Mental Flexibility: Age Effects on Switching.

Mental flexibility is required to track and systematically alternate between 2 response sets. In this study, 719 individuals, 20 to 89 years old, engaged in 3 different tasks that required verbal and nonverbal cognitive switching. Of importance, each task allowed for independent measurement of component skills that are embedded in the higher level tasks. When gender, education, Full Scale IQ, and component skills were partialed out by multiple regression analyses, significant age effects were revealed for each task. This study provides evidence that executive functions-and verbal and nonverbal cognitive switching in particular-are affected by age independently from age-related changes in component skills. The results are discussed in terms of theories of executive control and neurologic correlates across the adult life span. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Efficient Processing of Client Transactions in Real-Time

In traditional client-server databases, a transaction and its requisite data have to be colocated at a single site for the operation to proceed. This has usually been achieved by moving either the data or the transaction. However, the availability of high-bandwidth networking options has led users of today's systems to expect real-time guarantees about the completion time of their tasks. In order to offer such guarantees in a client-server database system, a transaction should be processed by any means that allows it to meet its deadline. To this end, we explore the option of moving both transactions and data to the most promising sites for successful completion. We propose a load-sharing framework that oversees the shipment of data and transactions so as to increase the efficiency of a cluster consisting of a server and a number of clients. Here, efficiency is defined as the percentage of transactions successfully completed within their deadlines by the cluster. The suitability of a client for processing a transaction is measured with respect to the availability of the transaction's required data in its local cache. In addition to the load-sharing algorithm, we use the concept of grouped locks, along with transaction deadline information, in order to schedule the movement of data objects in the cluster in a more efficient manner. We evaluate the real-time processing performance of the client-server architecture using detailed experimental testbeds. Our evaluation indicates that it is possible, in many situations, to achieve better performance than a centralized system.     

Asymmetries in Global-Local Processing Ability in Elderly People With the Apolipoprotein E-ε4 Allele.

Previous studies have identified cognitive asymmetries in elderly people at increased risk for Alzheimer's disease (AD) by comparing standardized neuropsychological tests of verbal and spatial abilities in both preclinical AD and apolipoprotein ε4+ elderly groups. This prospective study investigated cognitive asymmetries within a single test by comparing cognitively intact elderly (with and without the ε4+ allele) on a learning and memory measure that uses global and local visuospatial stimuli. Both groups demonstrated comparable overall learning and recall. But the ε4+ group had a significantly larger discrepancy between their global and local learning scores and had a greater proportion of individuals with more than a one standard deviation difference between their immediate recall of the global and local elements, relative to the ε4- group. These findings build on previous studies identifying subgroups of elderly people at greater risk for AD who often demonstrate increased cognitive asymmetries relative to groups without significant risk factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of spatial impairment in Alzheimer's disease subgroups: Differential breakdown of directed attention to global-local stimuli.

Global–local stimuli (e.g., a large 1 composed of small 2s) were presented to subgroups of patients with Alzheimer's disease (AD) and to normal controls in a directed-attention reaction time (RT) experiment. Pronounced dissociations in performance were found among the AD subgroups. Those patients who displayed greater impairment in verbal than in spatial skills on traditional clinical tests had particular difficulty processing local (detail) forms, whereas patients who had greater spatial than verbal impairment exhibited striking deficits in processing global (configural) forms. Results indicate that the AD patients were impaired primarily in inhibiting responses associated with their strong area when attending to forms in their weak area, although they did evince mild impairment in the perceptual processing of forms in their weak area as well. Thus, it appears that the AD patients' global–local processing deficits interacted with deficient inhibitory mechanisms to produce their patterns of deficits on the directed attention task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive and neuropathologic correlates of Stroop Color-Word Test performance in Alzheimer's disease.

The Stroop Color-Word Test (SCWT; C. Golden, 1978) was examined in 59 patients with probable Alzheimer's disease (AD) and in 51 demographically comparable normal control (NC) participants. AD patients produced significantly larger Stroop interference effects than NC participants, and level of dementia severity significantly influenced SCWT performance. Principal -components analyses demonstrated a dissociation in the factor structure of the Stroop trials between NC participants and AD patients, suggesting that disruption of semantic knowledge and speeded verbal processing in AD may be a major contributor to impairment on the incongruent trial. Results of clinicopathologic correlations in an autopsy-confirmed AD subgroup further suggest the invocation of a broad network of integrated cortical regions and executive and language processes underlying successful SCWT performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory for the Rey-Osterrieth Figure: Perceptual clustering, encoding, and storage.

Administered copy, immediate recall, and delayed recall conditions of the Rey-Osterrieth Complex Figure (ROCF) test to 50 neuropsychiatric patients (aged 23–83 yrs). Measures of copy accuracy, perceptual clustering, encoding, and savings were computed. Perceptual clustering in the copy condition was a better predictor of memory performance than was copy accuracy. An absence of association between the encoding score and the savings score suggests that these indices reflect different cognitive processes. The need to assess both immediate and delayed recall of the ROCF is emphasized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive disk scheduling with workload-dependent anticipation intervals

Anticipatory scheduling (AS) of I/O requests has become a viable choice for block-device schedulers in open-source OS-kernels as prior work has established its superiority over traditional disk-scheduling policies. An AS-scheduler selectively stalls the block-device right after servicing a request in hope that a new request for a nearby sector will be soon posted. Clearly, this decision may introduce delays if the anticipated I/O does not arrive on time. In this paper, we build on the success of the AS and propose an approach that minimizes the overhead of unsuccessful anticipations. Our suggested approach termed workload-dependent anticipation scheduling (WAS), determines the length of every anticipation period in an on-line fashion in order to reduce penalties by taking into account the evolving spatio-temporal characteristics of running processes as well as properties of the underlying computing system. We harvest the spatio-temporal features of individual processes and employ a system-wide process classification scheme that is re-calibrated on the fly. The resulting classification enables the disk scheduler to make informed decisions and vary the anticipation interval accordingly, on a per-process basis. We have implemented and incorporated WAS into the current Linux kernel. Through experimentation with a wide range of diverse workloads, we demonstrate WAS benefits and establish reduction of penalties over other AS-scheduler implementations.     

Discriminating Patients With Frontal-Lobe Epilepsy and Temporal-Lobe Epilepsy: Utility of a Multilevel Design Fluency Test.

Patients with frontal-lobe epilepsy (FLE) or temporal-lobe epilepsy (TLE) and matched control participants were given a design fluency test that assessed nonverbal fluency and switching ability. Patients with FLE generated fewer designs in the switching condition relative to the TLE patients and controls, whereas group differences did not emerge in the basic fluency conditions. When the side of the seizure focus and the presence or absence of a structural lesion were considered in patients with FLE, only those with left-lesional FLE generated fewer designs than controls did in the switching condition. Furthermore, patients with left-lesional and nonlesional FLE produced a greater proportion of set-loss errors than did controls. These results indicate that patients with FLE are impaired when they must simultaneously generate new designs and engage in cognitive switching; however, the pattern of impairment may depend on the side of the seizure focus and the presence of a structural lesion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)