completion task. Depressed and control subjects recalled more emotional, i.e., positive and negative, words than neutral ones. They recognized less negative than neutral words. In contrast, to recall and recognition performance, word-completion performance was not sensitive to the affective valence of words: depressed and control subjects exhibited equivalent priming of positive, negative and neutral words. These results indicate that, in depressed and normal subjects, the affective valence of words influences memory when conscious, intentional recollection is required but is devoid of effect when such a recollection is not required.     

Further Exploration of Controlled and Automatic Memory Processes in Early Alzheimer's Disease.

The authors' aim in this study was to explore automatic and controlled processes in Alzheimer's disease (AD) by using a variant of the word-stem completion task that applies the process-dissociation procedure. Several methodological precautions were taken in order to limit problems observed in previous studies (e.g., poor task sensitivity, ceiling and/or floor effects, no control over comprehension of instructions). Our results (a) confirmed the marked deterioration in controlled processes and (b) showed that when psychometric constraints were limited, automatic memory processes were preserved in AD. These data are in line with those from more global studies in suggesting that AD is characterized by an early deterioration in controlled processes and an initial preservation of automatic processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of two rice MADS box genes that control flowering time

This study utilised positron emission tomography (PET) to identify the cortical areas involved in verbal initiation and suppression in normal subjects whilst performing a sentence completion test (the Hayling Test). In the first condition (response initiation) subjects were required to complete a sentence from which the last word was omitted, whereas in the second condition (response suppression) subjects were asked to complete a sentence with a word which made no sense in the context of the sentence. Subjects were also required to perform a control task in which they had to read out the last word of given sentences. Compared to the control task, response initiation was associated with left-sided activation of the frontal operculum, inferior frontal gyrus, middle temporal gyrus and the right anterior cingulate gyrus, whereas response suppression was associated with left frontal operculum, inferior frontal gyrus and right anterior cingulate gyrus activation. The difference in activation between the two conditions of the Hayling Test lay in the increased activation of the left middle temporal gyrus and the left inferior frontal gyrus during response initiation.     

Visual specificity effects on word stem completion: Beyond transfer appropriate processing?

Explored the determinants of perceptual specificity effects (PSEs) in visual word-stem completion. 256 undergraduates participated in 4 experiments. In Exp 1, Ss completed a stem completion task after a number-search task in study-condition and -case phases. Ss were assessed for their awareness of the study-task relationship and compliance with instructions. In Exp 2, retrieval instructions and study task were manipulated within Ss and between 4 study-test blocks. Ss in Exp 3 completed study-test blocks with unintentional test instructions as in Exp 2. In Exp 4, retention interval, and study-task and -case were manipulated within the Ss. In Exp 1, PSEs on the stem completion task depended on perceptual encoding when Ss' awareness of the study-test relationship was limited. In Exps 2–4, these effects depended on semantic encoding. PSEs after short retention intervals were independent of encoding task. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cross-form priming in normal aging and in mild dementia of the Alzheimer type

Twenty patients at early stages of Alzheimer's disease (AD), 20 elderly control subjects and 20 young subjects completed a cross-form priming task, followed by a free recall task. Results show that patients with mild AD display priming effects, and that these priming effects are strictly comparable to those obtained by elderly and young control subjects. Moreover, while the patients' performances are normal in the implicit part of the task, they are massively impaired in the explicit free recall task. These results don't support the hypothesis of a dissociation of performances between identification tasks and generation tasks in Alzheimer's disease, and show that conceptual priming can be observed at early stages of the disease, despite semantic memory impairments.     

Effects of reducing attentional resources on implicit and explicit memory after severe traumatic brain injury.

Implicit and explicit memory were examined in individuals with severe traumatic brain injury (TBI) under conditions of full and divided attention. Participants included 12 individuals with severe TBI and 12 matched controls. In Experiment 1, participants carried out an implicit test of word-stem completion and an explicit test of cued recall. Results demonstrated that TBI participants exhibited impaired explicit memory but preserved implicit memory. In Experiment 2, a significant reduction in the explicit memory performance of both TBI and control participants, as well as a significant decrease in the implicit memory performance of TBI participants, was achieved by reducing attentional resources at encoding. These results indicated that performance on an implicit task of word-stem completion may require the availability of additional attentional resources that are not preserved after severe TBI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sentence comprehension in Alzheimer's disease: Effects of grammatical complexity, speech rate, and repetition.

Caregivers of patients diagnosed with Alzheimer's disease (AD) are often advised to modify their speech to facilitate the patients' sentence comprehension. Three common recommendations are to (a) speak in simple sentences, (b) speak slowly, and (c) repeat one's utterance, using the same words. These three speech modifications were experimentally manipulated in order to investigate their individual and combined effects on sentence comprehension in AD. Fifteen patients with mild to moderate AD and 20 healthy older persons were tested on a sentence comprehension task with sentences varying in terms of (a) degree of grammatical complexity, (b) rate of presentation (normal vs. slow), and (c) form of repetition (verbatim vs. paraphrase). The results indicated a significant decline in sentence comprehension for the AD group. Sentence comprehension improved, however, after the sentence was repeated in either verbatim or paraphrased form. However, the patients' comprehension did not improve for sentences presented at the slow speech rate. This pattern of results is explained vis-à-vis the patients' working memory loss. The findings challenge the appropriateness of several clinical recommendations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

ERP assessment of visual and auditory language processing in schizophrenia.

