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PubMed1984

On the predictive control of foveal eye tracking and slow phases of optokinetic and vestibular nystagmus.

Smooth pursuit and saccadic components of foveal visual tracking as well as more involuntary ocular movements of optokinetic (o.k.n.) and vestibular nystagmus slow phase components were investigated in man, with particular attention given to their possible input-adaptive or predictive behaviour. Each component in question was isolated from the eye movement records through a computer-aided procedure. The frequency response method was used with sinusoidal (predictable) and pseudo-random (unpredictable) stimuli. When the target motion was pseudo-random, the frequency response of pursuit eye movements revealed a large phase lead (up to about 90 degrees) at low stimulus frequencies. It is possible to interpret this result as a predictive effect, even though the stimulation was pseudo-random and thus 'unpredictable'. The pseudo-random-input frequency response intrinsic to the saccadic system was estimated in an indirect way from the pursuit and composite (pursuit + saccade) frequency response data. The result was fitted well by a servo-mechanism model, which has a simple anticipatory mechanism to compensate for the inherent neuromuscular saccadic delay by utilizing the retinal slip velocity signal. The o.k.n. slow phase also exhibited a predictive effect with sinusoidal inputs; however, pseudo-random stimuli did not produce such phase lead as found in the pursuit case. The vestibular nystagmus slow phase showed no noticeable sign of prediction in the frequency range examined (0 approximately 0.7 Hz), in contrast to the results of the visually driven eye movements (i.e. saccade, pursuit and o.k.n. slow phase) at comparable stimulus frequencies.

Eye Movements↗
PubMed2002

Coevolving avian eye size and brain size in relation to prey capture and nocturnality.

Behavioural adaptation to ecological conditions can lead to brain size evolution. Structures involved in behavioural visual information processing are expected to coevolve with enlargement of the brain. Because birds are mainly vision-oriented animals, we tested the predictions that adaptation to different foraging constraints can result in eye size evolution, and that species with large eyes have evolved large brains to cope with the increased amount of visual input. Using a comparative approach, we investigated the relationship between eye size and brain size, and the effect of prey capture technique and nocturnality on these traits. After controlling for allometric effects, there was a significant, positive correlation between relative brain size and relative eye size. Variation in relative eye and brain size were significantly and positively related to prey capture technique and nocturnality when a potentially confounding variable, aquatic feeding, was controlled statistically in multiple regression of independent linear contrasts. Applying a less robust, brunching approach, these patterns also emerged, with the exception that relative brain size did not vary with prey capture technique. Our findings suggest that relative eye size and brain size have coevolved in birds in response to nocturnal activity and, at least partly, to capture of mobile prey.

Animals↗
PubMed2003

Spatial representation of predictive motor learning.

A key feature of skilled motor behavior is the ability of the CNS to predict the consequences of its actions. Such prediction occurs when one hand pulls on an object held in the other hand; the restraining hand generates an anticipatory increase in grip force, thereby preventing the object from slipping. When manipulating a novel object, the CNS adapts its predictive response to ensure that predictions are accurately tuned to the dynamics of the object. Here we examine whether learning to predict the consequences of an action on a novel object is restricted to the actions performed during manipulation or generalizes to novel actions. A bimanual task in which subjects held an object in each hand and the relationship between actions on one object and the motion of the other could be computer controlled from trial-to-trial was used. In four conditions we varied the spatial relationship between the direction of force subjects applied to the left-hand object and the consequent direction of motion of an object held in their right hand, which subjects were required to restrain. The results show that predictive learning was local to the direction of forces experienced during learning and that the magnitude of predictive responses was greatly reduced for novel directions of action of the left hand. The pattern of generalization shows that the representation of predictive learning is spatially local and can be approximated as having a spatially narrow Gaussian basis function.

Conditioning, Psychological↗
PubMed2003

Reexamining adaptation and the set point model of happiness: reactions to changes in marital status.

