Search

Background:With the proportion of older adults in Hong Kong projected to double in size in the next 30 years, it is important to develop measures for detecting individuals in the earliest stage of Alzheimer's disease (AD, 0.5 in Clinical Dementia Rating, CDR). We tested the utility of a non-verbal prospective memory task (PM, ability to remember what one has to do when a specific event occurs in the future) as an early marker for AD in Hong Kong Chinese.Methods:A large community dwelling sample of older adults who are healthy controls (CDR 0, N = 125), in the earliest stage of AD (CDR 0.5, N = 125), or with mild AD (CDR 1, N = 30) participated in this study. Their reaction time/accuracy data were analyzed by mixed-factor analyses of variance to compare the performance of the three CDR groups. Logistic regression analyses were performed to test the discriminative power of these measures for CDR 0 versus 0.5 participants.Results:Prospective memory performance declined as a function of AD severity: CDR 0 > CDR 0.5 > CDR 1, suggesting the effects of early-stage AD and AD progression on PM. After partialling out the variance explained by psychometric measures (e.g., ADAS-Cog), reaction time/accuracy measures that reflected the PM still significantly discriminated between CDR 0 versus 0.5 participants in most of the cases.Conclusion:The effectiveness of PM measures in discriminating individuals in the earliest stage of AD from healthy older adults suggests that these measures should be further developed as tools for early-stage AD discrimination. [ABSTRACT FROM PUBLISHER]

In 3 experiments, auditory massed repetition was used to examine age-related differences in habituation by means of the verbal transformation paradigm. Participants heard 10 words (5 high frequency and 5 low frequency), each presented 180 times, and they reported perceived changes in the repeated words (verbal transformations). In these experiments, older adults reported fewer illusory percepts than young adults. Older adults' loss of auditory acuity and slowing of processing, stimulus degradation (in young adults), and instructions biasing the report of these illusory percepts did not account for the fewer illusory percepts reported by the older adults. These findings suggest that older adults' reduced susceptibility to habituation arises from centrally located declines in the transmission of information within the word-recognition pathway. The discussion focuses on the implications that these age-related declines may have on word identification during on-line speech perception. [ABSTRACT FROM AUTHOR]

The present study examined age differences in the influence of 3 factors that previous research has shown to influence word-naming performance. The influence of word frequency, orthographic length, and orthographic neighborhood measures was examined using large-scale regression analyses on the naming latencies for 2,820 words. Thirty-one younger adults and 29 older adults named all of these words, and age differences in the influence of these factors were examined. The results revealed that all 3 factors predicted reliable amounts of variance in word-naming latencies for both groups. However, older adults showed a larger influence of word frequency and reduced influences of orthographic length and orthographic neighborhood density compared with younger adults. Overall, these results suggest that lexical level factors increase in influence in older adults whereas sublexical factors decrease in influence. [ABSTRACT FROM AUTHOR]

Two experiments investigated age differences in the encoding of associative information during a speeded naming task. In both experiments, semantically unrelated prime-target word pairs were presented 4 times, in either massed or spaced fashion, during the learning phase. An immediate or delayed test trial was presented following the fourth presentation. In Experiment 1, participants named both the primes and the targets. Younger and older adults showed similar benefits when naming targets that were part of a consistent prime-target pairing compared with targets presented with different primes at each presentation. In Experiment 2, participants named only the target word. Younger adults showed a benefit for consistently paired words, whereas older adults showed no benefit for consistently paired words. The results of the test trials showed a greater benefit for massed repeated words than for spaced repeated words at the immediate test and a reversed pattern at the delayed test. This spacing by test delay interaction was evident in response latency in Experiment 1 and in cued recall performance in Experiment 2. [ABSTRACT FROM AUTHOR]