Language disturbance in schizophrenia has been recently attributed to disturbed priming mechanisms. In the present study, event-related potentials (ERPs), were recorded to final words in sentences presented to 13 chronic patients with schizophrenia and 12 normal controls. Half of the final words fit a sentence context and another half did not. The N400 (the ERP sensitive to language) latency was prolonged, and its amplitude was more negative to both correct and incorrect sentence endings in the group with schizophrenia relative to the group of normal controls. The early ERP components, N100 and P200, were similar in both groups. These results suggest that language abnormalities in schizophrenia are related to a dysfunction in the language system and not to a general cognitive dysfunction, and may be related to poor use of context in patients with schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adult age differences in implicit and explicit memory: Time course and encoding effects.

Young and older adults were tested at three delays on word-stem completion or cued recall following semantic or structural word judgments. Identical three-letter stems were present at retrieval for both implicit (completion) and explicit (cued recall) tasks; only the intention to recall list words differed. The young adults outperformed the older adults on both implicit and explicit task at all test delays. Under some conditions, the older but not the young adults performed more poorly on cued recall than on stem completion, suggesting a possible failure to use implicitly available information to support explicit remembering. These results suggest that some forms of implicit memory decline with normal aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Word-stem completion priming in healthy aging and Alzheimer's disease: The effects of age, cognitive status, and encoding.

There are many conflicting results concerning the effects of age and Alzheimer's disease (AD) on word-stem completion priming. To examine potential sources of this variability, the authors examined the influences on such priming of age, cognitive status, and encoding in a large sample of young, old, and AD individuals. At study, words were processed aloud by reading, reading and rating likeability, or generating from definition. Old participants had less priming than young participants and more priming than AD patients. For the healthy old participants, priming decreased with advancing age and with cognitive loss following generation only. For AD patients, priming decreased as dementia severity increased; patients with the mildest dementia did not differ from healthy old participants. Thus, age, cognitive status, and encoding differentially influenced the magnitude of priming in healthy aging and AD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Low body weight in Alzheimer's disease is associated with mesial temporal cortex atrophy

There are reports of weight loss and low body mass index (BMI) in patients with AD. The mesial temporal cortex (MTC) is involved in feeding behavior and memory and is preferentially involved in AD. We studied 74 subjects, including 58 AD patients and 16 control subjects, to determine whether BMI is associated with atrophy of the MTC or other brain regions. We used MRI morphometric analysis to provide measures of regional brain atrophy. AD patients had significant brain atrophy in all measured brain regions, except the white matter, compared with normal control subjects. The MTC was the only brain region significantly associated with BMI in AD patients (r = 0.39, p = 0.003). Multiple-regression analysis indicated that addition of brain regions other than the MTC to the model did not significantly add to the prediction of BMI. We conclude that low BMI correlates best and specifically with MTC atrophy. This finding supports a connection between limbic system damage and low body weight in AD.     

Performance of adult aphasics on a sentence evaluation and revision task

Adult aphasics completed a sentence evaluation and revision task to test some aspects of their linguistic competence. Grammatical and ungrammatical sentences served as the stimuli. Ungrammatical sentences were characterized by violations of syntactic or semantic structure, or both. Aphasics evaluated correctly the grammaticality of most stimulus sentences. Incorrect evaluations were associated with sentences characterized by violations of syntactic structure. Aphasics' revisions of sentences that they judged to be ungrammatical were in the direction of appropriate grammatical structures. Omission of morphological endings was the most frequent sentence revision error. Aphasics' errors on both tasks could be accounted for by performance deficits such as inattentiveness to syntactic detail, auditory perceptual impairments, and inefficient lexical retrieval. These findings lend support to the argument that aphasia is best characterized as a performance rather than competence disruption.     

