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PubMed1996

Visual stabilization of posture in persons with central visual field loss.

PURPOSE: To determine whether people with central visual field loss (CFL) show a smaller visual contribution to posture stabilization than people with normal vision and to determine the visual factors that predict the magnitude of visual stabilization in people with central visual field loss. METHODS: Posture information was recorded in 19 subjects with CFL and in 20 subjects with normal vision. Data were collected as the subject stood in a dark environment and also as he or she viewed a stationary visual display. In both conditions, somatosensory feedback was concurrently altered. The central visual fields of the subjects with CFL were measured by static perimetry with the confocal scanning laser ophthalmoscope. Binocular visual acuity and contrast sensitivity were measured on all subjects using the ETDRS and Pelli-Robson charts, respectively. Image-displacement thresholds were measured in a subset of the subjects. RESULTS: On average, subjects with central field loss showed a smaller visual contribution to posture stabilization than subjects with normal vision. The reduction in sway caused by visual stimuli was only 29% for the subjects with CFL compared to 41% for the subjects with normal vision. Displacement thresholds accounted for 45% of the variance in the visual stabilization magnitude of the subjects with CFL. No other visual factor significantly increased the coefficient of determination. CONCLUSIONS: The visual self-motion cues generated by small body oscillations may be undetectable and, thus, unusable as cues to postural sway by people with central field loss.

Aged↗
PubMed2004

Visual memory and visual perception recruit common neural substrates.

This human neuroimaging review aims to determine the degree to which visual memory evokes activity in neural regions that have been associated with visual perception. A visual perception framework is proposed to identify cortical regions associated with modality-specific processing (i.e., visual, auditory, motor, or olfactory), visual domain-specific processing (i.e., "what" versus "where," or face versus visual context), and visual feature-specific processing (i.e., color, motion, or spatial location). Independent assessments of visual item memory studies and visual working memory studies revealed activity in the appropriate cortical regions associated with each of the three levels of visual perception processing. These results provide compelling evidence that visual memory and visual perception are associated with common neural substrates. Furthermore, as with visual perception, they support the view that visual memory is a constructive process, in which features or components from disparate cortical regions bind together to form a coherent whole.

Cerebral Cortex↗
PubMed1994

Visual imagery and visual representation.

Among many controversies in visual neuroscience is whether visual imagery of objects, scenes and living beings is based upon contributions of the early visual areas or depends on hierarchical higher visual areas only, and whether the cortical areas subserving visual imagery are identical to those underlying visual perception. These questions are important for furthering our understanding of vision, since areas active in visual imagery might tell us how the visual cortex represents objects, scenes and living beings. Here, P.E. Roland and B. Gulyás present their hypothesis, based on experimental evidence in man and primates, that the visual areas subserving visual imagery are parieto-occipital and temporo-occipital visual association areas, and that these areas form only a subset of the visual areas engaged in perception. This hypothesis is consistent with the view that objects, scenes and living beings are represented, stored and re-evoked outside the domain of the primary visual cortex and its immediate neighbours.

Animals↗
PubMed2005

Visual acuity and the causes of visual loss in a population-based sample of 6-year-old Australian children.

PURPOSE: To describe the distribution of visual acuity and causes of visual loss in a representative sample of Australian schoolchildren. DESIGN: Population-based cross-sectional study. PARTICIPANTS: One thousand seven hundred thirty-eight predominantly 6-year old children examined during 2003 to 2004. METHODS: Logarithm of the minimum angle of resolution (logMAR) visual acuity was measured in both eyes before and after pinhole correction and with spectacles if worn. Cycloplegic autorefraction (cyclopentolate) and detailed dilated fundus examination were performed. MAIN OUTCOME MEASURES: Visual impairment was defined as any (visual acuity <20/40; <40 letters) or severe (visual acuity < or =20/200; 0-5 letters) for both better and worse eyes. Myopia was defined as spherical equivalent (SE) refraction < or =-0.50 diopters (D), and hyperopia as SE refraction > or =+2.0 D, deemed significant when > or =+3.0 D. Astigmatism was defined as cylinder > or =1.0 D and anisometropia as SE refraction difference between eyes at least 1.0 D. Amblyopia was defined as corrected visual acuity <0.3 logMAR units (<20/40; <40 letters) in the affected eye not attributable to any underlying structural abnormality of the eye or visual pathway, together with a 2-logMAR line difference between the eyes and presence of an amblyogenic risk factor. RESULTS: The mean visual acuity of this sample was 20/25 (49.3 letters). Uncorrected visual impairment was found in the better eye of 23 children (1.3%) and in the worse eye of 71 children (4.1%). The prevalence was higher in girls than boys and among children of lower socioeconomic status. Refractive error was the most frequent cause, accounting for 69.0%, followed by amblyopia (22.5%). Astigmatism was the principle refractive error causing visual impairment and was frequently uncorrected. Presenting visual impairment (using current glasses if worn) was found in the better and worse eyes of 15 children (0.9%) and 54 children (2.8%), respectively. This was mainly due to under corrected or uncorrected refractive error. CONCLUSIONS: This study has documented a relatively low prevalence of visual impairment in a population of Australian children. Uncorrected astigmatism and amblyopia were the most frequent causes.