Although often unmeasured in studies of cognition, many older adults possess Alzheimer disease (AD) pathologies such as beta-amyloid (Aβ) deposition, despite being asymptomatic. We were interested in examining whether the behavior-structure relationship observed in later life was altered by the presence of preclinical AD pathology. A total of 511 cognitively unimpaired adults completed magnetic resonance imaging and three attentional control tasks; a subset (n = 396) also underwent Aβ-positron emissions tomography. A vertex-wise model was conducted to spatially represent the relationship between cortical thickness and average attentional control accuracy, while moderation analysis examined whether Aβ deposition impacted this relationship. First, we found that reduced cortical thickness in temporal, medial- and lateral-parietal, and dorsolateral prefrontal cortex, predicted worse performance on the attention task composite. Subsequent moderation analyses observed that levels of Aβ significantly influence the relationship between cortical thickness and attentional control. Our results support the hypothesis that preclinical AD, as measured by Aβ deposition, is partially driving what would otherwise be considered general aging in a cognitively normal adult population., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Introduction: Progression to symptomatic Alzheimer disease (AD) occurs slowly over a series of preclinical stages. Declining functional mobility may be an early indicator of loss of brain network integration and may lead to an increased risk of experiencing falls. It is unknown whether measures of functional mobility and falls are preclinical markers of AD. The purpose of this study is to examine (1) the relationship between falls and functional mobility with AD biomarkers to determine when falls occur within the temporal progression to symptomatic Alzheimer disease, and (2) the attentional compared with perceptual/motor systems that underlie falls and functional mobility changes seen with AD., Methods and Analysis: This longitudinal cohort study will be conducted at the Knight Alzheimer Disease Research Center. Approximately 350 cognitively normal participants (with and without preclinical AD) will complete an in-home visit every year for 4 years. During each yearly assessment, functional mobility will be assessed using the Performance Oriented Mobility Assessment, Timed Up and Go, and Timed Up and Go dual task. Data regarding falls (including number and severity) will be collected monthly by self-report and confirmed through interviews. This study will leverage ongoing neuropsychological assessments and neuroimaging (including molecular imaging using positron emission tomography and MRI) performed by the Knight Alzheimer Disease Research Center. Relationships between falls and biomarkers of amyloid, tau and neurodegeneration will be evaluated., Ethics and Dissemination: This study was approved by the Washington University in St. Louis Institutional Review Board (reference number 201807135). Written informed consent will be obtained in the home prior to the collection of any study data. Results will be published in peer-reviewed publications and presented at national and international conferences., Trial Registration Number: NCT04949529; Pre-results., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

The present study investigated the contribution of dispositional factors in accounting for the perplexing negative relationship between aging and mind-wandering (MW). First, we sought to examine whether experimentally manipulating participants' motivation during a modified Sustained Attention to Response Task (SART) would modulate sustained attention performance and MW reports for younger and older adults. Results indicated that a performance-based motivational incentive influenced self-reported motivation and objective measures of sustained attention performance for younger, but not older, adults as compared to a control block. However, the motivation manipulation did not significantly modulate either younger or older adults' MW reports. Second, we tested the unique contributions of conscientiousness, interest, and motivation in predicting state-level, trait-level, and SART MW reports along with a composite measure of all three predictors. The results from a series of mediation and regression analyses indicated (a) that conscientiousness and interest fully accounted for the relationship between age and four different self-reported MW estimates and (b) that self-reported motivation did not account for any unique variance in predicting MW reports above and beyond age. The dispositional factors also accounted for the observed differences in No-Go accuracy but did not fully account for the age differences in the coefficient of variation. Discussion focuses on distinctions between self-report and objective measures of MW and more general implications of considering dispositional factors in cognitive aging research. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Background/aims: Age-related cognitive decline is a pervasive problem in our aging population. To date, no pharmacological treatments to halt or reverse cognitive decline are available. Behavioral interventions, such as physical exercise and Mindfulness-Based Stress Reduction, may reduce or reverse cognitive decline, but rigorously designed randomized controlled trials are needed to test the efficacy of such interventions., Methods: Here, we describe the design of the Mindfulness, Education, and Exercise study, an 18-month randomized controlled trial that will assess the effect of two interventions-mindfulness training plus moderate-to-vigorous intensity exercise or moderate-to-vigorous intensity exercise alone-compared with a health education control group on cognitive function in older adults. An extensive battery of biobehavioral assessments will be used to understand the mechanisms of cognitive remediation, by using structural and resting state functional magnetic resonance imaging, insulin sensitivity, inflammation, and metabolic and behavioral assessments., Results: We provide the results from a preliminary study (n = 29) of non-randomized pilot participants who received both the exercise and Mindfulness-Based Stress Reduction interventions. We also provide details on the recruitment and baseline characteristics of the randomized controlled trial sample (n = 585)., Conclusion: When complete, the Mindfulness, Education, and Exercise study will inform the research community on the efficacy of these widely available interventions improve cognitive functioning in older adults.

