[Factors affecting the threshold of depth vision in schoolchildren and preschool children exposed to a visual load].
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Adaptation, Ocular↗
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Projection of pulmonary rapidly adapting receptors to the medulla of the cat: an antidromic mapping study.
The activity of pulmonary rapidly adapting receptor (r.a.r.) neurones was recorded extracellularly in the nodose ganglion of the decerebrate cat. The receptors were identified by their rapid adaptation to 'ramp and hold' hyperinflations of the lung. The antidromic mapping technique was used to determine the sites of projection and branching patterns within the nucleus of the tractus solitarius (n.t.s.) of eleven r.a.r.s. The medulla was explored with a stimulating electrode to activate the r.a.r.s. antidromically. In each penetration, depth-threshold measurements were made for each antidromic response characterized by a distinct latency. Using the anatomical sites of the minimum threshold points, the locations of central branches of individual r.a.r.s. were determined. The main axons of all of them coursed within the tractus solitarius (t.s.) at levels from 2 mm rostral to 0.5 mm caudal to the obex. The axonal conduction velocities within the t.s. were 6.2-9.7 m/s, where the peripheral conduction velocities were 11.2-20.4 m/s (28 degrees C). Different latencies of response evoked in a single penetration were considered to indicate branching. The densest branching was found in the ipsilateral commissural subnucleus of the n.t.s. at levels 0.3-1.3 mm caudal to the obex and, to a lesser degree, in the contralateral commissural subnucleus. All r.a.r.s. sent a few branches to the medial n.t.s. rostral to the obex. Four r.a.r.s. ramified in the ventrolateral n.t.s. where inspiratory cells are located. Depth-threshold graphs were interpolated by best fitting parabolic equations: Ith = Ad2 + Bd + C; where Ith is the threshold current, d the corresponding depth of stimulation, and A, B and C are coefficients. Coefficient A is a measure of steepness of the parabola. The A coefficients were inversely related to the conduction velocity (v) of the stimulated branch. An analysis of the data from the present study (v = 5.0-9.7 m/s) combined with data from the literature (v = 2.2-85 m/s) led to a simple relationship between the A coefficient and the conduction velocity of the stimulated fibre: A = 6500/v, where A is expressed in microA/mm2 and v is expressed in m/s. Within the range 3-35 m/s, the formula is useful in predicting the effective current spread when the conduction velocity is known, or to estimate the conduction velocity from the shape of a depth-threshold curve. Two slowly adapting pulmonary stretch receptors (p.s.r.s) were studied.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Evolutionary patterns and repeated adaptive strategies of deep-sea anemones.
Sea anemones occupy the full depth range of the oceans, yet their evolutionary patterns and adaptive strategies to the enigmatic deep sea have remained contentious and poorly resolved. Here, we assemble genomes (n = 13) and transcriptomes for 15 species collected between 432 and 6,000 m and integrate them with publicly available actiniarian data. We find support for a shallow-water origin of Actiniaria through a framework that emphasizes genome-scale changes associated with habitat transitions. Most strikingly, these changes include repeated dismantling of the circadian toolkit across deep-sea lineages. In addition to convergent gene losses in photo- and temperature-regulatory genes, we find that some deep-sea lineages have experienced recurrent loss or pseudogenization of key meiotic genes (e.g., Meiosin, Ythdc2, Spo11, and Mlh3), suggesting reduced meiotic capacity in some lineages. Despite this extensive genomic erosion, deep-sea anemones exhibit molecular tuning: specific amino acid substitutions improve enzyme performance under low-temperature conditions relevant to the deep sea, while selective expansions of gene families related to neural excitability, membrane systems, and other functions may help maintain physiological performance in this environment. Functional assays in yeast indicate enhanced performance of the deep-sea variants at 4°C. These results define a "loss-optimization-innovation" triad that underlies bathymetric adaptations and may apply to other deep-sea fauna worldwide.
Actiniaria↗
The effect of disparity on motion coherence.
