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PubMed1999

Accommodative error, adaptation and myopia.

Accommodative adaptation, resulting from the sustained output of slow blur-driven accommodation during the course of a sustained near-vision task, has generally been assessed under open-loop conditions. This study examined whether adaptation influences closed-loop accommodation during the course of a sustained near-vision task. Accommodative adaptation was assessed in 18 fully-corrected subjects by comparing pre- and post-task values of dark accommodation recorded objectively with an infra-red optometer. Subjects performed a continuous 10 min binocular near-vision task at a viewing distance of 33 cm, with the within-task accommodative response being assessed at 1 min intervals during this period. Subjects were categorized into adaptors (N = 11) and non-adaptors (N = 7) on the basis of whether their initial 10 sec post-task adaptation exceeded +0.30D. The adapting group exhibited a significant decline in the lag of accommodation during the first 3 min of the near-task, whereas no significant change in the within-task response over time was observed in the non-adapting group. These results indicate that accommodative adaptation increases the accuracy of the within-task, closed-loop accommodative response. Furthermore, we speculate that a deficit in accommodative adaptation, being accompanied by increased retinal defocus during near fixation, may contribute to the development of nearwork-induced myopia.

Accommodation, Ocular↗
PubMed2025

Laboratory Evolution Reveals Transcriptional Mechanisms Underlying Thermal Adaptation of Escherichia coli.

Adaptive laboratory evolution is able to generate microbial strains, which exhibit extreme phenotypes, revealing fundamental biological adaptation mechanisms. Here, we use adaptive laboratory evolution to evolve Escherichia coli strains that grow at temperatures as high as 45.3 °C, a temperature lethal to wild-type cells. The strains adopted a hypermutator phenotype and employed multiple systems-level adaptations that made global analysis of the DNA mutations difficult. Given the challenge at the genomic level, we were motivated to uncover high-temperature tolerance adaptation mechanisms at the transcriptomic level. We employed independently modulated gene set (iModulon) analysis to reveal five transcriptional mechanisms underlying growth at high temperatures. These mechanisms were connected to acquired mutations, changes in transcriptome composition, sensory inputs, phenotypes, and protein structures. They are as follows: (i) downregulation of general stress responses while upregulating the specific heat stress responses, (ii) upregulation of flagellar basal bodies without upregulating motility and upregulation fimbriae, (iii) shift toward anaerobic metabolism, (iv) shift in regulation of iron uptake away from siderophore production, and (v) upregulation of yjfIJKL, a novel heat tolerance operon whose structures we predicted with AlphaFold. iModulons associated with these five mechanisms explain nearly half of all variance in the gene expression in the adapted strains. These thermotolerance strategies reveal that optimal coordination of known stress responses and metabolism can be achieved with a small number of regulatory mutations and may suggest a new role for large protein export systems. Adaptive laboratory evolution with transcriptomic characterization is a productive approach for elucidating and interpreting adaptation to otherwise lethal stresses.

Escherichia coli↗
PubMed2025

The Relationship Among Range Adaptation, Social Anhedonia, and Social Functioning: A Combined Magnetic Resonance Spectroscopy and Resting-State fMRI Study.

BACKGROUND AND HYPOTHESIS: Social anhedonia is a core feature of schizotypy and correlates significantly with social functioning and range adaptation. Range adaptation refers to representing a stimulus value based on its relative position in the range of pre-experienced values. This study aimed to examine the resting-state neural correlates of range adaptation and its associations with social anhedonia and social functioning. STUDY DESIGN: In study 1, 60 participants completed resting-state magnetic resonance spectroscopy and fMRI scans. Range adaptation was assessed by a valid effort-based decision-making paradigm. Self-reported questionnaires was used to measure social anhedonia and social functioning. Study 2 utilized 26 pairs of participants with high (HSoA) and low levels of social anhedonia (LSoA) to examine the group difference in range adaptation's neural correlates and its relationship with social anhedonia and social functioning. An independent sample of 40 pairs of HSoA and LSoA was used to verify the findings. STUDY RESULTS: Study 1 showed that range adaptation correlated with excitation-inhibition balance (EIB) and ventral prefrontal cortex (vPFC) functional connectivity, which in turn correlating positively with social functioning. Range adaptation was specifically determined by the EIB via mediation of ventral-medial prefrontal cortex functional connectivities. Study 2 found HSoA and LSoA participants exhibiting comparable EIB and vPFC connectivities. However, EIB and vPFC connectivities were negatively correlated with social anhedonia and social functioning in HSoA participants. CONCLUSIONS: EIB and vPFC functional connectivity is putative neural correlates for range adaptation. Such neural correlates are associated with social anhedonia and social functioning.

