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PubMed2001

The processing of stereoscopic information in human visual cortex: psychophysical and electrophysiological evidence.

Three-dimensional depth perception relies in part on the binocular fusion of horizontally disparate stimuli presented to the left and right eye. The mammalian visual system offers a unique possibility to study electrophysiologically cortical neuronal mechanisms: since the input of the two eyes remains separated up to the level of the visual cortex, evoked potential components that are generated exclusively by cortical structures may be explored when dynamic random-dot stereograms (dRDS) are presented. In a series of independent studies, we determined the scalp topography of dRDS evoked brain activity in different groups of healthy subjects, and we found consistent results. Major differences between stereoscopic and contrast evoked brain activity are seen in the strength of the potential fields as well as in their topography. Our findings suggest that there are fewer neurons in the human visual cortex that are responsive to horizontal disparity, and that higher visual areas like V2 are more engaged with stereoscopic processing than the primary visual cortex. On the other hand, component latencies of evoked brain activity show no effect signifying that the binocular information flow to the visual cortex has a similar time course for both the processing of contrast information and of dRDS stimuli. We could also verify that healthy subjects can learn to perceive 3D structure contained in dRDS. Changes in perceptual ability as measured with psychophysical tests are paralleled by systematic alterations in the topography of stereoscopically evoked potential fields. Stereoscopic VEP recordings may also be of clinical use: in patients with selectively disturbed depth perception but normal visual acuity there is a high correlation between clinical symptoms, perceptual deficiency, and altered VEP amplitudes and latencies.

Brain Mapping↗
PubMed2000

[The effect of attention on visual evoked potentials elicited by a newly designed stereogram].

PURPOSE: To investigate whether the visual evoked potentials (VEPs) obtained by a newly designed stereogram were generated by some higher function like depth perception, we examined the effect of attention on the VEPs. SUBJECTS AND METHOD: Eight subjects participated in the experiments. The VEPs were recorded according to the international 10/20 system. The stimulus consisted of circles with or without disparity presented on 4 locations around the fixation point, and they appeared in one of 3 patterns in random order when viewed through red/green spectacles 1. at the same distance as the fixation point, 2. in front of it, or 3. at the back of it. The near pattern was defined as the target. In Experiment 1, the subjects just fixated on the fixation point. In Experiments 2 and 3, they were required to respond to the target by pressing a button and counting the number (target discrimination task). RESULTS: A scalp negative potential with a latency of 170-280 msec was elicited in the lateral occipital area. For each of the 3 patterns the amplitude was greater in Experiments 2 and 3 than in Experiment 1. In Experiments 2 and 3, stimuli with disparity resulted in larger amplitude than without disparity. The target stimulus also evoked larger potentials than non-target stimuli did, although no such effect was apparent in Experiment 1. CONCLUSION: Attention, as well as disparity, increased the VEPs amplitude, which indicates that the potential could be generated by neural activity higher than V 1 including depth perception. Moreover, the potential showed characteristics similar to attention-related potentials modulated by visuo-spatial attention.

Adult↗
PubMed2000

Influence of two-dimensional and three-dimensional imaging on endoscopic bowel suturing.

Several three-dimensional (3-D) video-endoscopic systems have been introduced in surgical practice to enhance depth perception during minimal access surgery (MAS), but the facilitation of endoscopic manipulations by the current 3-D systems remains unproved. The aim of the study was to investigate the influence of 2-D and 3-D imaging modalities on intracorporeal suturing. The standard task consisted of suture closure of 60 mm enterotomies made in porcine small bowel with continuous seromuscular 3/0 Polysorb. Ten experienced surgeons participated in the study. The imaging systems were Storz (2-D), Welch Allyn (3-D), and Zeiss (as both 2-D and 3-D). Each surgeon performed two tasks with each modality in a random sequence. The outcome measures were execution time, suture line leakage pressure, and suture placement score. In addition, the participating surgeons assigned subjective scores on the image quality and the adverse effects of the imaging systems. There was no significant difference in the execution time, leakage pressure, and suture placement score among the various imaging modalities. Depth perception was rated as similar with 2-D and 3-D imaging. Surgeons experienced visual strain with the three systems, but it was rated higher with 3-D imaging. With the current technology, we have not documented any significant difference in task efficiency and quality of endoscopic bowel suturing by trained surgeons between 2-D and 3-D imaging systems.

Analysis of Variance↗
PubMed2004

Sensitivity to linear-speed-gradient of radial expansion flow in infancy.