The present study investigated age-related differences in the ability to constrain attention to the current task, without contamination (bleeding) from an upcoming decision. Each experiment included two blocks of trials. During Block 1, participants initially incidentally encoded a list of high- and low-frequency words, after which they pronounced aloud the studied words intermixed with a new set of words during a test phase. Block 2 was identical to Block 1 with the exception that after pronouncing each word aloud, participants made an additional decision (episodic recognition decision in Experiments 1 and 2 and animacy decision in Experiment 3). In the first two experiments, older adults showed disproportionate slowing in their response times to pronounce the words when they additionally had to make a recognition judgment afterward (Block 2) compared to when they only pronounced the words aloud (Block 1). Importantly, the difference between high-frequency and low-frequency words (the word frequency effect) was disproportionately attenuated for older adults in Block 2 compared to Block 1 and compared to younger adults. These results suggest that older adults experience greater cross-task bleeding than younger adults because word frequency has opposing effects in pronunciation and recognition tasks. As predicted, this age modulation of the word frequency effect in pronunciation performance was not replicated in Experiment 3 when participants made an animacy judgment, wherein word frequency effects act in concert with those of the pronunciation task. Discussion focuses on age-related differences in the ability to constrain attention to a current task. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Recent evidence indicates that older adults' decreased ability to inhibit irrelevant information may lead to increased processing and greater memory for distractor information compared with younger adults. The present experiments examine the generality of this finding in a series of Stroop studies. In Experiment 1, participants studied a list of words then received a Stroop color naming task, with to-be-remembered words embedded within the Stroop task. Although there was evidence of a disproportionate age-related Stroop effect, there was no evidence of an age difference in episodic recognition memory for words from the Stroop task. Experiment 2 extended this paradigm to a more implicit demasking task. Again, there was evidence of an age-related disproportionate Stroop effect, however, there were no differences in memory for unattended words in demasking performance. Experiment 3 was a direct replication of a previous study which reported age differences in the influence of unattended words, via implicit priming in a general knowledge test. The results did not replicate the original study such that younger adults showed slightly more priming from distractors than older adults. The results provide converging evidence that although older adults have more difficulty inhibiting irrelevant information in the Stroop task, distractor information does not seem to disproportionately influence later memory for older adults compared with younger adults. These studies suggest that it is critical to consider the locus of memory encoding in distractor tasks to better understand the relationship between inhibitory processes during the distractor task and later memory performance. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Although the majority of research in visual word recognition has targeted single-syllable words, most words are polysyllabic. These words engender special challenges, one of which concerns their analysis into smaller units. According to a recent hypothesis, the organization of letters into groups of successive consonants (C) and vowels (V) constrains the orthographic structure of printed words. So far, evidence has been reported only in French with factorial studies of relatively small sets of items. In the present study, we performed regression analyses on corpora of megastudies (English and British Lexicon Project databases) to examine the influence of the CV pattern in English. We compared hiatus words, which present a mismatch between the number of syllables and the number of groups of adjacent vowel letters (e.g., client), to other words, controlling for standard lexical variables. In speeded pronunciation, hiatus words were processed more slowly than control words, and the effect was stronger in low-frequency words. In the lexical decision task, the interference effect of hiatus in low-frequency words was balanced by a facilitatory effect in high-frequency words. Taken together, the results support the hypothesis that the configuration of consonant and vowel letters influences the processing of polysyllabic words in English.