Humans↗
PubMed1979

Comparison and adaptation.

It has sometimes been suggested that the term adaptation should be reserved for differences with a known genetic basis. We argue that adaptation should be defined by its effects rather than by its causes as any difference between two phenotypic traits (or trait complexes) which increases the inclusive fitness of its carrier. This definition implies that some adaptations may arise by means other than natural selection. It is particularly important to bear this in mind when behavioural traits are considered. Critics of the 'adaptationist programme' have suggested that an important objection to many adaptive explanations is that they rely on ad-hoc arguments concerning the function of previously observed differences. We suggest that this is a less important problem (because evolutionary explanations generally claim some sort of generality and are therefore testable) than the difficulties arising from confounding variables. These are more widespread and more subtle than is generally appreciated. Not all differences between organisms are directly adapted to ecological variation. The form of particular traits usually constrains the form of value that other traits can take, presenting several obstacles to attempts to relate variation in morphological or behavioural characteristics directly to environmental differences. We describe some of the repercussions of differences in body size among vertebrates and ways in which these can be allowed for. In addition, a variety of evolutionary processes can produce non-adaptive differences between organisms. One way of distinguishing between these and adaptations is to investigate adaptive trends in phylogenetically different groups of species.

Adaptation, Biological↗
PubMed2006

Dim light adaptation attenuates acute melatonin suppression in humans.

Abstract Studies in rodents with retinal degeneration indicated that neither the rod nor the cone photoreceptors obligatorily participate in circadian responses to light, including melatonin suppression and photoperiodic response. Yet there is a residual phase-shifting response in melanopsin knockout mice, which suggests an alternate or redundant means for light input to the SCN of the hypothalamus. The findings of Aggelopoulos and Meissl suggest a complex, dynamic interrelationship between the classic visual photoreceptors and SCN cell sensitivity to light stimuli, relative to various adaptive lighting conditions. These studies raised the possibility that the phototransductive physiology of the retinohypothalamic tract in humans might be modulated by the visual rod and cone photoreceptors. The aim of the following two-part study was to test the hypothesis that dim light adaptation will dampen the subsequent suppression of melatonin by monochromatic light in healthy human subjects. Each experiment included 5 female and 3 male human subjects between the ages of 18 and 30 years, with normal color vision. Dim white light and darkness adaptation exposures occurred between midnight and 0200 h, and a full-field 460-nm light exposure subsequently occurred between 0200 and 0330-h for each adaptation condition, at 2 different intensities. Plasma samples were drawn following the 2-h adaptation, as well as after the 460-nm monochromatic light exposure, and melatonin was measured by radioimmunoassay. Comparison of melatonin suppression responses to monochromatic light in both studies revealed a loss of significant suppression after dim white light adaptation compared with dark adaptation (p < 0.04 and p < 0.01). These findings indicate that the activity of the novel circadian photoreceptive system in humans is subject to subthreshold modulation of its sensitivity to subsequent monochromatic light exposure, varying with the conditions of light adaptation prior to exposure.

Adaptation, Ocular↗
PubMed1996

Life domains and adaptive strategies of a group of low-income, well older adults.

Older adults are at increased risk for a variety of physical and functional limitations that threaten their ability to lead independent and fulfilling lives. Consequently, they stand to benefit from personalized strategies of adaptation that enable them to achieve successful outcomes in their daily activities and desired goals. In the current investigation, a qualitative descriptive methodology was used to document the perceived life domains of importance and associated strategies of adaptation of 29 residents of Angelus Plaza, a federally subsidized apartment complex in downtown Los Angeles for low-income, well older adults. On the basis of interview data, 10 life domains were identified, and within each domain, a typology of adaptive strategies was derived. The domains were activities of daily living (ADL), adaptation to a multicultural environment, free time usage, grave illness and death-spirituality, health maintenance, mobility maintenance, personal finances, personal safety, psychological well-being and happiness, and relationships with others. Although the typology should not be generalized to a geriatric population, therapists may wish to refer to it to gain a sense of the extent to which certain adaptive strategies may be applicable to the lives of particular older adults to whom they deliver services. The teaching of these adaptive strategies could then be incorporated into an individualized treatment plan. The typology also provides a broad picture of the kinds of adaptive strategies used by the older adults as a way of coping and adapting to their setting. Although some of the domains do not differ from those typically addressed in occupational therapy textbooks on geriatric care (e.g., ADL, health maintenance), others seem uniquely tailored to the specifics of the Angelus Plaza context (e.g., personal safety). Finally, certain domains emerged that may be highly relevant to older adults in most settings but are not typically the focus of occupational therapy programs (e.g., grave illness and death-spirituality, relationships with others). The emergence of these domains from our data suggests that therapists may wish to consider them more in treatment if they are convinced that they possess local relevance.

