Primary Memory Research Articles

Simultaneous optimization of dynamic multileaf collimation and scanning patterns or compensation filters using a generalized pencil beam algorithm.

A very flexible iterative method for simultaneous optimization of dynamic multileaf collimation, scanning patterns and compensation filters has been developed. The algorithm can account for and optimize almost all the degrees of freedom available in a modern radiation therapy clinic. The method has been implemented for three dimensional treatment planning. The algorithm has been tested for a number of cases where both traditional wedge filters and block collimators, and modern equipment such as scanned beams and multileaf collimators are available. It is shown that the algorithm can improve heavily on traditional uniform dose plans with respect to the probability of achieving tumor control without causing severe complications (P+) simply by finding the optimal beam weights and block collimator settings. By allowing more complex equipment to deliver the dose and by accounting for their increased flexibility during the optimization, the dose plan can be substantially improved with respect to the applied objective functions. It is demonstrated that flexible lateral collimation combined with compensators or scanned beams in most cases allow close to optimal dose delivery. Here both the calculation time and the amount of primary computer memory needed has been reduced by performing the dose calculations in a cone beam coordinate system allowing the use of approximately spatially invariant energy deposition kernels. A typical calculation time for optimization of a two-field technique in a three dimensional volume is about 20 s per iteration step on a Hewlett-Packard 735 workstation. A well converged solution is normally obtained within about 50-100 iterations or within 15-30 min.

Very rapid forgetting: Reply to Muter

We reply to the commentary in which Muter (1995) disputes the findings and arguments of Cunningham, Healy, Till, Fendrich, and Dimitry (1993) concerning the rate of forgetting from primary memory. Although Muter (1980) had reported very rapid forgetting when secondary memory processes were minimized, Cunningham et al. found that the rate of forgetting from primary memory was no more rapid when secondary memory processes were minimal than it was when secondary memory processes were substantial. We locate the discrepancy between the two studies specifically at recall performance on the 0-sec retention interval, and we argue that the very rapid forgetting found by Muter (1980) can be attributed in large part to the fact that although subjects in his experiments did not expect to recall the letters after a filled retention interval, at the time of encoding and after an unfilled delay they did have a high overall expectancy to recall the letters.

Very rapid forgetting: reply to Cunningham, Healy, Till, Fendrich, and Dimitry.

In this comment, it is argued that the experiments by Cunningham, Healy, Till, Fendrich, and Dimitry (1993) do not constitute failures to replicate Muter’s (1980) finding of very rapid forgetting and do not undermine the conclusion of more rapid forgetting from primary memory than had previously been estimated. In Cunningham et al.’s experiments, expectancy of recall after a filled retention interval, a crucial variable in very rapid forgetting, was more than an order of magnitude higher than in Muter’s experiments, and the distracting task was substantially easier.

Mismatch negativity (MMN) as an index of impaired auditory sensory memory in schizophrenia

An experiment is described which shows that a nonverbal task performed concurrently with list presentation causes a decrement in primary-memory recall for visual lists but not for auditory lists. It is concluded that continued attention is necessary to maintain information in primary memory, that a preattentive echoic store can mediate terminal item recall for auditory lists, and that forgetting from primary memory is related to the difficulty of an additional task.

Episodic memory and visuospatial ability in detecting and staging dementia in a community-based sample of very old adults.

This study examined the efficacy of a cognitive test battery in detecting and staging dementia in a community-based sample of very old adults. The sample consisted of 398 nondemented and 108 demented adults taken from all the inhabitants in the Kungsholmen parish of Stockholm, Sweden (2,368 individuals), aged 75 years and older, who were part of a large-scale epidemiological study on aging and dementia. Participants received a cognitive test battery that consisted of specialized episodic memory tasks, as well as standardized psychometric measures of visuospatial ability and primary memory. A discriminant analysis revealed that highly supported episodic memory tasks (recognition, cued recall) were primarily responsible for correctly classifying normal old adults (94.5%) from those with the diagnosis of dementia (66.7%). Using the Mini-Mental State Exam (MMSE) as the criterion of dementia severity, a correct classification of 88.9% was achieved for mildly demented subjects and 77.8% for moderately demented subjects. Visuospatial tasks made the greatest contribution in distinguishing those at different levels of dementia severity. The results of this investigation indicate that cognitively supported measures assessing episodic memory may be particularly useful in the detection of dementia, whereas visuospatial measures are more effective in staging the disease. Consistent with biological models of the progression of dementia, this suggests that visuospatial abilities may deteriorate later and/or at a slower rate than episodic memory skills in the early stages of dementia. It is noteworthy that these conclusions are based on samples of very old adults taken from the general population.

