Browsing by Subject "Statistics as Topic"

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    Auditory signals evolve from hybrid- to eye-centered coordinates in the primate superior colliculus.
    (Journal of neurophysiology, 2012-07) Lee, Jungah; Groh, Jennifer M
    Visual and auditory spatial signals initially arise in different reference frames. It has been postulated that auditory signals are translated from a head-centered to an eye-centered frame of reference compatible with the visual spatial maps, but, to date, only various forms of hybrid reference frames for sound have been identified. Here, we show that the auditory representation of space in the superior colliculus involves a hybrid reference frame immediately after the sound onset but evolves to become predominantly eye centered, and more similar to the visual representation, by the time of a saccade to that sound. Specifically, during the first 500 ms after the sound onset, auditory response patterns (N = 103) were usually neither head nor eye centered: 64% of neurons showed such a hybrid pattern, whereas 29% were more eye centered and 8% were more head centered. This differed from the pattern observed for visual targets (N = 156): 86% were eye centered, <1% were head centered, and only 13% exhibited a hybrid of both reference frames. For auditory-evoked activity observed within 20 ms of the saccade (N = 154), the proportion of eye-centered response patterns increased to 69%, whereas the hybrid and head-centered response patterns dropped to 30% and <1%, respectively. This pattern approached, although did not quite reach, that observed for saccade-related activity for visual targets: 89% were eye centered, 11% were hybrid, and <1% were head centered (N = 162). The plainly eye-centered visual response patterns and predominantly eye-centered auditory motor response patterns lie in marked contrast to our previous study of the intraparietal cortex, where both visual and auditory sensory and motor-related activity used a predominantly hybrid reference frame (Mullette-Gillman et al. 2005, 2009). Our present findings indicate that auditory signals are ultimately translated into a reference frame roughly similar to that used for vision, but suggest that such signals might emerge only in motor areas responsible for directing gaze to visual and auditory stimuli.
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    Cognitive and neural contributors to emotion regulation in aging.
    (Social cognitive and affective neuroscience, 2011-04) Winecoff, Amy; Labar, Kevin S; Madden, David J; Cabeza, Roberto; Huettel, Scott A
    Older adults, compared to younger adults, focus on emotional well-being. While the lifespan trajectory of emotional processing and its regulation has been characterized behaviorally, few studies have investigated the underlying neural mechanisms. Here, older adults (range: 59-73 years) and younger adults (range: 19-33 years) participated in a cognitive reappraisal task during functional magnetic resonance imaging (fMRI) scanning. On each trial, participants viewed positive, negative or neutral pictures and either naturally experienced the image ('Experience' condition) or attempted to detach themselves from the image ('Reappraise' condition). Across both age groups, cognitive reappraisal activated prefrontal regions similar to those reported in prior studies of emotion regulation, while emotional experience activated the bilateral amygdala. Psychophysiological interaction analyses revealed that the left inferior frontal gyrus (IFG) and amygdala demonstrated greater inverse connectivity during the 'Reappraise' condition relative to the 'Experience' condition. The only regions exhibiting significant age differences were the left IFG and the left superior temporal gyrus, for which greater regulation-related activation was observed in younger adults. Controlling for age, increased performance on measures of cognition predicted greater regulation-related decreases in amygdala activation. Thus, while older and younger adults use similar brain structures for emotion regulation and experience, the functional efficacy of those structures depends on underlying cognitive ability.
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    Cost of capital to the hospital sector.
    (J Health Econ, 1988-03) Sloan, FA; Valvona, J; Hassan, M; Morrisey, MA
    This paper provides estimates of the cost of equity and debt capital to for-profit and non-profit hospitals in the U.S. for the years 1972-83. The cost of equity is estimated using, alternatively, the Capital Asset Pricing Model and Arbitrage Pricing Theory. We find that the cost of equity capital, using either model, substantially exceeded anticipated inflation. The cost of debt capital was much lower. Accounting for the corporate tax shield on debt and capital paybacks by cost-based insurers lowered the net cost of capital to hospitals.
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    Diffusion of surgical technology. An exploratory study.