Activities of Daily Living↗
PubMed2003

Do weak adapting backgrounds uncover multiple components in the electroretinogram of the horseshoe crab?

The lateral eye of the horseshoe crab, Limulus polyphemus, has been used as a model system for over a century to study visual and circadian processes. One advantage of this system is the relative simplicity of the retina. The input pathway of the retina consists of photoreceptor cells that are electrically coupled to the dendrite of a second-order cell, which sends action potentials to the brain. Electroretinograms (ERGs) recorded from the lateral eye show a biphasic shape, with a leading negative wave and a later positive peak. The purpose of these experiments was to determine whether adapting backgrounds could be used to uncover multiple adaptation mechanisms within the ERG. To test this idea, ERGs were elicited using variable intensity flashes presented under dark-adapted conditions, as well as in the presence of weak adapting backgrounds. Flashes and backgrounds were generated using green LEDs (lambda max = 525 nm) under software control. ERGs were recorded using a corneal wick electrode placed on the lateral eye of the horseshoe crab. Preliminary results suggest that ERGs recorded in the presence of adapting backgrounds are linearly scaled versions of dark-adapted FRGs. This suggests that there is a single adaptation stage in the Limulus retina. This is in contrast with analogous results from mammals, including mouse, cat and monkey, which show multiple stages of adaptation within their more complex retinas.

Adaptation, Ocular↗
PubMed2026

Polygenic and monogenic adaptation drive evolutionary rescue at different magnitudes of environmental change.

Understanding the genetic basis of rapid adaptation is key to predicting species' evolutionary responses to environmental change. However, it is still debatable whether many small-effect mutations or a few large-effect mutations underlie rapid adaptation, and how this knowledge can predict population survival or extinction. To address this question, we performed a series of ecologically grounded forward-in-time genetic simulations to study rapid adaptation and extinction with increasing magnitudes of environmental change. These simulations were seeded with genomic variation of the plant Arabidopsis thaliana to have a realistic genomic structure, with one (monogenic) to 1,000 (polygenic) variants with varying heritabilities contributing to an environmental adaptive trait. Our results revealed two distinct scenarios of rapid adaptation and population rescue. Under small-to-moderate environmental shifts, high polygenic traits increased evolutionary rescue probability. Under extreme environmental shifts, high polygenic traits lead predictably to extinction, yet monogenic traits sometimes produce one-off winning adaptive genotypes. We interpret our rapid evolutionary rescue findings in terms of the fundamental theorem of natural selection, where trait polygenicity shapes the distribution of genetic variance in fitness across replicates and, in turn, the probability of population survival, with polygenic architectures producing more stable and predictable fitness variance and monogenic architectures generating highly skewed and variable outcomes. These results highlight the insights genomics gives us into the (un)predictability of species' evolutionary responses to global change, with management implications for assisted adaptation and conservation.

Arabidopsis↗
PubMed2000

Epidermal growth factor is critical for intestinal adaptation following small bowel resection.

The loss of small intestinal mucosal surface area is a relatively common clinical situation seen in both the pediatric and adult population. The most frequent causes include mesenteric ischemia, trauma, inflammatory bowel disease, necrotizing enterocolitis, and volvulus. Following surgical resection, the remnant intestine compensates or adapts to the loss of native bowel by increasing its absorptive surface area and functional capacity. Unfortunately, many patients fail to adapt adequately, and are relegated to lifelong intravenous nutrition. Research into intestinal adaptation following small bowel resection (SBR) has evolved only recently from the gross and microscopic level to the biochemical and genetic level. As understanding of this process has increased, numerous therapeutic strategies to augment adaptation have been proposed. Epidermal growth factor (EGF) is an endogenous peptide that is secreted into the gastrointestinal tract and able to influence gut ontogeny, as well as mucosal healing. Early studies have demonstrated its ability to augment the adaptive process. Focusing on a murine model of massive intestinal loss, the morphological, structural, biochemical, and genetic changes that occur during the intestinal adaptive process will be reviewed. The role of EGF and its receptor as critical mediators of the adaptive process will be discussed. Additionally, the ability of EGF to augment intestinal proliferation and diminish programmed cell death (apoptosis) following SBR will be examined. Enhancing adaptation in a controlled manner may allow patients to transition off parenteral nutrition to enteral feeding and, thereby, normalize their lifestyle.

