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 37 records · Page 2Linked to original sources
PubMed1993

A proximity-contingent stereoscopic depth aftereffect: evidence for adaptation to disparity gradients.

Prolonged inspection of a surface slanted in the third dimension of visual space typically results in a negative aftereffect such that, after adaptation, a surface in the fronto-parallel plane will appear slanted in the opposite direction. Binocular disparity is not necessary to generate such effects, since they can be obtained monocularly, presumably via adaptation to texture gradient. Six experiments demonstrated durable stereoscopic depth aftereffects in the absence of a texture gradient--by using discrete disparate objects rather than slanted surfaces--and demonstrated that adaptation was to the interobject disparity gradient rather than to the relative disparity of the objects per se. The disparity required to null the obtained aftereffects was inversely proportional to the horizontal separation of elements, for a constant disparity, and directly proportional to the separation of subsequently presented probes. When elements differed in depth (disparity), but were not laterally separated, nulling disparity was significant but invariant with changes in the horizontal separation of probe elements. In that case, adaptation was (i) either to the disparity gradient generated by the vertical separation of probe elements (of which the relative disparity component was tapped); or (ii) to relative disparity per se.

Adult↗
PubMed1990

A simulation model of water depth in mangrove basin forests.

The construction and validation of a model simulating the water depth within mangrove basin forests is described. Rainfall, water table, water depth and tide data collected from a red mangrove basin forest on Marco Island, FL, was used to estimate model parameters. These included the basin spillover height, evapotranspiration-infiltration rate and the functional relationship of water depth change to rainfall, tide and basin spillover. The model was constructed with LOTUS 123 and calibrated from staff gauge water depth records. The model proved accurate and adaptable. Water depths from the model and staff gauge were correlated highly (r = 0.98). Data from an adjacent black mangrove forest featuring complex wet-dry cycling were used to modify the model. After calibration, the model provided an accurate record of water depths at the site (r = 0.89). This model will provide water depths used in a model of Aedes taeniorhynchus population dynamics.

Aedes↗
PubMed2006

A neuromorphic depth-from-motion vision model with STDP adaptation.

We propose a simplified depth-from-motion vision model based on leaky integrate-and-fire (LIF) neurons for edge detection and two-dimensional depth recovery. In the model, every LIF neuron is able to detect the irradiance edges passing through its receptive field in an optical flow field, and respond to the detection by firing a spike when the neuron's firing criterion is satisfied. If a neuron fires a spike, the time-of-travel of the spike-associated edge is transferred as the prediction information to the next synapse-linked neuron to determine its state. Correlations between input spikes and their timing thus encode depth in the visual field. The adaptation of synapses mediated by spike-timing-dependent plasticity is used to improve the algorithm's robustness against inaccuracy caused by spurious edge propagation. The algorithm is characterized on both artificial and real image sequences. The implementation of the algorithm in analog very large scale integrated (aVLSI) circuitry is also discussed.

Animals↗
PubMed1990

Flicker adaptation in the periphery at constant perceived modulation depth.

At constant physical flicker modulation depth, the time taken to adapt to flicker in the periphery varies inversely with temporal frequency. It has recently been suggested that this effect may indicate differential susceptibility to adaptation of the underlying temporal mechanisms. Using suprathreshold gratings, temporally modulated in contrast at constant perceived, rather than physical, modulation depth, we found the opposite result: the time required to adapt increased with temporal frequency. Given some uncertainty concerning the appropriateness of employing apparent or physically constant modulation depths, we conclude that rate of adaptation does not, at present, provide clear evidence as to the nature of the underlying temporal mechanisms.

Adaptation, Ocular↗
PubMed2000

Effect of varying the depth of heat application on the adaptability of gutta-percha during warm vertical compaction.

The purpose of this study was to compare the adaptability of gutta-percha after varying the depth of heat application in the obturation of a set of standard root canals. A split-tooth model was constructed using a human maxillary central incisor. The root canal was cleaned and shaped using a step-back preparation to a size #60 FlexOFile at the working length (WL). Five shallow depressions were produced on the root canal wall. Twenty obturations without sealer were performed for each technique (thermoplasticized injectable (TI), lateral condensation, and warm vertical compaction (WVC) with heat applications at 3, 4, 5, and 7 mm from the WL). After each obturation the model was separated and the mesial and distal sides of each obturation were examined and videotaped at x 32 magnification. The quality of the obturation was graded based on the replication to the WL, replication of the artificial depressions, surface adaptation, and homogenicity of the gutta-percha. The Kruskal-Wallis analysis and the Student-Newman-Keuls tests indicated that all the techniques were significantly different from each other (p < 0.05) except for the TI group versus the WVC group with the heat application to within 3 mm from the WL (p > 0.05). The TI technique was ranked best followed by the WVC with heat applications at 3, 4, 5, and 7 mm. The lateral condensation technique received the lowest ranking.

Analysis of Variance↗
PubMed2001

Adaptation to disparity but not to perceived depth.

The purpose of the present study was to investigate whether adaptation can occur to disparity per se. The adapting stimuli were large random-dot patterns of which the two half-images were transformed such that the depth effects induced by the vertical transformations were nulled by horizontal transformations. Thus, the adapting stimuli were perceptually the same, whereas the disparity fields differed from each other. The adapting stimuli were presented for five minutes. During that period, the percept of a fronto-parallel surface did not change. After the adapting period, subjects perceived a thin untransformed strip as either slanted or curved depending on the adapting transformation. The thin strips provided negligible information about the vertical disparity field. In a forced-choice task we measured the amount of horizontal transformation that was required to null the acquired adaptation. We found that the amounts of horizontal transformation required to perceive the test strip fronto-parallel were significantly different from zero. We conclude that the visual system can adapt to disparity signals in the absence of a perceptual drive.