According to adaptation theory, individuals react to events but quickly adapt back to baseline levels of subjective well-being. To test this idea, the authors used data from a 15-year longitudinal study of over 24.000 individuals to examine the effects of marital transitions on life satisfaction. On average, individuals reacted to events and then adapted back toward baseline levels. However, there were substantial individual differences in this tendency. Individuals who initially reacted strongly were still far from baseline years later, and many people exhibited trajectories that were in the opposite direction to that predicted by adaptation theory. Thus, marital transitions can be associated with long-lasting changes in satisfaction, but these changes can be overlooked when only average trends are examined.

Adaptation, Psychological↗
PubMed1990

Psychological adjustment and experiences with peers during early adolescence: reciprocal, incidental, or unidirectional relationships?

This study examined the relationship over time involving three types of experiences with peers (amount of contact with friends, intimacy with best friend, rejection by peers) and two indices of psychological adjustment (self-perceived social acceptance and depressive affect) using longitudinal and causal analytic procedures developed within the life stress paradigm. Data were collected twice on a sample of 73 young adolescents, with a 6-month interval between measurements. The results provide partial support for a model of reciprocal influences between experiences with peers and adaptation, since adaptation was predictive of change over time in peer experiences in several instances as well as vice versa. Implications for intervention and further research are presented.

Adaptation, Psychological↗
PubMed1989

IQ as a prognostic indicator in adult psychiatric first-admissions.

This study used IQ, along with measures of premorbid adjustment, health-sickness, symptom level, diagnostic severity and demographic data, to predict to 2-year outcome measures of level of functioning, health-sickness, and symptoms for a sample of 145 adult psychiatric first-admissions. It was hypothesized that IQ as an indicator of cognitive ability, or of general ability to adapt, would predict positively to improvement over the 2-year period. Data analysis was conducted with bivariate correlations and multiple regressions, using both absolute-level and residualized outcome variables. IQ showed modest, significant relationships with all absolute outcome indices and six of seven residualized measures, especially for a subsample of those with non-average IQ scores. Regressions showed that IQ provided independent prediction of symptom outcomes.

Adolescent↗
PubMed2004

Mothers' perceptions of benefit following pediatric stem cell transplantation: a longitudinal investigation of the roles of optimism, medical risk, and sociodemographic resources.

BACKGROUND: This longitudinal study investigated the course and predictors of benefit finding among 144 mothers of children undergoing hematopoietic stem cell transplantation (HSCT), a severely stressful and life-threatening medical procedure. PURPOSE: Children's medical risk and mothers' dispositional optimism and sociodemographic resources were examined as predictors of benefit finding. The association between benefit finding and mothers' psychosocial adaptation was also investigated. METHODS: Assessments occurred during hospitalization for HSCT (Time 1 [T1]) and 6 months later (Time 2 [T2]). RESULTS: Hierarchial multiple regression analyses revealed that predictors of benefit finding differed systematically across assessments, with optimism and medical risk predicting benefit finding at both time points but sociodemographic resources predicting only T2 benefit findings. Benefit finding did not predict psychosocial adaptation until optimism was considered as a moderator of their relation: T1 benefit finding was positively associated with T2 adaptation only for mothers high in optimism. CONCLUSION: The need for longitudinal research on posttrauma adaptation and the utility of considering the natural history of the trauma are discussed.

Adaptation, Psychological↗
PubMed2005

The evolution of a Müllerian mimic in a spatially distributed community.