A radial expansion flow having a linear-speed-gradient (linear-grad) creates robust perception of a rigid object moving-in-depth [Perception 19 (1990) 21]. It has been reported that sensitivity to a linear-grad of radial expansion emerges at 2 months of age [Infant Behavior and Development 17 (1994) 165]. In the present study, we examined the development of sensitivity to the linear-grad of radial expansion after 2 months of age with three experiments. A total of 197 2- to 5-month-old infants participated. The results showed that sensitivity to the linear-grad improves between 2 and 3 months of age (Experiment 1), and that the infants may discriminate between an expansion having linear-grad and that having zero-grad based on their perception of motion-in-depth (Experiments 2 and 3).

Aging↗
PubMed2003

Vision screening practices in central Iowa: a follow-up evaluation.

In response to data from the initial survey published in October 2001, interventions were developed to increase vision screening knowledge and promote use of the Iowa Vision Screening Program Guidelines. The purpose of this evaluation was to measure differences in practice after interventions, including attendance at a half-day workshop and practice session. Results of the study indicate that participants of the workshop and practice session were more likely to conduct yearly distance and near vision, and depth perception screening. In addition, they were more likely to use the recommended screening instruments for distance and near vision, and depth perception. They were also much more likely to use recommended referral criteria for all types of screening and to have changed some aspect of their vision screening practice in the past year. Results are presented with implications for school nursing practice.

Child↗
PubMed2000

Local disparity not perceived depth is signaled by binocular neurons in cortical area V1 of the Macaque.

Binocular neurons that are closely related to depth perception should respond selectively for stimuli eliciting an appropriate depth sensation. To separate perceived depth from local disparity within the receptive field, sinusoidal luminance gratings were presented within a circular aperture. The disparity of the aperture was coupled to that of the grating, thereby rendering unambiguous the psychophysical matching between repeating cycles of the grating. In cases in which the stimulus disparity differs by one horizontal period of the grating, the portion of the grating that locally covers a receptive field is binocularly identical, but the depth sensation is very different because of the aperture. For 117 disparity-selective V1 neurons tested in two monkeys, the overwhelming majority responded equally well to configurations that were locally identical but led to different perceptions of depth. Because the psychophysical sensation is not reflected in the firing rate of V1 neurons, the signals that make stereo matches explicit are most likely elaborated in extrastriate cortex.

Animals↗
PubMed1979

Three-dimensional display of ultrasonic images using a fly's-eye lens.

In order to form a three-dimensional image from a set of two-dimensional cross-sectional ultrasonic images, a simple method making use of a fly's-eye lens in proposed. The depth perception obtained from the reconstructed image using the fly's-eye lens is analysed and an optical configuration that maximizes the depth perception is devised. With this configuration, the synthesis of a three-dimensional image is performed by using a simple object. Results of the experiment show clearly the three-dimensional aspect of the reconstructed image.

Data Display↗
PubMed2002

Conditions under which stereopsis and motion perception are blind.

We describe modified random-dot stereograms in which the corresponding elements differ from non-corresponding elements in colour, size, and luminance. Despite these visible differences between the elements, depth perception collapses when the spatially integrated luminous flux is similar for the corresponding and non-corresponding elements. Our results suggest that a low-pass spatial filter precedes the mechanism that recognises disparity. A similar phenomenon is observed for the perception of coherent motion in random-dot kinematograms. Our modified stereograms and kinematograms may find other uses when experimenters wish to study the contribution of colour to visual processes and require a method of eliminating edge artifacts.

Adult↗
PubMed2003

Stereoscopic vision: solving the correspondence problem.

Neurons in early visual areas respond to horizontal disparity in images that do not give rise to stereopsis. False binocular matches, however, are discarded at the apex of the visual pathway: the activity of neurons in the primate inferior temporal cortex correlates directly with conscious depth perception.

Animals↗
PubMed1994

Quantitative stereoscopic depth without binocular correspondence.

What features in a stereogram define the disparities that lead to stereoscopic depth? The usual answer is that luminance-defined edges from the two eyes are matched and produce depth perception. But parts of an object may be occluded by other objects and absent from one eye's view. It was suggested that unpaired monocular elements might signal occlusion in depth, and the qualitative perception of depth associated with unmatched elements has been shown to be consistent with the geometry of occlusion. We designed a stereogram that simulates a particular occlusion situation: an opaque white rectangle is stereoscopically in front of a large black rectangle pasted on a white background. The position of the occluder is adjusted so that its left edge obscures the left-hand edge of the black rectangle in the right eye view and its right edge obscures the right-hand edge of the black rectangle in the left eye view. We report here that quantitative stereopsis can be seen from this stereogram, even though there are no binocular corresponding luminance edges to match.

