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At least 775 records · Page 43Linked to original sources
PubMed2001

Magnetoencephalography and stereopsis: rhythmic cortical activity in humans recorded over the parieto-occipital cortex.

We have studied human stereopsis by analysing magnetoencephalographic signals during the presentation of stereograms using frequency analysis. The study of synchronised firing of cortical neurones is a new way of understanding information processing in the brain and it is hypothesised that frequencies greater than 35 Hz are used for higher-order processing. We report the response of cortical neurones involved in stereopsis recorded from over the occipital and parietal cortices using a single channel axial superconducting quantum interference device neuromagnetometer. Our main result was increased cortical activity in the gamma-band at frequencies apparently related to stereopsis and the perception of depth. Our results are consistent with reports in the literature that suggest that frequencies above 40 Hz are involved in attention, pattern recognition and higher order visual activity.

Adult↗
PubMed2002

New visualization technique with a three-dimensional video-assisted stereoendoscopic system: application of the BVHIS display method during endolaryngeal surgery.

A three-dimensional video-assisted stereoendoscopic system (3D video system) developed by the Shinko Optical Company, Ltd. (Tokyo, Japan), and referred to as the binocular vision by horizontal image shifting display method (BVHIS display method), has been developed to digitally process ordinary video signals obtained with a video camera connected to a direct videolaryngoscope. The three-dimensional video system provides the surgeon with stereoendoscopic video images and enhances the ability of the surgeon to perform delicate endoscopic procedures. The three-dimensional video-assisted stereoendoscopic laryngosurgical procedure and its underlying principles are described in this paper. A total of 12 patients with laryngeal lesions causing dysphonia underwent three-dimensional video-assisted stereoendoscopic laryngosurgery. Although the video image obtained with the BVHIS display method is only pseudo-three-dimensional, this method enables the surgeon to perceive both depth perception and realism. We describe a surgical procedure using this new visualizing technique and the underlying principles of the technique. Preoperative and postoperative evaluations of the patients' vocal functions are also described. This system is a useful tool for the treatment of laryngeal lesions causing dysphonia.

Adult↗
PubMed2003

Stereopsis activates V3A and caudal intraparietal areas in macaques and humans.

Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically compared using the same stimuli and analysis methods. In order to examine the global architecture of stereoscopic processing in primate visual cortex, we studied fMRI activity in alert, fixating human and macaque subjects. In macaques, we found strongest activation to near/far compared to zero disparity in areas V3, V3A, and CIPS. In humans, we found strongest activation to the same stimuli in areas V3A, V7, the V4d topolog (V4d-topo), and a caudal parietal disparity region (CPDR). Thus, in both primate species a small cluster of areas at the parieto-occipital junction appears to be specialized for stereopsis.

Animals↗
PubMed1996

Decreased Performance of Skilled Laparoscopic Surgeons at Microlaparoscopy versus Traditional Laparoscopy

The skill requirements for microlaparoscopy are significantly higher than those for the traditional technique. This program was designed to meet the demands of compensated two-dimensional depth perception, instrument accuracy, and ambidexterity. Three specialized drills were constructed and 60 experienced laparoscopists with advanced operative skills were evaluated. The three skill-assessment tasks were first performed using traditional laparoscopic instrumentation (10-mm laparoscopes, 5-mm accessory instruments). The performance of the study group was compared with an extensive database of over 1000 laparoscopic surgeons from around the world and did not reveal any significant deficits with traditional-size equipment. Next, the tasks were performed using miniature 2-mm laparoscopes and accessory instruments. Performance levels for all tasks were significantly lower than with traditional-size equipment. These results demonstrate the increased difficulty of performing laparoscopy with 2-mm instruments and underscore the importance of formal training and objective skill assessment. The relationship of skill to credentialing must be considered.

Journal Article↗
PubMed2001

Crystallographic autostereograms.

Perspective drawings of crystal structures can be presented as autostereograms (or single-image stereograms), and their performance for in-depth perception is similar or even more advantageous than of stereopairs. The autostereograms offer a convenient means for realistic insight into crystal structures without excessive size reduction of their drawings, as required when preparing stereopairs; thus structures either as simple as elements or as complex as proteins can be illustrated in enhanced resolution. The mathematical background and guidelines for preparing crystallographic autostereograms are described.

Computer Graphics↗
PubMed2000

Seeing in three dimensions: the neurophysiology of stereopsis.

From the pair of 2-D images formed on the retinas, the brain is capable of synthesizing a rich 3-D representation of our visual surroundings. The horizontal separation of the two eyes gives rise to small positional differences, called binocular disparities, between corresponding features in the two retinal images. These disparities provide a powerful source of information about 3-D scene structure, and alone are sufficient for depth perception. How do visual cortical areas of the brain extract and process these small retinal disparities, and how is this information transformed into non-retinal coordinates useful for guiding action? Although neurons selective for binocular disparity have been found in several visual areas, the brain circuits that give rise to stereoscopic vision are not very well understood. I review recent electrophysiological studies that address four issues: the encoding of disparity at the first stages of binocular processing, the organization of disparity-selective neurons into topographic maps, the contributions of specific visual areas to different stereoscopic tasks, and the integration of binocular disparity and viewing-distance information to yield egocentric distance. Some of these studies combine traditional electrophysiology with psychophysical and computational approaches, and this convergence promises substantial future gains in our understanding of stereoscopic vision.

