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Results for “Vision, Monocular”

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PubMed1999

The use of vergence information in the programming of prehension.

Human prehension requires accurate information on the properties of an object and on the position of the object relative to the body. In principle, prehension might be more accurate with binocular rather than monocular vision. Previous studies have shown that the kinematics of prehension are altered when one eye is covered. Unfortunately, the source of the useful binocular information cannot be established using this approach. In the current study, we used a perturbation technique to explore whether the human nervous system uses a signal from vergence in prehension. Perturbing vergence caused predictable changes in the kinematics of prehension. Our results thus provide clear evidence that the nervous system uses vergence information in the programming of prehensile movement.

Adult↗

PubMed2006

Epistemology of visual imaging in endoscopic surgery.

Little work has been done on aspects of visual perception and related defects as they affect the proficiency level for endoscopic surgery, in which the surgeon must operate from images rather than reality (indirect perception). Newer metrics of image quality should be used to assess image displays for endoscopic surgery because they provide more objective data. Ergonomic considerations relating to operations from images have likewise been inadequately researched. The monitor optimal working distance is highly variable from surgeon to surgeon. This problem could be overcome easily by the use of floor markings. Data from visual ergonomic experimental studies indicate that the best performance in endoscopic surgery is obtained by frontal gaze-down viewing because this restores the alignment of the visual with the motor axes of the operator.

Attention↗

PubMed2006

Multiple landmarks, the encoding of environmental geometry and the spatial logics of a dual brain.

A series of place learning experiments was carried out in young chicks (Gallus gallus) in order to investigate how the geometry of a landmark array and that of a walled enclosure compete when disoriented animals could rely on both of them to re-orient towards the centre of the enclosure. A square-shaped array (four wooden sticks) was placed in the middle of a square-shaped enclosure, the two structures being concentric. Chicks were trained to ground-scratch to search for food hidden in the centre of the enclosure (and the array). To check for effects of array degradation, one, two, three or all landmarks were removed during test trials. Chicks concentrated their searching activity in the central area of the enclosure, but their accuracy was inversely contingent on the number of landmarks removed; moreover, the landmarks still present within the enclosure appeared to influence the shape of the searching patterns. The reduction in the number of landmarks affected the searching strategy of chicks, suggesting that they had focussed mainly on local cues when landmarks were present within the enclosure. When all the landmarks were removed, chicks searched over a larger area, suggesting an absolute encoding of distances from the local cues and less reliance on the relationships provided by the geometry of the enclosure. Under conditions of monocular vision, chicks tended to rely on different strategies to localize the centre on the basis of the eye (and thus the hemisphere) in use, the left hemisphere attending to details of the environment and the right hemisphere attending to the global shape.

Animals↗

PubMed1987

Vertical and horizontal visual whole-field motion differently affect the metabolic activity of the rat medial terminal nucleus.

The metabolic activity of the medial terminal nucleus (MTN) of the Accessory Optic System was studied by means of the [14C]2-deoxyglucose (2-DG) method in Long-Evans rats exposed to moving and stationary visual stimuli. In particular we explored the rate of local cerebral glucose utilization (LCGU) and the spatial distribution of 2-DG uptake within MTN related to visual stimuli capable of triggering optokinetic nystagmus. It was found that increases in MTN metabolism accompanied the retinal slip signals evoked by whole-field visual patterns moving in the vertical as well as in the horizontal direction. At the same level of luminous flux neither the same but stationary pattern, nor constant, diffuse illumination were able to elicit comparable changes in MTN metabolic rates. The effects of vertical and horizontal motions differed, however, from each other. In binocular testing LCGU rates resulted significantly higher after vertically moving patterns and upon the same stimulus condition the spatial distribution of 2-DG matched very closely the spatial distribution of the retinal afferents and the cellular density within MTN, in sharp contrast with the diffuse spreading out of the label across the nucleus following horizontal motion. In monocular testings only the vertically moving patterns were able to increase LCGU rates significantly and then in contralateral MTN alone. However, comparison between the levels of glucose consumption measured in binocular and in monocular vision also showed the involvement of the uncrossed retinal path in relaying the retinal slip signals to MTN. No difference in LCGU and in spatial distribution of the label were finally observed in relation to the upward or to the downward direction of the moving pattern.

