Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ADAPTATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources
PubMed1982

Early dark adaptation, the receptor potential and lateral effects on the retina.

The rapid threshold drop in early dark adaptation has been found to slow, following saturating adaptation levels in the rod monochromat, and following cone-saturating flashes in normal subjects. This supports the idea that early dark adaptation reflects the decay of the receptor potential to the adapting light, but contrast effects also influence the shape of the early dark adaptation curve. It is proposed that early dark adaptation reflects both receptor potential decay and loss of lateral effects following an adapting light. Variations of curve shapes are discussed from this point of view, with their theoretical significance.

Action Potentials↗
PubMed1987

A central binocular mechanism affects chromatic adaptation.

Two experiments explored the role of central binocular mechanisms in color perception. The first experiment examined the effect of adapting to simultaneous, binocularly fused fields. Each eye adapted to a slowly flickering (0.5 Hz) long-wavelength light. The two eyes were adapted either inphase (both eyes stimulated at the same moment) or out-of-phase (only one eye stimulated at any given moment). Both adapting procedures shifted equilibrium yellow toward longer wavelengths, but a significantly greater shift was found when adapting light stimulated both eyes simultaneously. This reveals that a central binocular mechanism affects chromatic adaptation. The second experiment tested whether the binocular mechanism could shift equilibrium yellow measurements made with both eyes (identical, binocularly fused fields presented to each eye) outside of the range of measurements established by left-eye monocular viewing and right-eye monocular viewing. Differences were found between monocular left-eye and monocular right-eye color appearance under conditions of moderate chromatic adaptation, but binocularly fused measurements fell within the range established by the monocular results. This is consistent with the view that central mechanisms serve to keep the two eyes in balance, rather than systematically alter color appearance from colors perceived under monocular viewing.

Adaptation, Ocular↗
PubMed1988

Interactions among spatial frequency and orientation channels adapted concurrently.

Interactions between size and orientation-specific mechanisms in the human visual system were investigated using a sequential adaptation technique. Subjects adapted to a vertical, 4 c/deg high-contrast (0.7) sinewave grating that was interleaved at a rate of 0.5 Hz with another adapting grating differing either in (1) spatial frequency or (2) orientation. Before and after adaptation contrast thresholds were measured for a vertical 4 c/deg sinewave test grating. The resultant elevation in contrast threshold was plotted as a function of the (1) spatial frequency or (2) orientation differences between the first and second adapting gratings. Maximum threshold elevation was found when both adapting gratings shared the same spatial frequency and orientation. Minimum elevations were found when the second grating's spatial frequency or orientation differed by approx. 1.5 octaves or 45 deg, respectively. Beyond these values threshold elevations reapproached the baseline value measured in a control condition, where the 4.0 c/deg adapting grating was interleaved with a blank. The minimum threshold elevations were 0.2-0.3 log units below the baseline level. The results suggest the existence of inhibitory interactions between neural mechanisms tuned to the size and orientation of retinal images.

Adaptation, Ocular↗
PubMed1988

Adaptational effects of short wave cone signals on red-green chromatic detection.

The red-green chromatic detection mechanism that responds to the difference of L and M cone test signals was isolated in forced-choice experiments. Detection contours in an L, M cone space were measured with 2 Hz Gabor test signals comprising different amplitude ratios of antiphase flickering red and green lights, which formed the 1.2 degree center of a 7.2 degree uniform adapting field. To compare the effect of short wave cone adapting levels on the red-green detection sensitivity, thresholds were measured on pairs of adapting fields that were shown to be tritanopic metamers for our individual observers: violet and green adapting lights that produce equal quantal catches in M cones and in L cones but very differently stimulate S cones. The degree to which the adapting field stimulated S cones had little effect on the red-green detection sensitivity, although the red appearance of the adapting field varied considerably owing to the S cone stimulation. Thus, while the S cones may affect the red-green hue dimension, S cone signals appear to have little adaptational effect on red-green detection mediated by the difference of L and M cone test signals.

Adaptation, Ocular↗
PubMed1989

Retinoids bound to interstitial retinol-binding protein during light and dark-adaptation.

High-performance liquid chromatography was used to determine the types and amounts of retinoids bound to interstitial retinol-binding protein (IRBP) during light- and dark-adaptation in frogs. IRBP was separated from CRBP and CRA1BP by ion-exchange chromatography and quantitated by determining the amount of Serva Blue R dye bound to it in stained sodium dodecyl sulfate polyacrylamide gels. The amount of IRBP was not significantly different in light- and dark-adapted eyes (0.15 +/- 0.05 nmol/eye compared with 0.18 +/- 0.08 nmol/eye). In the dark-adapted state, IRBP bound mainly 11-cis retinol and 11-cis retinal in quantities that summed to about 1 mol/mol IRBP. After the onset of light-adaptation, all-trans retinol increased from its very low dark-adapted level, peaked at 0.2 mol/mol IRBP and then declined to the dark-adapted level again. Concomitantly, the total retinoid bound to IRBP fell, mainly because there was a drop in the amount of 11-cis retinal. During dark-adaptation, the amount of 11-cis retinal increased. No significant changes were seen in the amount of 11-cis retinol in light and darkness. These findings support the hypothesis that when rhodopsin is bleached IRBP transports all-trans retinol from the retina to the pigment epithelium and that it delivers 11-cis retinal to the rod outer segments for rhodopsin regeneration.

