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Results for “Depth Perception”

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At least 847 records · Page 47Linked to original sources
PubMed2002

Adaptive control of vergence in humans.

Vergence eye alignment minimizes horizontal, vertical, and cyclodisparities to optimize stereo-depth perception. Only the horizontal component of vergence is under voluntary control. Couplings with voluntary version and horizontal vergence guide vertical vergence and cyclovergence. Can these couplings be modified in response to sensory demands on binocular vision? We have modified vertical vergence and cyclovergence in response to optical changes in disparity. Vertical vergence was stimulated with aniseikonic lenses that exaggerated vertical disparity in tertiary gaze. Vertical vergence adapted in an hour to produce nonconcomitant changes in vertical phoria that varied with vertical eye position in tertiary gaze. Cyclovergence was stimulated with cyclodisparities that varied with gaze elevation and convergence angle. Cyclovergence adapted within 2 hours to produce nonconcomitant changes in cyclophoria that varied with gaze elevation and convergence. The adaptive couplings for vertical vergence and cyclovergence are modeled as a combination of passive orbital mechanics and active gain control of the vertical recti and obliques. Vergence adaptation is a calibration process that adjusts the innervation for horizontal, vertical, and torsion components of vergence to the physical constraints set by the extraocular muscles and orbital connective tissues. Passive orbital mechanics simplify the neural control for precise vertical vergence and cyclovergence that are needed to achieve binocular alignment under open-loop conditions in response to perceived spatial location.

Adaptation, Physiological↗
PubMed1988

Parallel integration of vision modules.

Computer algorithms have been developed for several early vision processes, such as edge detection, stereopsis, motion, texture, and color, that give separate cues to the distance from the viewer of three-dimensional surfaces, their shape, and their material properties. Not surprisingly, biological vision systems still greatly outperform computer vision programs. One of the keys to the reliability, flexibility, and robustness of biological vision systems is their ability to integrate several visual cues. A computational technique for integrating different visual cues has now been developed and implemented with encouraging results on a parallel supercomputer.

Algorithms↗
PubMed1971

Perception.

Explore the source record for details and available documents.

Afterimage↗
PubMed1975

Perception.

Explore the source record for details and available documents.

Adaptation, Ocular↗
PubMed1977

Application of longitudinal magnification effect to magnification stereoscopic angiography: a new method of cerebral angiography.

A new method of stereoscopic cerebral angiography has been developed which employs 2X radiographic magnification. In order to obtain the same depth perception in the object as with conventional contact stereoscopic angiography, one can made the x-ray exposures at two focal spot positions which are separated by only 1 inch (2.5 cm), whereas the contact technique requires a separation of 4 inches (10 cm). The smaller distance is possible because, with 2X magnification, the transverse detail in the object is magnified by a factor of two, but the longitudinal detail, which is related to the stereo effect, is magnified by a factor of four, due to the longitudinal magnification effect. The small focal spot separation results in advantages such as improved stereoscopic image detail, better image quality, and low radiation exposure to the patient.

Cerebral Angiography↗
PubMed2003

Functional connectivity of disparity-tuned neurons in the visual cortex.

Different mechanisms have been proposed concerning how disparity-tuned neurons might be connected to produce the signals for depth perception. Here we present neurophysiological evidence providing insight on this issue. We have recorded simultaneously from pairs of disparity-tuned neurons in the cat's striate cortex. The purpose was to determine the relationships between disparity tuning and functional connectivity revealed through neural cross-correlograms. Monosynaptic connections tend to be stronger between pairs of cells with similar disparity tuning. Pairs of complex cells tend to have either similar tuning or nearly opposite tuning with an absence of quadrature relations. Pairs with at least one simple cell do have some nearly quadrature relationships when they are recorded from the same electrode. Coarse-to-fine connections (i.e., the presynaptic cell has lower disparity frequency and larger disparity range) tend to be stronger but less frequent than those of a fine-to-coarse nature. Our results are consistent with a system that produces weighted averaging across cells that are tuned to similar disparities but different disparity scales to reduce false matches.