Strong positive density-dependence should lead to a loss of diversity, but warning-colour and Müllerian mimicry systems show extraordinary levels of diversity. Here, we propose an analytical model to explore the dynamics of two forms of a Müllerian mimic in a heterogeneous environment with two alternative model species. Two connected populations of a dimorphic, chemically defended mimic are allowed to evolve and disperse. The proportions of the respective model species vary spatially. We use a nonlinear approximation of Müller's number-dependent equations to model a situation where the mortality for either form of the mimic decreases hyberbolically when its local density increases. A first non-spatial analysis confirms that the positive density-dependence makes coexistence of mimetic forms unstable in a single isolated patch, but shows that mimicry of the rarer model can be stable once established. The two-patch analysis shows that when models have different abundance in different places, local mimetic diversity in the mimic is maintained only if spatial heterogeneity is strong, or, more interestingly, if the mimic is not too strongly distasteful. Therefore, mildly toxic species can become polymorphic in a wider range of ecological settings. Spatial dynamics thus reveal a region of Müllerian polymorphism separating classical Batesian polymorphism and Müllerian monomorphism along the mimic's palatability spectrum. Such polymorphism-palatability relationship in a spatial environment provides a parsimonious hypothesis accounting for the observed Müllerian polymorphism that does not require quasi-Batesian dynamics. While the stability of coexistence depends on all factors, only the migration rate and strength of selection appear to affect the level of diversity at the polymorphic equilibrium. Local adaptation is predicted in most polymorphic cases. These results are in very good accordance with recent empirical findings on the polymorphic butterflies Heliconius numata and H. cydno.

Adaptation, Physiological↗
PubMed2005

Measure dynamics on a one-dimensional continuous trait space: theoretical foundations for adaptive dynamics.

The measure dynamics approach to modelling single-species coevolution with a one-dimensional trait space is developed and compared to more traditional methods of adaptive dynamics and the Maximum Principle. It is assumed that individual fitness results from pairwise interactions together with a background fitness that depends only on total population size. When fitness functions are quadratic in the real variables parameterizing the one-dimensional traits of interacting individuals, the following results are derived. It is shown that among monomorphisms (i.e. measures supported on a single trait value), the continuously stable strategy (CSS) characterize those that are Lyapunov stable and attract all initial measures supported in an interval containing this trait value. In the cases where adaptive dynamics predicts evolutionary branching, convergence to a dimorphism is established. Extensions of these results to general fitness functions and/or multi-dimensional trait space are discussed.

Adaptation, Physiological↗
PubMed1986

Self-blame among parents of infants with perinatal complications: the role of self-protective motives.

According to the literature on defensive attribution, behavioral self-blame can bolster a sense of personal efficacy and is more likely to occur when victims perceive their misfortune as severe. In this study, mothers of infants with severe perinatal complications rated the severity of their child's condition, were asked about its causes, and completed a measure of emotional adaptation. As predicted according to the defensive attribution hypothesis, behavioral self-blame was associated with greater perceived severity and preventability of recurrence. The pattern of correlations suggests that greater perceived severity may produce greater self-blame, which in turn may play an indirect role in adaptation through its association with the belief that a recurrence could be prevented. Results of a post hoc path analysis were consistent with this hypothesis. These findings are discussed in terms of the adaptive features of behavioral self-blame, its relation to perceived control, methodological issues in the study of coping with victimization, and implications for helping professionals.

Adaptation, Psychological↗
PubMed1994

Prediction of long saphenous vein graft adaptation.

The ability of vein to dilate may allow smaller veins to be used for bypass if this change could be predicted. Sixty patients undergoing femorodistal popliteal or infrapopliteal bypass have had their long saphenous vein studied. Diameter measurements of the long saphenous vein have been performed using an ATL Duplex scanner at the groin, mid-thigh and knee. Measurements were performed preoperatively both at rest and with a venous occlusion cuff to dilate the vein and subsequently at 7 days and 3, 6, 9, 12 months after implantation. The mean diameter of the vein at the mid thigh was 4.2 mm non dilated, 5.1 mm with occlusion, 5.4 mm 7 days postoperatively and 5.5 mm at 12 months (p < 0.01 ANOVA). The mean diameter of the vein at the knee was 3.8 mm non-dilated, 4.8 mm with occlusion, 4.8 mm at 7 days and 5.0 mm at 12 months after operation (p < 0.01 ANOVA). If the minimum resting internal diameter of vein regarded as being suitable for bypass was 3 mm, this technique would have increased the vein utilisation rate by 22%. These results show that by using a technique of venous occlusion at the time of preoperative vein mapping the adaptive response of the vein can be predicted and this can result in an increased rate of vein utilisation.