Primary visual memory of stroke patients.

This matched control group study assesses primary visual memory of stroke patients using the GEMAT visual-memory test. Primary visual memory of 29 stroke patients who scored 24 or more on the MMSE was compared with that of 33 age and sex-matched controls. Patients were recruited from physiotherapy outpatient clinics. Measured variables were the total time needed to complete the test (GTT) and the number of correct answers (GCA). Patients were slower (p < 0.01) and made more mistakes (p < 0.01) than controls. 'Young' (60-71) subjects made fewer mistakes (p < 0.01) than old subjects (72-89) and patients who scored 24-26 on MMSE were slower than patients who scored 27-30. It should be taken into consideration that stroke patients whose cognitive function is within a normal range of the MMSE might have impaired primary visual memory.

Grouping in primary memory: The case of the compound suffix.

Appending a nominally irrelevant item, or "suffix," to the end of a short list of items impairs recall of the list. Appending a second such item, however, does not increase the impairment. The research reported here shows that the impairment can in fact be increased if the suffix items are physically dissimilar. Thus, Experiments 1-4 show that memory for a sequence of digits is impaired more by the addition of two zeros uttered in different voices than by either a single zero or two zeros uttered in the same voice. Experiment 5 shows a similar pattern of results in the visual modality, with physical similarity defined by typefont. The findings are contrary to at least two theories of the suffix effect but can be accounted for by assuming that physically similar items tend to form a cohesive group.

Grouping in primary memory: The case of the compound suffix.

Grouping in primary memory: The case of the compound suffix.

Intact primary memory in mild to moderate Alzheimer disease: Indices from the California Verbal Learning Test

The California Verbal Learning Test (CVLT; Delis, Kramer, Kaplan, & Ober, 1987) was administered to patients with mild to moderate Alzheimer disease (AD) (Group AD; n = 13) and to a control group of normal older adults (Group NC; n = 13) matched on age and education. Two measures were used to determine whether primary memory (PM) is impaired in early AD. One measure, considered a relatively "pure" measure of PM, is based on the procedure developed by Tulving and Colotla (1970) which considers an item to be recalled from PM if no more than six items intervene between its presentation and recall. The other measure is the more commonly used recall from recency. No significant difference between the AD and NC Groups was found, both on the Tulving and Colotla measure, as well as on the recall from recency measure of PM. A significant difference was obtained on two measures of secondary memory (SM), namely, Tulving and Colotla's measure and recall from the primacy and middle regions of the list of words. In comparison to NC, and AD patients showed little evidence of learning over the five trials, and poor retention even over short delays. In addition, the patients with AD showed deficits in clustering words by taxonomic category at recall. We conclude that impairment in PM cannot be used as a diagnostic marker of AD in the early stages of the disease process.

An 18FDG-PET study of cortical activation during a short-term visual memory task in humans.

Studies of subhuman primates and man have shown that the prefrontal cortex is important for spatial working memory. We have used 18fluorodeoxyglucose positron emission tomography (18FDG-PET) to study a non-spatial, abstract visual memory task of in man. Using a regions-of-interest approach with discriminant analysis of the relative regional cerebral metabolic rate of glucose consumption (rCMRGlc), we found that changes in dorsal prefrontal, premotor/motor frontal and posterior cingulate areas differentiated the primary memory task from the control task. Less robust increases in glucose uptake were observed in lateral parietal cortex, while some subcortical and limbic regions showed decreases. This is the first activation study with a non-spatial, visual task. These results complement previous studies in that they substantiate the role of the prefrontal cortex in the mediation of cross-temporal contingencies of behavior, and point to a role of the premotor region in this mediation as well.