Animals↗

PubMed1985

Suprathreshold contrast perception at different luminance levels.

Magnitude estimation experiments show that the perceived contrast of sine waves is a linear function of stimulus contrast at some mean luminance (Lm), spatial frequency and contrast levels, but not at others. For monocular vision at both low and high contrast levels, linearity is observed within a limited zone which, at high Lm levels, does not include intermediate frequencies. Binocular vision gives similar results at high contrast levels, while for low levels, the linearity zone comprises intermediate frequencies in a wide Lm range. It is demonstrated that if a threshold correction is introduced into the obtained psychophysical functions, the described linearity zones extend to wider Lm and contrast ranges.

Adult↗

PubMed1982

Behavioral recovery from binocular deprivation in the cat.

Visuo-motor behavior and visual acuity were assessed in animals who experienced monocular vision after a prolonged period of binocular deprivation. In animals who experienced initial binocular suture, there was limited recovery and no difference between the initially opened and late opened eye. In animals who experienced initial dark-rearing, the initially opened eye recovered to normal levels and the late opened eye showed severe amblyopia. These differences in behavioral recovery between dark-rearing and binocular suture are compared with physiological differences between the two rearing conditions.

Animals↗

PubMed1986

Sex differences in latencies of bilateral electrodermal responses.

The present study examined sex differences in the latencies of bilateral electrodermal responses to stimuli presented in monocular vision. The stimuli were spatial-emotional, verbal-emotional, spatial-neutral and verbal-neutral slides, presented for either 35 ms or 1 s. Subjects were 15 males and 15 females. Bilateral latencies were not influenced by type of stimulus or by right/left hemisphere stimulation, which is in keeping with the most recent findings of bilateral electrodermal activity studies. However, females gave a faster right hand than left hand response and appeared to be more lateralized than males. Males showed shorter latencies on the left hand than on the right. These results confirm the importance of gender in experiments using the bilateral recordings of electrodermal activity.

Adolescent↗

PubMed2004

Eye position affects orienting of visuospatial attention.

The ability to detect an incoming visual stimulus is enhanced by knowledge of stimulus location (orienting of visuospatial attention). Although the brain mechanisms at the basis of this enhancement are not yet fully clarified, there is evidence that orienting of attention is accompanied by the activation of oculomotor circuits. It remains unclear, however, whether this oculomotor activity is an epiphenomenon or is functionally related to the attentional process. Attentional benefits are usually measured by the classical Posner paradigm. When subjects fixate centrally and are requested to detect a visual stimulus that could appear in an attended or unattended location, they react faster to stimuli appearing in the attended one. Here, we demonstrate that in monocular vision visuospatial attention was significantly modulated by the position of the eye in the orbit. When the screen was placed 40 degrees to the right or to the left of subjects' sagittal plane, attentional benefits for stimuli appearing in subjects' temporal spatial hemifield dramatically decayed, even if the retinal stimulation was exactly the same as in the classical paradigm. The finding that eyes and attention show a common limit stop point supports their close functional coupling.

Attention↗

PubMed2006

Microsaccades counteract visual fading during fixation.

Our eyes move continually, even while we fixate our gaze on an object. If fixational eye movements are counteracted, our perception of stationary objects fades completely, due to neural adaptation. Some studies have suggested that fixational microsaccades refresh retinal images, thereby preventing adaptation and fading. However, other studies disagree, and so the role of microsaccades remains unclear. Here, we correlate visibility during fixation to the occurrence of microsaccades. We asked subjects to indicate when Troxler fading of a peripheral target occurs, while simultaneously recording their eye movements with high precision. We found that before a fading period, the probability, rate, and magnitude of microsaccades decreased. Before transitions toward visibility, the probability, rate, and magnitude of microsaccades increased. These results reveal a direct link between suppression of microsaccades and fading and suggest a causal relationship between microsaccade production and target visibility during fixation.