Objective: To assess whether family history (FH) of Alzheimer disease (AD) alone influences AD biomarker abnormalities., Design: Adult Children Study., Setting: Washington University's Charles F. and Joanne Knight Alzheimer's Disease Research Center., Participants: A total of 269 cognitively normal middle- to older-aged individuals with and without an FH for AD., Main Outcome Measures: Clinical and cognitive measures, magnetic resonance imaging-based brain volumes, diffusion tensor imaging-based white matter microstructure, cerebrospinal fluid biomarkers, and molecular imaging of cerebral fibrillar amyloid with positron emission tomography using the [(11)C] benzothiazole tracer, Pittsburgh compound B., Results: A positive FH for AD was associated with an age-related decrease of cerebrospinal fluid Aβ42; the ε4 allele of apolipoprotein E (APOE4) did not alter this effect. Age-adjusted cerebrospinal fluid Aβ42 was decreased for individuals with APOE4 compared with the level for those without, and the decrease was larger for individuals with a positive FH compared with the decrease for those without. The variation of cerebrospinal fluid tau and Pittsburgh compound B mean cortical binding potential increased by age. For individuals younger than 55, an age-related increase in mean cortical binding potential was associated with APOE4 but not FH. For individuals older than 55, a positive FH and a positive APOE4 implied the fastest age-related increase in mean cortical binding potential. A positive FH was associated with decreased fractional anisotropy from diffusion tensor imaging in the genu and splenium of the corpus callosum., Conclusion: Independent of APOE4, FH is associated with age-related change of several cerebrospinal fluid, Pittsburgh compound B, and diffusion tensor imaging biomarkers in cognitively normal middle- to older-aged individuals, suggesting that non- APOE susceptibility genes for AD influence AD biomarkers.

Better tools for assessing cognitive impairment in the early stages of Alzheimer's disease (AD) are required to enable diagnosis of the disease before substantial neurodegeneration has taken place and to allow detection of subtle changes in the early stages of progression of the disease. The National Institute on Aging and the Alzheimer's Association convened a meeting to discuss state of the art methods for cognitive assessment, including computerized batteries, as well as new approaches in the pipeline. Speakers described research using novel tests of object recognition, spatial navigation, attentional control, semantic memory, semantic interference, prospective memory, false memory and executive function as among the tools that could provide earlier identification of individuals with AD. In addition to early detection, there is a need for assessments that reflect real-world situations in order to better assess functional disability. It is especially important to develop assessment tools that are useful in ethnically, culturally and linguistically diverse populations as well as in individuals with neurodegenerative disease other than AD.

Visual word recognition studies commonly measure the orthographic similarity of words using Coltheart's orthographic neighborhood size metric (ON). Although ON reliably predicts behavioral variability in many lexical tasks, its utility is inherently limited by its relatively restrictive definition. In the present article, we introduce a new measure of orthographic similarity generated using a standard computer science metric of string similarity (Levenshtein distance). Unlike ON, the new measure-named orthographic Levenshtein distance 20 (OLD20)-incorporates comparisons between all pairs of words in the lexicon, including words of different lengths. We demonstrate that OLD20 provides significant advantages over ON in predicting both lexical decision and pronunciation performance in three large data sets. Moreover, OLD20 interacts more strongly with word frequency and shows stronger effects of neighborhood frequency than does ON. The discussion section focuses on the implications of these results for models of visual word recognition.

Previous studies of associative encoding that used explicit retrieval tasks have shown both age- and dementia of the Alzheimer type (DAT)-related declines, but such results may be biased by group differences in explicit retrieval. In the present experiment, the authors assessed implicit associative encoding for 25 younger adults (ages 18-25), 73 healthy older adults (ages 59-91), and 65 adults with DAT (ages 59-91) during a speeded word-naming task using an episodic priming measure. Episodic priming refers to the facilitation in responding to a target word after repetition of both words in a prime-target pair, in comparison with simple repetition of the target word with a new prime on each presentation. In contrast with other studies of implicit associative encoding that did not use an implicit episodic priming measure, the present study found both age- and DAT-related declines in associative encoding under conditions of massed learning trials.