Child↗
PubMed2000

Visual function tests, eye disease and symptoms of visual disability: a population-based assessment.

PURPOSE: To examine associations between eye disease and tests of visual function with self-reported visual disability. METHODS: The Blue Mountains Eye Study is a cross-sectional census-based survey of eye disease in two postcode areas in the Blue Mountains, west of Sydney, Australia. Of 4433 eligible residents, 3654 (82,4%) participated. Subjects had a detailed eye examination, including tests of visual acuity, contrast sensitivity, disability glare and visual field. Lens and retinal photographs were taken and graded according to standardized protocols for presence of cataract, early and late age-related maculopathy, glaucoma, diabetic retinopathy, retinal vein occlusion and other eye diseases. An interviewer-administered questionnaire included questions about perception of visual disability. RESULTS: Scores on all tests of visual function significantly decreased with age (P < 0.0001). This decrease persisted for all tests except disability glare after excluding subjects with identifiable eye disease. The presence of one or more eye diseases was significantly associated with all (self-reported) measures of visual disability (trouble driving at night, difficulty recognizing a friend across the street, reading a newspaper or recognizing detail on televsion): mixed cataract (cortical and nuclear, or posterior subcapsular and nuclear) was associated with trouble driving at night and difficulty recognizing a friend across the street. A 10-letter (two-line) decrease in best corrected or presenting visual acuity was significantly associated with all self-reported measures of vsual dsability, as was a two-step decrease in contrast sensitvity. A five-point increase in points missing in the visual field was weakly but significantly associated with all self-reported measures of visual disability except trouble driving at night. CONCLUSIONS: Visual function declines with age. Impaired visual function was strongly, and eye disease relatively weakly associated with reports of visual disability.

Aged↗
PubMed1979

Effect of visual experience on tubulin synthesis during a critical period of visual cortex development in the hooded rat.

1. In some species, restriction of visual experience in early life may affect normal functional development of visual cortical cells. The purpose of the present study was to determine if visual deprivation during post-natal development in the hooded rat also affects the production in brain cells of certain molecular components such as tubulin, that are needed for growth and maintenance of synapses and neurites. 2. Norwegian black hooded rats were reared under a variety of conditions of visual deprivation. At various stages of development the animals were killed and the rate of synthesis of tubulin in visual and motor cortex determined. Tritiated colchicine was used to assay tubulin and L-[14C]leucine injected into the brain ventricles 2 hr before death was used to measure rate of tubulin synthesis. 3. In rats reared in normal light there is a marked elevation in visual cortex tubulin synthesis that spans the period from eye-opening (13 days) until approximately 35 days. This elevation in tubulin synthesis is absent in animals reared in darkness from birth or deprived of pattern vision by eyelid suture. Also the effect of visual deprivation on tubulin synthesis was specifically confined to visual cortex and was not found for the motor cortex. Similarly, the incorporation of L-[14C]leucine into total protein in visual cortex was unaffected by dark rearing. Hence the stimulation of tubulin synthesis by visual experience in rat visual cortex is not attributable to a general non-specific stimulation of protein synthesis. 4. Rats that were dark-reared from birth and then exposed to a lighted environment for 24 hr during a certain critical period that extends from eye-opening (13 days) until approximately 35 days, displayed a significant increase in visual cortex tubulin rats that were brought into the light later than 35 days showed no significant increase in tubulin synthesis when compared with their continuously dark-rearer controls. 5. It is suggested that the number of synapses and cytoplasmic processes that a developing cell can maintain depends on the size of the tubulin pool available to that cell. Tubulin in brain only has a half-life of about 4 days, so when the level of tubulin drops this could result in competition between different synapses for the limited supply of tubulin needed for their maintenance, a factor which may contribute to the structural plasticity of the visual cortex during the critical period.

