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PubMed2006

Understanding team adaptation: a conceptual analysis and model.

This endeavor provides a multidisciplinary, multilevel, and multiphasic conceptualization of team adaptation with theoretical roots in the cognitive, human factors, and industrial-organizational psychology literature. Team adaptation and the emergent nature of adaptive team performance are defined from a multilevel, theoretical standpoint. An input-throughput-output model is advanced to illustrate a series of phases unfolding over time that constitute the core processes and emergent states underlying adaptive team performance and contributing to team adaptation. The cross-level mixed-determinants model highlights team adaptation in a nomological network of lawful relations. Testable propositions, practical implications, and directions for further research in this area are also advanced.

Adaptation, Psychological↗
PubMed2003

Attention during adaptation weakens negative afterimages.

The effect of attention during adaptation on subsequent negative afterimages was examined. One of 2 overlapped outline figures was attended during a 7-10-s adaptation period. When the figures were readily perceptually segregated (on the basis of color or motion), the subsequent afterimages were initially weaker for the previously attended figure. This effect was confirmed by demonstrations that the onset of a single afterimage was delayed when an afterimage inducer was attended during adaptation compared with when a central digit stream or an overlapped (brightness-balanced) figure that did not generate an afterimage was attended. The attention effect was further confirmed using a criterion-independent (dot-integration) paradigm. The fact that selective attention during adaptation weakened or delayed afterimages suggests that attention primarily facilitates the adaptation of polarity-independent processes that modulate the visibility of afterimages rather than facilitating the adaptation of polarity-selective processes that mediate the formation of afterimages.

Adaptation, Psychological↗
PubMed2001

The rhythm of microbial adaptation.

The evolutionary biologist "studies the steps by which the miraculous adaptations so characteristic of every aspect of the organic world have evolved". But the general nature of such adaptive steps is still unclear. Evolution is often thought to be random and dependent on unpredictable events. In this light, one might expect the steps taken by adaptation to be completely random, both biologically and temporally. Here I present a mathematical derivation to show that, on the contrary, adaptive steps can have fairly strong rhythm. I find that the strength of the adaptive rhythm, that is its relative temporal regularity, is equal to a constant that is the same for all microbial populations. As a consequence, numbers of accumulated adaptations are predicted to have a universal variance/mean ratio. The theory derived here is potentially applicable to the study of molecular evolution.

Adaptation, Physiological↗
PubMed1992

Subtractive and divisive adaptation in the human visual system.

Sensory systems can adapt to the conditions imposed on them. In the visual system, adapting to a pattern increases the threshold of the ability to see that pattern, and reduces the perceived contrast of the pattern above threshold. Most neurons of the striate cortex reduce their responsiveness after being stimulated for some time by a high-contrast pattern. Such an effect may lie behind these psychophysical adaptation phenomena. These adaptation effects have been reported to be confined to patterns of similar orientation, which is understandable in that the visual neurons that adapt are only excited by a small range of orientations. Neurophysiological evidence suggests that neurons with different orientation preferences have inhibitory interconnections. It is therefore of interest to explore the possible effects of these connections on perception. Here we show that adapting to a horizontal pattern can reduce the perceived contrast of a vertical test pattern more than a horizontal test pattern. These 'cross-orientation' effects are modelled by a division-like process, whereas the more normal 'similar-orientation' effects are modelled by a subtractive process.

Adaptation, Ocular↗
PubMed1993

Protein kinase C is required for light adaptation in Drosophila photoreceptors.

Protein kinase C (PKC) is a key enzyme for many cellular processes but its physiological roles are poorly understood. An excellent opportunity to investigate the function of PKC has been provided by the identification of an eye-specific PKC in Drosophila and a null PKC mutant, inaCP209 (refs 5,6). Bright conditioning lights delivered to inaC photoreceptors lead to an abnormal loss of sensitivity in whole cell recordings from dissociated ommatidia; this has been interpreted as 'hyper-adaptation' and PKC's role has been suggested to be distinct from light adaptation. A presumably related finding is that during intense light, the response of inaC declines to baseline. Invertebrate photoreceptors use the phosphoinositide signalling cascade, responding to single photons with so-called quantum bumps which sum to form the macroscopic response to light. Light adaptation allows photoreceptors to adjust their sensitivity over the enormous range of ambient intensities. Although the molecular mechanism of light adaptation remains obscure, it is a negative-feedback process mediated by a rise in cytosolic calcium and a decrease in bump size. We now show that under physiological conditions light adaptation is severely reduced in inaC, suggesting that eye-specific PKC, itself activated by a rise in cytosolic calcium and diacylglycerol, is required for adaptation. Furthermore, we show that in the absence of PKC individual bumps fail to terminate normally, an effect that can account for the pleiotropic manifestations of the inaC phenotype.

