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PubMed2003

Unconscious adaptation: a new illusion of depth induced by stimulus features without depth.

Here, we show a new illusion of depth induced by psychophysical adaptation to dynamic random-dot stereograms (RDS) that are interocularly anticorrelated (i.e., in which the images for the two eyes have reversed contrast polarity with each other). After prolonged viewing of anticorrelated RDS, the presentation of uncorrelated RDS (i.e., in which two images are mutually independent random-dot patterns) produces the sensation of depth, although both anticorrelated and uncorrelated RDSs are perceptually rivalrous with no consistent depth by themselves. Contrary to other aftereffects demonstrated in a number of visual dimensions, including motion, orientation, and disparity, this illusion results from unconscious adaptation; observers are not aware of what they are being adapted to during the process of adaptation. We further demonstrate that this illusion can be predicted from the simulated responses of disparity-selective neurons based on a local filtering model. Model simulations indicate that the inspection of anticorrelated RDS causes the adaptation of all disparity detectors except one sensitive to its disparity; therefore, those selectively unadapted detectors show relatively strong activation in response to the subsequent presentation of uncorrelated RDS and produce depth perception.

Adaptation, Psychological↗
PubMed2006

Spike-frequency adaptation and intrinsic properties of an identified, looming-sensitive neuron.

We investigated in vivo the characteristics of spike-frequency adaptation and the intrinsic membrane properties of an identified, looming-sensitive interneuron of the locust optic lobe, the lobula giant movement detector (LGMD). The LGMD had an input resistance of 4-5 MOmega, a membrane time constant of about 8 ms, and exhibited inward rectification and rebound spiking after hyperpolarizing current pulses. Responses to depolarizing current pulses revealed the neuron's intrinsic bursting properties and pronounced spike-frequency adaptation. The characteristics of adaptation, including its time course, the attenuation of the firing rate, the mutual dependency of these two variables, and their dependency on injected current, closely followed the predictions of a model first proposed to describe the adaptation of cat visual cortex pyramidal neurons in vivo. Our results thus validate the model in an entirely different context and suggest that it might be applicable to a wide variety of neurons across species. Spike-frequency adaptation is likely to play an important role in tuning the LGMD and in shaping the variability of its responses to visual looming stimuli.

Action Potentials↗
PubMed2004

A possible role of midbrain dopamine neurons in short- and long-term adaptation of saccades to position-reward mapping.

Dopamine (DA) neurons respond to sensory stimuli that predict reward. To understand how DA neurons acquire such ability, we trained monkeys on a one-direction-rewarded version of memory-guided saccade task (1DR) only when we recorded from single DA neurons. In 1DR, position-reward mapping was changed across blocks of trials. In the early stage of training of 1DR, DA neurons responded to reward delivery; in the later stages, they responded predominantly to the visual cue that predicted reward or no reward (reward predictor) differentially. We found that such a shift of activity from reward to reward predictor also occurred within a block of trials after position-reward mapping was altered. A main effect of long-term training was to accelerate the within-block reward-to-predictor shift of DA neuronal responses. The within-block shift appeared first in the intermediate stage, but was slow, and DA neurons often responded to the cue that indicated reward in the preceding block. In the advanced stage, the reward-to-predictor shift occurred quickly such that the DA neurons' responses to visual cues faithfully matched the current position-reward mapping. Changes in the DA neuronal responses co-varied with the reward-predictive differentiation of saccade latency both in short-term (within-block) and long-term adaptation. DA neurons' response to the fixation point also underwent long-term changes until it occurred predominantly in the first trial within a block. This might trigger a switch between the learned sets. These results suggest that midbrain DA neurons play an essential role in adapting oculomotor behavior to frequent switches in position-reward mapping.

Adaptation, Physiological↗
PubMed1995

Elderly people's adaptability to complete denture therapy: usability of a geriatric behaviour-rating scale as a predictor.