Aging↗
PubMed2006

Influence of differences of visual acuity in various visual field conditions on spectral characteristics of the center of pressure sway.

This study examined the influence of visual acuity and visual field on the spectral characteristics of the center of pressure during standing. 17 men and 20 women participated in High and Low visual acuity groups. Both groups underwent center of pressure measurements under three visual field conditions: No vision: subjects were given no visual information, Central vision: they were given only central visual field information, and Full vision: they were given full visual information. To assess the spectral characteristics of center of pressure, mean power frequency and frequency of maximal power were calculated from medial-lateral and anterior-posterior center of pressure directions. The Friedman test and Scheffé pairwise comparison tests showed that frequency of maximal power was higher in the No vision than in the Central and Full vision conditions in the High visual acuity group. In conclusion, people with high visual acuity are more susceptible to visual field conditions than those with low visual acuity. It is suggested that postural control characteristics differ with visual acuity or resolution in the central visual field.

Adult↗
PubMedDate not supplied

Visual resolution with epi-retinal electrical stimulation estimated from activation profiles in cat visual cortex.

Blinds with receptor degeneration can perceive localized phosphenes in response to focal electrical epi-retinal stimuli. To avoid extensive basic stimulation tests in human patients, we developed techniques for estimating visual spatial resolution in anesthetized cats. Electrical epi-retinal and visual stimulation was combined with multiple-site retinal and cortical microelectrode recordings of local field potentials (LFPs) from visual areas 17 and 18. Classical visual receptive fields were characterized for retinal and cortical recording sites using multifocal visual stimulation combined with stimulus-response cross-correlation. We estimated visual spatial resolution from the size of the cortical activation profiles in response to single focal stimuli. For comparison, we determined activation profiles in response to visual stimuli at the same retinal location. Activation profiles were single peaked or multipeaked. In multipeaked profiles, the peak locations coincided with discontinuities in cortical retinotopy. Location and width of cortical activation profiles were distinct for retinal stimulation sites. On average, the activation profiles had a size of 1.28 +/- 0.03 mm cortex. Projected to visual space this corresponds to a spatial resolution of 1.49 deg +/- 0.04 deg visual angle. Best resolutions were 0.5 deg at low and medium stimulation currents corresponding to a visus of 1/30. Higher stimulation currents caused lower spatial, but higher temporal resolution (up to 70 stimuli/s). In analogy to the receptive-field concept in visual space, we defined and characterized electrical receptive fields. As our estimates of visual resolutions are conservative, we assume that a visual prosthesis will induce phosphenes at least at this resolution. This would enable visuomotor coordinations and object recognition in many indoor and outdoor situations of daily life.

Animals↗
PubMed1994

Visual outcome after laser photocoagulation for subfoveal choroidal neovascularization secondary to age-related macular degeneration. The influence of initial lesion size and initial visual acuity. Macular Photocoagulation Study Group.

OBJECTIVE: To provide detailed information specific to the initial visual acuity and initial lesion size on the outcome of patients with subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration. DESIGN AND PATIENTS: The 189 eyes assigned to laser photocoagulation and the 184 eyes assigned to observation in the Subfoveal New CNV Study were divided into nine subgroups based on initial visual acuity and initial lesion size. MAIN OUTCOME MEASURES: The pattern of visual acuity loss for both treated and untreated eyes through 4 years of follow-up was compared among the subgroups. Reading speed and contrast thresholds also were examined. RESULTS: Four patterns (A, B, C, D) of visual acuity loss in treated eyes relative to untreated eyes were identified. Eyes in group A (small lesion and moderate or poor initial visual acuity or medium lesion and poor visual acuity) had the best visual outcome with treatment; treated eyes were better throughout follow-up. Eyes in group B (small lesion and good initial visual acuity or medium lesion and moderate or good visual acuity) had substantial treatment benefit by 12 months, but were worse immediately after treatment. Eyes in group C (large lesion and poor initial visual acuity) had a small treatment benefit throughout follow-up. Eyes in group D (large lesion and moderate or good visual acuity) had the worst visual outcome with treatment; treated eyes were substantially worse for the first 18 months and were not appreciably better through 4 years of follow-up. CONCLUSIONS: Recommendations for treatment of subfoveal CNV should take account of the initial visual acuity and lesion size. Eyes in group D are poor candidates for laser treatment.

Aged↗
PubMed2002

Insensitivity of visual short-term memory to irrelevant visual information.