Animals↗
PubMed1991

Spatial-frequency-tuned attenuation and enhancement of the steady-state VEP by grating adaptation.

Steady-state visual evoked potentials (VEPs) were recorded from adults using 10% C fast spatial frequency (SF) sweeps of horizontal gratings under two conditions: (a) after exposure to a 40% C grating of 6 or 4 c/deg, and (b) after exposure to a blank screen equalling the adapting gratings in space-averaged luminance. SF adaptation attenuated VEP amplitude near the adapting SF, but maximum attenuation was displaced from the adapting SF for 6 c/deg adaptation. Small displacements in maximum attenuation would be expected if underlying neural subunits are tuned to a small number of different center SFs. In addition, SF adaptation caused amplitude enhancement 1.0-2.0 octaves below the adapting SF, providing electrophysiological evidence in humans for coinhibitory relationships among neural mechanisms that have been postulated on the basis of analogous psychophysical findings. The results are consistent with coinhibition between SF-tuned subunits and between transient and sustained mechanisms.

Adaptation, Ocular↗
PubMed1991

Short-term nonconjugate adaptation of human saccades to anisometropic spectacles.

It has been demonstrated before that the long-term wearing of anisometropic spectacles may induce nonconjugate adaptations of saccades. Saccades then become different in size in the two eyes. We examined the time-course and the limits of such adaptations of horizontal and vertical saccades during the short-term (1-6 hr) wearing of anisometropic spectacles. After only 1 hr of conditioning to 2 D of anisometropia, the nonconjugate size-adaptations were almost complete along the horizontal meridian. For progressively larger anisometropias (up to 8 D) the adaptative nonconjugacies after 1 hr became also systematically larger. An anisometropia larger than 6 D did not further increase the rate of adaptation during the first 6 hr of conditioning, which suggests that about 6 D of difference in spectacle correction, causing size differences of about 12%, may be the upper limit of the nonconjugate adaptive range of the saccadic subsystem. Post-saccadic drift of horizontal saccades was also adequately changed. In addition, nonconjugate adaptations had developed in smooth-pursuit eye movements. All of these plastic changes persisted during monocular viewing, indicating that the basic programming of these eye movements was changed.

Adaptation, Ocular↗
PubMed1991

Polarity specific adaptation to motion in the human visual system.

Three experiments investigated polarity specific adaptation to movement. Experiment 1 tested for temporal polarity specific adaptation, using counterphase sawtooth gratings as adapting and test stimuli. Each counterphase grating contained oppositely moving sawtooth components, and was thus balanced for direction, but both components of the adapting grating created only one polarity of luminance change over time, whereas the components of the test grating presented different signs. After adaptation, only the test component containing the unadapted temporal change was visible. A second experiment, using an analogous procedure, found evidence for spatial polarity specific adaptation. Experimental results can be explained by motion detectors which preserve information about spatial and temporal polarity. A third experiment found that spatial and temporal polarity specific adaptation differ in their dependence on temporal frequency.

Adaptation, Ocular↗
PubMed1992

Binocular measurements of chromatic adaptation.

In this paper we present asymmetric matching data that were obtained with a binocular presentation method. Our main motivation was the question whether chromatic adaptation, one of the important mechanisms that contribute to colour constancy, has evolved towards a better performance in the range of colours that are present in the natural image. For the eye adapted to a bluish illuminant for example the presence of an object with a deep yellow colour is very unlikely. So, it was expected that the colour difference between adapting light and target has an influence on the extent of chromatic adaptation. It was found that the colour shift in the observers' matches that can be attributed to chromatic adaptation indeed has a maximum. The location of the maximum, however, was unexpected, i.e. colour differences between target and adapting light that lie around 0.05 u'v'-chromaticity units. Additionally, several models for chromatic adaptation were fitted to our data. It was found that, except for the simple von Kries model, Retinex Theory and difference contrast, a number of models gave good predictions for the L-wave and M-wave fundamental systems, but that predictions for the S-wave system were less accurate.

Adaptation, Ocular↗
PubMed1992

Chromatic adaptation to natural and incandescent illuminants.

