Effect Of Set Size Research Articles

Positive schizotypy and negative schizotypy are associated with differential patterns of episodic memory impairment

Cognitive impairment is a hallmark of schizophrenia; however, studies have not comprehensively examined such impairments in non-clinically ascertained schizotypic young adults. The present study employed a series of measures to assess episodic memory in high positive schizotypy, high negative schizotypy, and comparison groups (each group n=25). Consistent with diminished cognitive functioning seen in negative symptom schizophrenia, the negative schizotypy group exhibited deficits on free recall, recognition, and source memory tasks. The positive schizotypy group did not demonstrate deficits on the above mentioned tasks. However, in contrast to the other groups, the positive schizotypy group showed an unexpected set-size effect on the cued-recall task. Set-size effect, which refers to the finding that words that have smaller networks of associates tend to have a memory advantage, is usually found in associative-cuing, but not cued-recall, tasks. The finding for the positive schizotypy group is consistent with heightened spreading activation and reduced executive control suggested to underlie psychotic symptoms. The findings support a multidimensional model of schizotypy and schizophrenia, and suggest that positive and negative schizotypy involve differential patterns of cognitive impairment.

What limits working memory capacity?

We review the evidence for the 3 principal theoretical contenders that vie to explain why and how working memory (WM) capacity is limited. We examine the possibility that capacity limitations arise from temporal decay; we examine whether they might reflect a limitation in cognitive resources; and we ask whether capacity might be limited because of mutual interference of representations in WM. We evaluate each hypothesis against a common set of findings reflecting the capacity limit: The set-size effect and its modulation by domain-specificity and heterogeneity of the memory set; the effects of unfilled retention intervals and of distractor processing in the retention interval; and the pattern of correlates of WM tests. We conclude that-at least for verbal memoranda-a decay explanation is untenable. A resource-based view remains tenable but has difficulty accommodating several findings. The interference approach has its own set of difficulties but accounts best for the set of findings, and therefore, appears to present the most promising approach for future development. (PsycINFO Database Record

Computer-aided detection system for nerve identification using ultrasound images: A comparative study

Ultrasound-Guided Regional Anesthesia (UGRA) has been gaining importance in the last few years, offering numerous advantages over alternative methods of nerve localization (neurostimulation or paraesthesia). However, nerve detection is one of the most difficult tasks that anesthetists can encounter in the UGRA procedure. The context of the present work is to provide practitioners with a computer-aided system to facilitate the practice of UGRA. However, automatic detection and segmentation in US images is still a challenging problem in many medical applications. This paper addresses two main issues, first proposing an efficient framework for nerve detection and segmentation, and second, reviewing literature methods and evaluating their performance for this new application. The proposed system consists of four main stages: (1) despeckling filter, (2) feature extraction, (3) feature selection, (4) classification and segmentation. A comparative study was performed in each of these stages to measure their influence over the whole system. Sonographic videos were acquired with the same ultrasound machine in real conditions from 19 volunteer patients. Evaluation was designed to cover two important aspects: measure the effect of training set size, and evaluate consistency using a cross-validation technique. The results obtained were significant and indicated which method was better for a nerve detection system. The proposed scheme achieved high scores (i.e.80% on average of 1900 tested images), demonstrating its validity.

Does working memory load facilitate target detection?

Previous studies demonstrated that increasing working memory (WM) load delays performance of a concurrent task, by distracting attention and thus interfering with encoding and maintenance processes. The present study used a version of the change detection task with a target detection requirement during the retention interval. In contrast to the above prediction, target detection was faster following a larger set-size, specifically when presented shortly after the memory array (up to 400ms). The effect of set-size on target detection was also evident when no memory retention was required. The set-size effect was also found using different modalities. Moreover, it was only observed when the memory array was presented simultaneously, but not sequentially. These results were explained by increased phasic alertness exerted by the larger visual display. The present study offers new evidence of ongoing attentional processes in the commonly-used change detection paradigm.

Serial vs. parallel models of attention in visual search: accounting for benchmark RT-distributions.

