PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “depth adaptation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 271 records · Page 15Linked to original sources
PubMed1995

Differences in influence between pitched-from-vertical lines and slanted-from-frontal horizontal lines on egocentric localization.

The visual field exerts powerful effects on egocentric spatial localization along both horizontal and vertical dimensions. Thus, (1) prism-produced visual pitch and visual slant generate similar mislocalizations of visually perceived eye level (VPEL) and visually perceived straight ahead (VPSA) and (2) in darkness curare-produced extraocular muscle paresis under eccentric gaze generates similar mislocalizations in VPEL and VPSA that are essentially eliminated by introducing a normal visual field. In the present experiments, however, a search for influences of real visual slant on VPSA to correspond to the influences of visual pitch on VPEL failed to find one. Although the elevation corresponding to VPEL changes linearly with the pitch of a visual field consisting of two isolated 66.5 degrees-long pitched-from-vertical lines, the corresponding manipulation of change in the slant of either a horizontal two-line or a horizontal four-line visual field on VPSA did not occur. The average slope of the VPEL-versus-pitch function across 5 subjects was +0.40 over a +/- 30 degrees pitch range, but was indistinguishable from 0.00 for the VPSA-versus-slant function over a +/- 30 degrees slant range. Possible contributions to the difference between susceptibility of VPEL and VPSA to visual influence from extraretinal eye position information, gravity, and several retinal gradients are discussed.

Adult↗
PubMed1995

Light and dark adaptation of visually perceived eye level controlled by visual pitch.

The pitch of a visual field systematically influences the elevation at which a monocularly viewing subject sets a target so as to appear at visually perceived eye level (VPEL). The deviation of the setting from true eye level average approximately 0.6 times the angle of pitch while viewing a fully illuminated complexly structured visual field and is only slightly less with one or two pitched-from-vertical lines in a dark field (Matin & Li, 1994a). The deviation of VPEL from baseline following 20 min of dark adaptation reaches its full value less than 1 min after the onset of illumination of the pitched visual field and decays exponentially in darkness following 5 min of exposure to visual pitch, either 30 degrees topbackward or 20 degrees topforward. The magnitude of the VPEL deviation measured with the dark-adapted right eye following left-eye exposure to pitch was 85% of the deviation that followed pitch exposure of the right eye itself. Time constants for VPEL decay to the dark baseline were the same for same-eye and cross-adaptation conditions and averaged about 4 min. The time constants for decay during dark adaptation were somewhat smaller, and the change during dark adaptation extended over a 16% smaller range following the viewing of the dim two-line pitched-from-vertical stimulus than following the viewing of the complex field. The temporal course of light and dark adaptation of VPEL is virtually identical to the course of light and dark adaptation of the scotopic luminance threshold following exposure to the same luminance. We suggest that, following rod stimulation along particular retinal orientations by portions of the pitched visual field, the storage of the adaptation process resides in the retinogeniculate system and is manifested in the focal system as a change in luminance threshold and in the ambient system as a change in VPEL. The linear model previously developed to account for VPEL, which was based on the interaction of influences from the pitched visual field and extraretinal influences from the body-referenced mechanism, was employed to incorporate the effects of adaptation. Connections between VPEL adaptation and other cases of perceptual adaptation of visual direction are described.

Adult↗
PubMedDate not supplied

Prism adaptation for esotropia with a distance-near disparity.

A series of 64 patients who had surgery for esotropia with a distance-near disparity of at least 10 prism diopters was reviewed. Thirty-three patients were prism adapted for their distance deviation (PA distance). Thirty-one patients were prism adapted for near deviation (PA near). Both groups were divided into responders and nonresponders. In the PA distance group, 22 (67%) patients were responders. All responders had surgery for their prism-adapted angle. Postoperatively, 19 (86%) responders had fusion. Thirteen (68%) required bifocals to maintain fusion. In the PA near group, 21 (68%) patients were responders. All responders had surgery for their prism-adapted angle. Ninety-four percent of responders had fusion postoperatively. None needed bifocals for fusion postoperatively and none were overcorrected. The results show that those patients who were prism adapted for their near angle, responded with fusion, and had surgery for their full amount of esotropia at prism response obtained better postoperative fusion, without the need for a bifocal at near and without overcorrection at distance.