Adaptation, Ocular↗
PubMed1995

Colour constancy influenced by contrast adaptation.

Visual sensitivity is controlled by at least two distinct types of adaptation: light adaptation adjusts sensitivity to the mean luminance and colour in the stimulus, and contrast adaptation adjusts sensitivity to the variations in luminance and colour. Light adaptation is thought to be important in maintaining the perceived colour of objects despite changes in illumination ('colour constancy'), compensating for the mean changes in the light reflected from scenes under different illuminants. But for naturalistic colour signals, we show here that changes in an illuminant can also alter colour contrasts in images (how colours are distributed around the mean) enough to alter the state of contrast adaptation. Thus perceived colour under different illuminants may also be noticeably influenced by contrast adaptation.

Adaptation, Ocular↗
PubMed2001

Spatial scale and cellular substrate of contrast adaptation by retinal ganglion cells.

Human visual perception and many visual system neurons adapt to the luminance and contrast of the stimulus. Here we describe a form of contrast adaptation that occurs in the retina. This adaptation had a local scale smaller than the dendritic or receptive fields of single ganglion cells and was insensitive to pharmacological manipulation of amacrine cell function. These results implicate the bipolar cell pathway as a site of contrast adaptation. The time required for contrast adaptation varied with stimulus size, ranging from approximately 100 ms for the smallest stimuli, to seconds for stimuli the size of the receptive field. The differing scales and time courses of these effects suggest that multiple types of contrast adaptation are used in viewing natural scenes.

Adaptation, Ocular↗
PubMed1999

Adaptation to low energy intakes: the responses and limits to low intakes in infants, children and adults.

Reduction in energy intake below the acceptable level of requirement for an individual results in a series of physiological and behavioural responses, which are considered as an adaptation to the low energy intake. This ability of the human body to adapt to a lowering of the energy intake is without doubt beneficial to the survival of the individual. However, what is more controversial is the view held by some that the body can metabolically adapt in a beneficial manner to a lowered intake and consequently that the requirements for energy are variable given the same body size and composition and physical activity levels. Much of this confusion is the result of considerable evidence from studies conducted in well-nourished adults who, for experimental or other reasons, have lowered their intakes and consequently demonstrated an apparently enhanced metabolic efficiency resulting from changes in metabolic rates which are disproportionate to the changes in body weight. Similar increases in metabolic efficiency are not readily seen in individuals who on long-term marginal intakes, probably from childhood, have developed into short-statured, low-body-weight adults with a different body composition. It would thus appear that the generally used indicator of metabolic efficiency in humans, that is a reduced oxygen consumption per unit fat free mass, is fraught with problems since it does not account for variations in contributions from sub-compartments of the fat free mass which include those with high metabolism at rest such as brain and viscera and those with low metabolism at rest such as muscle mass. Metabolic rate per unit fat free mass thus, does not reflect true variations in metabolic efficiency and is due largely to variations in body composition. This finding combined with the evidence that behavioural adaptation in habitual physical activity patterns which occurs on energy restriction is not necessarily beneficial to the individual raises doubts about the role of adaptation to low intakes in determining one's requirement for energy. The evidence is overwhelming that both in children and adults, changes in body size and composition as well as in levels of habitual physical activity may be the most important consequences of a lowered energy intake and cannot be assumed to be a part of a beneficial adaptation that influences energy requirements.

Adaptation, Physiological↗
PubMed1998

Importance of glucose-6-phosphate dehydrogenase in the adaptive response to hydrogen peroxide in Saccharomyces cerevisiae.