Several authors have hypothesized that visuo-spatial working memory is functionally analogous to verbal working memory. Irrelevant background speech impairs verbal short-term memory. We investigated whether irrelevant visual information has an analogous effect on visual short-term memory, using a dynamic visual noise (DVN) technique known to disrupt visual imagery (Quinn & McConnell, 1996b). Experiment I replicated the effect of DVN on pegword imagery. Experiments 2 and 3 showed no effect of DVN on recall of static matrix patterns, despite a significant effect of a concurrent spatial tapping task. Experiment 4 showed no effect of DVN on encoding or maintenance of arrays of matrix patterns, despite testing memory by a recognition procedure to encourage visual rather than spatial processing. Serial position curves showed a one-item recency effect typical of visual short-term memory. Experiment 5 showed no effect of DVN on short-term recognition of Chinese characters, despite effects of visual similarity and a concurrent colour memory task that confirmed visual processing of the characters. We conclude that irrelevant visual noise does not impair visual short-term memory. Visual working memory may not be functionally analogous to verbal working memory, and different cognitive processes may underlie visual short-term memory and visual imagery.

Adolescent↗
PubMed1998

Reciprocal inhibitory visual-vestibular interaction. Visual motion stimulation deactivates the parieto-insular vestibular cortex.

The vestibular system--a sensor of head accelerations--cannot detect self-motion at constant velocity and thus requires supplementary visual information. The perception of self-motion during constant velocity movement is completely dependent on visually induced vection. This can be linear vection or circular vection (CV). CV is induced by large-field visual motion stimulation during which the stationary subject perceives the moving surroundings as being stable and himself as being moved. To determine the unknown cortical visual-vestibular interaction during CV, we conducted a PET activation study on CV in 10 human volunteers. The PET images of cortical areas activated during visual motion stimulation without CV were compared with those with CV. Hitherto, CV was explained neurophysiologically by visual-vestibular convergence with activation of the vestibular nuclei, thalamic subnuclei and vestibular cortex. If CV were mediated by the vestibular cortex, one would expect that an adequate visual motion stimulus would activate both the visual and vestibular cortex. Contrary to this expectation, it was shown for the first time that visual motion stimulation with CV not only activates a medial parieto-occipital visual area bilaterally, separate from middle temporal/medial superior temporal areas, it also simultaneously deactivates the parieto-insular vestibular cortex. There was a positive correlation between the perceived intensity of CV and relative changes in regional CBF in parietal and occipital areas. These findings support a new functional interpretation: reciprocal inhibitory visual-vestibular interaction as a multisensory mechanism for self-motion perception. Inhibitory visual-vestibular interaction might protect visual perception of self-motion from potential vestibular mismatches caused by involuntary head accelerations during locomotion, and this would allow the dominant sensorial weight during self-motion perception to shift from one sensory modality to the other.

Adult↗
PubMed1995

The fragile X female: a case report of the visual, visual perceptual, and ocular health findings.

BACKGROUND: Fragile X syndrome is one of the most frequently encountered etiologies of X-linked mental retardation. Even though it is second only to Down syndrome in prevalence among children with chromosomal abnormalities, few studies have investigated the visual, visual perceptual and ocular health anomalies associated with this syndrome. No studies have been published that report on these areas for females with fragile X. This case report describes a 10-year-old white female with fragile X syndrome who exhibited numerous oculo-visual and perceptual abnormalities. METHODS: A 10-year, 7-month-old white female diagnosed as having fragile X syndrome was examined in the Illinois Eye Institute/Illinois College of Optometry Department of Pediatrics and Binocular Vision using diagnostic techniques appropriate for special populations. These techniques included a battery of tests that determine binocular vision function, ocular health status and visual perceptual abilities. RESULTS: Oculo-visual abnormalities noted include a non-active chorioretinal lesion, refractive amblyopia, anisometropia, accommodative insufficiency, and convergence excess, as well as mild to severe dysfunctions in visual motor integration, ocular motilities, laterality/directionality, visual figure ground, visual closure, visual form constancy, visual memory and visual sequential memory. CONCLUSION: Although thousands of articles, monographs, and textbooks have been written describing the numerous anomalies associated with the fragile X syndrome, little has been published in the area of oculo-visual and visual perceptual dysfunctions associated with this frequently encountered genetic abnormality. This paper is the first to demonstrate the presence of ocular health anomalies and learning-related vision problems that could adversely affect the individual's academic performance and rehabilitative program. Additional research is needed to ascertain the prevalence of these disorders within the fragile X community.

Child↗
PubMed2005

Visual fields correlate better than visual acuity to severity of diabetic retinopathy.