Adaptation, Ocular↗
PubMedDate not supplied

Cryosurgery plus adjuvant systemic alpha2-interferon for HPV-associated lesions.

OBJECTIVE: The authors report their experience in patients with adjuvant systemic 2-interferon with the aim of defining the effectiveness, side-effects, indications and limitations of this treatment. MATERIALS AND METHODS: From January 1989 to December 1996, 123 patients with genital, anorectal and perineal HPV lesions were treated with cryosurgery; adjuvant systemic a2-interferon was administered to 38 of them. There were 76 female and 47 male patients (median age of 29 years, range; 15-56 years). Clinical examinations included: digital rectal examination, head and neck examination, urethral meatus inspection and, in female patients, gynaecological examination; they underwent colposcopylurethroscopy, proctosigmoidoscopy, cystoscopy (in advanced disease); scraping for cytology and PCR analysis, and biopsy for histology. Twenty-three percent of patients had more than one site involved; upper digestive tract involvement was observed in 6.6% and 47% had lesions larger than 6 sqcm. Twenty-five females with genital lesions had esocervical lesions only; ten of them had SIL1, while seven a SIL3. RESULTS: Ninety-eight out of 123 patients (79.7%) were recurrence-free after a median follow-up of 32 months. A recurrence was observed in 25 patients: in univariate analysis, recurrence of disease occurred more frequently in females (p = 0.04), in patients with longer duration of symptoms (p = 0.0002),with wider lesions (p = 0.00015), with head and neck involvement (p < 0.01), and in HIV-positive patients (p = 0.03). In multivariate analysis, duration of symptoms (p = 0.005), head and neck involvement (p = 0.01), and width of lesion > 3 sq cm (p = 0.025) were associated with increased risk CONCLUSION: Our findings confirm the value of cryosurgery in the treatment HPV lesions; it is less traumatic, and gives good aesthetic and functional results; moreover, large lesions may be treated and the depth of cryonecrosis is more suitably adapted. Patients amenable to adjuvant treatment with a2-interferon should have multiorgan involvement, HPV type 16 or 18, lesions >3 sqcm, long lasting symptoms (>6 months) and presence of SIL.

Adolescent↗
PubMed2002

Monocular motion adaptation affects the perceived trajectory of stereomotion.

Perceived stereomotion trajectory was measured before and after adaptation to lateral motion in the dominant or nondominant eye to assess the relative contributions of 2 cues: changing disparity and interocular velocity difference. Perceived speed for monocular lateral motion and perceived binocular visual direction (BVD) was also assessed. Unlike stereomotion trajectory perception, the BVD of static targets showed an ocular dominance bias, even without adaptation. Adaptation caused equivalent biases in perceived trajectory and monocular motion speed, without significantly affecting perceived BVD. Predictions from monocular motion data closely match trajectory perception data, unlike those from BVD sources. The results suggest that the interocular velocity differences make a significant contribution to stereomotion trajectory perception.

Adaptation, Psychological↗
PubMed1990

[Anamnesis of brain-originated vision disorders].

A questionnaire for the subjective assessment of cerebral visual disorders was administered to 269 brain damaged patients. The patients' subjective complaints were correlated with the outcome of objective diagnostic procedures (visual perimetry, visual search, spatial contrast sensitivity, visual evoked potentials, depth perception, light- and dark-adaptation, reading, colour vision). A significant correlation was found between subjective complaints and objective diagnostic results for all fields. The prediction of visual impairments on the basis of subjective complaints and verified by objective tests was correct in 80 to 98% of the brain damaged patients tested. Interrater reliability was about 0.84. Thus, the questionnaire is suitable for the assessment of cerebral visual disorders because of its simplicity, short administration time (10-15 min) and high predictive value.

Accommodation, Ocular↗
PubMed1985

The effect of vertical differential prism on the binocular contrast sensitivity function.

The binocular contrast sensitivity function is measured using horizontal sinusoidal gratings with base-down prism before the right eye. In photopic conditions one prism-dioptre causes a significant drop in sensitivity at all spatial frequencies and in mesopic conditions as little as a half prism-dioptre has a similar effect. The implications for a physiological tolerance for unintended vertical differential prism in spectacles are discussed.