Action Potentials↗
PubMed1997

Genome size, secondary simplification, and the evolution of the brain in salamanders.

Compared to other vertebrates, even including lampreys and hagfishes in some respects, salamanders exhibit a relatively simple organization of brain and sense organs which is illustrated here using the visual system as an example. The greatest simplicity is found in the bolitoglossine salamanders, yet all bolitoglossines possess highly projectile tongues and rely on vision for survival; furthermore, some species are agile and acrobatic. The unusual features of the visual system of salamanders include small numbers of large neurons, a low degree of morphological differentiation among neurons, a small proportion of myelinated axons in the optic nerve, and an optic tectum consisting essentially of a periventricular cellular layer and a superficial fiber layer. Similar features are found throughout the central nervous system of salamanders and in the lateral line, auditory and olfactory systems as well. Phylogenetic analysis shows that the most parsimonious interpretation of these data is that the simple organization of the brain and sense organs of salamanders was derived secondarily from a more complex ancestral state. We hypothesize that increased genome size has led to simplification of the nervous system in salamanders. Increased genome size appears to have had profound effects on neural development in salamanders, leading to paedomorphosis, the retention of juvenile or even embryonic characteristics into adulthood. In particular, large genome size is associated with large cell size and reduced rates of cell proliferation, migration and differentiation. Secondary simplification has constrained the function of the salamanders' visual system, primarily by increasing cell size and decreasing cell numbers. However, it also has provided an opportunity for the evolution of compensating mechanisms, which have helped to restore or even enhance visual function. Most apparent among the compensatory mechanisms of bolitoglossine salamanders is the presence of well developed ipsilateral retinotectal projections, which apparently enhance depth perception. It is difficult to explain the unusual history of the nervous system in salamanders solely in terms of natural selection and adaptation. Increasing genome size through selfish replication appears to have played a major role in the evolution of salamander brains by imposing functional constraints as well as creating opportunities for overcoming them.

Animals↗
PubMedDate not supplied

Scrape cytology of meningioangiomatosis: a report of two cases with diagnostic cytologic features.

BACKGROUND: Meningioangiomatosis is a rare, probably hamartomatous condition characterized by nonneoplastic intracortical proliferation of meningothelial cells, capillaries and fibroblasts. The lesion may mimic a tumor both clinically and radiologically. We present two cases of the entity, including its cytologic features. CASES: A 71-year-old man presented with an eight-month history of headache, change in vision, loss of depth perception and unsteady gait. Magnetic resonance imaging (MRI) revealed an infiltrative lesion of the left occipital lobe, diffuse in nature. Cytologic smears prepared at the time of intraoperative consultation showed numerous thin-walled capillaries together with bland spindle cells. Occasional large cells with prominent nucleoli were also present. Frozen section confirmed the presence of linear, small capillaries surrounded by fibroblasts and meningothelial cells, consistent with meningioangiomatosis. The second case was a 3-year-old girl who presented with a one-day history of seizure, vomiting, fever and perioral cyanosis. MRI revealed an enhancing lesion in a temporal lobe of the cerebrum. The patient underwent excision of the lesion. Intraoperative cytology showed numerous meningothelial whorls together with neurons and occasional capillaries. Both patients were well, one after three months and the other after six. CONCLUSION: Meningioangiomatosis is a lesion characterized by linear capillaries, meningothelial cells and neurons, some exhibiting nuclear atypia. The combination can lead to an erroneous diagnosis of more common conditions, such as meningioma (with intracortical extension) and anaplastic astrocytoma. Contrary to these more sinister diagnoses, meningioangiomatosis is a completely benign, presumably hamartomatous entity.

Aged↗
PubMed2006

Blinded evaluation of the effects of high definition and magnification on perceived image quality in laryngeal imaging.