Visual search is central to the investigation of selective visual attention. Classical theories propose that items are identified by serially deploying focal attention to their locations. While this accounts for set-size effects over a continuum of task difficulties, it has been suggested that parallel models can account for such effects equally well. We compared the serial Competitive Guided Search model with a parallel model in their ability to account for RT distributions and error rates from a large visual search data-set featuring three classical search tasks: 1) a spatial configuration search (2 vs. 5); 2) a feature-conjunction search; and 3) a unique feature search (Wolfe, Palmer & Horowitz Vision Research, 50(14), 1304-1311, 2010). In the parallel model, each item is represented by a diffusion to two boundaries (target-present/absent); the search corresponds to a parallel race between these diffusors. The parallel model was highly flexible in that it allowed both for a parametric range of capacity-limitation and for set-size adjustments of identification boundaries. Furthermore, a quit unit allowed for a continuum of search-quitting policies when the target is not found, with "single-item inspection" and exhaustive searches comprising its extremes. The serial model was found to be superior to the parallel model, even before penalizing the parallel model for its increased complexity. We discuss the implications of the results and the need for future studies to resolve the debate.

The effects of age and set size on the fast extraction of egocentric distance

ABSTRACTAngular direction is a source of information about the distance to floor-level objects that can be extracted from brief glimpses (near one's threshold for detection). Age and set size are two factors known to impact the viewing time needed to directionally localize an object, and these were posited to similarly govern the extraction of distance. The question here was whether viewing durations sufficient to support object detection (controlled for age and set size) would also be sufficient to support well-constrained judgments of distance. Regardless of viewing duration, distance judgments were more accurate (less biased towards underestimation) when multiple potential targets were presented, suggesting that the relative angular declinations between the objects are an additional source of useful information. Distance judgments were more precise with additional viewing time, but the benefit did not depend on set size and accuracy did not improve with longer viewing durations. The overall pattern suggests that distance can be efficiently derived from direction for floor-level objects. Controlling for age-related differences in the viewing time needed to support detection was sufficient to support distal localization but only when brief and longer glimpse trials were interspersed. Information extracted from longer glimpse trials presumably supported performance on subsequent trials when viewing time was more limited. This outcome suggests a particularly important role for prior visual experience in distance judgments for older observers.

Visual Working Memory Capacity for Own- and Other-race Faces: Effects of Set Size and Face Features

Visual Working Memory Capacity for Own- and Other-race Faces: Effects of Set Size and Face Features

Exploring Visual Search as a Paradigm for Predicting Medication Errors

According to the FDA, over a million injuries occur each year in the United States due to medication errors. Furthermore, medication management is considered an Instrumental Activity of Daily Living (IADL), and inability to manage one’s medications can threaten an individual’s independence. These errors occur for a number of reasons, including similar sounding/looking medication names and labels, but also due to pills that look extremely similar. We present initial work looking at whether a visual search paradigm might be used to help predict medication mix-ups. We extracted images of pills from the NIH’s Pillbox database, and observers were asked to search for a target pill among similar or dissimilar distractors. Set size was also manipulated (3, 6, 9 items). Results indicated that search slopes may serve as a sensitive and continuous measure of pill confusability. For example, two pills that were extremely similar in terms of color, shape, and size produced relatively steep search slopes (28 ms/item target present, 80ms/item absent), while two pills that were similar in shape and size, but different in color produced parallel search slopes (< 2 ms/item for present and absent conditions). In this case, neither target present nor absent conditions indicated a significant effect of set size (t(27) = -.22, p = .83 and t(27) = .59, p = .56, respectively). Overall, these results indicate potential for this paradigm to be used to study and predict medication errors, and future work will extend findings to take into account changes in acuity and color perception associated with advancing age by testing younger and older adults. Meeting abstract presented at VSS 2015

The role of selective attention during visual search using random dot motion stimuli.

