Memory Demands (memory + demand)

Distribution by Scientific Domains

Selected Abstracts

Memory demands on facial composite identification

Karl M. Oswald
Face composites created with FACES 3.0 composite software were used to identify target photographs under varying conditions of memory load. Composites created while viewing a mugshot were presented concurrently with a five-photograph lineup of actual criminal suspects, immediately preceding the lineup, or with a filled delay between composite and lineup. Compared to a baseline using the mock witness technique, results demonstrated above-chance identification of target photographs from their composites in all four experiments. Identification was highest with concurrent composite-lineup presentation and lower under immediate, 30-second-delayed, and 4-minute-delayed conditions, with no significant identification differences across the three memory conditions. Confidence ratings in target selection only weakly predicted identification accuracy at best. These findings extend the limited research on computerized facial composite systems while addressing composite software use, efficacy, guidelines and limitations. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Watermarking in halftone images with mixed halftone techniques

Jing-Ming Guo
Abstract Ordered dithering and error diffusion are the two most popular processes to produce halftone results for printing industry. Ordered dithering inherently has the benefit of efficiency. On the other hand, error diffusion has high quality and reasonable complexity. In this article, we propose a watermarking that adopts the ordered dithering to produce the referenced halftone image, then applying the noise-balanced error diffusion to embed the watermark. A low computational complexity, low memory demand, and good embedded image quality are achieved with the proposed technique. From the experimental results, this technique can guard against the cropping and print-and-scan two major degradation processes in halftone images. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 303,314, 2007 [source]

Does weak reading comprehension reflect an integration deficit?

Alice L. R. Spooner
Seven- and eight-year-old skilled and less-skilled comprehenders were compared on a sentence recognition task in two conditions varying in memory load and retention interval. Integration of story information during comprehension was indexed by inflated recognition errors of foils that had been constructed by integrating information across original story sentences. Skilled comprehenders exhibited more accurate memory for sentences than less-skilled comprehenders. However, the groups did not differ in the degree to which they integrated information with minimal memory demand, or in their tendency to integrate information and retain the integrated representations with increased memory demand. These results were interpreted as evidence that integration deficits do not lie at the root of reading comprehension difficulties in mainstream children. [source]

Effects of hippocampal lesions on the monkey's ability to learn large sets of object-place associations,

HIPPOCAMPUS, Issue 4 2006
Annabelle M. Belcher
Abstract Earlier studies found that recognition memory for object-place associations was impaired in patients with relatively selective hippocampal damage (Vargha-Khadem et al., Science 1997; 277:376,380), but was unaffected after selective hippocampal lesions in monkeys (Malkova and Mishkin, J Neurosci 2003; 23:1956,1965). A potentially important methodological difference between the two studies is that the patients were required to remember a set of 20 object-place associations for several minutes, whereas the monkeys had to remember only two such associations at a time, and only for a few seconds. To approximate more closely the task given to the patients, we trained monkeys on several successive sets of 10 object-place pairs each, with each set requiring learning across days. Despite the increased associative memory demands, monkeys given hippocampal lesions were unimpaired relative to their unoperated controls, suggesting that differences other than set size and memory duration underlie the different outcomes in the human and animal studies. © 2005 Wiley-Liss, Inc. [source]

Neural correlates of noncanonical syntactic processing revealed by a picture-sentence matching task

Ryuta Kinno
Abstract It remains controversial whether the left inferior frontal gyrus subserves syntactic processing or short-term memory demands. Here we devised a novel picture-sentence matching task involving Japanese sentences with different structures to clearly contrast syntactic reanalysis processes. Using event-related functional magnetic resonance imaging (fMRI), activations under three main conditions were directly compared: a canonical/subject-initial active sentence (AS), a noncanonical/subject-initial passive sentence (PS), and a noncanonical/object-initial scrambled sentence (SS). We found that activation in the dorsal region of the left inferior frontal gyrus (dF3t) was enhanced more by the noncanonical processing under the PS and SS conditions than by the canonical processing under the AS condition, and this enhancement was independent of domain-general factors, such as general memory demands and task difficulty. Moreover, the left posterior superior/middle temporal gyrus (pSTG/MTG) showed more enhanced responses to object-initial sentences under the SS condition than to subject-initial sentences under the AS and PS conditions, which were not significantly affected by task difficulty. Furthermore, activation in the left lateral premotor cortex (LPMC) increased under the AS, PS, and SS conditions, in that order. It is possible that task difficulty affects the left LPMC, but the three distinct activations patterns suggest that these frontal and temporal regions work in concert to process syntactic structures, with their respective contributions dynamically regulated by linguistic requirements. Hum Brain Mapp 2008. © 2007 Wiley-Liss, Inc. [source]

Functional magnetic resonance imaging response to increased verbal working memory demands among patients with multiple sclerosis