Aged↗
PubMed2003

On-line compensation for perturbations of a reaching movement is cerebellar dependent: support for the task dependency hypothesis.

Although the cerebellum has been shown to be critical for the acquisition and retention of adaptive modifications in certain reflex behaviors, this structure's role in the learning of motor skills required to execute complex voluntary goal-directed movements still is unclear. This study explores this issue by analyzing the effects of inactivating the interposed and dentate cerebellar nuclei on the adaptation required to compensate for an external elastic load applied during a reaching movement. We show that cats with these nuclei inactivated can adapt to predictable perturbations of the forelimb during a goal-directed reach by including a compensatory component in the motor plan prior to movement initiation. In contrast, when comparable compensatory modifications must be triggered on-line because the perturbations are applied in randomized trials (i.e., unpredictably), such adaptive responses cannot be executed or reacquired after the interposed and dentate nuclei are inactivated. These findings provide the first demonstration of the condition-dependent nature of the cerebellum's contribution to the learning of a specific volitional task.

Algorithms↗
PubMedDate not supplied

The two faces of adolescents' success with peers: adolescent popularity, social adaptation, and deviant behavior.

This study assessed the hypothesis that popularity in adolescence takes on a twofold role, marking high levels of concurrent adaptation but predicting increases over time in both positive and negative behaviors sanctioned by peer norms. Multimethod, longitudinal data, on a diverse community sample of 185 adolescents (13 to 14 years), addressed these hypotheses. As hypothesized, popular adolescents displayed higher concurrent levels of ego development, secure attachment, and more adaptive interactions with mothers and best friends. Longitudinal analyses supported a popularity-socialization hypothesis, however, in which popular adolescents were more likely to increase behaviors that receive approval in the peer group (e.g., minor levels of drug use and delinquency) and decrease behaviors unlikely to be well received by peers (e.g., hostile behavior with peers).

Achievement↗
PubMed2005

Neonatal abandonment in Japanese macaques.

This study analyzed long-term demographic data relative to a captive colony of Japanese macaques (Macaca fuscata) in order to evaluate factors predicting increased probability of infant neonatal abandonment. Overall, 7.7% of liveborn infants were abandoned at birth. Probability of abandonment was significantly increased in primiparous and, to a lesser extent, low-ranking mothers. Primiparous mothers abandoned about 40% of their infants at birth. Mother age and infant sex had no independent effects on the probability of neonatal abandonment. Primiparous mothers that did not abandon their infants suffered increased infant mortality and showed longer interbirth intervals compared to same-age multiparous mothers. These results are partially consistent with adaptive hypotheses predicting maternal divestment under unfavorable conditions, and with proximate explanations linking abandonment to inexperience and stress.

Adaptation, Biological↗
PubMed1995

Validity of the Allen Cognitive Levels Assessment: a tri-ethnic comparison.

Schizophrenia is a mental illness which is characterized by severe cognitive deficits and impairments in adaptive functioning. The Allen Cognitive Levels (ACL) Assessment is a screening instrument designed to assess cognitive functioning and to aid clinicians in making judgments about how a patient will be able to perform basic activities of daily living. While the ACL has been widely used, the validity of ACL scores for predicting concurrent adaptive functioning has not been established empirically. The present study examined ACL scores in 110 schizophrenic patients. Scores on the ACL were found to be highly related to scores on the Functional Needs Assessment (r = 0.66), which measures a patient's ability to perform basic activities of daily living. Findings provided some of the first strong evidence that ACL scores reflect adaptive functioning. Correlations between the ACL and the Functional Needs Assessment were equally strong in non-Hispanic whites (n = 31, r = 0.67), Mexican-Americans (n = 58, r = 0.60), and African-Americans (n = 21, r = 0.46). Mean scores did not differ between patients from different ethnic groups. In addition, there was no relationship between ACL scores and level of acculturation within the Mexican-American group. Our data strongly support the hypothesis that the ACL provides a valid and culturally unbiased measure of cognitive functioning that can be helpful in determining how a patient is likely to perform activities of daily living.