Finding objects among distractors is an essential everyday skill, which is often tested with visual search tasks using static items in the display. Although these kinds of displays are ideal for studying search behavior, the neural encoding of the visual stimuli can occur rapidly, which limits the analysis that can be done on the accumulation of evidence. Searching for a target among multiple random dot motion (RDM) stimuli should allow us to study the effect of attention on the accumulation of information during visual search. We trained an animal to make a saccade to a RDM stimulus with motion in a particular direction (the target). The animal began the task by fixating a central square. After a short delay, it changed to a dotted hollow square and one, two or four RDM stimuli appeared equally spaced in the periphery for 700 ms. The animal was rewarded for looking at the target, if present, or for maintaining fixation if the target was absent from the display. In the spread attention condition, all the dots in the RDM stimuli were the same color. In the focused attention condition, the color of the fixation square and the dotted hollow square matched the color of the dots in one RDM stimulus, which was a 100% valid cue. We varied the coherence of the RDM stimuli for each condition from 65 to 100% (100 ms limited lifetime). At the lower coherences, there were strong effects of set size and attention condition on both performance and reaction time. Our data show that using a RDM visual search task allows us to clearly illustrate the role of attention in the accumulation of perceptual evidence, which increases response accuracy and shortens reaction time. Meeting abstract presented at VSS 2015

Scene context reduces distractor set-size effects during search

Scene context reduces distractor set-size effects during search

A Multi-Area Stochastic Model for a Covert Visual Search Task.

Decisions typically comprise several elements. For example, attention must be directed towards specific objects, their identities recognized, and a choice made among alternatives. Pairs of competing accumulators and drift-diffusion processes provide good models of evidence integration in two-alternative perceptual choices, but more complex tasks requiring the coordination of attention and decision making involve multistage processing and multiple brain areas. Here we consider a task in which a target is located among distractors and its identity reported by lever release. The data comprise reaction times, accuracies, and single unit recordings from two monkeys’ lateral interparietal area (LIP) neurons. LIP firing rates distinguish between targets and distractors, exhibit stimulus set size effects, and show response-hemifield congruence effects. These data motivate our model, which uses coupled sets of leaky competing accumulators to represent processes hypothesized to occur in feature-selective areas and limb motor and pre-motor areas, together with the visual selection process occurring in LIP. Model simulations capture the electrophysiological and behavioral data, and fitted parameters suggest that different connection weights between LIP and the other cortical areas may account for the observed behavioral differences between the animals.

Lithology prediction by support vector classifiers using inverted seismic attributes data and petrophysical logs as a new approach and investigation of training data set size effect on its performance in a heterogeneous carbonate reservoir

Abstract Lithology prediction is one the most affective requirements in all of the petroleum engineering embranchments. Petrophysical analysis, geophysical modeling, statistical methods and artificial intelligent approaches have been used to lithology prediction. Support vector machines (SVMs) based on statistical learning theory (SLT) and the principles of structural risk minimization (SRM) and empirical risk minimization (ERM) use an analytical approach to classification and regression. In this research, SVM classification method is used to lithology prediction from inverted seismic attributes data and petrophysical logs based on petrographic studies of cores lithology in a heterogeneous carbonate reservoir in Iran. Also, because of high impact of the data set size on most of machine learning techniques, effect of training data set size on different SVMs was deliberated by training and testing SVMs by six different partitioned cases according to the learning ratio of each case. Data preparation including normalization, attribute selection, kernel parameters optimization by grid search technique and data partitioning to construct training and testing data sets were performed on the data. The results showed that the SVM performs well in lithology prediction using inverted seismic attributes data and petrophysical logs, and by training data set size reduction, SVM performance has not affected too much, which it is an advantage for SVM as a machine learning method. Also, in order to predict lithology by SVMs using small training data sets, it is recommended to use normalized polynomial kernel function. Kernel functions and generally SVMs are not affected by the training data set size when the learning ratio varies in normal learning ratios. Using the kernels with their associated optimum values of the parameters obtained from grid search technique, it is possible to predict lithology in the investigated reservoir.