Adaptation, Ocular↗
PubMed1977

A closed-flow water caloric system.

This paper describes a new method and apparatus to induce nystagmus. Flow of fluid into the ear to induce nystagmus is eliminated by utilization of a closed-flow system. A probe adapted for insertion to a standardized depth into the ear, provides a flow-through path for nystagmus-inducing liquid while expanding in response to the pressurized liquid to conform to the contours of the external auditory canal and tympanic membrane. Thermal conductivity through the membrane-like probe material permits heat exchange between the flowing liquid, and the external auditory canal and/or tympanic membrane to induce nystagmus.At this time, the authors can state only that the quality of nystagmus produced is similar to that produced by current conventional methods. In the small number of patients tested, discomfort appeared to be almost negligible. The system appears to be a promising improvement dependent on the establishment of accurate parameters for diagnosis.

Caloric Tests↗
PubMed2006

Adaptive filtering with the self-organizing map: a performance comparison.

In this paper we provide an in-depth evaluation of the SOM as a feasible tool for nonlinear adaptive filtering. A comprehensive survey of existing SOM-based and related architectures for learning input-output mappings is carried out and the application of these architectures to nonlinear adaptive filtering is formulated. Then, we introduce two simple procedures for building RBF-based nonlinear filters using the Vector-Quantized Temporal Associative Memory (VQTAM), a recently proposed method for learning dynamical input-output mappings using the SOM. The aforementioned SOM-based adaptive filters are compared with standard FIR/LMS and FIR/LMS-Newton linear transversal filters, as well as with powerful MLP-based filters in nonlinear channel equalization and inverse modeling tasks. The obtained results in both tasks indicate that SOM-based filters can consistently outperform powerful MLP-based ones.

Algorithms↗
PubMed1983

Short-term adaptation to the induced effect.

The short-term adaptation (1-4 h) to the induced effect was investigated on four subjects. A 4% meridional afocal magnifier axis 180 was worn before one eye in normal binocular conditions, which produced vertical retinal-image disparity. In certain circumstances this vertical disparity will give rise to the induced effect, i.e. a surface in the objective frontal plane will appear to be rotated around a vertical axis with the apparently closer edge on the same side as the magnifying lens. Adaptation, which is considered as a reduction in the induced effect over time, was measured with a modified Howard - Dolman apparatus. Both the maximal induced effect and the maximal short-term adaptation occurred within the first 30 min and ranged from 40 to 85%. The final level of short-term adaptation to the induced effect ranged from 20 to 45%. These results suggest a rapid recalibration of binocular depth perception by higher-level perceptual centers.

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↗
PubMed1980

The paradoxical moon illusions.

An adaptation theory of visual space is developed and applied to the data of a variety of studies of visual space perception. By distinguishing between the perceived distance of an object and that of the background or sky, the theory resolves the paradox of the moon illusions and relates both perceived size and perceived distance of the moon to the absolute level of spatial adaptation. The theory assumes that visual space expands or contracts in adjustment to changes in the sensory indicators of depth and provides a measure, A, of this adaptation-level. Changes in A have two effects--one on perceived size, one on perceived distance. Since A varies systematically as a function of angle of regard, availability of cues, and the total space-value, A is a measure of the moon illusions, and a practical index of individual differences by pilots and astronauts in the perception of the size and distance of objects on the ground and in the air.

Distance Perception↗
PubMed2001

The effect of initial concentration of carbofuran on the development and stability of its enhanced biodegradation in top-soil and sub-soil.