Many moving plaid stimuli are ambiguous, and perception switches between a coherent plaid pattern and two transparent gratings. Here, experiments are reported that examined the effect of stereodepth between the two gratings of the moving plaid stimulus on the perception of coherence or motion transparency. Increasing disparity increased the percentage of time that two independently drifting transparent gratings were perceived. This was studied for plaids with various levels of intersection luminance. Using intersection luminances beyond conditions of physical transparency increased the percentage of time that one coherent plaid was seen. These two opposing influences could be pitted against each other to achieve constant levels of coherence. An adaptation paradigm was also used in which observers adapted to a stationary stimulus with either zero, crossed or uncrossed disparity between the gratings, and then indicated the occurrence of coherence and motion transparency in test stimuli of drifting plaids with zero, crossed or uncrossed disparity. Adaptation to crossed and uncrossed stereo-depth increased relative perceived coherence equally, especially for zero test disparity. An analysis of the length of the episodes of coherence and motion transparency indicated that the effect of adaptation was to decrease the length of motion transparency episodes, while the length of coherence episodes did not change. It is concluded that mechanisms involved in the processing of stereo-depth must have an input to the integration stage of the motion channel and that pattern and component motion mechanisms can operate quite independently.
Adaptation, Ocular↗
Multisensory integration: strategies for synchronization.
Recent studies have shown that our ability to match the timing of inputs from objects that can be both seen and heard is highly adaptable and takes into account target depth and the relatively slow speed of sound.
Acoustic Stimulation↗
A comparison of palatal adaptation in acrylic resin denture bases using conventional and anchored polymerization techniques.
PURPOSE: The study investigated the effects of palatal depth and a resin anchoring system on the adaptation of denture base resin to the master cast after compression molding and heat polymerization. MATERIALS AND METHODS: Forty-eight virtually identical polymethyl methacrylate dentures were fabricated on master casts with either a deep or shallow palatal vault. One half of the master casts of each palate type were altered by the addition of anchoring holes along the posterior land area, as well as perpendicularly in the midsaggital area. Anchoring holes were made with a #8 round bur to a depth of 5 mm. Twenty-four hours after polymerization, the bases on their casts were sectioned at the posterior border and evaluated for degree of adaptation using a traveling microscope. Maladaptation at the interface of the denture base and master cast was measured at predetermined mediolateral locations. A split-plot analysis of variance (alpha = 0.05) was performed followed by a post-hoc Dunn Multiple Comparison Test. RESULTS: In general, depth of the palatal vault did not significantly influence denture palatal discrepancy (p =.0780), but the use of the anchoring system significantly reduced mean gap distances (p =.000). At lateral and midpalate locations, gap distances between the denture bases and their casts were reduced from approximately 0.3 mm to approximately 0.1 mm when the anchoring system was used. CONCLUSIONS: Mean gap distances for steep palate dentures were significantly less than shallow palate dentures at vestibule and lateral palate locations, and anchoring holes placed in an edentulous master cast along the posterior land area and at the midline significantly improved the adaptation of denture bases.
Acrylic Resins↗
Interlimb transfer of novel inertial dynamics is asymmetrical.
Mechanisms underlying interlimb transfer of adaptation to visuomotor rotations have recently been explored in depth. However, little data are available regarding interlimb transfer of adaptation to novel inertial dynamics. The present study thus investigated interlimb transfer of dynamics by examining the effect of initial training with one arm on subsequent performance with the other in adaptation to a 1.5-kg mass attached eccentrically to the forearm. Using inverse dynamic analysis, we examined the changes in torque strategies associated with adaptation to the extra mass, and with interlimb transfer of that adaptation. Following initial training with the dominant arm, nondominant arm performance improved substantially in terms of linearity and initial direction control as compared with naïve performance. However, initial training with the nondominant arm had no effect on subsequent performance with the dominant arm. Inverse dynamic analysis revealed that improvements in kinematics were implemented by increasing flexor muscle torques at the elbow to counter load-induced increases in extensor interaction torques as well as increasing flexor muscle torques at the shoulder to counter the extensor actions of elbow muscle torque. Following opposite arm adaptation, the nondominant arm adopted this dynamic strategy early in adaptation. These findings suggest that dominant arm adaptation to novel inertial dynamics leads to information that can be accessed and utilized by the opposite arm controller, but not vice versa. When compared with our previous findings on interlimb transfer of visuomotor rotations, our current findings suggest that adaptations to visuomotor and dynamic transformations are mediated by distinct neural mechanisms.
Adolescent↗
Specificity of saccadic adaptation in three-dimensional space.