Subjective frequency estimates for large sample of monosyllabic English words were collected from 574 young adults (undergraduate students) and from a separate group of 1,590 adults of varying ages and educational backgrounds. Estimates from the latter group were collected via the internet. In addition, 90 healthy older adults provided estimates for a random sample of 480 of these words. All groups rated words with respect to the estimated frequency of encounters of each word on a 7-point scale, ranging from never encountered to encountered several times a day. The young and older groups also rated each word with respect to the frequency of encounters in different perceptual domains (e.g., reading, hearing, writing, or speaking). The results of regression analyses indicated that objective log frequency and meaningfulness accounted for most of the variance in subjective frequency estimates, whereas neighborhood size accounted for the least amount of variance in the ratings. The predictive power of log frequency and meaningfulness were dependent on the level of subjective frequency estimates. Meaningfulness was a better predictor of subjective frequency for uncommon words, whereas log frequency was a better predictor of subjective frequency for common words. Our discussion focuses on the utility of subjective frequency estimates compared with other estimates of familiarity. The raw subjective frequency data for all words are available at http://www.artsci.wustl.edu/dbalota/labpub.html.

Five groups of participants (young, healthy old, healthy old-old, very mild dementia of the Alzheimer type [DAT], and mild DAT) studied 12-item lists of words that converged on a critical nonpresented word (cold) semantically (chill, frost, warm, ice), phonologically (code, told, fold, old), or in a hybrid list of both (chill, told, warm, old). The results indicate that (a) veridical recall decreased with age and dementia; (b) recall of the nonpresented items increased with age and remained fairly stable across dementia; and (c) false recall varied by list type, with hybrid lists producing superadditive effects. For hybrid lists, individuals with DAT were 3 times more likely to recall the critical nonpresented word than a studied word. When false memory was considered as a proportion of veridical memory, there was an increase in relative false memory as a function of age and dementia. Results are discussed in terms of age- and dementia-related changes in attention and memory.

In two experiments, we investigated the influence of word frequency in speeded word naming and in a relatively novel regularization task in which participants were required to pronounce words on the basis of spelling-to-sound correspondences instead of giving their normal pronunciations (e.g., pronounce pint so that it rhymes with hint). Participants were presented high- and low-frequency regular words and exception words, along with a set of nonwords. The results indicated that there was a normal word frequency effect (i.e., high-frequency words faster than low-frequency words) in the standard speeded naming task, whereas, for the regularization task, the word frequency effect was reversed for regular words, even though the regular words were pronounced in an identical fashion in both the normal naming and the regularization tasks. This reversal of the word frequency effect was not obtained for the exception words. The discussion focuses on the implication of these results for attentional control models of lexical processing.

The present research examines the nature of the interference effects in a number of selective attention tasks. All of these tasks result in interference in performance by presenting information that is irrelevant to task performance but competes for selection. The interference from this competing information slows the response time (RT) of participants relative to a condition where the competition is minimized. The authors use a convolution of an exponential and a Gaussian (ex-Gaussian) distribution to examine the influence of interference on the characteristics of RT distributions. Consistent with previous research, the authors show that interference in the Stroop task is reflected by both the Gaussian and exponential portions of the ex-Gaussian. In contrast, in 4 experiments they show that several other interference tasks evidence interference that is reflected only in the Gaussian portion of the ex-Gaussian distribution. The authors suggest that these differences reflect the operation of different selection mechanisms, and they examine how sequential sampling models accommodate these effects.

A modified priming task was used to investigate whether skilled readers are able to adjust the degree to which lexical and sublexical information contribute to naming. On each trial, participants named 5 low-frequency exception word primes or 5 nonword primes before a target. The low-frequency exception word primes should have produced a greater dependence on lexical information, whereas the nonword primes should have produced a greater dependence on sublexical information. Across 4 experiments, the effects of lexicality, regularity, frequency, and imageability were all modulated in predictable ways on the basis of the notion that the primes directed attention to specific processing pathways. It is argued that these results are consistent with an attentional control hypothesis.