AIMS/HYPOTHESIS: We compared the outcomes of perimetric and visual acuity tests in patients with diabetic retinopathy. METHODS: We examined 59 diabetic patients with different degrees of retinopathy using stereo fundus photography in accordance with the Early Treatment of Diabetic Retinopathy Study (ETDRS) and fluorescein angiography. Conventional white-on-white perimetry (WWP) and short wavelength automated perimetry (SWAP) were performed and analysed with reference to normal values. Visual acuity was measured with ETDRS charts. RESULTS: Regression analysis revealed that visual acuity was significantly associated with increasing severity of retinopathy according to the ETDRS scale when visual acuity was estimated by counting logarithm of minimum angle of resolution (LogMar) scores, but not when visual acuity was measured by the conventional reading of the smallest line that could be seen. Visual acuity decreased by 0.02 LogMar per ETDRS step (p=0.03). The degree of visual field loss was significantly associated with increasing severity of retinopathy according to the ETDRS scale, perimetric sensitivity decreasing by 0.44 dB per ETDRS step (p=0.0001) using WWP, and by 0.40 dB per ETDRS step (p=0.04) with SWAP. The size of the area of the foveal avascular zone and adjacent perifoveal intercapillary areas (PIAs) also affected the central visual field as obtained both by WWP (-2.6 dB/mm2, p=0.03), and by SWAP (-7.9 dB/mm2, p=0.002), but did not affect visual acuity. The regression model fit for peripheral retinopathy according to the ETDRS scale was better using WWP than SWAP or visual acuity, while SWAP testing was superior to both WWP and visual acuity when measuring effects caused by enlarged foveal avascular zones and PIAs. CONCLUSIONS/INTERPRETATION: Perimetry can provide more useful information than visual acuity on functional loss in diabetic retinopathy, particularly when the perifoveal capillary network is damaged.

Adult↗
PubMed1979

The contribution of the 'second' visual system to directed visual attention in man.

The visual functions of a patient suffering from a brain lesion incorporating the left n. pulvinar was examined in order to assess the contribution of this structure to human vision. With the exception of the following abnormalities visual functions were normal. First, there was a decrease in the critical flicker frequency in the periphery (but not in the parafoveal region) of the right visual hemifield, that is, that contralateral to the pulvinar lesion. However, the second and most striking characteristic was--as shown by presenting visual stimuli bilaterally and simultaneously-a 'neglect' for the periphery of this contralateral visual half-field. This 'neglect' was a function of (a) position in the visual field (eccentricity), (b) stimulus properties (size and luminance), (c) temporal properties (length of presentation and interstimulus interval). In addition to this reduced capacity to detect stimuli appearing in the periphery of the right visual hemifield, there was also prolonged latency of visually evoked saccadic eye movements and a paucity of spontaneous eye movements directed towards the right visual hemifield. These results are interpreted in terms of a contribution of the n. pulvinar to the detection of light stimuli presented in the periphery of the visual field, and support the view that the tectopulvinar extrastriate visual pathway plays an important role in the control of visual attention.

Attention↗
PubMed1999

Neural correlates of visual form and visual spatial processing.

Cortico-cortical projections for visual processing that originate from the striate cortex are organized into two streams. The dorsal stream projects to the parietal region and the ventral stream to the inferior temporal region. One hypothesis is that the dorsal stream processes visual spatial information, and the ventral stream processes visual object information. Although recognition of human faces or common objects has been shown preferentially to activate the ventral stream, the issue of when such processing starts to engage the ventral or the dorsal stream is not clear. The question explored in this study is whether processing of visual form per se without evoking the brain mechanisms that are associated with recognition of human faces or common objects is sufficient to activate the ventral stream more significantly relative to the condition when only visual spatial processing is involved. Functional magnetic resonance images were acquired while subjects performed a delayed comparison task in which either visual spatial or visual form information was processed. Cortical areas that were preferentially activated in visual spatial or visual form processing showed not only ventral-dorsal segregation, but also hemispheric laterality. The results extended previous findings by showing that preferential activation in the ventral pathway is not contingent upon such powerful stimuli as faces and common objects. Processing of simple visual form information is cause enough for such activation to be observed. A strong left hemisphere dominance in visual form recognition was also revealed. The observed laterality may be a reflection that the left hemisphere is more important in symbolic and/or semantic coding of visual form information.

Adult↗
PubMed2001

Comparison of contrast sensitivity, visual acuity, and Humphrey visual field testing in patients with glaucoma.