Working memory and retrieval: a resource-dependent inhibition model.

Four experiments examined individual differences in working memory (WM) capacity and how those differences affect performance on retrieval from both primary and secondary memory. The results showed that WM differences appear only in retrieval from primary memory and then only under conditions that lead to interference or response competition within the task. This suggests that WM capacity is important to retrieval that is based on controlled effortful search but not search that is based on automatic activation. A view is presented suggesting that individual differences in attentional resources lead to differences in the ability to inhibit or suppress irrelevant information. The paradigm also allowed more general comparisons between the processes involved in retrieval from primary and secondary memory. As expected, it was found that retrieval from primary memory was a function of set size. However, for sets larger than 2 items, retrieval from secondary memory was independent of set size.

Primary memory in patients with frontal and primary generalized epilepsy

A control group, a group with frontal lobe epilepsy, and a group with primary generalized epilepsy were tested on a task of primary, or working, memory. Another task controlled for attention, motivation, and habituation. The frontal lobe group showed impairment on both tasks, particularly the primary memory task and the worst performance on all measures. This was true of patients with or without obvious structural lesions. The primary generalized group performed normally on the task of attention but were impaired on the task of primary memory. Neither of these effects could be attributed solely to poor motor skills or anticonvulsant drugs. They may be due to persistent postictal effects, interictal spikes, or spike wave complexes or to the underlying pathophysiology that is also responsible for the epileptic state.

Cognition in humans and the borderline to dementia

From a psychometric point of view, cognitive performance in humans has to be examined as a multidimensional quantitative construct. Models of memory and intelligence may serve to describe the complex interactions of cognitive functioning. Based on memory research and reliable psychometric methods a three-dimensional model including “Primary Memory”, “Secondary Memory” and a “Speed factor” is proposed. Using models of intelligence “Fluid Intelligence” and “Crystallized Intelligence” are outlined as separate performance factors. “Cognitive Speed” is demonstrated as a market variable of “Fluid Intelligence”. It is shown, that “Cognitive Speed” is clearly age-associated and constitutes a key function for other cognitive domains and for activities-of-daily-living. Furthermore “Cognitive Speed” is a crucial cognitive domain to separate normal from pathological aging. As an example to assess “Cognitive Speed”, the Zahlen-Verbindungs-Test G (1), a modified trail-making test, is discussed to diagnose beginning and ongoing dementias.

Cognitive functioning of patients with chronic fatigue syndrome.

Neuropsychological problems are a distressing and frequent component of the symptom complex associated with chronic fatigue syndrome. Objective assessment of these difficulties is essential to understanding the nature of this illness. Results of the studies discussed in this paper suggest that impaired information processing, rather than primary memory dysfunction, may be at the root of the cognitive problems that afflict so many patients with CFS.

Hippocampal formation size in normal human aging: a correlate of delayed secondary memory performance.

Although mild progressive memory impairment is commonly associated with normal human aging, it is unclear whether this phenomenon can be explained by specific structural brain changes. In a research sample of 54 medically healthy and cognitively normal elderly persons (ages 55-87, x = 69.0 +/- 7.9), magnetic resonance imaging (MRI) was used to derive head-size-adjusted measurements of the hippocampal formation (HF) (dentate gyrus, hippocampus proper, alveus, fimbria, subiculum), the superior temporal gyrus (STG), and the subarachnoid cerebrospinal fluid (CSF) (to estimate generalized cerebral atrophy). Subjects were administered tests of primary memory (digit span) and tests of secondary memory with immediate and delayed recall components (paragraph, paired associate, list recall; facial recognition). Separate composite scores for the immediate and delayed components were created by combining, with equal weighting, the subtests of each category. The WAIS vocabulary subtest was used as a control measure for language and intelligence. A highly significant correlation (P < 0.001), independent of age, gender, and generalized cerebral atrophy was found between HF size and delayed memory performance. No significant correlations were found between HF size and primary or immediate memory performance. STG size was not significantly correlated with any of the composite memory variables. These results suggest that HF atrophy may play an important independent role in contributing to the memory loss experienced by many aging adults.