Adaptation, Physiological↗
PubMed2005

Adaptive behavior in children with CHARGE syndrome.

The "R" in the mnemonic "CHARGE" has historically stood for "Retardation of Growth and Development." Early medical reports describing mental retardation in CHARGE syndrome have not used convincing means to assess this attribute. This article investigated the range of developmental ability in individuals with CHARGE as measured through an adaptive behavior scale, the Adaptive Behavior Evaluation Scale (ABES) [Carney (1995): The Adaptive Behavior Evaluation Scale home version technical manual-revised. 126p.], over time. Parents of individuals with CHARGE syndrome were surveyed twice over a 4-year time span (N=100, 85) to obtain information about adaptive behavior and specific CHARGE characteristics. There was a significant decline in ABES scores over the 4-year period. However, at Time two, one-half of the children achieved a standard score above 70. Correlation and regression analyses at Time one and Time two revealed negative relationships between (a) age at walking, (b) degree of hearing impairment, (c) degree of visual impairment, and (d) medical involvement variables and the dependent variable, adaptive behavior. In both studies, age at walking was the best predictor of scores. Analysis of variance confirmed that medical involvement and degree of vision impairment were related to adaptive behavior scores because they were also related to age at walking. Age at walking and medical involvement at Time one were found to be significantly different between those who improved and declined in adaptive behavior scores over time. Adaptive behavior scores from both studies revealed a much broader and higher-reaching range of ability for this population than has been previously reported in the literature.

Abnormalities, Multiple↗
PubMed1995

Transient adaptation to oxidative stress in yeast.

Adaptive responses to the oxidative stress of hydrogen peroxide (H2O2) were studied in the yeast Saccharomyces cerevisciae strain RZ53. Our results show that the growth of naive cells is readily arrested by H2O2 challenge. In contrast, cells that have been preexposed to relatively low H2O2 priming treatments (i.e., cells that have first been pretreated with low H2O2 concentrations) are able to survive a subsequent challenge dose and continue to divide at normal rates. The most effective adaptation was observed with the following conditions: 5 x 10(6) cells/ml at pretreatment, pretreatment or priming peroxide addition of 0.4 mM H2O2, interval between pretreatment and challenge of 45 min, challenge peroxide concentration of 0.8 mM H2O2 for 2 h. Under these conditions cells that were challenged without pretreatment exhibited a 90% loss of plating efficiency. In contrast, peroxide-pretreated cells grew and divided at rates that were actually 15-30% faster than those of nonpretreated cells, and some 90-100% of such pretreated cells continued to divide at normal rates even following exposure to the H2O2 challenge concentration. The increased H2O2 resistance of pretreated cells was transient, being readily reversed during 60-90 min of growth in the absence of H2O2. Furthermore, cells that were allowed to deadapt over a 4-h period again exhibited a transient adaptive response when reexposed to H2O2 pretreatment. These results, plus the high survival rates (90-100%) of H2O2 pretreated and challenged cells, demonstrates that our results represent a true transient adaptation, rather than a selection for any preexisting peroxide resistant subpopulation. H2O2 adaptation required protein synthesis as evidenced by studies with the translational inhibitor, cycloheximide. At least 21 proteins exhibited increased expression following H2O2 adaptation, while the expression of some 8 other proteins was decreased. Adaptation is now widely reported in bacterial strains and has also been observed in some mammalian cell lines. We propose that the basis for such adaptive responses rests in increased expression of genes that encode protective enzymes and repair enzymes.

Adaptation, Physiological↗
PubMed2000

Taste adaptation during the eating of sweetened yogurt.