Journal Article↗
PubMedDate not supplied

The transitional process of retirement for nurses.

Retirement exemplifies one of the most important transitions in life. A job provides structure to daily life, adds to a sense of self-worth and self-esteem, and is a means of self-expression, all of which define and identify the person. This work activity links individuals to a society and to a social network. When an individual retires, there is a loss of one role and a beginning of a new one. The purpose of this research was to explore the preretirement period of nurses to better understand the transitional process. A qualitative approach was chosen to enable the researchers to explore in-depth perceptions and opinions of this subjective experience. Interview questions were developed from the literature to determine the perceptions of preparation, barriers, and facilitators in the process, losses, gains, and coping strategies that were helpful. A purposive sample of female nurses from academic institutions and hospitals were invited to participate in one of three focus groups. All were invited to a fourth focus group session during which the findings from the researchers were presented and the participants verified the results. Of the 19 participants, 11 had retired, whereas 8 were in the preretirement phase. Four nurses had accepted an incentive retirement offered at their institution. The conversations were taped, transcribed, and analyzed. Thematic analysis identified both positive and negative aspects of the experience with concerns related to finances, timing of retirement, discretionary time, and relationships. Participants frequently expressed feelings of inadequacy with the numerous decisions related to finances and wished the institution had provided more information. They perceived the most enjoyable gain to be the time to enjoy and do the things they wished. The prevalent feeling among the groups was that the loss of work friends was very difficult. Old relationships would need to be fostered and new ones developed in the retiree role. Based on the findings, support services, including advisers and counselors, are recommended to ease the movement through this transitional process. The assumption is that if individuals have a better understanding of the retirement process and their new role, they will prepare and adjust better.

Adaptation, Psychological↗
PubMedDate not supplied

Color constancy by asymmetric color matching with real objects in three-dimensional scenes.

Color matching experiments use, in general, stimuli that are poor representations of the natural world. The aim of this work was to compare the degree of color constancy for a range of illuminant pairs using a new matching technique that uses both real objects and three-dimensional (3-D) real scenes. In the experiment, observers viewed a 3-D real scene through a large beamsplitter that projects on the right-hand side of the scene (match scene), the virtual image of a 3-D object (match object) such it appeared part of the scene. On the left-hand side of the scene (test scene), observers viewed a symmetrical scene containing a test object identical to the match object. Test and match objects were both surrounded by the same reflectances with identical spatial arrangement. The illuminant on the test scene had always a correlated color temperature of 25,000 K. The illuminant on the match scene could be any of seven different illuminants with correlated color temperatures in the range 25,000 K-4000 K. In each trial, the observers, who were instructed to perform surface color matches, adjusted the illuminant on the match object. Constancy indices were very high (0.81-0.93), varied with the color of the match object, and increased with the extent of the illuminant change. Observer's mismatches, however, were independent of the extent of the illuminant change.

Color Perception↗
PubMedDate not supplied

Electrophysiological correlates of human texture segregation, an overview.

'Texture segregation' results from parallel processing in the visual cortex. It occurs when the stimulus contains spatial gradients within a visual dimension. We here present an introductory overview of the field, concentrating on electrophysiological correlates in the human EEG ('tsVEPs') of the neuronal processes underlying texture segregation. We describe the isolation of the tsVEP from the background EEG, give examples of the correlation between saliency and tsVEP amplitude and compare texture segregation between visual dimensions.

Animals↗
PubMed1992

Selective reaching: evidence for action-centered attention.

Most studies of selective attention briefly present static 2-dimensional stimuli and require arbitrary responses such as verbal naming or a keypress. Many of our perceptual-motor interactions with the environment, however, require reaching directly toward an object while ignoring other objects in the scene. A series of experiments examines selective attention in the latter reaching situation. Effects previously observed in the traditional experimental procedures were obtained, suggesting that the models developed (which propose inhibitory mechanisms, e.g.) apply to ecologically valid situations. Attention accesses action-centered internal representations during such tasks.

Adult↗
PubMed1994

Perception of rigid motion in depth from the optical deformations of shadows and occlusion boundaries.

Three experiments were designed to examine the abilities of observers to determine an object's 3-dimensional structure and motion from various types of optical deformations. Observers were required to discriminate whether pairs of moving ellipsoids were rotating rigidly about a single axis or nonrigidly about different axes that varied in slant. Discrimination thresholds were significantly influenced by whether the ellipsoids were intersecting or nonintersecting and whether they contained identifiable texture elements. Performance was unaffected by precession movements of the axis of rotation, by increasing the number of intersecting ellipsoids beyond 2, or by replacing the deforming silhouettes with the projected motions of cast shadows presented in isolation against a planar background. These findings indicate that observers can perceive structure from motion based on several different types of optical deformation, including the deformations of shadows and silhouettes that do not contain identifiable features on which most existing theoretical analyses are designed to operate.

