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PubMed2005

Exposure to a rotating virtual environment during treadmill locomotion causes adaptation in heading direction.

The objective of this study was to investigate the adaptive effects of variation in the direction of optic flow, experienced during linear treadmill walking, on modifying locomotor trajectory. Subjects (n=30) walked on a motorized linear treadmill at 4.0 km h(-1) for 24 min while viewing the interior of a 3D virtual scene projected on to a screen 1.5 m in front of them. The virtual scene depicted constant self-motion equivalent to either (1) walking around the perimeter of a room to one's left (Rotating Room group) or (2) walking down the center of a hallway (Infinite Corridor group). The scene was static for the first 4 min and then constant rate self-motion was simulated for the remaining 20 min. Before and after the treadmill locomotion adaptation period subjects performed five stepping trials. In each trial they marched in place to the beat of a metronome at 90 steps min(-1) for a total of 100 steps while blindfolded in a quiet room. The subject's final heading direction (deg) and final X (fore-aft, cm) and final Y (medio-lateral, cm) positions were measured for each trial. During the treadmill locomotion adaptation period subjects' 3D torso position was measured. We found that subjects in the Rotating Room group, as compared with the Infinite Hallway group: (1) showed significantly greater deviation during post-exposure testing in the heading direction and Y position opposite to the direction of optic flow experienced during treadmill walking; and (2) showed a significant monotonically increasing torso yaw angular rotation bias in the direction of optic flow during the treadmill adaptation exposure period. Subjects in both groups showed greater forward translation (in the +X direction) during the post-treadmill stepping task that differed significantly from their pre-exposure performance. Subjects in both groups reported no perceptual deviation in position during the stepping tasks. We infer that viewing simulated rotary self-motion during treadmill locomotion causes adaptive modification of sensorimotor integration in the control of position and trajectory during locomotion, which functionally reflects adaptive changes in the integration of visual, vestibular, and proprioceptive cues. Such an adaptation in the control of position and heading direction during locomotion, because of the congruence of sensory information, demonstrates the potential for adaptive transfer between sensorimotor systems and suggests a common neural site for processing and self-motion perception and concurrent adaptation in motor output.

Adaptation, Physiological↗
PubMed2005

Measurement and nature of firing rate adaptation in turtle spinal neurons.

There is sparse literature on the profile of action potential firing rate (spike-frequency) adaptation of vertebrate spinal motoneurons, with most of the work undertaken on cells of the adult cat and young rat. Here, we provide such information on adult turtle motoneurons and spinal ventral-horn interneurons. We compared adaptation in response to intracellular injection of 30-s, constant-current stimuli into high-threshold versus low-threshold motoneurons and spontaneously firing versus non-spontaneously-firing interneurons. The latter were shown to possess some adaptive properties that differed from those of motoneurons, including a delayed initial adaptation and more predominant reversal of adaptation attributable to plateau potentials. Issues were raised concerning the interpretation of changes in the action potentials' afterhyperpolarization shape parameters throughout spike-frequency adaptation. No important differences were demonstrated in the adaptation of the two motoneuron and two interneuron groups. Each of these groups, however, was modeled by its own unique combination of action potential shape parameters for the simulation of its 30-s duration of spike-frequency adaptation. Also, for a small sample of the very highest-threshold versus lowest-threshold motoneurons, the former group had significantly more adaptation than the latter. This finding was like that shown previously for cat motoneurons supplying fast- versus slow twitch motor units.

Action Potentials↗
PubMed2000

Structural and cellular adaptation of duodenal iron uptake in rats maintained on an iron-deficient diet.

Iron deficiency induced in rats maintained on a commercial diet with a low iron content has been used to investigate adaptive mechanisms that enhance duodenal iron uptake. These adaptive changes have been divided into those that result from changes in villus surface area (structural adaptation) and those that reflect changes in the way individual enterocytes express iron transport function (cellular adaptation). Cellular adaptation was assessed by carrying out microdensitometry of autoradiographs prepared from duodenal tissue previously incubated for 5 min in 200 micromol/l 59Fe2+-ascorbate. Structural adaptation was studied by performing image analysis of microdissected and sectioned villi. Cellular adaptation involved increased iron uptake by enterocytes present in the lower villus. Thus iron deficiency resulted in a threefold enhanced expression of uptake in the lower 100 microm villus (3.9+/-2.4 versus 12.6+/-1.5 arbitrary units, P<0.001). Maximal uptake was reached in the upper region of both control and iron-deficient villi, but iron deficiency had no effect on cellular uptake at this part of the villus. Structural adaptation involved the lengthening (+16%, P<0.05) and broadening (+14%) of villi in the duodenum of iron-deficient rats. The resultant expansion in villus area caused a further increase in uptake that was mostly expressed in the upper villus. Maximal uptake corrected for structure occurred in the middle third of villi from control and iron-deficient rats. Cellular plus structural adaptation produced a twofold increase in iron uptake. More than half of this effect was caused by changes in villus structure. [3H]Thymidine labelling experiments revealed a slightly earlier expression of enterocyte iron uptake in iron deficiency.