Depth Perception↗
PubMed2002

Imaging for endoscopic surgery: new developments applicable to pediatric surgical interventions.

To introduce pediatric surgeons to new developments in imaging that are already or soon to become available that permit "in-line" work and three-dimensionality, five new approaches to imaging were evaluated in 419 children over a 3-year period: (1) Image projection onto the abdomen (n = 4). As opposed to conventional video camera positions, with this modality the line of view and the line of work are aligned. (2) Image projection onto a plate mounted just above the abdomen (n = 280). As in the first approach, screen arrangement position obviates looking up at the monitor. (3) A touch screen mounted above the abdomen, enabling the surgeon to not only monitor the procedure, but also to control all the equipment (n = 128). As with the first two modalities, the line of view is aligned with the direction of the work. (4) A three-dimensional (3-D) head display (n = 6). With this approach the use of a headset is required. (5) A 3-D screen (n = 1) for which, no goggles or headsets are required. The 3-D picture can be appreciated from a wide angle of view, and thus can be used by the surgeon and assisting team. Direct imaging projection onto the abdominal surface is a visual process that at present is too complicated for routine surgery. Projection onto a flat plate or touch screen is a major improvement; the surgeon looks and works in the same direction. Headsets for 3-D imaging remain heavy and the image is not as sharp as that provided by two-dimensional monitors. The most significant practical progress was felt to be with the flat 3-D monitor because with this equipment, depth perception and ergonomic positioning were both rated as very good. New imaging modalities are exciting, albeit still in their early developmental stages. The novel imaging provided by a 3-D monitor is most promising, because it combines good depth perception with physiologic in-line visual-manual coordination. These developments should further facilitate the transition from conventional, open techniques to videoscopic approaches.

Adolescent↗
PubMed2003

Vision and driving self-restriction in older adults.

OBJECTIVES: To assess driving self-restriction (vision related and nonvision related) in relation to vision test performance of older adults. DESIGN: Cross-sectional study. SETTING: Population-based cohort of community-dwelling older adults. PARTICIPANTS: Six hundred twenty-nine current drivers aged 55 and older had driving behavior, health, and physical function assessed and vision function tested in 1993-95. MEASUREMENTS: Self-report of driving restriction as vision or non-vision related and performance on a comprehensive battery of vision tests (visual acuity; contrast sensitivity; effects of illumination level, contrast, and glare on acuity; visual fields with and without attentional load; color vision; temporal sensitivity; and the effect of dim light on walking ability). RESULTS: Demographic, health, and functional characteristics differed significantly between restrictors and nonrestrictors but not between vision- and nonvision-related restrictors. Controlling for potential confounding, only vision-related driving self-restriction was significantly associated with reduced performance on nonstandard measures of acuity. Poor depth perception was significantly associated with restriction for both vision- and nonvision-related reasons. Poor performance on attentional visual field tests, analyzed individually and in combination with standard field tests, was not associated with driving self-restriction. CONCLUSION: Older adults with early changes in spatial vision function and depth perception appear to recognize their limitations and restrict their driving even if they do not acknowledge the visual impairment as the cause for restriction. Poor visual attention, a risk factor for crashes, may not be recognized. Additional studies of driving self-restriction in relation to risk factors for crashes in older adults may help refine this strategy of reducing driving-related injury and death.

Aged↗
PubMed2000

Surface integration influences depth discrimination.

Image fragments arising from partial occlusion may be perceptually unified by a surface integration process on the basis of similar color or texture. In a new objective measure pitting surface feature similarity against binocular disparity, observers discriminated whether a colored circle had either crossed or uncrossed disparity relative to a surrounding gray rectangle. Sensitivity to disparity was impaired only when (1) the configuration of the other surface fragments in the display supported the integration of a surface behind the rectangle and circle, and (2) matched the color of the central circle. Results were consistent with the hypothesis that a surface integration process integrated similarly-colored surface fragments into a smooth surface, even when those fragments were at different depths. Surface integration caused small and reliable effects on depth perception despite unambiguous disparity information. Perceived depth does not depend solely upon disparity, and may be determined after three-dimensional figural unity is established.

Color Perception↗
PubMed1992

Modulation of neural stereoscopic processing in primate area V1 by the viewing distance.