A color CRT image display system was used to present adapting backgrounds that were spatially and temporally varied. Three observers adjusted the chromaticity of test stimuli to produce an achromatic appearance under a variety of adapting conditions. The achromatic-appearing chromaticities were used as measures of the observers' states of chromatic adaptation. The spatial configuration of the adapting background was varied to measure the spatial extent of the mechanisms responsible for chromatic adaptation. The temporal configuration of the adapting background was varied to measure the time-course of these mechanisms. The results show that chromatic adaptation is spatially localized with a time-course on the order of 10 sec. Since the mechanisms were shown to be spatially localized, the observed temporal integration across eye movements is required to allow these mechanisms to adjust to the spatially integrated scene chromaticity.

Adaptation, Ocular↗
PubMed1992

Nonconjugate adaptation of human saccades to anisometropic spectacles: meridian-specificity.

Recently it has been demonstrated that saccades become different in size in the two eyes if a subject is adapted to anisometropic spectacles, which provide visual images of different magnitude to the two eyes. These nonconjugate adaptations adequately meet the requirements of those spectacles and, once acquired, they persist (with some reduction) even during monocular viewing. We now demonstrate that such nonconjugate adaptations of saccades can be meridian-specific, if there is a pressure for such meridian-specificity. This pressure was provided by means of a cylindrical spectacle-lens. Adaptations along a vertical, horizontal or oblique meridian did not transfer to the orthogonal meridian. These results demonstrate a capability of saccadic adaptation to deal with calibration problems restricted not only to one eye, but even to one specific plane of muscular action. Our results also suggest that the meridian-specific adaptations of oblique saccades take place at a stage before the decomposition of motor commands into separate horizontal and vertical components. The meridian-specific nonconjugacies were also expressed in smooth-pursuit eye movements. Post-saccadic drift adapted only along the horizontal meridian.

Adaptation, Ocular↗
PubMed1993

Retinal adaptation of visual processing time delays.

A significant proportion of the processing delays within the visual system are luminance dependent. Thus placing an attenuating filter over one eye causes a temporal delay between the eyes and thus an illusion of motion in depth for objects moving in the fronto-parallel plane, known as the Pulfrich effect. We have used this effect to study adaptation to such an interocular delay in two normal subjects wearing 75% attenuating neutral density filters over one eye. In two separate experimental periods both subjects showed about 60% adaptation over 9 days. Reciprocal effects were seen on removal of the filters. To isolate the site of adaptation we also measured the subjects' flicker fusion frequencies (FFFs) and contrast sensitivity functions (CSFs). Both subjects showed significant adaptation in their FFFs. An attempt to model the Pulfrich and FFF adaptation curves with a change in a single parameter in Kelly's [(1971) Journal of the Optical Society of America, 71, 537-546] retinal model was only partially successful. Although we have demonstrated adaptation in normal subjects to induced time delays in the visual system we postulate that this may at least partly represent retinal adaptation to the change in mean luminance.

Adaptation, Ocular↗
PubMed1991

The effects of food schedule adaptation on the ability of naloxone to suppress the acquisition of schedule-induced polydipsia.

Naloxone suppressed the acquisition of schedule-induced polydipsia (SIP) in rats given no previous exposure to the feeding schedule. Adaptation to the feeding schedule prior to SIP acquisition attenuated this suppression. Specifically, water consumption, bout probability, licks/bout and maximum lick rates during the interpellet interval (IPI) were significantly increased by adaptation. Although adaptation attenuated the suppressive effects of naloxone on SIP, this attenuation was not complete. Adapted, naloxone-treated subjects displayed both decreased water consumption and bout probability as compared to distilled water-treated controls. Unlike the effects of adaptation on naloxone's suppression of SIP, adaptation completely eliminated naloxone's suppression of feeding. That adapted subjects ate at control levels while still displaying a lower level of SIP suggests that the suppressive effect of naloxone on the acquisition of SIP is not an indirect effect of naloxone on feeding, but rather a direct effect of naloxone on developing SIP. Given that naloxone has a general suppressive effect on drinking (including SIP), what remains to be determined is why naloxone has no effect on established SIP. Possible explanations for this are discussed.

Adaptation, Psychological↗
PubMed1992

Lack of adaptive response to low doses of ionizing radiation in human lymphocytes from five different donors.

Various investigators reported a reduced yield of chromosome and chromatid aberrations in short-term cultures of human lymphocytes if a 'challenge' exposure to ionizing radiation was preceded by an 'adaptive' exposure. In order to examine the cell cycle dependence of the 'adaptive response', chromosome and chromatid aberration yields were estimated after challenge doses in the G1, S or G2 phase of lymphocytes which had been adapted in the early G1 phase. On testing two donors no protective adaptive response was found. Blood samples of four donors were tested for their capability to evoke the adaptive response in a standard experiment with the adaptive dose in the S phase and the challenge dose in the G2 phase. A synergistic response occurred in one out of two similar experiments performed with the same blood sample. The three other blood samples tested did not respond. Apparently these data indicate a high frequency of human lymphocyte cultures that do not display an adaptive response.