PURPOSE: To investigate the relationship between large-letter contrast sensitivity, high-contrast visual acuity, and visual field defects in patients with glaucoma. METHODS: Patients with a diagnosis of glaucoma, glaucoma suspect, or ocular hypertension whose visual acuity was 20/40 (logMAR = 0.3) on better were included in the study. Visual acuity was measured using the Lighthouse visual acuity charts. Contrast sensitivity was measured using the Pell-Robson (PR) chart. The mean depression (MD) score from the most recent Humphrey visual field was used to quantify the visual field defect. RESULTS: A total of 120 eyes were studied. The PR contrast sensitivity score correlated more strongly with the MD of the visual field (r = .589, P < .001) than did the logMAR visual acuity (r = .193, P = .035). When just the eyes with open-angle glaucoma were considered (N = 54), the correlation was even greater for the PR score (r = .638). In ocular hypertensive eyes (N = 25), the correlations to PR and logMAR were not that different (r = .394 for PR, r = .303 for logMAR). Pseudophakic eyes did not show as strong a correlation (r = .335) as did phakic eyes (r = .591). CONCLUSION: For glaucomatous eyes with visual acuity of 20/40 or better, a decrease in the contrast sensitivity correlates with increased visual field loss. We speculate that this decrease in contrast sensitivity in glaucoma patients may account for their complaints of poor vision despite normal or near normal visual acuity.

Contrast Sensitivity↗
PubMed1999

The development of visual functions in cerebrally blind children during a systematic visual field training.

Sixteen children aged 1 to 15 years who were blind due to an ischemic postgeniculate cerebral lesion after perinatal asphyxia and 6 children aged 1 to 13 years who were blinded after a postgeniculate traumatic cerebral lesion participated in a systematic visual field training. Thirty-one children who were blind due to a postgeniculate lesion following perinatal asphyxia and 12 children who suffered from blindness after a traumatic postgeniculate lesion served as controls. These children received no visual field training or an ineffective visual field training. The extension of the functional visual field and the functional luminance difference threshold were assessed with a specially designed arc perimeter. In all children blindness had already persisted for at least one year. Visual functions developed within a training period of three months in 15 of 22 children who received visual field training whereas there was no spontaneous recovery in the control group. The functional luminance difference threshold was still elevated above normal in the case of 5 children who recovered from blindness. In 2 children the latency of saccades elicited by light targets in the formerly blind visual area was significantly longer than the latency of saccades elicited by targets in the normal area of the visual field. Light scatter was controlled in order to exclude that the widening of the visual field during training which we interpreted as a sign of the development of visual functions was an effect of scattering light. The findings support the assumption that systematic stimulation of cerebrally blind areas may facilitate the development of visual functions in brain damaged children. The cerebral lesions associated with the impaired visual functions which improved during the treatment are in agreement with the assumption that spared tissue in the striate and extrastriate visual cortex and underlying white matter is the anatomical basis of the shrinkage of the blind areas.

Journal Article↗
PubMed2006

Control of adaptive locomotion: effect of visual obstruction and visual cues in the environment.

Visual information regarding obstacle position and size is used for planning and controlling adaptive gait. However, the manner in which visual cues in the environment are used in the control of gait is not fully known. This research examined the effect of obstacle position cues on the lead and trail limb trajectories during obstacle avoidance with and without visual information of the lower limbs and obstacle (termed visual exproprioception). Eight subjects stepped over obstacles under four visual conditions: full vision without obstacle position cues, full vision with position cues, goggles without position cues and goggles with position cues. Goggles obstructed visual exproprioception of the lower limbs and the obstacle. Position cues (2 m tall) were placed beside the obstacle to provide visual cues regarding obstacle position. Obstacle heights were 2, 10, 20 and 30 cm. When wearing goggles and without position cues, a majority of the dependent measures (horizontal distance, toe clearance and lead stride length) increased for the 10, 20 and 30 cm obstacles. Therefore lower limb-obstacle visual exproprioception was important for the control of both limbs, even though with normal vision the trail limb was not visible during obstacle clearance. When wearing goggles, the presence of position cues, which provided on-line visual exproprioception of the self relative to the obstacle position in the anterior-posterior direction, returned lead and trail foot placements to full vision values. Lead toe clearance was not affected by the position cues, trail clearance decreased but was greater than values observed during full vision. Therefore, visual exproprioception of obstacle location, provided by visual cues in the environment, was more relevant than visual exproprioception of the lower limbs for controlling lead and trail foot placement.

Adaptation, Physiological↗