    (J Health Econ, 1986-03) Sloan, FA; Valvona, J; Perrin, JM; Adamache, KW
    The study presents an empirical analysis of the diffusion patterns of five surgical procedures. Roles of payer mix, regulatory policies, physician diffusion, competition among hospitals, and various hospital characteristics such as size and the spread of technologies are examined. The principal data base is a time series cross-section of 521 hospitals based on discharge abstracts sent to the Commission on Professional and Hospital Activities. Results on the whole are consistent with a framework used to study innovations in other contexts in which the decisions of whether to innovate and timing depend on anticipated streams of returns and cost. Innovation tends to be more likely to occur in markets in which the more generous payers predominate. But the marginal effects of payer mix are small compared to effects of location and hospital characteristics, such as size and teaching status. Hospital rate-setting sometimes retarded diffusion. Certificate of need programs did not.
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    Emerging Technologies to Conserve Biodiversity.
    (Trends in ecology & evolution, 2015-11) Pimm, Stuart L; Alibhai, Sky; Bergl, Richard; Dehgan, Alex; Giri, Chandra; Jewell, Zoë; Joppa, Lucas; Kays, Roland; Loarie, Scott
    Technologies to identify individual animals, follow their movements, identify and locate animal and plant species, and assess the status of their habitats remotely have become better, faster, and cheaper as threats to the survival of species are increasing. New technologies alone do not save species, and new data create new problems. For example, improving technologies alone cannot prevent poaching: solutions require providing appropriate tools to the right people. Habitat loss is another driver: the challenge here is to connect existing sophisticated remote sensing with species occurrence data to predict where species remain. Other challenges include assembling a wider public to crowdsource data, managing the massive quantities of data generated, and developing solutions to rapidly emerging threats.
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    Environmental management for malaria control: knowledge and practices in Mvomero, Tanzania.
    (Ecohealth, 2010-12) Randell, Heather Fawn; Dickinson, Katherine L; Shayo, Elizabeth H; Mboera, Leonard EG; Kramer, Randall A
    Environmental conditions play an important role in the transmission of malaria; therefore, regulating these conditions can help to reduce disease burden. Environmental management practices for disease control can be implemented at the community level to complement other malaria control methods. This study assesses current knowledge and practices related to mosquito ecology and environmental management for malaria control in a rural, agricultural region of Tanzania. Household surveys were conducted with 408 randomly selected respondents from 10 villages and qualitative data were collected through focus group discussions and in-depth interviews. Results show that respondents are well aware of the links between mosquitoes, the environment, and malaria. Most respondents stated that cleaning the environment around the home, clearing vegetation around the home, or draining stagnant water can reduce mosquito populations, and 63% of respondents reported performing at least one of these techniques to protect themselves from malaria. It is clear that many respondents believe that these environmental management practices are effective malaria control methods, but the actual efficacy of these techniques for controlling populations of vectors or reducing malaria prevalence in the varying ecological habitats in Mvomero is unknown. Further research should be conducted to determine the effects of different environmental management practices on both mosquito populations and malaria transmission in this region, and increased participation in effective techniques should be promoted.
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    Experience rating: does it make sense for medical malpractice insurance?
    (Pap Proc Annu Meet Am Econ Assoc, 1990-05) Sloan, FA
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    Introduction to metrology series.
    (Statistical methods in medical research, 2015-02) Sullivan, Daniel C; Bresolin, Linda; Seto, Belinda; Obuchowski, Nancy A; Raunig, David L; Kessler, Larry G
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    Memory and coping with stress: the relationship between cognitive-emotional distinctiveness, memory valence, and distress.
    (Memory, 2008) Boals, Adriel; Rubin, David C; Klein, Kitty
    Cognitive-emotional distinctiveness (CED), the extent to which an individual separates emotions from an event in the cognitive representation of the event, was explored in four studies. CED was measured using a modified multidimensional scaling procedure. The first study found that lower levels of CED in memories of the September 11 terrorist attacks predicted greater frequency of intrusive thoughts about the attacks. The second study revealed that CED levels are higher in negative events, in comparison to positive events and that low CED levels in emotionally intense negative events are associated with a pattern of greater event-related distress. The third study replicated the findings from the previous study when examining CED levels in participants' memories of the 2004 Presidential election. The fourth study revealed that low CED in emotionally intense negative events is associated with worse mental health. We argue that CED is an adaptive and healthy coping feature of stressful memories.
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    Metacognition in monkeys during an oculomotor task.