Lawrence H. Sweet
Abstract Multiple sclerosis (MS) patients frequently experience impaired verbal working memory (VWM). Functional magnetic resonance imaging (fMRI) may help identify neural mechanisms underlying these deficits. Neuroimaging studies of healthy adults have characterized responses associated with increased VWM demands during the n-Back task, suggesting that this experimental paradigm could help identify neural correlates of VWM deficits among MS patients. Fifteen MS patients and 15 matched control participants completed the n-Back during whole-brain fMRI. Mean signal during adjacent 0-Back blocks was subtracted, on a voxel-wise basis, from mean signal observed during n-Back blocks. Resulting difference scores for 1-, 2-, and 3-Back were compared across groups and difficulty levels. Signal intensity was positively related to difficulty level in anterior regions, including premotor, supplementary motor, and dorsolateral prefrontal cortices. MS patients exhibited significantly greater intensity in these areas compared to controls during the 1-Back, while portions of the left superior frontal gyrus, cingulate, and parahippocampal gyri were relatively less intense at more difficult levels. MS group responses were slower during the 1-Back and tended to be slower during the 3-Back; however, accuracy did not differ at any level. Lesion load was positively related to only 1-Back activity and unrelated to any performance measure. Results suggest that compensatory activity occurs among MS patients matched on performance accuracy. Furthermore, compensatory activity occurs predominantly in regions associated with VWM, and this may decline relative to controls as task demands increase. These findings may help to explain why MS patient performance decreases as a function of effort on neuropsychological tests. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source]

Neural basis for sentence comprehension: Grammatical and short-term memory components

Ayanna Cooke
Abstract We monitored regional cerebral activity with BOLD fMRI while subjects were presented written sentences differing in their grammatical structure (subject-relative or object-relative center-embedded clauses) and their short-term memory demands (short or long antecedent-gap linkages). A core region of left posterior superior temporal cortex was recruited during all sentence conditions in comparison to a pseudofont baseline, suggesting that this area plays a central role in sustaining comprehension that is common to all sentences. Right posterior superior temporal cortex was recruited during sentences with long compared to short antecedent-gap linkages regardless of grammatical structure, suggesting that this brain region supports passive short-term memory during sentence comprehension. Recruitment of left inferior frontal cortex was most clearly associated with sentences that featured both an object-relative clause and a long antecedent-gap linkage, suggesting that this region supports the cognitive resources required to maintain long-distance syntactic dependencies during the comprehension of grammatically complex sentences. Hum. Brain Mapping 15:80,94, 2001. © 2001 Wiley-Liss, Inc. [source]

Executive functioning by 18-24-month-old children: effects of inhibition, working memory demands and narrative in a novel detour-reaching task

Nicola McGuigan
Abstract Infants can inhibit a prepotent but wrong action towards a goal in order to perform a causal means-action. It is not clear, however, whether infants can perform an arbitrary means-action while inhibiting a prepotent response. In four experiments, we explore this executive functioning in 18,24-month-old children. The working memory and inhibition demands in a novel means-end problem were systematically varied in terms of the type and combination of means-action(s) (causal or arbitrary) contained within the task, the number of means-actions (1 or 2), the goal visual availability and whether the task was accompanied by a narrative. Experiments 1 and 2 showed that children performed tasks that contained causal as opposed to arbitrary information more accurately; accuracy was also higher in tasks containing only one step. Experiment 2 also demonstrated that performance in the arbitrary task improved significantly when all sources of prepotency were removed. In Experiment 3, task performance improved when the two means-actions were intelligibly linked to the task goal. Experiment 4 demonstrated that the use of a narrative that provided a meaningful (non-causal) link between the two means-actions also improved children's performance by assisting their working memory in the generation of a rationale. Findings provide an initial account of executive functioning in the months that bring the end of infancy. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Algebraic preconditioning versus direct solvers for dense linear systems as arising in crack propagation problems

Erik Bängtsson
Abstract Preconditioned iterative solution methods are compared with the direct Gaussian elimination method to solve dense linear systems Ax=b which originate from problems, discretized by boundary element method (BEM) techniques. Numerical experiments are presented and compared with the direct solution method available in a commercial BEM package, which show that the preconditioned iterative schemes are highly competitive with respect to both arithmetic operations required and memory demands. Copyright © 2004 John Wiley & Sons, Ltd. [source]

The n -back as a dual-task: P300 morphology under divided attention

Scott Watter
The n -back task was hypothesized to be a dual task, permitting the imposition of parametrically increasing attentional and working memory demands, while keeping constant the demands of an embedded matching subtask. Visual targets were presented for 200 ms every 2.2 s at pseudorandomly varying positions on a computer screen. Participants were required to remember the most recent 0, 1, 2, or 3 positions and responded with a choice button push to whether the current target position matched the position presented n items previously. P300 peak latency was constant across n -back tasks, reflecting constant perceptual and cognitive demands of the matching subtask. P300 peak amplitude decreased with increasing memory load, reflecting reallocation of attention and processing capacity away from the matching subtask to working memory activity. These data support a dual-task nature of the n -back, which should be considered when employing this paradigm. [source]