Adult↗
PubMed1997

Selection by color and form in vision.

Whether attention to a local part of a visual display can prevent access to semantic information in form matching tasks with objects was studied. A first picture containing a line segment (the reference) was followed by 2 lateral objects also containing a line segment (a target and a distractor). Participants matched the line segments according to either their orientation or color. Effects of semantic information were assessed by manipulating the semantic relations among the pictures surrounding the reference, target, and distractor. Semantic information affected performance in the orientation matching task, but not in the color matching task. Results suggest the existence of separate selection mechanisms in vision. Selection of local colors for response purposes can be based on inhibition of the form pathway (eliminating semantic effects on matching). Selection within the form pathway can involve a bias toward global shape (the picture). Once attention is allocated to global shape associated semantic representations are activated and semantic effects on matching emerge.

Attention↗
PubMed2000

Attention to object files defined by transparent motion.

Two interspersed and differently colored sets of dots were rotated in opposite directions and were perceived as superimposed transparent surfaces. Probes consisting of brief changes in dot motion direction were reported. Two probes affecting the same surface were discriminated accurately. The 2nd probe was discriminated poorly if it affected a surface different from the 1st and if the time between probes was less than 600 ms. This reflects a difficulty in switching attention rapidly between surfaces. Spatial proximity increased the interference. Controls were incompatible with traditional spatial mechanisms (2- or 3-dimensional) or with simple sensory filters. Instead, probes were apparently selected by object files. The interference is not simply due to an inability to process 2 objects at once but requires close spatial proximity of incompatible motion signals.

Adult↗
PubMed2002

Lower region: a new cue for figure-ground assignment.

Figure-ground assignment is an important visual process; humans recognize, attend to, and act on figures, not backgrounds. There are many visual cues for figure-ground assignment. A new cue to figure-ground assignment, called lower region, is presented: Regions in the lower portion of a stimulus array appear more figurelike than regions in the upper portion of the display. This phenomenon was explored, and it was demonstrated that the lower-region preference is not influenced by contrast, eye movements, or voluntary spatial attention. It was found that the lower region is defined relative to the stimulus display, linking the lower-region preference to pictorial depth perception cues. The results are discussed in terms of the environmental regularities that this new figure-ground cue may reflect.

Cognition↗
PubMed1996

Attribute conjunctions and the part configuration advantage in object category learning.

Five experiments demonstrated that in object category learning people are particularly sensitive to conjunctions of part shapes and relative locations. Participants learned categories defined by a part's shape and color (part-color conjunctions) or by a part's shape and its location relative to another part (part-location conjunctions). The statistical properties of the categories were identical across these conditions, as were the salience of color and relative location. Participants were better at classifying objects defined by part-location conjunctions than objects defined by part-color conjunctions. Subsequent experiments revealed that this effect was not due to the specific color manipulation or the role of location per se. These results suggest that the shape bias in object categorization is at least partly due to sensitivity to part-location conjunctions and suggest a new processing constraint on category learning.

Adult↗
PubMed1996

Cognitive gender differences in very young children parallel biologically based cognitive gender differences in monkeys.

Infant humans were trained on 2 cognitive tests that have previously revealed, in infant monkeys, a double dissociation that was reversible by perinatal manipulations of androgens and ablations of specific brain sites. Children showed the same sex-linked behavior found with infant monkeys: young boys were superior on the object reversal task and young girls were superior on the concurrent discrimination task. As happened previously with infant monkeys, the gender difference was not apparent in older human subjects. Thus, early in ontogeny, cognitive gender differences have now been discovered in both humans and monkeys, probably a result of gender differences in androgens that influence the maturation rate of specific brain systems.

Adolescent↗
PubMed1991

Visual/cognitive correlates of vehicle accidents in older drivers.

Older drivers have more accidents per miles driven than any other age group and tend to have significant impairments in their visual function, which could interfere with driving. Previous research has largely failed to document a link between vision and driving in the elderly. We have taken a comprehensive approach by examining how accident frequency in older drivers relates to the visual/cognitive system at a number of levels: ophthalmological disease, visual function, visual attention, and cognitive function. The best predictor of accident frequency as recorded by the state was a model incorporating measures of early visual attention and mental status, which together accounted for 20% of the variance, a much stronger model than in earlier studies. Those older drivers with a visual attentional disorder or with poor scores on a mental status test had 3-4 times more accidents (of any type) and 15 times more intersection accidents than those without these problems.

Accidents, Traffic↗
PubMed2006

The time course of perception and retrieval in matching and recognition.

A four-part experiment was carried out to study the relationship between the time course of object-feature perception and the time course of retrieval of object information from memory. The experiment consisted of 2 perceptual matching tasks, and 2 perceptual recognition tasks. In all 4 tasks, participants provided speeded judgments of the identity of 2 objects. A stochastic feature-sampling model was used to estimate the time needed for feature perception and the time needed for retrieval of feature information. No evidence was found for a systematic relationship between perception times and retrieval times for individual features. Indeed, the model applications indicated that retrieval times were constant for different features, whereas perception rates varied across the features.

Adolescent↗