    (J Exp Psychol Learn Mem Cogn, 2011-03) Middlebrooks, Paul G; Sommer, Marc A
    This study investigated whether rhesus monkeys show evidence of metacognition in a reduced, visual oculomotor task that is particularly suitable for use in fMRI and electrophysiology. The 2-stage task involved punctate visual stimulation and saccadic eye movement responses. In each trial, monkeys made a decision and then made a bet. To earn maximum reward, they had to monitor their decision and use that information to bet advantageously. Two monkeys learned to base their bets on their decisions within a few weeks. We implemented an operational definition of metacognitive behavior that relied on trial-by-trial analyses and signal detection theory. Both monkeys exhibited metacognition according to these quantitative criteria. Neither external visual cues nor potential reaction time cues explained the betting behavior; the animals seemed to rely exclusively on internal traces of their decisions. We documented the learning process of one monkey. During a 10-session transition phase, betting switched from random to a decision-based strategy. The results reinforce previous findings of metacognitive ability in monkeys and may facilitate the neurophysiological investigation of metacognitive functions.
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    Misuse of methamphetamine and prescription stimulants among youths and young adults in the community.
    (Drug and alcohol dependence, 2007-07) Wu, Li-Tzy; Pilowsky, Daniel J; Schlenger, William E; Galvin, Deborah M
    Gender differences in the prevalence and characteristics of misuse of methamphetamine (meth) and prescription stimulants were examined in a representative US sample of youths and young adults aged 16-25 (N=24,409).Stimulant misusers were categorized into three mutually exclusive subgroups: meth users only, meth and prescription stimulant users, and prescription stimulant users only (e.g., Benzedrine, Ritalin, or Dexedrine). Multinominal logistic regression analyses identified the characteristics associated with misuse of meth and prescription stimulants.About 1 in 10 youths reported any misuse of stimulants in their lifetime. Prescription stimulant misuse occurred earlier and was more frequent than meth misuse. About 47% of meth misusers also reported prescription stimulant misuse. Among misusers of meth and prescription stimulants, males were more likely than females to misuse methylphenidate (82% versus 65%) but were less likely to misuse diet pills or amphetamines (37% versus 49%). Multinominal logistic regression analyses indicated that all subgroups of lifetime stimulant misuse were associated with past year substance abuse. The characteristics of meth misusers differed slightly from prescription stimulants misusers.Multidrug use is common among stimulant misusers. Parents should be informed about the risk of prescription stimulant misuse by their youths.
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    Neural mechanisms of context effects on face recognition: automatic binding and context shift decrements.
    (J Cogn Neurosci, 2010-11) Hayes, Scott M; Baena, Elsa; Truong, Trong-Kha; Cabeza, Roberto
    Although people do not normally try to remember associations between faces and physical contexts, these associations are established automatically, as indicated by the difficulty of recognizing familiar faces in different contexts ("butcher-on-the-bus" phenomenon). The present fMRI study investigated the automatic binding of faces and scenes. In the face-face (F-F) condition, faces were presented alone during both encoding and retrieval, whereas in the face/scene-face (FS-F) condition, they were presented overlaid on scenes during encoding but alone during retrieval (context change). Although participants were instructed to focus only on the faces during both encoding and retrieval, recognition performance was worse in the FS-F than in the F-F condition ("context shift decrement" [CSD]), confirming automatic face-scene binding during encoding. This binding was mediated by the hippocampus as indicated by greater subsequent memory effects (remembered > forgotten) in this region for the FS-F than the F-F condition. Scene memory was mediated by right parahippocampal cortex, which was reactivated during successful retrieval when the faces were associated with a scene during encoding (FS-F condition). Analyses using the CSD as a regressor yielded a clear hemispheric asymmetry in medial temporal lobe activity during encoding: Left hippocampal and parahippocampal activity was associated with a smaller CSD, indicating more flexible memory representations immune to context changes, whereas right hippocampal/rhinal activity was associated with a larger CSD, indicating less flexible representations sensitive to context change. Taken together, the results clarify the neural mechanisms of context effects on face recognition.
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    Object files can be purely episodic.
    (Perception, 2007) Mitroff, Stephen R; Scholl, Brian J; Noles, Nicholaus S
    Our ability to track an object as the same persisting entity over time and motion may primarily rely on spatiotemporal representations which encode some, but not all, of an object's features. Previous researchers using the 'object reviewing' paradigm have demonstrated that such representations can store featural information of well-learned stimuli such as letters and words at a highly abstract level. However, it is unknown whether these representations can also store purely episodic information (i.e. information obtained from a single, novel encounter) that does not correspond to pre-existing type-representations in long-term memory. Here, in an object-reviewing experiment with novel face images as stimuli, observers still produced reliable object-specific preview benefits in dynamic displays: a preview of a novel face on a specific object speeded the recognition of that particular face at a later point when it appeared again on the same object compared to when it reappeared on a different object (beyond display-wide priming), even when all objects moved to new positions in the intervening delay. This case study demonstrates that the mid-level visual representations which keep track of persisting identity over time--e.g. 'object files', in one popular framework can store not only abstract types from long-term memory, but also specific tokens from online visual experience.