Taste adaptation, a gradual decline of taste intensity with prolonged stimulation, is frequently observed in laboratory experiments. However, during normal eating the taste of food does not seem to decrease or disappear. During eating, the presence of saliva, the interactions between tastants and odorants, and mouth movements can influence the time course of taste intensity. Therefore, results from standard laboratory adaptation experiments about adaptation seem of limited relevance to the prediction of the time course of taste intensity when eating real foods. We studied whether taste adaptation occurs when subjects eat yogurt, sweetened with two concentrations of sucrose (3.75 and 7.5%). In addition, we examined whether this adaptation is related to taste adaptation measured with a filter paper method. During the eating of yogurt, sweetness intensity declined with time, whereas sourness intensity did not. As expected, taste adaptation in the "yogurt task" was only slightly correlated to adaptation measured with filter paper.

Adaptation, Physiological↗
PubMed1992

Light adaptation and the luminance-response function of the cone electroretinogram.

Cone electroretinograms are typically isolated by presenting stimulus flashes against rod-desensitizing adapting fields. To investigate the manner in which adapting-field luminance affects cone electroretinogram response properties, we measured cone electroretinogram luminance-response functions of two normal subjects, with stimuli presented against adapting fields that ranged in luminance from -1.2 to 2.1 log cd/m2. A flicker rate of 31.1 Hz was used to isolate cone electroretinograms under all adaptation conditions. A hyperbolic equation of the form (R/Rmax) = Ln/(Ln + Kn) was fitted to each luminance-response function by a least-squares criterion. As adapting field luminance increased, the best-fit values of the variables K and n increased, which is in general agreement with results of electrophysiologic studies of light adaptation in retinal neurons. However, Rmax values also increased with adapting field luminance. The change in all three of these variables with adapting field luminance must be considered in the interpretation of cone electroretinogram luminance-response functions from patients with retinal disorders.

Adaptation, Ocular↗
PubMed1995

Adaptational and learning processes during human split-belt locomotion: interaction between central mechanisms and afferent input.

Split-belt locomotion (i.e., walking with unequal leg speeds) requires a rapid adaptation of biomechanical parameters and therefore of leg muscle electromyographic (EMG) activity. This adaptational process during the first strides of asymmetric gait as well as learning effects induced by repetition were studied in 11 healthy volunteers. Subjects were switched from slow (0.5 m/s) symmetric gait to split-belt locomotion with speeds of 0.5 m/s and 1.5 m/s, respectively. All subjects were observed to adapt in a similar way: (1) during the first trial, adaptation required about 12-15 strides. This was achieved by an increase in stride cycle duration, i.e., an increase in swing duration on the fast side and an increase in support duration on the slow side. (2) Adaptation of leg extensor and flexor EMG activity paralleled the changes of biomechanical parameters. During the first strides, muscle activity was enhanced with no increase in coactivity of antagonistic leg muscles. (3) A motor learning effect was seen when the same paradigm was repeated a few minutes later--interrupted by symmetric locomotion--as adaptation to the split-belt speeds was achieved within 1-3 strides. (4) This short-time learning effect did not occur in the "mirror" condition when the slow and fast sides were inverted. In this case adaptation again required 12-15 strides. A close link between central and proprioceptive mechanisms of interlimb coordination is suggested to underlie the adaptational processes during split-belt conditions. It can be assumed that, as in quadrupedal locomotion of the cat, human bipedal locomotion involves separate locomotor generators to provide the flexibility demanded. The present results suggest that side-specific proprioceptive information regarding the dynamics of the movement is necessary to adjust the centrally generated locomotor activity for both legs to the actual needs for controlled locomotion. Although the required pattern is quickly learned, this learning effect cannot be transferred to the contralateral side.

Adaptation, Physiological↗
PubMed1989

In vitro dark adaptation and preservation of electrical light responses in the retina from bovine eyes.

A method is described which allows the in vitro dark adaptation of rod photoreceptors from cattle eyes, enucleated under ambient light in the slaughterhouse. Without in vitro dark adaptation these eyes are light adapted and cannot be used for certain delicate biochemical studies and for an electrophysiological characterisation of rod responses. The method is very simple and yields large amounts of dark adapted retinal material, allowing experiments that require bulk amounts of photoreceptor cells. The only source of dark adapted photoreceptors so far have been retinae from dark adapted laboratory animals, which had to be killed and processed under infrared light. Eye cups were opened under red light as soon as possible after their enucleation. Their vitreous humor was removed and their retina thoroughly rinsed with ringer's. Then the eye cup was placed in a moist, light-tight box, where dark adaptation took place. Photoreceptors could thus be kept alive for more than 24 h without showing signs of deterioration. Humidity and free access of oxygen to the retina were the only prerequisites for their survival. The physiological intactness of the photoreceptors and their degree of dark adaptation was demonstrated by measuring mass receptor potentials (ERGs). A simple device is described which can be used for the electrophysiological characterisation of these eyes.