Two experiments are reported that explore the influence of strength of the prime-target relationship on the observed priming effects in young, healthy old, and individuals diagnosed with dementia of the Alzheimer type (DAT). In Experiment 1, participants were auditorily presented primes (FURNITURE) and after varying delays presented visual targets that were (1) high-strength related (e.g., SOFA), (2) low-strength related (e.g., RUG), or (3) unrelated control words (e.g., COW or DEER). The results indicated that the DAT individuals produced relatively larger priming effects that both the young and the healthy old, but these data could be accommodated by increases in effect size due to general slowing of response latencies. In Experiment 2, the same cross-modal priming paradigm was used with ambiguous words presented as primes (e.g., BANK) and either high-dominant (e.g., MONEY) or low-dominant (e.g., RIVER) words as targets. The results of Experiment 2 produced a qualitatively distinct pattern of priming that indicated DAT individuals only produced priming for high-dominant targets and not for low-dominant targets, whereas, the healthy control groups produced equivalent priming for both high- and low-dominant targets. The discussion focuses on the implication that these results have for the interpretation of semantic priming effects, in general, along with implications for the apparent semantic memory loss in DAT individuals.

Research on group differences in response latency often has as its goal the detection of Group x Treatment interactions. However, accumulating evidence suggests that response latencies for different groups are often linearly related, leading to an increased likelihood of finding spurious overadditive interactions in which the slower group produces a larger treatment effect. The authors propose a rate-amount model that predicts linear relationships between individuals and that includes global processing parameters based on large-scale group differences in information processing. These global processing parameters may be used to linearly transform response latencies from different individuals to a common information-processing scale so that small-scale group differences in information processing may be isolated. The authors recommend linear regression and z-score transformations that may be used to augment traditional analyses of raw response latencies.

Functional neuroimaging was used to investigate three factors that affect reading performance: first, whether a stimulus is a word or pronounceable non-word (lexicality), second, how often a word is encountered (frequency), and third, whether the pronunciation has a predictable spelling-to-sound correspondence (consistency). Comparisons between word naming (reading) and visual fixation scans revealed stimulus-related activation differences in seven regions. A left frontal region showed effects of consistency and lexicality, indicating a role in orthographic to phonological transformation. Motor cortex showed an effect of consistency bilaterally, suggesting that motoric processes beyond high-level representations of word phonology influence reading performance. Implications for the integration of these results into theoretical models of word reading are discussed.

Response time (RT) distributions obtained from 3 word recognition experiments were analyzed by fitting an ex-Gaussian function to the empirical data to determine the main effects and interactive influences of word frequency, repetition, and lexicality on the nature of the underlying distributions. The ex-Gaussian analysis allows one to determine if a manipulation simply shifts the response time (RT) distribution, produces a skewing of the RT distribution, or both. In contrast to naming performance, the lexical decision results indicated that the main effects and interactions of word frequency, repetition, and lexicality primarily reflect increased skewing of the RT distributions, as opposed to simple shifts of the RT distributions. The implications of the results were interpreted within a hybrid 2-stage model of lexical decision performance.

The present experiment examined the effect of distraction on reading ability and comprehension in healthy aging and early stage dementia of the Alzheimer type (DAT). A modified version of the reading task used by Connelly, Hasher, and Zacks (1991, Experiment 2) was employed. Healthy young, healthy old (60-79 years, and 80 years and over), very mild DAT, and mild DAT participants read passages aloud and then answered comprehension questions. There were four experimental conditions in which distracting information was embedded in the text: (control), orthographic (xxxxx), lexical (unrelated), and semantic (related). The results indicated that there was greater susceptibility to increasing levels of distraction with age and increasing dementia severity. Moreover, there was a substantial slowdown in reading time in mild DAT when text was used as distracting information, especially conceptually related text. Furthermore, mild DAT participants were more likely to make false alarms in comprehension performance (i.e., choose as an answer the incorrect response which contained the related distracting information). Thus, in early stage DAT, there appears to be increased difficulty inhibiting partially activated information, especially when it is related to the relevant information being processed.