Accurately predicting prognosis of complete denture therapy requires a reasonable estimation of the ability of a patient to adapt. The aim of the current study was to test the usability of a geriatric behaviour-rating scale (BOP) as a predictor of elderly people's ability to adapt after complete denture therapy. Ninety-five complete denture-wearing residents of four nursing homes for somatically handicapped patients were randomly divided into two groups, 48 test subjects for whom replacement dentures were prepared and 47 test subjects whose current dentures were improved on. The results of these treatments were evaluated by comparing the scores on the so-called 'scale of appreciation' (complaints of and (dis)satisfaction with complete dentures) prior to and at 2 and 6 months post-treatment. Univariate correlations were computed between the scores on the 'scale of appreciation' or the differences in scores at the three evaluation-moments and the foremost BOP-subscale (BOP1, infirmity) and some factors that were considered to be of influence on the process of adaptation. The BOP1 was the only factor showing a significant correlation with the 'scale of appreciation' at 2 months posttreatment; this suggests that little infirmity was connected with a low value of complaints of and dissatisfaction with complete dentures or a positive alteration of this value. It is concluded that the BOP1 can be a useful predictor of complete denture therapy in this group of elderly people. A relationship between elderly people's adaptability to complete denture therapy and the BOP or any other geriatric behaviour-rating scale could be possible.

Adaptation, Psychological↗
PubMed1999

Caregiving and institutionalization: perceptions of family conflict and socioemotional support.

This study examines the impact of family conflict and socioemotional support among caregivers who institutionize their relatives. Fifty-two wives, forty-three husbands, and sixty-seven daughters were interviewed before and after the placement of a cognitively impaired relative. A repeated measures ANOVA was performed to examine differences in reports of family conflict and socioemotional support among caregivers. Husbands reported greater increases in family conflict than wives or daughters during the institutionization process. Conversely, wives and daughters indicated higher levels of socioemotional support than husbands. Hierarchical regression equations were then calculated to assess the independent contributions of family conflict and socioemotional support to postplacement adaptation. Decreases in socioemotional support during institutionalization significantly predicted postplacement anger among husbands and increases in family conflict significantly predicted postplacement depression among wives. Overall, family conflict and socioemotional support have important implications among caregivers who institutionalize their relatives.

Adaptation, Psychological↗
PubMed1998

Origins of individual swimming behavior in bacteria.

Cells in a cloned population of coliform bacteria exhibit a wide range of swimming behaviors--a form of non-genetic individuality. We used computer models to examine the proposition that these variations are due to differences in the number of chemotaxis signaling molecules from one cell to the next. Simulations were run in which the concentrations of seven gene products in the chemotaxis pathway were changed either deterministically or stochastically, with the changes derived from independent normal distributions. Computer models with two adaptation mechanisms were compared with experimental results from observations on individuals drawn from genetically identical populations. The range of swimming behavior predicted for cells with a standard deviation of protein copy number per cell of 10% of the mean was found to match closely the experimental range of the wild-type population. We also make predictions for the swimming behaviors of mutant strains lacking the adaptational mechanism that can be tested experimentally.

Bacteria↗
PubMed1993

Quantifying social development in autism.

OBJECTIVE: This study was concerned with the development of quantitative measures of social development in autism. METHOD: Multiple regression equations predicting social, communicative, and daily living skills on the Vineland Adaptive Behavior Scales were derived from a large, normative sample and applied to groups of autistic and nonautistic, developmentally disordered children. Predictive models included either mental or chronological age and other relevant variables. RESULTS: Social skills in the autistic group were more than two standard deviations below those predicted by their mental age; an index derived from the ratio of actual to predicted social skills correctly classified 94% of the autistic and 92% of the nonautistic, developmentally disordered cases. CONCLUSIONS: The findings are consistent with the idea that social disturbance is central in the definition of autism. The approach used in this study has potential advantages for providing more precise measures of social development in autism.

Adolescent↗
PubMed2005

Constraints on the evolution of adaptive phenotypic plasticity in plants.

The high potential fitness benefit of phenotypic plasticity tempts us to expect phenotypic plasticity as a frequent adaptation to environmental heterogeneity. Examples of proven adaptive plasticity in plants, however, are scarce and most plastic responses actually may be 'passive' rather than adaptive. This suggests that frequently requirements for the evolution of adaptive plasticity are not met or that such evolution is impeded by constraints. Here we outline requirements and potential constraints for the evolution of adaptive phenotypic plasticity, identify open questions, and propose new research approaches. Important open questions concern the genetic background of plasticity, genetic variation in plasticity, selection for plasticity in natural habitats, and the nature and occurrence of costs and limits of plasticity. Especially promising tools to address these questions are selection gradient analysis, meta-analysis of studies on genotype-by-environment interactions, QTL analysis, cDNA-microarray scanning and quantitative PCR to quantify gene expression, and two-dimensional gel electrophoresis to quantify protein expression. Studying plasticity along the pathway from gene expression to the phenotype and its relationship with fitness will help us to better understand why adaptive plasticity is not more universal, and to more realistically predict the evolution of plastic responses to environmental change.