Adult↗

PubMed2004

Transposition of the anterior superior oblique insertion as a treatment for excyclotorsion induced from limited macular translocation.

PURPOSE: To evaluate the transposition of the anterior superior oblique insertion as a treatment for cyclovertical diplopia accompanied by an awareness of tilted image perceived with the affected eye induced from limited macular translocation (LMT). DESIGN: Observational case series. METHODS: Transposition of the anterior part of the superior oblique tendon combined with or without vertical muscle surgery on the affected eye was retrospectively studied in seven patients. Clinical outcome was assessed for binocular and monocular vision. A successful result was defined as restoration of single binocular vision (SBV) at distance and near examined with the Bagolini test with disappearance of a tilted image perceived in the affected eye. RESULTS: Six of seven patients (86%) became unaware of tilted image, and three patients (43%) obtained successful results after the strabismus surgery. Of these three patients with successful results, one (33%) patient recognized metamorphopsia, whereas two (67%) of the three patients with unfavorable results reported metamorphopsia. Patients with successful results showed a visual acuity of 20/25 or better in the affected eye and a significantly smaller difference in visual acuity between the two eyes than those patients with unfavorable surgical results (0.133 logarithm of the minimal angle of resolution for SBV(+) vs 0.675 logarithm of the minimal angle of resolution for SBV(-); P =.0255). CONCLUSIONS: The relatively low success for restoration of SBV indicates that strabismus surgery is recommended for patients whose difference in visual acuity between the two eyes is small and who have a high level visual acuity of the affected eye.

Adult↗

PubMed1980

A fiberoptic fixation target for tonography.

Substituting a fiberoptic core for the standard Müller tonography plunger provides a fixation target for tonography. The fiberoptic is particularly useful for testing patients who are difficult to examine with the conventional plunger (those with monocular vision, phoriatropia, and the like).

Fiber Optic Technology↗

PubMed1991

Effects of flashing-diffuse light on [2-14C]deoxyglucose uptake in the visual system of the black-hooded rat.

What components of the visual system process diffuse light information? A [2-14C]deoxyglucose (2-DG) autoradiographic analysis revealed that exposure of freely moving rats (wearing light-diffusing masks) to flashing-diffuse light consistently elevated 2-DG uptake in the lateral geniculate nucleus and superior colliculus to levels rivalling those occurring in rats exposed to flashing-gratings. Uptake in visual cortex (area 17) in response to flashing-diffuse light, however, varied as a function of early contour experience, i.e. lower than that produced by darkness in rats reared with high contrast patterns, higher than darkness in rats which had been lid-sutured from the time of eye opening, and falling between these two extremes in 'ordinary' cage-reared rats. The findings point to subcortical mediation of discriminations based on diffuse light information. Cortex might participate in the processing of diffuse light information in the special case of animals lacking contour experience during development.

Animals↗

PubMed1980

Conditional discrimination training and interocular transfer in pigeons.

Four groups of pigeons were trained either monocularly or binocularly on a series of successive line orientation discriminations. The role in interocular transfer of both changes in viewing conditions and background cues was examined. Either red or green background illumination to the patterns was used as changes in background cues; whereas alterations in viewing conditions were obtained by transferring from binocular to monocular vision, or from the left to the right eye. The results suggest that the viewing condition can operate in the same way as an external cue does for a conditional discrimination. This finding provides an explanation of the learning of conflicting discriminations with each eye by animals that also show interocular transfer.

Animals↗

PubMed2002

Permanent blue discoloration of a hydrogel intraocular lens by intraoperative trypan blue.

A 79-year-old white man had cataract surgery in the right eye with implantation of an Acqua intraocular lens (IOL) (Mediphacos). Trypan blue 0.1% was used during surgery to stain the anterior capsule and enhance the contrast during capsulorhexis. Seven days after surgery, the patient presented with "dark and double" vision (monocular diplopia). The IOL was decentered superiorly and appeared dark blue. The lens was explanted 2 months after surgery and sent for gross and microscopic analyses in a dry state and after hydration. The same analyses were performed on 2 unused lenses of the same design that had been immersed in diluted trypan blue solutions (0.01% and 0.001%). On the explanted lens, the dark blue staining was denser in the optic, especially in its periphery. The blue discoloration could not be removed after 24 hours of lens immersion in a balanced salt solution at 37 degrees C. Permanent staining of the unused lenses was also obtained after immersion in the trypan blue solutions.