Glucose-6-phosphate dehydrogenase (G6PDH)-deficient cells of Saccharomyces cerevisiae showed increased susceptibility and were unable to induce adaptation to oxidative stress. Historically, mainly in human erythrocytes, it has been suggested and accepted that decreased cellular GSH, due to loss of the NADPH-dependent activity of glutathione reductase (GR), is responsible for the increased sensitivity to oxidative stress in G6PDH-deficient cells. In the present study we investigated whether the increased susceptibility and the inability to induce adaptation to H2O2 stress of G6PDH-deficient yeast is caused by incompleteness of glutathione recycling. We constructed G6PDH- and GR-deficient mutants and analysed their adaptive response to H2O2 stress. Although G6PDH-deficient cells contained comparable amounts of GSH and GR activity to wild-type cells, GSSG was not reduced efficiently, and intracellular GSSG levels and the ratio of GSSG to total glutathione (GSSG/tGSH) were higher in G6PDH-deficient cells than in wild-type. On the other hand, GR-deficient cells showed a susceptibility identical with that of wild-type cells and induced adaptation to H2O2 stress, even though the GSSG/tGSH ratio in GR-deficient cells was higher than in G6PDH-deficient cells. These results indicate that incompleteness of glutathione recycling alone is not sufficient to account for the increased sensitivity and inability to induce adaptation to H2O2 stress of G6PDH-deficient yeast cells. In S. cerevisiae, G6PDH appears to play other important roles in the adaptive response to H2O2 stress besides supplying NADPH to the GR reaction.

Adaptation, Physiological↗
PubMed1990

Acoustical durations of speech segments during stuttering adaptation.

Acoustical durations of stutter- and disfluency-free speech segments from Readings #1 and #5 in an adaptation series were measured in 4 adapting, 4 nonadapting, and 4 nonstuttering subjects. The segment durations measured were intervocalic interval, stop-gap, voice onset time, and vowel duration. No clear trends in the change of acoustical durations from Reading #1 to Reading #5 distinguished the adapting, nonadapting, or nonstuttering subjects. Moreover, on the basis of speech naturalness judgements, listeners did not differentiate the Reading #1 and #5 phrase segments of subjects with high adaptation versus those with low adaptation scores. From these findings and related literature, adaptation of stuttering, as well as other fluency-inducing conditions, are viewed as circumstances that reduce demands upon central motor-linguistic processes.

Adaptation, Physiological↗
PubMed2003

Re-adaptation of the colonic mucosa following protracted stress in rats.

BACKGROUND: We previously found that DNA synthesis of the colonic mucosa rises under protracted physical stress. At 8 stress weeks DNA values regained those of untreated animals, and was regarded as DNA adaptation to stress. AIMS: To assess whether the 8 weeks' DNA adaptation to stress could be maintained following stress-free intervals, ending with a stress stimulus. METHODS: Sixty rats were transported to the stress laboratory. Thirty were water plunged and 30 sham handled once a day, 5 days a week, for 8 weeks. After 8 stress weeks, groups of five animals were allowed to rest for 1, 2, 3 and 4 weeks, ending with single water plunging or sham handling. Five additional rats were untreated. All 65 animals received an i.p. injection of 3H-thymidine before sacrifice. The ratio radioactive DNA/total DNA reflected the DNA synthesis of the colonic mucosa. RESULTS: Following DNA adaptation at 8 stress weeks, DNA replication in the right colon of the stressed rats significantly increased at 9, 10 and 11 weeks (P < 0.05), but at 12 weeks it had decreased to 8-week values. CONCLUSIONS: DNA replication in the right colon of the stressed rats did not prevail: it increased considerably in the following weeks, but at 12 weeks (only 4 weeks later), re-adaptation to DNA synthesis had occurred. The review of the literature indicates that this is the first report in which, following adaptation to protracted stress, a re-adaptation phase to DNA replication is demonstrated in the colonic mucosa of experimental animals.

Adaptation, Physiological↗
PubMed1998

Perceived social support and community adaptation in schizophrenia.