Adaptation, Physiological↗
PubMed1990

[Effect of chronic intrauterine hypoxia on purine compound metabolism in the erythrocytes of newborn infants in the early neonatal period].

The content of purine compounds in red blood cells was measured and compared in 21 neonates with a history of chronic intrauterine hypoxia, depending on the condition at birth and the early period of adaptation. The content of purine compounds in whole blood was measured at the moment of birth and on days 1, 3 and 5 of life. It has been disclosed that the pattern of purine metabolism abnormality in funic red blood cells makes it possible to predict the course of the early period of adaptation. Changes in the content of hypoxanthine and inosine monophosphate appeared to be most remarkable.

Chronic Disease↗
PubMed1987

[Auditory adaptation and auditory fatigue].

Twenty subjects without otological disease were examined for auditory thresholds by Békésy audiometry and by the Feldmann Test (Adaptogramm), before and after noise exposure to one ear of 90 db SPL at 3 kHz for 15 minutes. The exposed ear was also tested for hearing fatigue (TTS). There was no significant correlation between Békésy audiometry and Feldmann test curves or between these adaptation tests and the hearing fatigue test (TTS) after noise exposure. Our results suggest that these methods of measuring adaptation do not correspond, and that adaptation measurements, prior to noise exposure, have no predictive value for hearing fatigue test results following noise exposure. After noise exposure changes were found in the non-exposed ear which were manifested as variability of the Békésy audiometry curves and flattened Feldmann curves. We thought that these results might indicate a central adaptation following noise exposure. There was interference of this so called "central adaptation" with peripheral fatigue in the exposed ear.

Audiometry, Pure-Tone↗
PubMedDate not supplied

Understanding patient preferences for HIV medications using adaptive conjoint analysis: feasibility assessment.

OBJECTIVE: Choosing among HIV medications involve making trade-offs among various efficacy, convenience, resistance, and side-effect attributes. This study tested the feasibility of using adaptive conjoint analysis (ACA) to assess preferences (utilities) for HIV medication attributes. METHODS: HIV individuals were recruited through newspaper advertisements. Participants completed a computerized ACA survey that assessed 12 attributes, including side effects, regimen convenience, resistance, and efficacy. Literature on third-agent HIV drugs was used to identify percentage risk and severity level descriptions for each attribute. Based on the ACA-derived utilities, we assessed the relative importance of the attributes by averaging individually calculated importance and estimated the percentages that would prefer selected HIV medications over others. To check validity of the ACA utilities, the survey also had respondents choose among medications with different attribute profiles. RESULTS: The 35 respondents were primarily African Americans (94%) and unemployed (54%). Of these, 28 (80%) provided consistent responses and were analyzed. Of the 12 medication attributes evaluated, the risk of developing resistance, regimen convenience, and the risk of sleep disturbance had the greatest impact on preferences; each accounting for more than 8.5% of the variation in preferences. These were followed by risk of drug failure (8.2%), cholesterol elevation (7.1%), diarrhea (7.1%) and nausea (6.9%). The ACA utilities accurately predicted patients' actual medication choices 75% of the time. CONCLUSIONS: Adaptive conjoint analysis was successful in predicting HIV treatment preferences under different medication scenarios. Resistance, regimen convenience, and sleep disturbance would likely make the most difference in the perceived value of a third-agent HIV medication.

Adult↗
PubMed2007

Reinforcement learning signals predict future decisions.

Optimal behavior in a competitive world requires the flexibility to adapt decision strategies based on recent outcomes. In the present study, we tested the hypothesis that this flexibility emerges through a reinforcement learning process, in which reward prediction errors are used dynamically to adjust representations of decision options. We recorded event-related brain potentials (ERPs) while subjects played a strategic economic game against a computer opponent to evaluate how neural responses to outcomes related to subsequent decision-making. Analyses of ERP data focused on the feedback-related negativity (FRN), an outcome-locked potential thought to reflect a neural prediction error signal. Consistent with predictions of a computational reinforcement learning model, we found that the magnitude of ERPs after losing to the computer opponent predicted whether subjects would change decision behavior on the subsequent trial. Furthermore, FRNs to decision outcomes were disproportionately larger over the motor cortex contralateral to the response hand that was used to make the decision. These findings provide novel evidence that humans engage a reinforcement learning process to adjust representations of competing decision options.

Adult↗
PubMed2001

Constraint to adaptive evolution in response to global warming.