Adaptation, Physiological↗
PubMed1986

The effect of standing contrast and pattern adaptation on the human visually evoked potential.

Human visually evoked potentials (VEPs) were recorded with sinusoidal gratings of low (0.5 c/deg), medium (4 c/deg) and high (16 c/deg) spatial frequency (SF). Simultaneous recording from Oz-A1, O2-A1 and Oz-O2 allowed the separation of the early and late VEP waves for most subjects. The effect of standing contrast and pattern adaptation on these waves was studied. At low SF both early and late waves were not affected by standing contrast or adaptation with motionless grating, while adaptation with a drifting grating reduced them. At medium and high SFs both principal negative waves. N1 and N2, were reduced by standing contrast and pattern adaptation. The amplitude of N2 saturated at low contrast level (0.1) and was reduced after adaptation regardless of the SF of test and adapting stimuli, while the amplitude of N1 did not saturate up to the contrast level of 0.3 and exhibited SF-selective adaptation. The adapted onset-VEP was similar to the offset-VEP. The data suggest that: the early wave is generated by multiple narrowly tuned SF-selective structures that are medially positioned while the generators of the late wave are not SF-selective and occupy a wider area centered laterally; the effects of standing contrast and pattern adaptation on VEPs, as well as the relationship of onset and offset VEPs, reflect the time-course of neural activity evoked by long-lasting stimuli.

Adaptation, Ocular↗
PubMed1984

Mechanisms of sensory adaptation in the isolated utricle.

The occurrence of receptor adaptation in utricular afferent fibers is now widely recognized. The experiments reported here explored the basic mechanisms of adaptation at the level of the receptor organ. Spike discharges from single utricular afferent fibers were recorded in isolated labyrinths of an elasmobranch, during three types of stimulation: (a) tilts in the gravity field, (b) vibrations, and (c) electrical polarization delivered through the nerve filaments from which recordings were also made. Experimental evidence supported the conclusion that polarization affects the discharge by acting at the level of the spike triggering mechanism, the point of the afferent fiber at which impulses normally arise. Three types of afferent fibers have been described: Types I and II fire spontaneously and show phasic-tonic responses to tilts. Type III fibers do not have spontaneous activity and respond to tilts in a phasic manner. Adaptation to polarizing currents was observed in all afferent fibers. Type II fibers adapted slowly to vibrations whereas types I and III afferent fibers did not. The functional processes situated near the spike triggering site of the sensory axon is referred to as neural whereas those occurring at earlier stages of transduction are called preneural. Adaptation to tilts exhibited two successive components: an early, fast phase and a late, slow one. Our results suggested that these phases can be related to the mechanisms of preneural and neural adaptation, respectively. Because the time course of adaptation to polarizing currents was similar in different afferent fibers, we concluded that preneural adaptation was the origin of the differences among afferent fibers that allowed their classification into phasic, phasic-tonic, and tonic groups. No attempts were made to separate the influence of mechanical coupling and transduction in the production of preneural adaptation.

Acoustic Stimulation↗
PubMed1991

Seasonal changes in seawater adaptability and plasma levels of prolactin and growth hormone in landlocked sockeye salmon (Oncorhynchus nerka) and amago salmon (O. rhodurus).

In order to clarify the roles of prolactin (PRL) and growth hormone (GH) in the development of seawater adaptability in salmonids, seasonal changes in salinity tolerance, plasma PRL, and plasma GH were examined in juvenile landlocked sockeye salmon (Oncorhynchus nerka) and amago salmon (O. rhodurus). Assessed by the 24-hr seawater-challenge test, the landlocked sockeye salmon possessed seawater adaptability as underyearlings in spring, which was maintained throughout the year, and a further increase was observed as yearlings the next spring. An increase in seawater adaptability was observed in silvery juvenile amago salmon as underyearlings from autumn to winter, when some of the wild population migrate to the sea. Precociously mature amago salmon, which did not develop a silvery body color but maintained distinct parr marks, also showed an improvement in seawater adaptability during autumn to winter, although plasma sodium levels after transfer to seawater were still higher than those of the silvery juveniles. In both sockeye and amago salmon, seasonal changes in plasma levels of PRL and GH were not correlated with development of seawater adaptability. In both species, acclimation to seawater resulted in decreased plasma levels of PRL irrespective of their adaptability to seawater, in agreement with the inhibitory effects of PRL in seawater adaptation. On the other hand, plasma GH levels increased only when seawater adaptability was high, in agreement with previous observations indicating an important role of GH in seawater adaptation of salmonids.