Prompted by the continuing transition to community care, mental health nurses are considering the role of social support in community adaptation. This article demonstrates the importance of distinguishing between kinds of social support and presents findings from the first round data of a longitudinal study of community adaptation in 156 people with schizophrenia conducted in Brisbane, Australia. All clients were interviewed using the relevant subscales of the Diagnostic Interview Schedule to confirm a primary diagnosis of schizophrenia. The study set out to investigate the relationship between community adaptation and social support. Community adaptation was measured with the Brief Psychiatric Rating Scale (BPRS), the Life Skills Profile (LSP) and measures of dissatisfaction with life and problems in daily living developed by the authors. Social support was measured with the Arizona Social Support Interview Schedule (ASSIS). The BPRS and ASSIS were incorporated into a client interview conducted by trained interviewers. The LSP was completed on each client by an informal carer (parent, relative or friend) or a professional carer (case manager or other health professional) nominated by the client. Hierarchical regression analysis was used to examine the relationship between community adaptation and four sets of social support variables. Given the order in which variables were entered in regression equations, a set of perceived social support variables was found to account for the largest unique variance of four measures of community adaptation in 96 people with schizophrenia for whom complete data are available from the first round of the three-wave longitudinal study. A set of the subjective experiences of the clients accounted for the largest unique variance in measures of symptomatology, life skills, dissatisfaction with life, and problems in daily living. Sets of community support, household support and functional variables accounted for less variance. Implications for mental health nursing practice are considered.

Adaptation, Psychological↗
PubMed2003

The adaptive response of Escherichia coli O157 in an environment with changing pH.

AIMS: To predict and validate survival of non-acid adapted Escherichia coli O157 in an environment mimicking the human stomach. METHODS AND RESULTS: Survival was predicted mathematically from inactivation rates at various, but constant pH values. Predictions were subsequently validated experimentally in a pH-controlled fermentor. Contrary to prediction, acid-sensitive cultures of E. coli O157 survived for a long period of time and died as rapidly as acid-resistant cultures. Experimental results showed that in an environment with changing pH, acid-sensitive cultures became acid-resistant within 17 min. Cyclo fatty acids was reported to be a factor in acid resistance. As synthesis of cyclo fatty acids does not require de novo enzyme synthesis and thus requires little time to develop, we analysed the membrane fatty acid composition of E. coli O157 during adaptation. No changes in membrane fatty acid composition were observed. CONCLUSIONS: Acid adaptation of E. coli O157 can occur during passage of the human gastric acid barrier, which can take up to 4 h. SIGNIFICANCE AND IMPACT OF THE STUDY: The ability of acid-adapted bacteria to survive the human stomach is an important virulence factor. The ability of non-acid adapted E. coli O157 to adapt within a very short period of time under extreme conditions further contributes to the virulence of E. coli O157.

Adaptation, Physiological↗
PubMed2004

Cross-resistance to antibiotics of Escherichia coli adapted to benzalkonium chloride or exposed to stress-inducers.

AIMS: To study the effects of adaptation and stress on the resistance to benzalkonium chloride (BC) and cross-resistance to antibiotics in Escherichia coli. METHODS AND RESULTS: Precultivation of E. coli ATCC 11775 and E. coli DSM 682 in the presence of subinhibitory concentrations of BC or stress inducers (salicylate, chenodeoxycholate and methyl viologen) resulted in higher minimum inhibitory concentration (MIC) of BC and chloramphenicol (CHL). Adaptation to growth in sixfold of the initial MIC of BC resulted in stable BC resistance and enhanced tolerance to several antibiotics and ethidium bromide (EtBr). The MIC of CHL increased more than 10-fold for both strains. Enhanced efflux of EtBr in adapted E. coli ATCC 11775 indicated that the observed resistance was due to efflux. Changes in outer membrane protein profiles were detected in the BC-adapted cells. There were no indications of lower membrane permeability to BC. CONCLUSIONS: Induction of stress response or gradual adaptation to BC or CHL results in acquired cross-tolerance between BC and antibiotics in E. coli. Enhanced efflux was one of the observed differences in adapted cells. SIGNIFICANCE AND IMPACT OF THE STUDY: Provided not taking due precautions, extensive use of disinfectants could lead to emergence of antibiotic-resistant isolates.

Adaptation, Physiological↗
PubMed1998

Factors associated with the adaptation of parents with a chronically ill child.

The purpose of this paper is to describe the adaptation of parents who have a child with a chronic condition and some factors connected to it. Data were collected by a questionnaire from 189 parents who had a child with a chronic condition, such as diabetes, rheumatoid arthritis or asthma. Most (85%) of the responses were from mothers. The data were analysed using factor analysis. A four-factor model turned out to describe best the adaptation of the parents and their coping with the care of a chronically ill child. Two factors showed good adaptation and two poor adaptation. Emotional and instrumental support were connected to adaptation on each of the four factors. Support from health care staff and the parents' need to obtain more information were not connected to adaptation as clearly as emotional and instrumental support. Parents wished for support more in families where the child was under nine years old than in families where the child was over nine years old.