We characterized the genetic architecture of three populations of a native North American prairie plant in field conditions that simulate the warmer and more arid climates predicted by global climate models. Despite genetic variance for traits under selection, among-trait genetic correlations that are antagonistic to the direction of selection limit adaptive evolution within these populations. Predicted rates of evolutionary response are much slower than the predicted rate of climate change.

Adaptation, Physiological↗
PubMed1999

Loading conditions and cortical bone construction of an artiodactyl calcaneus.

Customary nonuniform distributions of physiological bone strains are thought to evoke heterogeneous material adaptation in diaphyseal cortices of some limb bones. Recent studies of artiodactyl calcanei have suggested that the regional prevalence of specific mechanical strain features such as mode and magnitude correlate with specific variations in cortical bone ultrastructure, microstructure and mineralization. These data are also consistent with predictions of current algorithms of mechanically induced bone adaptation. However, detailed characterization of the customary functional strain environment of these bones is needed to understand better the mechanisms of these adaptations. An in vitro loading method and rosette strain gauges were used to record principal strains, maximum shear strains and principal strain angles at multiple locations on ten calcanei of adult male mule deer (Odocoileus hemionus hemionus). Each hind limb was fixed in an apparatus to mimic the mid-support phase of the gait and loaded via the Achilles tendon over a broad range of functional loads (0 to 2943 N). Strains were recorded on the craniolateral, craniomedial, caudal, medial and lateral cortices at mid-diaphysis. Loading variations included the progressive elimination of the ligament and tendon along the caudal calcaneus. The results showed that the cranial cortex experiences longitudinal compressive strains that are nearly equal to the principal minimum strains and that the caudal cortex receives longitudinal tensile strains that are nearly equal to the principal maximum strains. With a 981 N load, the mean principal compressive strain on the cranial cortex was -636+/-344 micro(&egr;) (mean +/- s.d., N=9) and the mean principal tensile strain on the caudal cortex was 1112+/-68 micro;(&egr;)x (N=9). In contrast to the cranial and caudal cortices, principal strains in the medial and lateral cortices displayed relatively large deviations from the longitudinal axis (medial, 24 degrees cranial; lateral, 27 degrees caudal). Although shear strains predominated at all gauge sites, variations in maximum shear strains showed no apparent regional pattern or consistent regional predominance. The plantar ligament and tendon of the superficial digital flexor muscle were shown to have important load-sharing functions. These results demonstrate that the functionally loaded artiodactyl calcaneus generally behaves like a cantilevered beam with longitudinal compression and tension strains predominating in opposing cranial and caudal cortices, respectively. Differences in osteon remodeling rates, osteon morphology and mineral content reported previously between the cranial and caudal cortices correlate, in part, with the magnitudes of the principal compressive and tensile strains, respectively. However, material differences that distinguish the medial and lateral cortices from the cranial and caudal cortices could not be primarily attributed to locally increased shear strains as previously suggested. Variations in osteon and/or collagen fiber orientation may correlate more strongly with principal strain direction.

Animals↗
PubMed1994

A simple method for predicting the cyclosporin A erythrocyte-to-plasma distribution ratio in blood, and its clinical assessment.

To adapt the monitoring of cyclosporin A (CyA) to clinical practice, we have developed a model to predict the CyA erythrocyte-to-plasma distribution ratio (CyA-EP), and evaluated its utility in clinical practice. We monitored CyA trough concentrations in whole blood and performed a series of biochemical tests during disease states in patients undergoing immunosuppressive therapy with CyA after transplantation. An estimate of CyA-EP (EPpr) was thus given by the following equation: EPpr = 6.0831 - 0.2944 x (TG+CHO) - 0.0037 x (CyAblood) - 0.0553 x (HCT) + 0.0463 x (BW) + 0.4447 x (CRE) - 0.0366 x (AGE). In this predictive model, EPpr is given as a function of the plasma lipid levels (TG+CHO, mM), the CyA concentration in whole blood (CyAblood, ng/ml), and the hematocrit (HCT, %), as well as the patient's body weight (BW, kg), serum creatinine (CRE, mg/dl) and age (AGE, years). The parameters TG+CHO, CyAblood, HCT, and AGE were negatively correlated with the CyA-EP, whereas BW and CRE exhibited a positive correlation. The predictive performance of this model was satisfactory for clinical use and changes in CyA-EP in transplant patients were obtained from monitoring CyA in whole blood and routine biochemical tests, without directly measuring CyA-EP. Since CyA-EP is an useful indicator for predicting a shift of CyA into tissues and its systemic clearance in plasma, our model to predict the CyA-EP will help the physician select a CyA regimen during immunosuppressive therapy in a variety of disease states after transplantation.