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    Oropharyngeal Dysphagia in Infants and Children with Infantile Pompe Disease.
    (Dysphagia, 2009-09) Jones, HN; Muller, CW; Lin, M; Banugaria, SG; Case, LE; Li, JS; O'Grady, G; Heller, JH; Kishnani, PS
    Pompe disease is a rare genetic progressive neuromuscular disorder. The most severe form, infantile Pompe disease, has historically resulted in early mortality, most commonly due to cardiorespiratory failure. Treatment with enzyme replacement therapy (ERT) using alglucosidase alfa (Myozyme((R))) has extended the lifespan of individuals with this disease. With the introduction of ERT and the resultant improved survival, dysphagia is being encountered clinically with increasing regularity though systematic data remain unavailable. We retrospectively studied the oropharyngeal swallowing of 13 infants and children with Pompe disease using videofluoroscopy before initiation of ERT, allowing for baseline swallow function to be established in an untreated cohort. Dysphagia was present in all 13 subjects, even in a participant only 15 days old. Oral stage signs were present in 77%, most frequently a weak suck in 69%. Pharyngeal stage signs were present in 100%, including a pharyngeal swallow delay in 92% and pharyngeal residue in 77%. Airway invasion was present in 76.9% of subjects, including penetration in five (38.46%) and silent aspiration in an additional five (38.46%). No relationship in the relative involvement of swallowing, gross motor function, and cardiac disease appeared to be present.
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    Rapid brain responses independently predict gain maximization and loss minimization during economic decision making.
    (J Neurosci, 2013-04-17) San Martín, René; Appelbaum, Lawrence G; Pearson, John M; Huettel, Scott A; Woldorff, Marty G
    Success in many decision-making scenarios depends on the ability to maximize gains and minimize losses. Even if an agent knows which cues lead to gains and which lead to losses, that agent could still make choices yielding suboptimal rewards. Here, by analyzing event-related potentials (ERPs) recorded in humans during a probabilistic gambling task, we show that individuals' behavioral tendencies to maximize gains and to minimize losses are associated with their ERP responses to the receipt of those gains and losses, respectively. We focused our analyses on ERP signals that predict behavioral adjustment: the frontocentral feedback-related negativity (FRN) and two P300 (P3) subcomponents, the frontocentral P3a and the parietal P3b. We found that, across participants, gain maximization was predicted by differences in amplitude of the P3b for suboptimal versus optimal gains (i.e., P3b amplitude difference between the least good and the best gains). Conversely, loss minimization was predicted by differences in the P3b amplitude to suboptimal versus optimal losses (i.e., difference between the worst and the least bad losses). Finally, we observed that the P3a and P3b, but not the FRN, predicted behavioral adjustment on subsequent trials, suggesting a specific adaptive mechanism by which prior experience may alter ensuing behavior. These findings indicate that individual differences in gain maximization and loss minimization are linked to individual differences in rapid neural responses to monetary outcomes.
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    Reduced comparison speed during visual search in late life depression.
    (Journal of clinical and experimental neuropsychology, 2013-01) Potter, Guy G; Madden, David J; Costello, Mathew C; Steffens, David C
    Slowed information processing is a prominent deficit in late-life depression (LLD). To better differentiate processing speed components in LLD, we examined characteristics of visual search performance in 32 LLD and 32 control participants. Data showed specific slowing in the comparison stage of visual search in LLD, rather than in encoding/response stages, but also greater overall slowing in LLD during inefficient versus efficient search. We found no group differences on traditional neuropsychological measures of processing speed. Slowed processing speed in LLD may be specific rather than general, which underscores the need to link components of processing speed to underlying neural circuitry.
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    Storage of correlated patterns in standard and bistable Purkinje cell models.