The J. D. Cohen, K. Dunbar, and J. L. McClelland (1990) model of Stroop task performance is used to model data from a study by D. H. Spielder, D. A. Balota, and M. E. Faust (1996). The results indicate that the model fails to capture overall differences between word reading and color naming latencies when set size is increased beyond 2 response alternatives. Further empirical evidence is presented that suggests that the influence of increasing response set size in Stroop task performance is to increase the difference between overall color naming and word reading, which is in direct opposition to the decrease produced by the Cohen et al. architecture. Although the Cohen et al. model provides a useful description of meaning-level interference effects, the qualitative differences between word reading and color naming preclude a model that uses identical architectures for each process, such as that of Cohen et al., to fully capture performance in the Stroop task.

Recognition and source memory were explored in healthy older adults, adults diagnosed with very mild dementia of the Alzheimer type (DAT), and adults diagnosed with mild DAT. Two sentence-completion tasks were used. In Task 1, half of the sentences were completed (clozed) by the participant, and half by the experimenter. In Task 2, half were participant clozed, and half were participant read (already clozed). Recognition of the cloze words and accuracy of categorizing them as participant generated or experimenter generated (Task 1) and participant generated or participant read (Task 2) were measured (source discrimination). Contrary to previous reports, the DAT groups showed the generation effect, that is, better recognition for participant-generated words than experimenter-generated words (Task 1) or read words (Task 2). Source discrimination was disproportionately impaired in the DAT groups.

In two experiments we investigated the extent to which individuals with dementia of the Alzheimer type (DAT) manage the activation of contextually appropriate and inappropriate meanings of ambiguous words during sentence comprehension. DAT individuals and healthy older individuals read sentences that ended in ambiguous words and then determined if a test word fit the overall meaning of the sentence. Analysis of response latencies indicated that DAT individuals were less efficient than healthy older individuals at suppressing inappropriate meanings of ambiguous words not implied by sentence context, but enhanced appropriate meanings to the same extent, if not more, than healthy older adults. DAT individuals were also more likely to allow inappropriate information to actually drive responses (i.e., increased intrusion errors). Overall, the results are consistent with a growing number of studies demonstrating impairments in inhibitory control, with relative preservation of facilitatory processes, in DAT.

In four experiments, semantic satiation was investigated in young and old adults. In the first two experiments, subjects were repeatedly presented a word (e.g., DOG) and then were presented a pair of words (e.g., DOG-CAT or DOG-CHAIR) for a relatedness decision. The results of both experiments indicated that for the young adults, the relatedness effect (the difference between response latency on related and unrelated trials) decreased as a function of the number of times the satiated word was repeated, whereas for the older adults, there was no evidence of a decrease in the relatedness effect across repetitions of the satiated word. In the third experiment, we investigated whether phonological codes are also susceptible to satiation. This experiment was similar to the first two experiments with the exception that subjects made rhyme decisions (SAME-CLAIM VS. SAME-DIME) instead of semantic relatedness decisions. The results of this experiment did not yield any evidence of satiation for either the young adults or the older adults. The final experiment eliminated a simple decrease in attentional alertness or fatigue account of the semantic satiation effects found in the first two experiments. In this experiment, the repeated word was always unrelated to the pair of words presented for the relatedness decision. The results of this experiment did not yield any evidence of semantic satiation for either the young or the older adults. The discussion focuses on the mechanisms underlying semantic satiation and the implications of age-related changes in these mechanisms.

Covert orienting of visuospatial attention in response to peripherally presented cues was assessed in healthy younger and older adults and those with dementia of the Alzheimer type (DAT) during a simple detection task. The results yield both an age-related increase (Experiments 1 and 2) and a DAT-related increase (Experiment 2) in the facilitatory effect of a single peripheral cue on detection. By contrast, equivalent inhibition of return (i.e., a slowing of target detection at previously cued locations) was observed for all 3 groups when a 2nd cue was presented at central fixation. Results suggest that both healthy older adults and individuals with DAT experience changes in the posterior attention system thought to subserve visuospatial attention. Results also suggest limitations on the generality of inhibitory deficits in healthy aging and DAT.