Active Set Size Effects at HSUPA in WCDMA Systems

WCDMA cellular networks support soft handover, which guarantees the continuity of wireless services and enhanced communication quality. Cellular networks performance depends upon Soft handover parameters. In this paper, we have shown the effect of soft handover parameters on the performance of WCDMA cellular networks. We consider timeToTrigger1a, timeToTrigger1b, timeToTrigger1c and maxactivesize as the Soft handover parameters. A very useful statistical measure for characterizing the performance of WCDMA cellular system is the mean active set size and soft handover region. It is shown through numerical results that above parameters have decisive effect on HSUPA, mean active set size and soft handover region and hence on the overall performance of the soft handover algorithm.

Costs of storing colour and complex shape in visual working memory: Insights from pupil size and slow waves

We investigated the impact of perceptual processing demands on visual working memory of coloured complex random polygons during change detection. Processing load was assessed by pupil size (Exp. 1) and additionally slow wave potentials (Exp. 2). Task difficulty was manipulated by presenting different set sizes (1, 2, 4 items) and by making different features (colour, shape, or both) task-relevant. Memory performance in the colour condition was better than in the shape and both condition which did not differ. Pupil dilation and the posterior N1 increased with set size independent of type of feature. In contrast, slow waves and a posterior P2 component showed set size effects but only if shape was task-relevant. In the colour condition slow waves did not vary with set size. We suggest that pupil size and N1 indicates different states of attentional effort corresponding to the number of presented items. In contrast, slow waves reflect processes related to encoding and maintenance strategies. The observation that their potentials vary with the type of feature (simple colour versus complex shape) indicates that perceptual complexity already influences encoding and storage and not only comparison of targets with memory entries at the moment of testing.

Linear scaling density matrix real time TDDFT: Propagator unitarity and matrix truncation.

Real time, density matrix based, time dependent density functional theory (TDDFT) proceeds through the propagation of the density matrix, as opposed to the Kohn-Sham orbitals. It is possible to reduce the computational workload by imposing spatial cutoff radii on sparse matrices, and the propagation of the density matrix in this manner provides direct access to the optical response of very large systems, which would be otherwise impractical to obtain using the standard formulations of TDDFT. Following a brief summary of our implementation, along with several benchmark tests illustrating the validity of the method, we present an exploration of the factors affecting the accuracy of the approach. In particular, we investigate the effect of basis set size and matrix truncation, the key approximation used in achieving linear scaling, on the propagator unitarity and optical spectra. Finally, we illustrate that, with an appropriate density matrix truncation range applied, the computational load scales linearly with the system size and discuss the limitations of the approach.

First-Principles Calculations of the Energy and Width of the (2)A(u) Shape Resonance in p-Benzoquinone: A Gateway State for Electron Transfer.

Quinones are versatile biological electron acceptors and mobile electron carriers in redox processes. We present the first ab initio calculations of the width of the (2)A(u) shape resonance in the para-benzoquinone anion, the simplest member of the quinone family. This resonance state located at 2.5 eV above the ground state of the anion is believed to be a gateway state for electron attachment in redox processes involving quinones. We employ the equation-of-motion coupled-cluster method for electron affinity augmented by a complex-absorbing potential (CAP-EOM-EA-CCSD) to calculate the resonance position and width. The calculated width, 0.013 eV, is in excellent agreement with the width of the resonant peak in the photodetachment spectrum, thus supporting the assignment of the band to resonance excitation to the autodetaching (2)A(u) state. The methodological aspects of CAP-EOM-EA-CCSD calculations of resonances positions and widths in medium-sized molecules, such as basis set and CAP box size effects, are also discussed.

Neural population coding of multiple stimuli.

In natural scenes, objects generally appear together with other objects. Yet, theoretical studies of neural population coding typically focus on the encoding of single objects in isolation. Experimental studies suggest that neural responses to multiple objects are well described by linear or nonlinear combinations of the responses to constituent objects, a phenomenon we call stimulus mixing. Here, we present a theoretical analysis of the consequences of common forms of stimulus mixing observed in cortical responses. We show that some of these mixing rules can severely compromise the brain's ability to decode the individual objects. This cost is usually greater than the cost incurred by even large reductions in the gain or large increases in neural variability, explaining why the benefits of attention can be understood primarily in terms of a stimulus selection, or demixing, mechanism rather than purely as a gain increase or noise reduction mechanism. The cost of stimulus mixing becomes even higher when the number of encoded objects increases, suggesting a novel mechanism that might contribute to set size effects observed in myriad psychophysical tasks. We further show that a specific form of neural correlation and heterogeneity in stimulus mixing among the neurons can partially alleviate the harmful effects of stimulus mixing. Finally, we derive simple conditions that must be satisfied for unharmful mixing of stimuli.