OBJECTIVES: Advances in commercial video technology have improved office-based laryngeal imaging. This study investigates the perceived image quality of a true high-definition (HD) video camera and the effect of magnification on laryngeal videostroboscopy. METHODS: We performed a prospective, dual-armed, single-blinded analysis of a standard laryngeal videostroboscopic examination comparing 3 separate add-on camera systems: a 1-chip charge-coupled device (CCD) camera, a 3-chip CCD camera, and a true 720p (progressive scan) HD camera. Displayed images were controlled for magnification and image size (20-inch [50-cm] display, red-green-blue, and S-video cable for 1-chip and 3-chip cameras; digital visual interface cable and HD monitor for HD camera). Ten blinded observers were then asked to rate the following 5 items on a 0-to-100 visual analog scale: resolution, color, ability to see vocal fold vibration, sense of depth perception, and clarity of blood vessels. Eight unblinded observers were then asked to rate the difference in perceived resolution and clarity of laryngeal examination images when displayed on a 10-inch (25-cm) monitor versus a 42-inch (105-cm) monitor. A visual analog scale was used. These monitors were controlled for actual resolution capacity. RESULTS: For each item evaluated, randomized block design analysis demonstrated that the 3-chip camera scored significantly better than the 1-chip camera (p < .05). For the categories of color and blood vessel discrimination, the 3-chip camera scored significantly better than the HD camera (p < .05). For magnification alone, observers rated the 42-inch monitor statistically better than the 10-inch monitor. CONCLUSIONS: The expense of new medical technology must be judged against its added value. This study suggests that HD laryngeal imaging may not add significant value over currently available video systems, in perceived image quality, when a small monitor is used. Although differences in clarity between standard and HD cameras may not be readily apparent on small displays, a large display size coupled with HD technology may impart improved diagnosis of subtle vocal fold lesions and vibratory anomalies.

Equipment Design↗
PubMedDate not supplied

Endotracheal intubation and Venturi (jet) ventilation for laser microsurgery of the larynx.

Meeting the exacting requirements for microsurgery of the larynx is a challenge for the anesthesiologist. To accomplish, the necessary dissection, the otolaryngologist has several requirements. They are a quiet relaxed field, excellent illumination with magnification, binocular vision for depth perception, and, above all, an unobstructed field. The management of anesthesia for suspension microsurgery on the larynx presents many problems, the most vexing of which is the fact that the otolaryngologist and anesthesiologist are in competition for access to the patient's airway. In sharing this, neither has been able to perform with the degree of control that he would like due to either inadequate operating conditions or insufficient access to ventilatory mechanisms. Several anesthetic techniques have been used for inspection or operative laryngoscopy: topical anesthesia, apneic techniques, translaryngeal topical anesthesia, chest respirator, neuroleptanalgesia, and general endotracheal anesthesia with muscle relaxants. The latter has proven most popular, particularly in children, because ventilation and surgical conditions are considered to be most controllable. However, the presence of the requisite endotracheal tube obscures the full view of the larynx and vocal cords, and the tube may itself become obstructed. Additionally, use of the laser involves the further risk of heat effects on the endotracheal tube if the beam hits the tube. This report presents our experience and development of the combined technique of endotracheal intubation and Venturi (jet) ventilation. We believe it represents the safest available approach while providing near ideal working conditions for the otolaryngologist during laser microsurgery of the larynx.

Adolescent↗
PubMed1999

Endoscopic middle ear surgery.

One hundred sixty-five middle ear procedures were performed with an endoscope, a camera, and a video monitor instead of the microscope. The endoscope offers the following advantages: 1) it visualizes the whole tympanic membrane and the ear canal without having to manipulate the patient's head or the microscope, 2) it extends the operative field in transcanal procedures into structures usually hidden from the microscope (anterior tympanic perforation, posterior retraction pocket, facial recess, and hypotympanum), and 3) it visualizes structures from multiple angles as opposed to the microscope's single axis along the ear canal. Disadvantages of the endoscope include the one-handed surgical technique, a loss of depth perception, limited magnification, and the need for training. The endoscope holds the greatest promise in tympanoplasty and cholesteatoma surgery and should increase the utilization of transcanal over postauricular procedures.

Audiometry↗