Six experiments addressed the combinatorial influence of multiple related primes in naming, lexical decision and relatedness judgment performance. Primes either converged on a single semantic representation (e.g., LION-STRIPES-TIGER) or diverged onto distinct semantic representations (e.g., KIDNEY-PIANO-ORGAN). The facilitatory influence of 2 related primes was well predicted by the sum of the influences from the single-related-prime conditions (a) for both convergent and divergent primes, (b) in lexical-decision and naming, (c) across varying prime-target stimulus onset asynchronies, and (d) under target-degradation conditions that increased the priming effects. The relatedness-judgment task yielded an additive pattern of priming for convergent prime conditions; however, an underadditive pattern of priming was found for divergent prime conditions. Discussion focuses on the role of attentional systems that modulate the type of information used to perform a given task.

Components of the Stroop task were examined to investigate the role that inhibitory processes play in cognitive changes in healthy older adults and in individuals with dementia of the Alzheimer's type (DAT). Inhibitory breakdowns should result in an increase in Stroop interference. The results indicate that older adults show a disproportionate increase in interference compared with younger adults. DAT individuals show interference proportionate to older adults but a disproportionate increase in facilitation for congruent color-word trials, and an increased intrusion of word naming on incongruent color naming trials. An ex-Gaussian analysis of response time distributions indicated that the increased interference observed in older adults was due to an increase in the tail of the distribution. Application of the process dissociation analysis of the Stroop task (D.S. Lindsay & L.L. Jacoby, 1994) indicated that older adults showed increased word process estimates, whereas DAT individuals showed differences in both color and word process estimates. Taken together, the results are consistent with an inhibitory breakdown in normal aging and an accelerated breakdown in inhibition in DAT individuals.

Hulme, Maughan, and Brown (1991) provided evidence that the contribution of long-term memory to memory span performance was additive to the contribution of rehearsal rate (e.g., Baddeley, 1986). The present study further explored the relationship between these two contributions in younger and older adults. Speech rates and spans for short, medium, and long words and nonwords were obtained from subjects. Older adults had slower speech rates and smaller spans than did younger adults. Both groups' data were fit well by linear functions relating speech rates to spans. However, the slope of the function that relates speech rate to memory span was greater for words than for nonwords. This finding supports the idea that long-term memory, as well as rehearsal rate, contributes to span performance, and that this contribution is not simply additive.

Positron emission tomography (PET) was used to investigate the functional brain anatomy associated with the short-term maintenance of linguistic information. Subjects were asked to retain five related words, unrelated words, or pseudowords silently for the duration of a 40 sec PET scan. When brain activity during these short-term maintenance tasks was compared with a visual fixation control task, increases were found bilaterally in the dorsolateral prefrontal cortex and cerebellum, and medially in the supplementary motor area. Furthermore, effects of stimulus condition and recall performance were found in the left frontal operculum. To investigate the role of articulatory systems in the maintenance of verbal information, regional activation was compared across the maintenance tasks and a covert articulation task (silent counting). The cerebellum was active in both task conditions, whereas activation in prefrontal regions was specific to the maintenance condition. Conversely, greater activation was found in a left middle insular region in the silent counting than in the maintenance tasks. Based on converging results in this and previous studies, dorsolateral prefrontal cortical areas appear to contribute to the maintenance of both verbal and nonverbal information, whereas left frontal opercular regions appear to be involved specifically in the rehearsal of verbal material. Contrary to results found in other studies of working memory, activation was not found in the inferior parietal cortex, suggesting that this area is involved in aspects of stimulus encoding and retrieval, which were minimized in the present study.

Four experiments addressed the influence of variables on lexical decision performance after response initiation has occurred. In Experiment 1, participants made an arm movement in one direction for word trials and pressed a button with the other hand for nonword trials. The results indicated that word frequency not only modulated the speed to initiate the arm movement, but also modulated the acceleration and force of the movement after initiation. The results of Experiment 2 indicated that word frequency and stimulus degradation produced large and additive effects on response latency, accuracy, and the force of the response after initiation. In Experiments 3 and 4, participants made the same arbitrary speech response in a modified lexical decision task for both high- and low-frequency words. The results indicated that both the onset and duration of the speech response were modulated by word frequency. The results are viewed as most consistent with an enabled response model, wherein early operations can enable appropriate action systems before central decisions are made.