    (PLoS Comput Biol, 2012) Clopath, Claudia; Nadal, Jean-Pierre; Brunel, Nicolas
    The cerebellum has long been considered to undergo supervised learning, with climbing fibers acting as a 'teaching' or 'error' signal. Purkinje cells (PCs), the sole output of the cerebellar cortex, have been considered as analogs of perceptrons storing input/output associations. In support of this hypothesis, a recent study found that the distribution of synaptic weights of a perceptron at maximal capacity is in striking agreement with experimental data in adult rats. However, the calculation was performed using random uncorrelated inputs and outputs. This is a clearly unrealistic assumption since sensory inputs and motor outputs carry a substantial degree of temporal correlations. In this paper, we consider a binary output neuron with a large number of inputs, which is required to store associations between temporally correlated sequences of binary inputs and outputs, modelled as Markov chains. Storage capacity is found to increase with both input and output correlations, and diverges in the limit where both go to unity. We also investigate the capacity of a bistable output unit, since PCs have been shown to be bistable in some experimental conditions. Bistability is shown to enhance storage capacity whenever the output correlation is stronger than the input correlation. Distribution of synaptic weights at maximal capacity is shown to be independent on correlations, and is also unaffected by the presence of bistability.
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    Strategic use of statistical thinking in drug development.
    (Stat Med, 2000-12-15) Rockhold, FW
    The role of the statistician and statistical thinking in the pharmaceutical industry has evolved greatly in the last four or five decades. Regulatory developments and the changing face of the science of drug development have driven this evolution. The increasing regulatory requirement for statistical input in critical areas has facilitated a wider range of applications. The pace of change of science in general has brought statisticians into contact with a wider range of potential customers. More importantly, it has allowed the statistician to become increasingly involved in strategic issues with the possibility of influencing the direction of the business. However, it is not clear that the statistical profession in industry is adequately prepared for these opportunities either in attitude or training. Changing the statisticians' approach to their role and acquiring the correct training and experience are critical for the profession to optimize their contribution to the drug discovery and development processes.
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    The architecture of cross-hemispheric communication in the aging brain: linking behavior to functional and structural connectivity.
    (Cereb Cortex, 2012-01) Davis, Simon W; Kragel, James E; Madden, David J; Cabeza, Roberto
    Contralateral recruitment remains a controversial phenomenon in both the clinical and normative populations. To investigate the neural correlates of this phenomenon, we explored the tendency for older adults to recruit prefrontal cortex (PFC) regions contralateral to those most active in younger adults. Participants were scanned with diffusion tensor imaging and functional magnetic rresonance imaging during a lateralized word matching task (unilateral vs. bilateral). Cross-hemispheric communication was measured behaviorally as greater accuracy for bilateral than unilateral trials (bilateral processing advantage [BPA]) and at the neural level by functional and structural connectivity between contralateral PFC. Compared with the young, older adults exhibited 1) greater BPAs in the behavioral task, 2) greater compensatory activity in contralateral PFC during the bilateral condition, 3) greater functional connectivity between contralateral PFC during bilateral trials, and 4) a positive correlation between fractional anisotropy in the corpus callosum and both the BPA and the functional connectivity between contralateral PFC, indicating that older adults' ability to distribute processing across hemispheres is constrained by white matter integrity. These results clarify how older adults' ability to recruit extra regions in response to the demands of aging is mediated by existing structural architecture, and how this architecture engenders corresponding functional changes that allow subjects to meet those task demands.
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    The emerging science of quantitative imaging biomarkers terminology and definitions for scientific studies and regulatory submissions.
    (Statistical methods in medical research, 2015-02) Kessler, Larry G; Barnhart, Huiman X; Buckler, Andrew J; Choudhury, Kingshuk Roy; Kondratovich, Marina V; Toledano, Alicia; Guimaraes, Alexander R; Filice, Ross; Zhang, Zheng; Sullivan, Daniel C; QIBA Terminology Working Group
    The development and implementation of quantitative imaging biomarkers has been hampered by the inconsistent and often incorrect use of terminology related to these markers. Sponsored by the Radiological Society of North America, an interdisciplinary group of radiologists, statisticians, physicists, and other researchers worked to develop a comprehensive terminology to serve as a foundation for quantitative imaging biomarker claims. Where possible, this working group adapted existing definitions derived from national or international standards bodies rather than invent new definitions for these terms. This terminology also serves as a foundation for the design of studies that evaluate the technical performance of quantitative imaging biomarkers and for studies of algorithms that generate the quantitative imaging biomarkers from clinical scans. This paper provides examples of research studies and quantitative imaging biomarker claims that use terminology consistent with these definitions as well as examples of the rampant confusion in this emerging field. We provide recommendations for appropriate use of quantitative imaging biomarker terminological concepts. It is hoped that this document will assist researchers and regulatory reviewers who examine quantitative imaging biomarkers and will also inform regulatory guidance. More consistent and correct use of terminology could advance regulatory science, improve clinical research, and provide better care for patients who undergo imaging studies.