Adaptation, Physiological↗
PubMed1983

Adaptation of airway stretch receptors in newborn and adult dogs.

We studied the adaptive properties of tracheal and bronchial slowly adapting mechanoreceptors as an index of their dynamic responsiveness in newborn and adult dogs. The receptors studied exhibited a marked rate dependency in their adaptive characteristics: faster inflations leading to a higher adaptation, a behavior typically found in other mechanoreceptors. During inflations of comparable rates airway slowly adapting mechanoreceptors of newborn dogs reach initial firing rates (Fi) that are lower than those of adult dogs. These increments in activity appear to be reduced in proportion to their lower static discharge (Fs). Therefore when adaptation is represented as adaptation index (A.I. = (Fi - Fs)/Fi X 100), i.e., in relative terms, it does not differ between age groups. Tracheal and bronchial slowly adapting mechanoreceptors do not differ in their adaptation for either of the age groups. In conclusion, since the dynamic sensitivity is lower in newborns, it it cannot be a factor contributing to their higher breathing rate. Nevertheless, since newborns breathe faster than adults, the activation of their stretch receptors should be greater than it would have otherwise been, perhaps contributing to their faster rate of breathing.

Action Potentials↗
PubMed1995

Human cones appear to adapt at low light levels: measurements on the red-green detection mechanism.

Recent physiological evidence suggests that cones do not light adapt at low light levels. To assess whether adaptation is cone-selective at low light levels, the red-green detection mechanism was isolated. Thresholds were measured with a large test flash, which stimulated the L and M cones in different fixed amplitude ratios, on different colored adapting fields. Thresholds were plotted in L and M cone contrast coordinates. The red-green mechanism responded to an equally-weighted difference of L and M cone contrast on each colored field, demonstrating equivalent, Weberian adaptation of the L and M cone signals. The L and M cone signals independently adapted for illuminance levels as low as 60 effective trolands (e.g. M-cone trolands). Since this adaptation is entirely selective to cone type, it suggests that the cones themselves light-adapt. The red-green detection contour on reddish fields was displaced further out from the origin of the cone contrast coordinates, revealing an additional sensitivity loss at a subsequent, spectrally-opponent site. This second-site effect may arise from a net "red" or "green" signal that represents the degree to which the L and M cones are differently hyperpolarized by the steady, colored adapting field. Such differential hyperpolarization is compatible with equivalent, Weberian adaptation of the L and M cones.

Adaptation, Ocular↗
PubMed1996

Biochemical changes associated with the adaptive response of human keratinocytes to N-methyl-N'-nitro-N-nitrosoguanidine.

Exposure of cells to low doses of radiation or chemicals renders them more resistant to higher doses of these agents. This phenomenon, termed adaptive response, was studied in quiescent human keratinocytes exposed to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The cells were adapted with 2.5 nM MNNG for 60 min and challenged immediately thereafter with 2.5 microM MNNG for 30, 45 or 60 min. Clonogenic survival studies revealed that adapted cells were more resistant to the subsequent challenge treatment (up to 30% higher survival) than unadapted cells. In addition, formation of DNA strand breaks was lower in adapted cells. We monitored poly-ADP-ribosylation activity during expression of the adaptive response both at the substrate as well as the product level. NAD+ utilization in adapted and non-adapted cells exposed to the high dose of MNNG was similar, but recovery from NAD+ depletion was faster in low-dose pretreated cells. Induction of poly(ADP-ribose) formation was more than 2 times higher in low-dose adapted cells and this was associated with the formation of a distinct class of ADP-ribose polymers, i.e., branched polymers. These polymers exhibit a very high binding affinity for histones and can displace them from DNA. Elevated levels of poly(ADP-ribose) and, particularly, synthesis of branched polymers may play a critical role in low-dose adaptation.

Adaptation, Physiological↗
PubMed2004

Adaptation of enzymes to temperature: searching for basic "strategies".