Aged↗

PubMed1999

Cortical plasticity: is it time for a change?

Classical studies of plasticity in the visual cortex have been interpreted in terms of heterosynaptic competition between inputs. But an alternative type of 'homosynaptic' plasticity can explain many recent observations and has recently received experimental support. Perhaps both types of plasticity are important.

Animals↗

PubMed1989

Photic responses of geniculo-hypothalamic tract neurons in the Syrian hamster.

The putative neural pacemaker controlling circadian rhythms in mammals is contained in the suprachiasmatic nuclei of the hypothalamus. These nuclei receive a projection, the geniculo-hypothalamic tract (GHT), from neurons in the intergeniculate leaflet (IGL) and portions of the ventral lateral geniculate nucleus (vLGN) of the thalamus. We examined the responses of putative GHT neurons to diffuse illumination using extracellular electrophysiological recordings. The great majority of IGL neurons showed sustained ON responses to diffuse retinal illumination; vLGN neurons showed more variation in their responses. Discharge rates of sustained ON neurons increased monotonically as light intensity was increased and saturated over 2-3 log units of intensity changes. Many IGL neurons had binocular input, and input from the ipsilateral eye was often inhibitory. These results indicate that GHT neurons may provide information about ambient light intensity to the suprachiasmatic nuclei.

Animals↗

PubMed1991

Directional dependence of intraocular transfer of stimulus detection in pigeons (Columba livia).

The eyes of the pigeon (Columba livia) are positioned laterally in the head. Thus, there is only a small area of binocular overlap, which constitutes the frontal visual field and a large area of monocular vision in the lateral visual fields. The conditions were examined under which intraocular transfer occurs in pigeons; that is, the transfer of information between both portions of the visual field of one eye. Different groups of head-fixed birds learned to discriminate the presence of a bright light from its absence in an instrumental conditioning situation with water as reinforcer. After the animals had acquired the task when the stimuli were viewed in either the frontal or lateral visual field, the stimuli were moved into the converse visual field. Transfer was shown to be directionally selective: It occurred when stimulus presentation was changed from the lateral to the frontal visual field but not when this change was in the opposite direction.

Animals↗

PubMed2005

Incidence of visual loss in the Ponza Eye Study, Italy.

AIM: To study the incidence of visual loss over a 12-year period in the survivors of an original cohort aged 40 years or older at baseline. METHODS: Visual acuity (VA) was measured by means of a standardized logMAR chart. World Health Organization definition of blindness and low vision was adopted (respectively, best-corrected VA >1.3 logMAR or a visual field <10 degrees around central fixation, and best-corrected VA >0.5-1.3 logMAR or a visual field <20 degrees around central fixation). Moreover, binocular visual loss incidence (VA>0.5 logMAR) was calculated in a 'healthy' group who had uncorrected VA of 0.0 logMAR or better in both eyes at baseline and absence of eye diseases. RESULTS: Of the 584 eligible survivors, 411 (70.7%) had a 12-year follow-up visit. The overall incidence figures were as follows: best-corrected binocular blindness (0.7%), binocular low vision (3.9%), monocular blindness (2.7%), and monocular low vision (5.0%), respectively. The results for presenting VAs were 1.2, 9.5, 4.2, and 15.3%. Figures for uncorrected, best-corrected, and presenting binocular visual loss incidence in the 'healthy' group were respectively 12.7, 0.9, and 3.7%. CONCLUSION: The discrepancy between the ideal and real situations that emerges from this study has important implications for health-care planning. Over a period of 12 years, a substantial percentage of 'healthy' subjects will have to seek medical care. Incident visual loss was caused mainly by untreated cataract, glaucoma, myopia, and age-related macular degeneration.

Adult↗