Adaptation, Physiological↗
PubMed2001

Perceptual continuation and depth in visual phantoms can be explained by perceptual transparency.

We try to explain perceptual continuation and depth in the visual-phantom illusion in terms of perceptual transparency. Perceptual continuation of inducing gratings across the occluder in stationary phantoms could be explained with unique transparency, a notion proposed by Anderson (1997 Perception 26 419-453). This view is consistent with a number of previous reports including that of McCourt (1994 Vision Research 34 1609-1617) who criticized the stationary phantom illusion from the viewpoint of his counterphase lightness induction or grating induction, which might involve invalid transparency. Here we confirm that the photopic phantom illusion (Kitaoka et al, 1999 Perception 28 825-834) really gives in-phase lightness induction and involves bistable transparency. It is thus suggested that perceptual continuation and depth in the visual-phantom illusion depend on perceptual transparency.

Analysis of Variance↗
PubMed1998

The physiological basis of diving to depth: birds and mammals.

There is wide diversity in the animals that dive to depth and in the distribution of their body oxygen stores. A hallmark of animals diving to depth is a substantial elevation of muscle myoglobin concentration. In deep divers, more than 80% of the oxygen store is in the blood and muscles. How these oxygen stores are managed, particularly within muscle, is unclear. The aerobic endurance of four species has now been measured. These measurements provide a standard for other species in which the limits cannot be measured. Diving to depth requires several adaptations to the effects of pressure. In mammals, one adaptation is lung collapse at shallow depths, which limits absorption of nitrogen. Blood N2 levels remain below the threshold for decompression sickness. No such adaptive model is known for birds. There appear to be two diving strategies used by animals that dive to depth. Seals, for example, seldom rely on anaerobic metabolism. Birds, on the other hand, frequently rely on anaerobic metabolism to exploit prey-rich depths otherwise unavailable to them.

Animals↗
PubMedDate not supplied

Depth of cure and marginal adaptation to dentin of xenon lamp polymerized resin composites.

Marginal adaptation of four resin composites (Clearfil APX, Estelite, Silux Plus and Z-100) cured with two xenon lamp units (Plasma Arc Curing System or Apollo 95E) or a halogen lamp unit (Witelite) were evaluated by measuring the wall-to-wall contraction gap width. A cylindrical dentin cavity (ø3 mm x 1.5 mm) prepared in an extracted human molar was treated with the Megabond system or an experimental bonding system consisting of 0.5 M EDTA, 35% GM and Clearfil Photo Bond prior to composite filling and was irradiated for three seconds (xenon lamp) or 40 seconds (halogen lamp). The contraction gap was measured with a light microscope. In addition, the curing capability of these three light sources was evaluated by measuring the curing depth of the composites filled in a split Teflon mold (ø4 mm x 8 mm). There was no marginal gap formation for Clearfil APX, Estelite and Silux Plus treated with the experimental bonding system regardless of the type of light sources. The curing depth of the xenon lamp was significantly higher than the halogen lamp, while marginal adaptation did not suffer any significant deterioration.

Analysis of Variance↗
PubMed1981

Depth perception, eye alignment and cortical ocular dominance of dark-related cats.

On first exposure to light, animals that have been reared from birth until about 4 months of age in total darkness exhibit substantial visual and visuomotor deficits, which decline in severity during the first few months following exposure to light. In order to determine whether dark-reared animals eventually acquire stereoscopic vision following exposure to light we examined the binocular status of 5 dark-reared animals two of which developed convergent eye alignment. The binocular status was assessed behaviorally by measurements of the ability of each animal to perceive depth using either one or both eyes, and physiologically by documentation of the distribution of cortical ocular dominance of a sample of visual acuity, their binocular depth perception remained very poor, comparable to the monocular performance of normal cats. In marked contrast to normal animals none of the dark-reared animals, even those with normal eye alignment, performed substantially better binocularly than monocularly, a result indicating the absence of a uniquely binocular mechanism for depth perception in these animals. Although the dark-reared animals were found to retain a substantial (but reduced) complement of binocularly influenced cortical neurons, the tuning of these cells for retinal disparity must be insufficiently precise to mediate depth perception under binocular viewing conditions that is superior to that which can be achieved monocularly.

Animals↗
PubMed1975

The role of perceptual cues in the trapezoid oscillatory illusion.

The present experiment was designed to test the hypothesis that binocular disparity functions as a veridical cue, and linear perspective as a nonveridical cue in the perception of a rotating trapezoid. Three trapezoids with proportionately increasing slope were viewed by 10 subjects through viewing screens designed to control the availability of binocular disparity. Monocular and binocular viewing conditions were employed. The dependent variable, proportion of perceived oscillation, was analyzed by a factorial analysis of variance and appropriate post hoc tests. The obtained data indicate that increasing the availability of binocular disparity by increasing viewing screen width favors veridical rotation perception. When the binocular depth cue was attenuated by decreasing viewing screen width, the observer relied on linear perspective, and non-veridical oscillation perception was favored. As linear perspective was increased by increasing trapezoid slope, perceived oscillation increased both monocularly and binocularly. However, for any level of linear perspective, monocular viewing invariabily produced more oscillation than binocular viewing, indicating that monocular depth cues (movement parallax and interposition) were not as effective at neutralizing the illusory perspective effect as the binocular disparity cue.

Adolescent↗