The pervasive influence of temperature on biological systems necessitates a suite of temperature--compensatory adaptations that span all levels of biological organization--from behavior to fine-scale molecular structure. Beginning about 50 years ago, physiological studies conducted with whole organisms or isolated tissues, by such pioneers of comparative thermal physiology as V.Ya. Alexandrov, T.H. Bullock, F.E.J. Fry, H. Precht, C.L. Prosser, and P.F. Scholander, began to document in detail the abilities of ectothermic animals to sustain relatively similar rates of metabolic activity at widely different temperatures of adaptation or acclimation. These studies naturally led to investigation of the roles played by enzymatic proteins in metabolic temperature compensation. Peter Hochachka's laboratory became an epicenter of this new focus in comparative physiology. The studies of the enzyme lactate dehydrogenase (LDH) that he initiated as a PhD student at Duke University in the mid-1960s and continued for several years at the University of British Columbia laid much of the foundation for subsequent studies of protein adaptation to temperature. Studies of orthologs of LDH have revealed the importance of conserving kinetic properties (catalytic rate constants (kcat) and Michaelis-Menten constants (Km) and structural stability during adaptation to temperature, and recently have identified the types of amino acid substitutions causing this adaptive variation. The roles of pH and low-molecular-mass organic solutes (osmolytes) in conserving the functional and structural properties of enzymes also have been elucidated using LDH. These studies, begun in Peter Hochachka's laboratory almost 40 years ago, have been instrumental in the development of a conceptual framework for the study of biochemical adaptation, a field whose origin can be traced largely to his creative influences. This framework emphasizes the complementary roles of three "strategies" of adaptation: (1) changes in amino acid sequence that cause adaptive variation in the kinetic properties and stabilities of proteins, (2) shifts in concentrations of proteins, which are mediated through changes in gene expression and protein turnover; and (3) changes in the milieu in which proteins function, which conserve the intrinsic properties of proteins established by their primary structure and modulate protein activity in response to physiological needs. This theoretical framework has helped guide research in adaptational biochemistry for many years and now stands poised to play a critical role in the post-genomic era, as physiologists grapple with the challenge of integrating the wealth of new data on gene sequences (genome), gene expression (transcriptome and proteome), and metabolic profiles (metabolome) into a realistic physiological context that takes into account the evolutionary histories and environmental relationships of species.

Adaptation, Physiological↗
PubMed2005

Acid-adaptation does not increase the resistance of Listeria monocytogenes to irradiation in a seafood salad.

Stress adaptation of microbial cells enables the cells to survive better when they are subsequently exposed to other types of stresses. In the food industry, pathogens are commonly stressed during food processing and this is a concern where pathogens such as Listeria monocytogenes are involved. Research was conducted to determine if acid adaptation of L. monocytogenes provides resistance to ionizing irradiation. Three different strains of L. monocytogenes were acid-adapted using three different acids (acetic, citric, lactic) in Tryptic Soy Broth, at a pH 5.5 for 1 h, 4 h, or continuous acid exposure. The acid-adapted L. monocytogenes were then exposed to a low level of gamma irradiation (0.59-0.72 kGy) along with a non-acid adapted L. monocytogenes control. In a test tube study, the 1-h acetic acid-adapted L. monocytogenes strains showed the greatest difference from the control, a reduced kill of 1.1 log CFU/g but this difference was not significant by ANOVA (p=0.054). The reduction achieved after 4 h and continuous acid exposure also did not significantly differ from the control. To determine whether acid adaptation affected radiation resistance within a food product, a refrigerated storage shelf-life study was completed. Acetic acid was used to acid adapt a three-strain cocktail of L. monocytogenes for a period of 1 h. The organisms were then inoculated into a seafood salad (pH 5.15) and subsequently exposed to low dose gamma irradiation (0.7 to 4.5 kGy). L. monocytogenes was reduced or eliminated by irradiation regardless of acid adaptation; no increased resistance was observed.

Acetic Acid↗
PubMed2006

Posterior parietal cortex and the dissociable components of prism adaptation.