Adaptation, Psychological↗
PubMed1999

Adaptation of Comamonas testosteroni TA441 to utilization of phenol by spontaneous mutation of the gene for a trans-acting factor.

Comamonas testosteroni TA441 adapts to utilization of phenol upon incubation with phenol as the major carbon source. Strain TA441 has a cluster of genes (aphKLMNOPQB) encoding the catabolic enzymes phenol hydroxylase and catechol 2,3-dioxygenase, and a divergently transcribed regulatory gene (aphR), but these genes are silent until adaptation occurs. We found another regulatory gene (aphS) downstream of aphR. AphS belongs to the GntR family of transcriptional regulators. All adapted strains were found to have mutations in the aphS gene or in the aphR-aphS intervening region. The adapted strains expressed phenol hydroxylase and catechol 2, 3-dioxygenase activity in the presence of phenol. The transcriptional activity of both the aphK and the aphR promoters was elevated in the adapted strains. A strain whose aphS gene was artificially disrupted was found to be able to grow using phenol, and the cells showed high levels of the above-mentioned transcriptional and enzymatic activities, indicating that adaptation was caused only by the mutation in the aphS gene. Gel retardation analysis revealed that AphS bound to two specific sites in the promoter region between aphK and aphR. These results indicate that the active aphS gene product acts as a trans-acting factor and represses transcription of the aph genes in strain TA441.

Adaptation, Physiological↗
PubMed2002

Orientation specificity of contrast adaptation in visual cortical pinwheel centres and iso-orientation domains.

Exposure to a high-contrast visual stimulus causes adaptation, a psychophysical phenomenon that is quite selective for stimulus orientation. Its mechanism is largely cortical but the underlying circuitry is still not unambiguously resolved. It has been suggested that adaptation could be the result of integration of inputs from cells within a large local pool, effectively scaling their outputs with respect to local contrast. In this case, orientation selectivity of neuronal adaptation should depend on the location of neurons within the cortical map of orientation preference. We tested this hypothesis by quantifying adaptation to optimally oriented and to orthogonal-to-optimum gratings among neurons recorded either from iso-orientation domains or orientation pinwheel centres, as identified by optical imaging of cat visual cortex. We did not find a significant difference in adaptation characteristics for these two populations of cells, implying that these characteristics do not depend on the local functional architecture. Surprisingly, however, we additionally observed that under isoflurane (but not halothane) anaesthesia, most neurons exhibited adaptation by cross-oriented gratings, regardless of their location within the orientation map. It seems likely that, under isoflurane, inputs became visible that were masked by the commonly used, deeper halothane anaesthesia. For individual cells, the presence of these inputs was independent of their location within the cortical orientation map.

Action Potentials↗
PubMed2006

Developmental characteristics of adapting mouse small intestine crypt cells.

BACKGROUND & AIMS: Following massive small bowel resection (SBR), the remnant intestine undergoes an adaptive process characterized by increases in a number of physiologic and morphologic parameters. These changes are the result of a stimulus that increases crypt cell mitosis and augments cellular progression along the villus axis. To better define this process, we identified patterns of gene expression specifically within adapting intestinal crypt cells following SBR. METHODS: Laser capture microdissection was used to isolate mouse intestinal crypt cells following SBR or sham operation. Multiple biological and technical complementary DNA microarray replicates allowed rigorous statistical analyses for identification of important expression profiles. Major groups of genes were classified as to site of action, functional pathway, and possible regulatory groups. RESULTS: A total of 300 genes differentially expressed at significant levels within adapting crypt enterocytes were analyzed. Comparison of this list of differentially expressed adapting crypt cell genes with a generalized mouse gene expression database (from 82 developing and adult mouse tissues) showed the greatest overlap with developing and immature intestinal tissues. We identified prominent groups of genes involved with cell growth, signal transduction, and nucleic acid binding. Genes not previously shown to be involved with adaptation or development and maturation were identified. CONCLUSIONS: Identification of similar genes coordinately regulated during both adaptation and development, processes that share key morphologic features, provides a basis for new mechanistic insights into these shared characteristics.

Adaptation, Physiological↗