The saccadic system is known to exhibit a considerable degree of short-term plasticity. Earlier studies have shown that saccadic adaptation, rather than being a global process affecting all saccades equally, has a certain degree of spatial resolution. Its localized nature has become apparent from studies in the frontal plane which have shown that short-term saccadic adaptation, induced along a given meridian, transfers to only a limited range of neighbouring directions. Considering that most natural gaze shifts also have a depth component, we investigated whether the directional specificity of the saccadic adaptive system can be generalized to three-dimensional (3-D) space. Binocular eye movements were recorded in seven subjects while they made saccades to visual stimuli in the horizontal plane of regard. Experiments began by recording baseline saccades, all starting from the same fixation point to either a farther target (far saccades) or an equally eccentric nearer target (near saccades). Next, by displacing the target intra-saccadically in opposite directions in alternating far and near trials, we attempted to simultaneously reduce the gain of the far saccades while increasing the gain of the near saccades. These experiments, aimed at eliciting a state of differential gain, were specifically designed to adapt only the saccadic response, since targets were shifted along corresponding iso-vergence circles. To investigate the effect of varying the radial direction difference, similar differential gain adaptation experiments were conducted in the frontal plane for saccades along two different meridians. Our results show that when the saccadic system is pressured, it is capable of adopting different gains simultaneously for equal-direction saccades to different depth planes. Similarly, opposite gain adaptation can also be achieved in the frontal plane, but only if radial saccade directions are sufficiently separated. The fact that short-term saccadic adaptation can be shown to be directionally specific in two perpendicular planes suggests that the adaptation process is restricted to a limited volume of 3-D oculomotor space.
Adaptation, Ocular↗
Contribution of middle temporal area to coarse depth discrimination: comparison of neuronal and psychophysical sensitivity.
Recent work suggests that the middle temporal (MT) area contributes to depth perception in addition to its well established roles in motion perception. To determine whether single MT neurons carry disparity signals with sufficient fidelity to account for depth perception, we have compared neuronal and psychophysical sensitivity to disparity while monkeys discriminated between two coarse disparities (near vs far) in the presence of noise. The strength of the visual stimulus was titrated around psychophysical threshold by varying the percentage of binocularly correlated dots in a random dot stereogram. We find that the average MT neuron has sensitivity equal to that of the monkey, as was reported previously for direction discrimination in MT. We further address some important factors that could bias the neuronal/psychophysical sensitivity comparison, including the possibility that monkeys reach a decision before the end of the stimulus presentation. Unlike the predictions of a simple model that uses Poisson spiking statistics, the sensitivity of many MT neurons has little dependence on the time interval over which spikes are counted to compute a neuronal threshold. Thus the response properties of many MT neurons appear to be adapted for rapid discrimination of depth, and we describe how temporal variations in both signal and noise contribute to this effect. We therefore predicted that psychophysical thresholds should exhibit little dependence on viewing duration in our task, and this was confirmed by additional behavioral experiments. Overall, our findings show that MT is well suited to provide sensory signals that form the basis for perceptual judgments of depth.
Action Potentials↗
[Ecophysiological properties of photosynthesizing bacteria from the Black Sea chemocline zone].
In May 1998, during the fifty-first voyage on board the research vessel Professor Vodyanitskii, a comparative study was conducted of the species diversity of green and purple sulfur bacteria in the water column of the chemocline zone at deep-sea stations and on the bottom surface of the Black Sea shallow regions. At three deep-sea stations, the accumulation of photosynthesizing bacteria in the chemocline zone at a depth of 85-115 m was revealed on the basis of the distribution of potential values of carbon dioxide light fixation. The location of the site of potential carbon dioxide light fixation suggests that the photosynthesis may be determined by the activity of the brown Chlorobium sp., revealed earlier at these depths. Enrichment cultures of brown sulfur bacteria were obtained from samples taken at the deep-sea stations. By morphology, these bacteria, assigned to Chlorobium sp., appear as nonmotile straight or slightly curved rods 0.3-0.5 x 0.7-1.2 microm in size; sometimes, they form short chains. Ultrathin sections show photosynthesizing antenna-like structures, chlorosomes, typical of Chlorobiaceae. The cultures depended on the presence of NaCl (20 g/l) for growth, which corresponds to the mineralization of Black Sea water. The bacteria could grow photoautotrophically, utilizing sulfide, but the Black Sea strains grew much more slowly than the known species of brown sulfur bacteria isolated from saline or freshwater meromictic lakes. The best growth of the strains studied in this work occurred in media containing ethanol (0.5 g) or sodium acetate (1 g/l) and low amounts of sulfide (0.4 mM), which is consistent with the conditions of syntrophic growth with sulfidogens. The data obtained allow us to conclude that the cultures of brown sulfur bacteria are especially adapted to developing at large depths under conditions of electron donor deficiency owing to syntrophic development with sulfate reducers. The species composition of the photosynthetic bacteria developing in the bottom sediments of shallow stations differed substantially from that observed at deep-sea stations. Pure cultures of the green Chlorobium sp. BS 1C and BS 2C (chlorobactin as the carotenoid), purple sulfur bacteria Chromatium sp. BS 1Ch (containing spirilloxanthine series pigments), and Thiocapsa marina BS 2Tc (containing the carotenoid okenone) were obtained from samples of sediments at shallow-water stations. Brown sulfur bacteria were absent in the sediment samples obtained from the Black Sea shallow-water stations 1 and 2.