Recent evidence has implicated posterior parietal cortex (PPC) in adaptation to optical displacing prisms. It has been suggested that PPC contributes to the strategic component of prism adaptation necessary for perceptual realignment (true adaptation). It has also been suggested, however, that the part of PPC responsible for corrections to ongoing movements (a putative strategic component) may not be necessary for successful adaptation. A patient presenting with bilateral posterior parietal damage (patient JJ) was tested with both hands on two versions of a prism adaptation task--one using prism goggles and one using a virtual prism arrangement. JJ displayed independent deficits: his right hand failed to show strategic control, yet adapted fully to the prisms whereas his left hand showed evidence of strategic control without subsequent adaptation. The data indicates that the ability to implement control strategies may not be necessary for successful adaptation to prisms. A proposed model for the role of posterior parietal cortex in prism adaptation is also presented.

Adaptation, Physiological↗
PubMed2001

Prism adaptation response is useful for predicting surgical outcome in selected types of intermittent exotropia.

PURPOSE: To evaluate the prevalence of prism adaptation response in Japanese patients with intermittent exotropia (X [T]) using the prism adaptation test and to assess whether patients with selected types of X [T] benefit from surgical outcome to which prism adaptation response may contribute. METHODS: In a prospective study, 128 consecutive patients with X [T] between 1990 and 1995 were enrolled. The prism adaptation test was conducted by neutralizing the angle of deviation for 2 to 3 hours. Patients who showed an increase in exodeviation by 10triangle up or more with the prism adaptation test were defined as having a prism adaptation response. For classification of the pattern of X [T], we chose a value of 15triangle up as the difference between the distance and near measurements. RESULTS: The percentage of patients in whom the prism adaptation response was observed at near fixation was significantly larger than those at distance fixation [35 (27%) patients versus 10 (8%) patients, P <.05]. Of 35 patients shown to have a prism adaptation response at near fixation, 21 patients (83%) had the basic type of exotropia. Fourteen patients (17%) with the basic type were changed to convergence insufficiency type because of an increase in near deviation and were defined as pseudo basic type. Patients with pseudo basic type had a significantly better surgical outcome compared with that of true basic type, whereas in the convergence insufficiency type, no definite tendency was found between the two subtypes, true and pseudo types. CONCLUSION: Patients with the pseudo basic type of X [T] in whom a prism adaptation response was demonstrated had a more favorable surgical outcome.

Adaptation, Ocular↗
PubMed2002

Contribution of vergence adaptation to difference in vertical deviation between distance and near viewing in patients with superior oblique palsy.

PURPOSE: To evaluate the adaptive vertical vergence aftereffect and determine whether it contributes to a difference of vertical deviation with respect to gaze distance in patients with vertical strabismus. DESIGN: Prospective noncomparative studies. METHODS: Eighty-four patients with unilateral superior oblique palsies were enrolled and classified into three types-A, B, and C-based on the difference in vertical deviation between distant and near viewing. The prism adaptation test was performed for 2 to 3 hours to correct vertical deviation and the response of vertical deviation to the prism adaptation test was compared among the three types RESULTS: Adaptive vertical vergence aftereffect, defined as an increase of deviation by 5 prism diopters or more with the prism adaptation test, was identified in 13 patients (16%) at distance and in 23 patients (27%) at near viewing. Among the three types, the adaptive vergence aftereffect contributed mostly to the type B, in which distance deviation exceeds near deviation. Nine patients (39%) of type B changed to type A category with the prism adaptation test; and of these, 7 increased near deviation so that the deviation difference between distant and near viewing decreased. CONCLUSION: The adaptive vertical vergence aftereffect contributes to a difference in vertical deviation between distant and near viewing. The vertical prism adaptation test is specifically useful to determine the extent of surgery by breaking fusional vergence in patients with hypertropia in whom deviation differs with respect to viewing distance.

Adaptation, Ocular↗
PubMed2000

Intestinal adaptation occurs independent of transforming growth factor-alpha.

BACKGROUND/PURPOSE: Signal transduction via the epidermal growth factor receptor (EGFR) is critical for intestinal adaptation after massive small bowel resection (SBR). Although it has been assumed that the major ligand for the EGFR during adaptation is EGF, the role for transforming growth factor-alpha (TGF-alpha), another major ligand for the EGFR is unknown. The purpose of this study was to test the hypothesis that TGF-alpha is an important ligand for the EGFR during intestinal adaptation. METHODS: Wild-type mice (C57BI/6) underwent a 50% proximal SBR or sham operation (bowel transection or reanastomosis) and were then assigned randomly to receive either intraperitoneal TGF-alpha or placebo. In a separate experiment, SBR or sham operations were performed in mice lacking TGF-alpha (Waved-1). After 3 days, adaptation was measured in the ileum. RESULTS: Exogenous TGF-alpha enhanced intestinal adaptation in the wild-type mice after SBR as shown by increased ileal wet weight and DNA content. Normal adaptation occurred in the mice lacking TGF-alpha as shown by increased ileal wet weight, protein and DNA content, proliferation, villus height, and crypt depth. CONCLUSIONS: Although exogenous TGF-alpha enhanced adaptation after massive SBR, adaptation was preserved in TGF-alpha-absent mice. These results refute TGF-alpha as an essential ligand for EGFR signaling during intestinal adaptation.