Concurrent compacting garbage collection of a persistent heap

We describe a replicating garbage collector for a persistent heap. The garbage collector cooperates with a transaction manager to provide safe and efficient transactional storage management. Clients read and write the heap in primary memory and can commit or abort their write operations. When write operations are committed they are preserved in stable storage and survive system failures. Clients can freely access the heap during garbage collection because the collector concurrently builds a compact replica of the heap. A log captures client write operations and is used to support both the transaction manager and the replicating garbage collector.Our implementation is the first to provide concurrent and compacting garbage collection of a persistent heap. Measurements show that concurrent replicating collection produces significantly shorter pause times than stop-and-copy collection. For small transactions, throughput is limited by the logging bandwidth of the underlying log manager. The results suggest that replicating garbage collection offers a flexible and efficient way to provide automatic storage management in transaction systems, object-oriented databases and persistent programming environments.

Adaptive hashing with signatures

Adaptive hashing with signatures combines the adaptive hashing file structure together with superimposed signatures and several new algorithms to produce a new order-preserving data structure. This new technique has excellent direct retrieval performance, localized index organizations, and improved file index balance. In keeping with the principle advantage of the original adaptive hashing technique, algorithms to improve both primary and secondary memory storage utilization are also discussed. Furthermore, the new data structure has a high degree of flexibility, allowing it to be tailored for the optimum performance vs storage utilization ratio for a given application.

Performance of Subjects with Probable Alzheimer Disease and Normal Elderly Controls on the Gollin Incomplete Pictures Test

Our study was designed to evaluate perceptual ability measured by the Gollin Incomplete Pictures Test (in which subjects identify fragmented pictures of common objects) in Alzheimer Disease. We developed a standardized procedure for administering Gollin's test and compared the performance of 58 Alzheimer patients and 37 elderly controls on the Gollin, two design copying tests, the Mini-Mental State Examination, a verbal version of the Knox Cubes test, a recognition memory test, and a verbal fluency test. Alzheimer patients performed significantly more poorly than controls on all tests. Factor analysis demonstrated a visual perceptual factor, with loadings on the Gollin test and design copying, and three other factors representing primary memory, secondary memory, and language. Results indicate the Gollin test measures visual perceptual ability, but the precise nature of the task requires further study. Identification of fragmented pictures appears a practical and potentially useful measure for evaluating at least some aspects of visual perception in patients with generalized cognitive impairment.

Line fetch/prefetch in a stack cache memory

A line fetch/prefetch strategy is presented with reference to the architecture of a cache memory specialized to contain a portion of the stack area of the program address space. Our strategy takes advantage of the stack paradigm to predict the information items that have a high probability of being referenced soon and prefetch them. When the stack expands, the cache lines reserved for the new stack portions at the stack top are not initialized with quantities fetched from the primary memory, as the primary memory stores no valid information for these lines. When the stack shrinks, the lines made free at the stack top are not copied to the primary memory, as they contain discarded stack items. No address tag is used to translate memory addresses into line numbers in the cache line array. The resulting hardware savings are especially important in view of an on-chip implementation of the cache.

Data compression in full-text retrieval systems

When data compression is applied to full-text retrieval systems, intricate relationships emerge between the amount of compression, access speed, and computing resources required. We propose compression methods, and explore corresponding tradeoffs, for all components of static full-text systems such as text databases on CD-ROM. These components include lexical indexes, inverted files, bitmaps, signature files, and the main text itself. Results are reported on the application of the methods to several substantial full-text databases, and show that a large, unindexed text can be stored, along with indexes that facilitate fast searching, in less than half its original size—at some appreciable cost in primary memory requirements. © 1993 John Wiley & Sons, Inc.