Carbon Dioxide↗
Variation in stomatopod (Gonodactylus smithii) color signal design associated with organismal condition and depth.
In interactions, many tropical stomatopod species display conspicuous colored body spots that can communicate information about the sender's state (e.g., sex, aggressiveness, etc.). Species inhabiting a variety of depths experience large differences in illumination spectrum and intensity due to filtering of light by water and its constituents. Stomatopod spectral sensitivity is known to vary phenotypically with changes in light environment (associated with depth) that potentially affects the detection of color signals. Animals collected at different depths also have different body coloration. This study examines how spectral differences in colored body spots vary with organismal condition and models the effects of changing body coloration, light environment, and spectral sensitivity on the detection of color signals in a gonodactyloid species, Gonodactylus smithii. Of the seven conspicuous color spots that were measured in G. smithii, three had spectral differences that correlated with sex, aggression, and female reproductive state. A model of color detection in G. smithii indicates that longer-wavelength spectral content was affected most by varying body coloration and light conditions. Most color signals were perceived similarly both by shallow- and by deep-adapted photoreceptor sets over a range of depths (1-13 m). Eye spot ('meral spot') color detection also was invariant over the same depth range in shallow- and deep-adapted, long-wavelength receptors, but deep-adapted receptors continued to maintain a consistent detection of these spots down to 18 meters. These results suggest that meral spot coloration may have evolved as a constant signal when viewed by conspecifics from various depths.
Adaptation, Physiological↗
A three-dimensional motion aftereffect produced by prolonged adaptation to a rotation simulation.
After adaptation to a perspective simulation of a square plane rotating in depth, an ambiguous rotation simulation (ie one containing no perspective information) appears to rotate in the direction opposite that of adaptation. The strength of this three-dimensional motion aftereffect (MAE) is proportional to the amount of perspective available in the adaptation display and, in the dark, decays to about 75% of its initial strength within about 546 s. The nature of the testing situation and a control experiment suggest that the three-dimensional MAE is not caused by retinal adaptation of two-dimensional directionally selective mechanisms.
Adaptation, Physiological↗
[Managing conflict in psychiatric institutions].
Several observations made by the author in everyday practice during his activity as a supervisor of psychiatric therapy teams, are described. These can be classified as "subcultural phenomena". It is shown how the members of a therapy team will modify certain institutional conditions and parameters unconsciously but purposefully and make use of them for coping with conflict situations. This is demonstrated, inter alia, by the manner in which the duty schedule is handled and how the team deals with the sickness of a team member. This type of conflict management is then placed in relation to two major conflict potentials that come into play during everyday work in a psychiatric hospital: on the one hand, the pathogenic relationship offers made by the mentally ill patients, and on the other hand the adaptation strategies acquired during professional and institutional socialisation and moored in the conscious depths of the team member's soul. These adaptation strategies are interpreted by the team members as components of their professional identity. The therapeutic quality of an institution can thus be measured by the extent to which that institution succeeds in supporting these adaptive elements of its members and hence in relieving them of some of the mental stress to which they are exposed.
Conflict, Psychological↗
Equivalence between temporal frequency and modulation depth for flicker response suppression: analysis of a three-process model of visual adaptation.
We analyze adaptation processes responsible for eliciting and alleviating flicker response suppression, which is a class of phenomena characterized by the selective reduction of visual response to the ac component of a flickering light. Stimulus conditions were chosen that would allow characteristic features of flicker response suppression to be defined and manipulated systematically. Data are presented to show that reducing the sinusoidal modulation depth of an 11-Hz stimulus can correspond precisely to raising the temporal frequency of a fully modulated stimulus. In each case there is a nonmonotonic relation between flicker response and dc test illuminance. The nonmonotonic relation cannot be explained by adaptation models that postulate multiplicative and subtractive adaptation processes followed by a single static saturating nonlinearity, even when temporal frequency filters are incorporated into such models. A satisfactory explanation requires an additional contrast gain-control process. This process enhances flicker response at progressively lower temporal response contrasts as the illuminance of a surrounding field increases.