Carbofuran was incubated in top-soil and sub-soil samples from a pesticide-free site at a range of initial concentrations from 0.1 to 10 mg kg-1. Amounts of the incubated soils were removed at intervals over the subsequent 12 months, and the rate of degradation of a second carbofuran dose at 10 mg kg-1 was assessed. An applied concentration as low as 0.1 mg kg-1 to top-soil resulted in more rapid degradation of the fresh addition of carbofuran for at least 12 months. The degree of enhancement was generally more pronounced with the higher initial concentrations. When the same study was conducted in sub-soil samples from the same site, an initial dose of carbofuran at 0.1 mg kg-1 resulted in only small increases in rates of degradation of a second carbofuran dose. However, degradation rates in the sub-soil samples were, in many instances, considerably greater than in the corresponding top-soil samples, irrespective of pre-treatment concentration or pre-incubated period. Initial doses of 0.5 mg kg-1 and higher applied to sub-soil successfully activated the sub-soil microflora. Application of the VARLEACH model to simulate carbofuran movement through the soil profile indicated that approximately 0.01 mg kg-1 of carbofuran may reach a depth of 70 cm 400 days after a standard field application. The results therefore imply that adaptation of the sub-soil microflora (c 1 m depth) by normal field rate applications of carbofuran is unlikely to occur. In experiments to investigate this in soils exposed to carbofuran in the field, there was no apparent relationship between top-soil exposure and degradation rates in the corresponding sub-soils. The results further confirmed that same sub-soil samples have an inherent capacity for rapid biodegradation of carbofuran. The high levels of variability observed between replicates in some of the sub-soil samples were attributed to the uneven distribution of a low population of carbofuran-degrading micro-organisms in sub-surface soil. There was no apparent relationship between soil microbial biomass and degradation rates within or between top-soil and sub-soil samples.

Bacteria↗
PubMed1990

da Vinci stereopsis: depth and subjective occluding contours from unpaired image points.

Distant surfaces are occluded by nearer surfaces to different extents in the two eyes, leading to the existence of unpaired image points visible in one eye and not the other. An ecological analysis of the real world situation that could have given rise to such unpaired points indicates the presence of a depth constraint zone, defined by visibility lines between which possible real world points must lie. The leading edge of this zone starts at the edge of a fused binocular occluding surface and recedes linearly with increases in horizontal distance to the unpaired point. Psychophysical evidence indicates that the human visual system makes use of this unpaired information in a remarkably adaptive manner, showing an increase in perceived depth for increasing horizontal separations between the unpaired target and fused edge, at least over a significant angular range (approx. 25-40 min arc). We also show that unpaired points in binocular images can lead to the formation of subjective occluding contours and surface having the qualitatively appropriate sign of depth. Furthermore, we show that the visual system could not recover depth of unpaired points camouflaged from the other eye against silhouettes. Our findings indicate that the visual system makes use of occlusive relations in the real world to recover depth, contour, and surface from unpaired points. The fact that such processes must utilize eye-of-origin information implies that they share this essential characteristic with classical or Wheatstone stereopsis. The necessity of eye-of-origin information also suggests that the processing may begin relatively early in cortical visual processing, possibly as early as V1. Finally, the novel emergence of subjective occluding contours from unpaired monocular stimuli raises the possibility that this process is mediated by visual experience, built up by the association of unpaired points and occluding contours.

Depth Perception↗
PubMed2003

Low-light-adapted Prochlorococcus species possess specific antennae for each photosystem.

Prochlorococcus, the most abundant genus of photosynthetic organisms, owes its remarkably large depth distribution in the oceans to the occurrence of distinct genotypes adapted to either low- or high-light niches. The pcb genes, encoding the major chlorophyll-binding, light-harvesting antenna proteins in this genus, are present in multiple copies in low-light strains but as a single copy in high-light strains. The basis of this differentiation, however, has remained obscure. Here we show that the moderate low-light-adapted strain Prochlorococcus sp. MIT 9313 has one iron-stress-induced pcb gene encoding an antenna protein serving photosystem I (PSI)--comparable to isiA genes from cyanobacteria--and a constitutively expressed pcb gene encoding a photosystem II (PSII) antenna protein. By comparison, the very low-light-adapted strain SS120 has seven pcb genes encoding constitutive PSI and PSII antennae, plus one PSI iron-regulated pcb gene, whereas the high-light-adapted strain MED4 has only a constitutive PSII antenna. Thus, it seems that the adaptation of Prochlorococcus to low light environments has triggered a multiplication and specialization of Pcb proteins comparable to that found for Cab proteins in plants and green algae.

Adaptation, Physiological↗