Adaptation, Physiological↗
PubMed1996

Radioadaptive response: efficient repair of radiation-induced DNA damage in adapted cells.

To verify the hypothesis that the induction of a novel, efficient repair mechanism for chromosomal DNA breaks may be involved in the radioadaptive response, the repair kinetics of DNA damage has been studied in cultured Chinese hamster V79 cells with single-cell gel electrophoresis. The cells were adapted by priming exposure with 5 cGy of gamma-rays and 4-h incubation at 37 degrees C. There were no indication of any difference in the initial yields of DNA double-strand breaks induced by challenging doses from non-adapted cells and from adapted cells. The rejoining of DNA double-strand breaks was monitored over 120 min after the adapted cells were challenged with 5 or 1.5 Gy, doses at the same level to those used in the cytogenetical adaptive response. The rate of DNA damage repair in adapted cells was higher than that in non-adapted cells, and the residual damage was less in adapted cells than in non-adapted cells. These results indicate that the radioadaptive response may result from the induction of a novel, efficient DNA repair mechanism which leads to less residual damage, but not from the induction of protective functions that reduce the initial DNA damage.

Adaptation, Physiological↗
PubMed2003

Effects of prismatic adaptation on judgements of spatial extent in peripersonal and extrapersonal space.

Recent research has shown that visuomotor adaptation to a lateral displacement of the visual field induces significant perceptual aftereffects in normal observers, and in right hemisphere patients with spatial neglect [Neuroreport 11 (2000) 1899; Nature 395 (1998) 166]. These findings suggest that adaptive realignment following prism exposure induces a bias in visual space perception, even in tasks that require no visually guided motor response. Given recent neurophysiological and behavioural data suggesting independent visual representations for peripersonal and extrapersonal space, here we asked whether adaptive aftereffects extend beyond participants' immediate reaching space to stimuli presented beyond arms' reach (i.e. in extrapersonal space). Thirty-two participants underwent adaptive realignment to 10 degrees left- or right-displacing wedge-prisms. Before and after adaptation participants performed a visual landmark task that required estimation of the midpoint of horizontal line stimuli. There was a significant rightward shift in visual midpoint judgements following adaptation to left-deviating prisms, which was evident in both peripersonal and extrapersonal space. Paradoxically, a significant rightward shift also occurred following adaptation to right-deviating prisms, but only in extrapersonal space. We suggest that the pattern of adaptive aftereffects observed reflects the different reference frames used by participants to perform spatial judgements in peripersonal and extrapersonal space. We also propose that an underlying hemispheric asymmetry in the processing of spatial errors during adaptation may contribute to the direction of aftereffects in both normal observers, and in patients with unilateral lesions.

Adaptation, Physiological↗
PubMed2000

Time course of chromatic adaptation for color appearance and discrimination.

Adaptation to a steady background has a profound effect on both color appearance and discrimination. We determined the temporal characteristics of chromatic adaptation for appearance and discrimination along different color directions. Subjects were adapted to a large uniform background made up of a CRT screen and a 45x64 degrees wall, illuminated by computer controlled lamps. After an instant change in background color along a red-green or blue-yellow color axis, we measured thresholds for the detection of increments along the same axes at fixed times between 25 ms and 121 s. Analogously, color appearance was determined using achromatic matching. Three components of adaptation could be identified by their temporal characteristics. A slow exponential time course of adaptation with a half-life of about 20 s was common to appearance and discrimination. A faster component with a half-life of 40-70 ms--probably due to photoreceptor adaptation--was also common to both. Exclusive for color appearance, there was a third, extremely rapid mechanism with a half-life faster than 10 ms. This instantaneous process explained more than 50% of total adaptation for color appearance and could be shown to act in a multiplicative manner. We conclude that this instantaneous adaptation mechanism for color appearance is situated at a later processing stage, after mechanisms common to appearance and discrimination, and is based on multiplicative spatial interactions rather than on local, temporal adaptational processes. Color appearance, and thus color constancy, seems to be determined in large part by cortical computations.

Adaptation, Physiological↗