Adaptation, Physiological↗
PubMed1993

'High-pertension'--the uses of a chronic folk illness for personal adaptation.

Chronic illness exerts a lasting and pervasive influence on personal experience of the world. It is commonly viewed as a phenomenon to be coped with, requiring an adaptive response on the part of an individual. Chronic illness, however, is a culturally-influenced tool which in itself can be used to organize and implement an adaptive response to personal experience. Employing Hallowell's concept of the self in the behavioral environment, the uses of a chronic folk illness, 'high-pertension', for personal adaptation are discussed. Data from research on health beliefs about hypertension and illness behavior in a sample of 60 older African-American women in New Orleans are presented. 'High-pertension', a chronic folk illness related to the biomedical 'hypertension', and involving blood and 'nerves', is described. Health beliefs and illness behavior associated with high-pertension are considered as part of an individual's total effort at adaptation within the behavioral environment. These points are made: (1) Chronic illness can be used as a means to express one's self in relation to the behavioral environment. (2) Chronic illness can be used to manipulate and manage the relation of self to environment. (3) Chronic illness can be used to legitimize and announce role change. These uses are available to the individual by virtue of social interaction, cultural precedent and the chronicity and meaning of the illness itself. For persons in a severely stressed, constrained, and disadvantaged social position, as are many older African-American women, chronic illness offers one of the few means of controlling the behavioral environment available to the individual. Although in anthropology and biology we speak of adaptation in terms of human groups, we are ultimately considering person-environment fit, that is, personal adaptation. Chronic illness can be a part of a culturally-influenced adaptive response.

Adaptation, Psychological↗
PubMed1986

Gap junctions between horizontal cells in the cyprinid fish alter rapidly their structure during light and dark adaptation.

The dynamics of the structure of gap junctions between outer horizontal cells (HCs) and between their axonal terminals in the retina of the goldfish during light and dark adaptation is described by means of quantitative freeze-fracture replica examination. The light adaptation was performed in red light. In dark-adapted retinae the gap junctional connexons are arranged much more dense than in light-adapted retinae. The rearrangement during the first minutes of light adaptation proceeds faster than during the first minutes of dark adaptation. Since dark adaptation is accompanied by surround enhancement and presumably by coupling of HCs it is concluded that densification of HC gap junctions may correlate with coupling, and scattering of HC gap junctions with uncoupling of this type of electrotonic synapse.

Animals↗
PubMed1985

Adaptation effects on amplitude modulation detection: behavioral and neurophysiological assessment in the goldfish auditory system.

The ability of goldfish to detect the presence of amplitude modulations (AM) impressed on 200, 570 and 800 Hz tones was measured under stimulus conditions producing intermittent, short-term adaptation and continuous, long-term adaptation. Sensitivity to AM under intermittent conditions increased as a function of modulation rate, with thresholds of AM detection occurring between 10 and 25% modulation at 10 Hz and around 2% modulation at 100 Hz. AM sensitivity was independent of carrier frequency and did not change under randomly varying intensity changes. Under long-term adaptation, thresholds of AM detection ranged from 1.3% at 100 Hz to 2.1% at 10 Hz, showing increased sensitivity and less dependence on modulation rate. The effects of overall intensity on AM sensitivity were the same for both conditions, with sensitivity being relatively independent of overall signal level at 10 Hz modulation and dependent on level at 100 Hz. The responses of goldfish auditory neurons to modulated and unmodulated signals were measured under stimulus conditions similar to those for behavioral studies. Single saccular neurons responded to modulated signals with both an increase in average rate above that evoked by the unmodulated signal and with phase-locking to the AM envelope. Rate increments and phase-locking responses were observed in neurons showing significant short-term adaptation to the unmodulated signal, whereas neurons showing no increase in rate or synchronization to the AM envelope showed little or no adaptation to the unmodulated signal. The effects of overall intensity, modulation rate and adaptation duration on neural responses were similar to behaviorally measured effects. These results show that adaptation affects AM detection and that phase-locking to the AM envelope is the most likely basis for behavioral detection.

Acoustic Stimulation↗
PubMed1985

Adaptation in hearing-impaired ears: effects of intermediate duration stimuli.

Recovery from adaptation was measured in acoustically-traumatized ears of cats for pure-tone adapters 1-60 s in duration at levels of 60-100 dB SPL. Adaptation was assessed by measuring the whole nerve action potentials in response to pure-tone stimuli. Effects of changing probe frequency and of changing adapter duration were measured. Impaired ears showed less adaptation than normal ears for adapters of similar SPL, but they showed relatively normal spread of adaptation across probe frequency. The effect was larger for long duration stimuli than for short duration stimuli.

Acoustic Stimulation↗