Accurate binocular depth perception requires information about both stereopsis (relative depth) and distance (absolute depth). It is unclear how these two types of information are integrated in the visual system. In alert, behaving monkeys the responsiveness of a large majority of neurons in the primary visual cortex (area V1) was modulated by the viewing distance. This phenomenon affected particularly disparity-related activity and background activity and was not dependent on the pattern of retinal stimulation. Therefore, extraretinal factors, probably related to ocular vergence or accommodation, or both, can affect processing early in the visual pathway. Such modulations could be useful for (i) judging true distance and (ii) scaling retinal disparity to give information about three-dimensional shape.

Animals↗
PubMed2000

Relation of impairment to everyday competence in visual disorientation syndrome: evidence from a single case study.

OBJECTIVE: To determine the relation of neurology and neuropsychology to everyday competence. DESIGN: The association of these three domains was investigated using a single case multiple baseline design with two phases. Phase A comprised 6 weeks that coincided with an inpatient admission. Phase B comprised 3 months spent at home. A battery of visual spatial tests was completed every fortnight during the A phase and at the end of the B phase. Two new tests of relevant neurologic function with control data were developed and used weekly during the A phase and at the end of the B phase. The first test recorded the speed, accuracy, and efficiency of her walking, and the second test recorded her depth perception. SETTING: Tertiary care center. PARTICIPANT: A 35-year-old woman who suffered a venous sinus thrombosis with visual disorientation syndrome. RESULTS: During Phase A, she achieved significant functional gains in mobility, dressing, bathing, and domestic tasks, in the context of unchanging psychometric test scores and static relevant neurologic function. During Phase B, she achieved few functional gains, despite improvements in neurologic status, demonstrated by depth perception. CONCLUSIONS: Everyday function can progress without improvement in neurologic and cognitive status.

Activities of Daily Living↗
PubMed2005

Bilateral total knee arthroplasty increases the propensity to trip on an obstacle.

Tripping over an obstacle is the most frequent cause of falls. We examined the effects of total knee arthroplasty on obstacle avoidance success rates in older adults. Obstacle avoidance success rates, body mass index, visual acuity, contrast sensitivity, depth perception, and single-leg stance duration were evaluated in 29 subjects who had bilateral total knee arthroplasties (age range, 72.6 +/- 5.4 years) and 27 age-matched healthy control subjects (age range, 70.6 +/- 5.5 years). The patients who had total knee arthroplasties had a lower obstacle avoidance success rate, lower single-leg stance duration, and greater body mass index than control subjects. Age, contrast sensitivity, and depth perception were not different between patients who had total knee arthroplasties and control subjects. Obstacle avoidance success rates decreased linearly as single-leg stance duration decreased in the control group and across all groups, but not in the group that had total knee arthroplasties. Linear relationships between obstacle avoidance success rates and body mass index existed for all subjects but not for the group that had total knee arthroplasties or the control group individually. Total knee arthroplasty reduces obstacle avoidance success rate, suggesting that persons who have total knee arthroplasties have an increased propensity to trip on an obstacle and fall. Increased body mass index and decreased single-leg stance duration in patients who have total knee arthroplasties are associated with a decreased obstacle avoidance success rate.

Accidental Falls↗
PubMed1992

Variability in behavioral impairment involved in the rising and falling BAC curve.

The purpose of this pilot study was to measure variability in behavior impairment at specific levels of the rising and falling blood alcohol concentration (BAC) curve. Behavior impairment was measured for anticipation and reaction time in addition to a variety of visual skills. Also of interest was the variability in impairment involved at specific BAC levels under single-dose and double-dose conditions. The experimental design was a variation on a 2 x 2 factorial with repeated measures on the dose of alcohol. All subjects took part in two experimental sessions, single-dose and double-dose. Sixteen (8 male and 8 female) paid subjects ages 21-40 participated in the study. Testing procedures included repeated measures on reaction time, anticipation time, perceptual vision acuity and depth perception. Breath-alcohol measures were sampled continuously at 5-minute intervals and used to plot absorption time, peak BAC and elimination time. Results showed that the average peak BAC for the double-dose was significantly higher than that of the single-dose condition. However, there were no significant differences between the single-dose and double-dose condition in either absorption time or elimination time. The performance pattern for reaction time, anticipation time and depth perception showed more impairment in the rising BAC limb than in the falling BAC limb. It is noteworthy that specific individuals exhibited different levels of impairment at a given BAC level, depending on whether the session was single- or double-dose, suggesting that one's current BAC level is less a measure of impairment than is the total quantity of alcohol consumed. A follow-up procedure to examine practice effects was conducted on eight volunteer students. Identical testing procedures, using no alcohol, produced no significant practice effects after a 3-hour period.

Adult↗