Activities of Daily Living↗
PubMed1993

Calcium influx through stretch-activated cation channels mediates adaptation by potassium current activation.

While stretch-sensitive channels are found in many cells, their physiological significance is still controversial. Their ability to mediate receptor current adaptation, as predicted from macroscopic currents, was investigated to provide further evidence for their role in mechanoelectrical transduction. In sensory neurones of abdominal stretch receptor organs of crayfish, Ca2+ influx through stretch-activated channels is shown to activate potassium channels which are considered to be responsible for the fast phase of receptor current adaptation.

Adaptation, Physiological↗
PubMed1999

Prediction of common bile duct stones by noninvasive tests.

OBJECTIVE: To define accurate and useful predictors of common bile duct stones (CBDS). SUMMARY BACKGROUND DATA: The ability to predict CBDS with noninvasive tests can avoid unnecessary, costly, or risky procedures. METHODS: All patients referred for examination for CBDS by endoscopic ultrasonography (EUS) from 1993-1996 were prospectively entered in a database. In a first sample selected randomly from the whole population, predictors of CBDS were determined by univariate analysis and logistic regression. Predictors were subsequently tested in that sample and in the rest of the population. A separate analysis was done for patients planned for cholecystectomy. RESULTS: Eight hundred and eighty patients (328 men, 552 women), aged 57.8 +/- 17 years (range 16-94), were included. The prevalence of CBDS was 18.8%. Age, serum levels of bilirubin, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase (GGT), and alkaline phosphatase, and the existence of jaundice and fever, a dilated bile duct, and a pathologic gallbladder were found to be associated with CBDS. Logistic regression was undertaken separately for patients younger than 70 years (predictors: GGT >7 x normal; pathologic gallbladder; dilated bile duct) and older than 70 years (predictors: GGT >7 x normal; fever > 38 degrees C; dilated bile duct). Odds ratios were 3 to 6.7. The model was satisfactorily applicable to the second sample; age <70 years: chi2 = 3.3 (NS); age >70 years: chi2 = 3.8 (NS). In patients younger than age 70 and planned for cholecystectomy, the combination of the level of GGT and dilated bile duct predicted CBDS accurately. CONCLUSIONS: A simple screening of patients at risk for CBDS can be achieved with three predictive criteria adapted for the patient's age.

Adolescent↗
PubMed1996

Stochastic retinal mechanisms of light adaptation and gain control.

Under appropriate experimental conditions, the threshold intensity of a visual stimulus varies as the square-root of the background illuminance. This square-root law has been observed in both psychophysical threshold experiments and in measurements of the thresholds of individual ganglion cells. A signal detection theory developed in the 1940s by H. L. de Vries and A. Rose, and since elaborated by H. B. Barlow and others, explains the square-root law on the basis of 'noise' due to fluctuations in the number of photon absorptions per unit area and unit time at the cornea. An alternative account of the square-root law--and also other threshold-vs-intensity slopes--is founded on the assumption of physiological gain control (W. A. H. Rushton, Proc, Roy. Soc. (London) B 162, 20-46, 1965; W. S. Geisler, J. Physiol. (London) 312, 165-179, 1979). In this paper, a neural model of light adaptation and gain control is described that shows how these two accounts of the square-root law can be reconciled by a stochastic gain control mechanism whose gain depends on the photon fluctuation level. The process by which spikes are generated in a ganglion cell is modeled in terms of a stochastic integrate-and-fire mechanism; this model is used to quantitatively fit toad retinal ganglion cell threshold data. A psychophysical model is then outlined showing how a statistical observer could analyze the ganglion cell spike trains generated by 'signal' and 'noise' trials in order to statistically discriminate the two conditions. The model is also shown to account for some dynamic aspects of ganglion cell responses, including ON- and OFF-responses. The neural light adaptation model predicts that--under the proper conditions--brightness matching judgments will also be subject to a square-root law. Experimental tests of the model under superthreshold conditions are proposed.

Adaptation, Ocular↗