Adaptation, Physiological↗
PubMed1990

Changes in physiological and neuroendocrine properties during thermal adaptation of golden hamsters (Mesocricetus auratus).

Golden hamsters raised at 22 degrees C were adapted in the early summer for 3 weeks to either 28 degrees C or 5 degrees C. To achieve profound changes the photoperiod was also shortened from 14 h to 11 h during adaptation to cold. During the investigation body weight, food consumption, water intake, urine production, and osmolality, as well as secreted amounts of noradrenaline (NA) and dopamine (DA), were recorded in each animal before, during, and after the adaptation period. In another group of golden hamsters the brains were processed for immunocytochemical detection of arginine-vasopressin (AVP) and corticotropin releasing factor (CRF) in the third week of adaptation to a cold or warm environment. In warm-adapted animals food and water consumption and urine production remained unchanged or were only slightly reduced. NA and DA secretion were reduced by 50%. The AVP-immunoreactivity reflected an anti-diuretic state in these animals. In fibers influencing the adrenal axis, AVP-immunoreactivity was weak compared to CRF fibers. Food and water consumption, urine production, and DA secretion increased two-fold during cold adaptation. Daily secreted amounts of NA increased nine-fold. AVP-immunoreactivity was weak in projections to the neurohypophysis. Fibers influencing the adrenal axis, however, displayed strong AVP-immunoreactivity in comparison to that of CRF. The immunocytochemically determined patterns of AVP and CRF distribution indicated an activation of the osmoregulative axis in the warm-adapted animals and of the adrenal axis in the cold-adapted golden hamsters.

Adaptation, Physiological↗
PubMed1977

Alterations of alkaline phosphatase activity during adaptation of Escherichia coli to phosphite and hypophosphite.

When Escherichia coli cells were grown in media containing either phosphite or hypophosphite as the sole source of phosphorus, the responded to this situation primarily in the same way as phosphate-limited cultures: The activity of alkaline phosphatase increased drastically, which under natural conditions would enable the cells to compensate for the shortage of phosphate. Subsequent transfers, however, resulted in a quite different response: While the phosphatase activity of phosphate-limited cells stays at a high derepressed level, its increase was followed by a gradual decline in organisms grown on phosphite of hypophosphite. After eight to ten transfers on these P-compounds, phosphatase activity was back to its initial, repressed, low level, indicating that the cells were fully adapted to these substrates. Adaptation to either PO3-3 or PO3-2 was completely abolished if the cells were again grown with PO3-3 as P-source, whereafter the entire process of adaptation had to be repeated. The observed adaptation pattern, reflected by the alterations of phosphatase activity, was qualitatively equal with PO3-3 and PO3-2, but quantitatively different, because the response to hypophosphite gave much higher values than the increase obtained with phosphite. Phosphite-adapted cells are not simultaneously adapted to hypophosphite, but their response to the latter was less intense than observed after direct transfers from PO3-4 to PO3-2. Adaptation to hypophosphite, however, led simultaneously to phosphite adaptation, so that these cells can utilize both P-compounds as a substitute for phosphate.

Adaptation, Physiological↗
PubMed2002

Adaptation of arm trajectory during continuous drawing movements in different dynamic environments.

Human subjects can readily adapt their movement trajectories to different dynamic or visuomotor environments. The focus of the current study was to determine whether subjects could simultaneously adapt to multiple dynamic environments. Subjects ( n=5) drew ellipses continuously for 70 s using a torquable manipulandum under six distinct dynamic conditions, representing the combination of load type (spring, viscous, and inertia) and load direction (assisting and opposing). Each subject performed two control, ten load, and five washout trials. A significant effect of force condition on the trajectory of the movement was found in 26 of 30 cases (6 conditions x 5 subjects); the magnitude of the distortion differed across the conditions. The extent of adaptation also differed across the loads. Opposing inertia and viscosity led to fast adaptation. However, assisting inertia and viscosity were associated with relatively slow adaptation. The results of adaptation to the stiffness conditions were not consistent. Following sudden removal of the load we saw an additional disturbance of the trajectory (after-effect), which was often the mirror image of the original distortion. The shape and size of the after-effect were different across load conditions. These results show that human subjects can adapt to a variety of different dynamic transformations and that the time-course of adaptation is dependent on both the state space and the direction of the load.

Adaptation, Physiological↗