Adult↗
PubMedDate not supplied

The adaption to environmental factors: hazard or programme.

Any living structure, from cell to the entire organism, can adapt to internal or external factors only by triggering pre-existing mechanisms. All these mechanisms have a morphological support programmed within foetal inactive genes or adult genes with low activity. These genes are activated by a chain of reactions that usually starts with perceiving the stimulus at the membrane level and finishes with the synthesis of some proteins (enzymes, membrane receptors, etc.). The adaptative changes of the enzymatic and structural register would be impossible without the activation of genes other than those operating in normal condition. It is obvious that the same pre-existing genetic mechanism also functions in myocardial hypertrophy or neoangiogenesis. Actually, "a genetic orchestra" is ready to perform at a given moment the new tone suggested by the ever changing condition under which the myocardial fiber acts. However, the concept of programmed adaption has not only a theoretical value; in medical practice, the prediction, prevention and treatment of ischemic heart disease will benefit from the theoretic support of understanding the cardiac adaptative behaviour. It is obvious that this adaptation programmes cannot always save the heart from necrosis and the subject from death due to fatal arrhythmias or cardiogenic shock.

Adaptation, Physiological↗
PubMed2005

Substrate-dependent regulation of anaerobic degradation pathways for toluene and ethylbenzene in a denitrifying bacterium, strain EbN1.

Anaerobic biodegradation of toluene and ethylbenzene is of environmental concern and biochemical interest due to toxicity and novel reactions, respectively. The denitrifying strain EbN1 is unique in anaerobically degrading both alkylbenzenes via different pathways which converge at benzoyl coenzyme A. The organization of genes involved in both pathways was only recently determined for strain EbN1. In the present study, global expression analysis (DNA microarray and proteomics) indicated involvement of several thus-far-unknown proteins in the degradation of both alkylbenzenes. For example, orf68 and orf57, framing the ebd operon, are implicated in ethylbenzene degradation, and the ebA1932 and ebA1936 genes, located 7.2 kb upstream of the bbs operon, are implicated in toluene degradation. In addition, expression studies were now possible on the level of the complete pathways. Growth experiments demonstrated that degradative capacities for toluene and ethylbenzene could be simultaneously induced, regardless of the substrate used for adaptation. Regulation was studied at the RNA (real-time reverse transcription-PCR and DNA microarray) and protein (two-dimensional-difference gel electrophoresis) level by using cells adapted to anaerobic growth with benzoate, toluene, ethylbenzene, or a mixture of toluene and ethylbenzene. Expression of the two toluene-related operons (bss and bbs) was specifically induced in toluene-adapted cells. In contrast, genes involved in anaerobic ethylbenzene degradation were induced in ethylbenzene- and toluene-adapted cells, suggesting that toluene may act as a gratuitous inducer. In agreement with the predicted sequential regulation of the ethylbenzene pathway, Ebd proteins (encoding subunits of ethylbenzene dehydrogenase) were formed in ethylbenzene- but not in acetophenone-adapted cells, while Apc proteins (subunits of predicted acetophenone carboxylase) were formed under both conditions.

Anaerobiosis↗
PubMed2006

A cerebellar model for predictive motor control tested in a brain-based device.

The cerebellum is known to be critical for accurate adaptive control and motor learning. We propose here a mechanism by which the cerebellum may replace reflex control with predictive control. This mechanism is embedded in a learning rule (the delayed eligibility trace rule) in which synapses onto a Purkinje cell or onto a cell in the deep cerebellar nuclei become eligible for plasticity only after a fixed delay from the onset of suprathreshold presynaptic activity. To investigate the proposal that the cerebellum is a general-purpose predictive controller guided by a delayed eligibility trace rule, a computer model based on the anatomy and dynamics of the cerebellum was constructed. It contained components simulating cerebellar cortex and deep cerebellar nuclei, and it received input from a middle temporal visual area and the inferior olive. The model was incorporated in a real-world brain-based device (BBD) built on a Segway robotic platform that learned to traverse curved paths. The BBD learned which visual motion cues predicted impending collisions and used this experience to avoid path boundaries. During learning, the BBD adapted its velocity and turning rate to successfully traverse various curved paths. By examining neuronal activity and synaptic changes during this behavior, we found that the cerebellar circuit selectively responded to motion cues in specific receptive fields of simulated middle temporal visual areas. The system described here prompts several hypotheses about the relationship between perception and motor control and may be useful in the development of general-purpose motor learning systems for machines.

Cerebellum↗