Adaptation, Physiological↗
Stereo-slant adaptation is high level and does not involve disparity coding.
We have investigated the potential stages of visual processing at which adaptation may occur to a slanted surface produced by horizontal magnification. Predictions of three hypotheses were tested utilizing a property of depth from binocular disparity, namely that slant scales with distance. If adaptation occurs at the disparity level, then the after-effect expressed in units of horizontal magnification will be independent of the test distance. If adaptation occurs at either a perceived slant or mapping level, then the after-effect, expressed in units of slant, will be independent of the test distance. If adaptation is contingent on distance, then the after-effect will not transfer over distance. Subjects adapted to a stereo-defined slanted surface at a distance of 57 cm. The after-effect was measured with a test stimulus at a distance of 28, 57, 85, or 114 cm by means of a nulling method. When the after-effect was expressed in units of slant, we found that it was larger at the adapting distance than other test distances, and that the after-effect was constant at test distances different from the adaptation distance. These results suggest that two types of adaptation occurred, namely adaptation on a mapping/perception level and adaptation contingent on distance.
Adaptation, Ocular↗
The oxygen distribution in the prelaminar optic nerve head of the cat.
Oxygen-sensitive microelectrodes were used to measure oxygen profiles from the prelaminar region of the cat optic nerve head. From the profiles, the oxygen distribution of this tissue was determined. Changes in oxygen levels in response to flicker stimulation were obtained. Also, the regulatory ability of this tissue was assessed by acutely increasing IOP and by presenting the cat with periods of hyperoxia. The cells in the optic nerve head were found to exist in the same oxygen environment as cells of the inner retina. Oxygen tensions usually varied between 0 and 40 mmHg, with the mean being between 10 and 20 mmHg. There was no difference in oxygen levels between central and peripheral parts of the optic nerve head, nor was there a difference as a function of depth. Different levels of light adaptation of the retina had no effect on oxygen levels in the optic nerve head, but flicker stimulation of the retina resulted in decreases in tissue oxygen tension. A small number of experiments in which the intraocular pressure was raised showed that oxygen levels in the optic nerve head were not drastically altered during acute decreases in perfusion pressure. Based on the size of changes in tissue oxygen tensions during hyperoxia, it appeared that blood vessels in the optic nerve head constricted in response to systemic hyperoxia.
Adaptation, Ocular↗
Investigating the mechanism and machinery of RNA editing.
RNA editing in trypanosomes produces mature mRNAs by posttranscriptional guide RNA (gRNA)-directed uridylate insertion and deletion. This article describes methods for the study of RNA editing with an emphasis on an in vitro editing system that was used to explore the general mechanism of editing and that can be adapted for more in-depth studies of this intriguing and important process. Methods used to investigate the macromolecular complex that catalyzes RNA editing are also described. This complex is composed of multiple proteins and contains several catalytic activities. It is in the early stages of characterization. The methods described here are intended to assist in its further analysis.
Animals↗
Origin of the desmoplasia in desmoplastic malignant melanoma.
Four cases of desmoplastic malignant melanoma were examined light microscopically and immunohistochemically. Electron microscopy was performed in three cases. Light microscopy showed that all tumors were composed of neoplastic spindle cells that infiltrated between mature collagen bundles in the reticular dermis. Some of the spindle cells had bizarre nuclei, whereas other spindle cells resembled normal fibroblasts. Melanin could not be demonstrated in any of the tumors by histochemical techniques. Electron microscopic examination of the spindle cells showed prominence of rough endoplasmic reticulum, which was dilated and filled with flocculent material and occasional collagen fibrils. The same cells contained aggregates of non-membrane-bound melanin granules and pre-melanosomes. Some cells also showed features of myofibroblasts. Immunoperoxidase staining with anti-S100 protein antibody demonstrated positivity of the spindle cells as well as of melanocytes in the basal layer of the epidermis. Scar tissue and fibroblasts did not stain. These findings show that the desmoplastic component of these malignant melanomas derives from melanocytes that have undergone adaptive fibroplasia. Therefore, in assessing depth of invasion in a malignant melanoma, measurements should include the desmoplastic areas.
Adult↗