Aging effects in cueing tasks as assessed by the ideal observer: peripheral cues.

Previous aging and cueing studies suggest that automatic orienting driven by peripheral cues is preserved with aging; however, inconsistencies can be found. One issue might be the use of response times (RT) to assess cueing effects (invalid RT--valid RT), which, in many cases, may not have clear quantitative predictions. We propose an ideal observer (IO) analysis of accuracy estimating participants' internal value of cue validity, or weight, which should equal the actual cue validity. The weight measures the use of information provided by the cue and is insensitive to variations in set size and difficulty, thus potentially providing advantages to RT. Older (n = 54) and younger (n = 58) participants performed a yes/no detection task of a two-dimensional (2-D) Gaussian (60 ms). Square peripheral precues (150 ms) indicated likely target locations (70% valid) across two or six locations (set sizes). For cueing effects, (valid--invalid hit rates), younger participants had set-size effects (larger cueing effects for set size 6), while older participants did not. The opposite pattern was found for weights (younger: no set-size effects, older: set-size effects) due to the IO predicting larger cueing effects for larger set sizes. Comparisons to the ideal weight (cue validity) suggested that older participants used the cue information effectively with set size 2 (as or more so than younger participants), but not with set size 6. These results suggest that attentional deficits from aging in peripheral cueing tasks may only arise as difficulty increases, such as larger set sizes.

The prevalence effect in lateral masking and its relevance for visual search.

In stimulus displays with or without a single target amid 1,644 identical distractors, target prevalence was varied between 20, 50 and 80 %. Maximum gaze deviation was measured to determine the strength of lateral masking in these arrays. The results show that lateral masking was strongest in the 20 % prevalence condition, which differed significantly from both the 50 and 80 % prevalence conditions. No difference was observed between the latter two. This pattern of results corresponds to that found in the literature on the prevalence effect in visual search (stronger lateral masking corresponding to longer search times). The data add to similar findings reported earlier (Wertheim et al. in Exp Brain Res, 170:387-402, 2006), according to which the effects of many well-known factors in visual search correspond to those on lateral masking. These were the effects of set size, disjunctions versus conjunctions, display area, distractor density, the asymmetry effect (Q vs. O's) and viewing distance. The present data, taken together with those earlier findings, may lend credit to a causal hypothesis that lateral masking could be a more important mechanism in visual search than usually assumed.

Working memory contributions to reinforcement learning impairments in schizophrenia.

Previous research has shown that patients with schizophrenia are impaired in reinforcement learning tasks. However, behavioral learning curves in such tasks originate from the interaction of multiple neural processes, including the basal ganglia- and dopamine-dependent reinforcement learning (RL) system, but also prefrontal cortex-dependent cognitive strategies involving working memory (WM). Thus, it is unclear which specific system induces impairments in schizophrenia. We recently developed a task and computational model allowing us to separately assess the roles of RL (slow, cumulative learning) mechanisms versus WM (fast but capacity-limited) mechanisms in healthy adult human subjects. Here, we used this task to assess patients' specific sources of impairments in learning. In 15 separate blocks, subjects learned to pick one of three actions for stimuli. The number of stimuli to learn in each block varied from two to six, allowing us to separate influences of capacity-limited WM from the incremental RL system. As expected, both patients (n = 49) and healthy controls (n = 36) showed effects of set size and delay between stimulus repetitions, confirming the presence of working memory effects. Patients performed significantly worse than controls overall, but computational model fits and behavioral analyses indicate that these deficits could be entirely accounted for by changes in WM parameters (capacity and reliability), whereas RL processes were spared. These results suggest that the working memory system contributes strongly to learning impairments in schizophrenia.