Task demands and sentence comprehension in patients with dementia of the Alzheimer's type

Patients with dementia of the Alzheimer's type (DAT) and matched normal controls were given three tests of syntactic comprehension in which nonlinguistic visual and memory task demands were varied. In all tasks, subjects were presented spoken semantically reversible sentences with a variety of syntactic structures and required to match the sentence to a picture. In the first experiment, subjects matched the spoken sentence to one of two pictures that appeared either before or immediately following the presentation of the sentence. The target picture depicted the spoken sentence correctly and the foil depicted the reversed thematic roles to those in the sentence (i.e., it was a syntactic foil). The second experiment employed a sentence video-verification task in which subjects were required to determine if the spoken sentence matched a videotaped depiction of the action in the sentence or a syntactic foil. In the third experiment, in different conditions, subjects were required to determine whether the spoken sentence matched a single picture or to choose the picture that matched the sentence from an array of two or three pictures. In this experiment, both lexical and syntactic foils were used. In all tasks, DAT patients were affected by the number of propositions in the presented sentence, but not by the syntactic complexity of the sentence. Control subjects also were unaffected by the syntactic complexity of the sentence; the number-of-proposition effect was present in some experiments in the control population. Comparison of performance across the one-, two-, and three-picture versions of the task showed that the magnitude of the effect of number of propositions increased as the number of pictures in the array increased. In addition, analysis of the data from each of the tasks separately showed that the effect of number of propositions only occurred when subjects were attempting to match the target to a syntactic foil (one-picture version) or to choose between the target and a syntactic foil (two- and three-picture versions). The results support the view that patients with DAT do not have disturbances affecting syntactic processing. In addition, they suggest that the effect of number of propositions arises at a stage of analysis that is partially separate from assigning sentence meaning, such as in holding a representation of the sentence in memory until the pictures can be analyzed and encoded and/or in comparing the results of the picture analysis with a stored representation of the sentence meaning.     

Font-specific priming following global amnesia and occipital lobe damage.

Font-specificity in visual word-stem completion priming was examined in patients with global amnesia and Patient M.S., who had a right-occipital lobectomy. Word-stems appeared in the same or different font as study words. Amnesic patients showed normal font-specific priming (greater priming for words studied in the same than different font as test), despite impaired word-stem cued recall. Patient M.S. failed to exhibit font-specific priming, despite preserved declarative memory. Therefore, perceptual specificity in visual priming depends on visual processes mediated by the right-occipital lobe rather than medial temporal and diencephalic regions involved in declarative memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In vitro receptor imaging for characterization of human solid tumors

Artificial neural networks have been applied to a variety of pattern recognition tasks in medical imaging and have been shown to be a powerful classification tool. The potential usefulness to discriminate normal from abnormal cerebral perfusion patterns was investigated. METHODS: Cerebral perfusion imaging with 99mTc-labeled hexamethylpropyleneimine oxime was performed on 52 normal control subjects, 29 patients with clinically diagnosed Alzheimer's disease (AD) and 25 patients with chronic cocaine polydrug abuse. Each study was registered and scaled to a common anatomic coordinate system, yielding 120 standardized cortical regions. A back-propagation neural network classifier based on regional perfusion was used to classify normal and abnormal perfusion patterns. The neural network was trained to discriminate patients with AD from age-matched normal controls and cocaine polydrug abuse patients from normal controls. The performance of the neural network in these two tasks was evaluated quantitatively by receiver operating characteristic (ROC) analysis using cross-validation. RESULTS: For patients with AD, the area under the ROC curve was 0.93 +/- 0.04. When testing with the cocaine polydrug abuser data, the area under the ROC curve was 0.89 +/- 0.04. CONCLUSION: Neural networks provide a potentially useful tool in the decision-making task to discriminate patients with AD and cocaine abuse from normal controls.     

Level-of-processing effects in word-completion priming: A neuropsychological study.

Recent reviews (A. S. Brown & D. B. Mitchell, see record 82:16176; B. Challis & D. R. Brodbeck, see record 79:30007) concluded that level-of-processing (LOP) manipulations affect priming in perceptual tasks, contrary to earlier suggestions that such tasks are insensitive to LOP. In 3 experiments with amnesic patients and control Ss, the authors examined the effect of LOP manipulations on priming in word-stem and word-fragment completion and on recognition memory. Amnesic patients exhibited reduced or near-zero LOP effects in word-completion priming compared with controls. LOP affected recognition memory for both amnesic patients and control Ss, confirming that the LOP manipulation affected explicit memory. When the effect of explicit retrieval on control performance was reduced by using a low-level encoding task, priming was the same for amnesic patients and controls. The authors suggest that LOP effects in word-completion priming tasks reflect the influence of explicit retrieval, which can be used usefully by control Ss but much less so by amnesic patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of semantic context by patients with Alzheimer's disease.

Used semantic-priming procedures to examine limitations in the use of semantic context by 18 patients (mean age 68.9 yrs) with Alzheimer's disease (AD) and to determine whether any such contextual effects were mediated solely through automatic processes or whether attentional processes were also involved. Three tasks were applied to examine the effect of semantic context on the performance of 18 normal elderly Ss (mean age 67.2 yrs), 18 normal young Ss (mean age 24.1 yrs), and the AD Ss. When normal and AD Ss were asked to decide whether a given item was a member of a certain category, their response times were equally affected by the item's dominance in the category. The time that AD Ss took to recognize a word was actually affected more by the semantic context provided by a priming sentence than was that of normal Ss. When asked to generate the final word of an incomplete sentence, AD Ss performed very poorly unless potential responses were highly constrained by sentence context. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)