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PubMed1987

Hemispace-visual field interactions in visual extinction.

Visual extinction was studied in a patient with neglect from a right hemispheric lesion. Extinction occurred during double simultaneous stimulation within the same visual hemi-field (VHF). This finding suggests that interhemispheric rivalry is not a critical factor. During double simultaneous stimulation within the same VHF as well as with stimuli in different VHFs, the severity of extinction was determined by both the retinotopic and the hemi-spatial position of the extinguished stimulus. The location of the other stimulus, however, did not seem relevant. It is proposed that damage to a corticolimbic-reticular system reduces attentional capacity and that extinction during double simultaneous stimulation in the visual modality reflects an inability to distribute the limited attentional resources equally to two different locations. The severity of extinction is a measure of an unequal distribution of attention along a gradient within visual space.

Attention↗

PubMed1985

Role of visual experience in activating critical period in cat visual cortex.

Cats were reared in total darkness from birth until 4-5 mo of age (DR cats, n = 7) or with very brief visual experience (1 or 2 days) during an otherwise similar period of dark rearing [DR(1) cats, n = 3; DR(2) cats, n = 7]. Single-cell recordings were made in area 17 of visual cortex at the end of this rearing period and/or after a subsequent prolonged period of monocular deprivation. Control observations were made in normal cats (n = 3), cats reared with monocular deprivation from birth (n = 4), and cats monocularly deprived after being reared normally until 4 mo of age (n = 2). After rearing cats in total darkness, the majority of visual cortical cells were binocularly driven and the overall distribution of ocular dominance was not different from that of normal cats. Orientation-selective cells were very rare in dark-reared cats. Monocular deprivation imposed after dark rearing resulted in selective development of connections from the open eye. Most cells were responsive only to the open eye and the majority of these were orientation selective. These results were similar to, though less severe than, those found in cats reared with monocular deprivation from birth. Monocular deprivation imposed after 4 mo of normal rearing did not produce selective development of connections from the open eye in terms of either ocular dominance or orientation selectivity. In DR(1) cats visual cortical physiology was degraded in comparison to dark-reared cats after the rearing period. Most cells were binocularly driven but there was a higher frequency of unresponsive cells and a reduced frequency of orientation-selective cells. Subsequent monocular deprivation resulted in a further decrease in the number of binocularly driven cells and an increase in unresponsive cells. However, it did not produce a bias in favor of the open eye in terms of either ocular dominance or orientation selectivity. In DR(2) cats there was a high incidence of unresponsive cells and a marked loss of binocularly driven cells after the rearing period. Subsequent monocular deprivation failed to produce any significant changes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1979

Visual field-cerebral hemisphere differences in perception of visual nonverbal stimuli.

16 subjects were tested for differences between left and right visual fields in accuracy of recognition for paired verbal and nonverbal stimuli presented at below threshold duration and at minimal intensity. Performance on the visual recognition task was also compared with scores on a written n-Ach test. The data clearly indicated superior recognition of physiognomic stimuli presented in the left visual field and above-chance-level performance of subjects' manual responses for these below-threshold stimuli. The data also hint at a possible relationship between n-Ach and accuracy of visual recognition in the left hemisphere.

Achievement↗

PubMed1995

Infant visual development: an overview of studies using visual evoked potential measures from Harter to the present.

Studies of sensory and perceptual abilities in infants require creative, innovative techniques. Although the young infant's response repertoire may appear limited to the naive individual, a number of highly refined procedures have been developed and implemented with these non-verbal humans over the last twenty years. The most successful protocols for evaluating visual development rely either on behavioral responses or on electrophysiological recordings. The first published report using visual evoked potentials to study the development of pattern vision in human infants was presented by M. Russell Harter. This work provided the impetus for a wealth of studies exploring issues of visual information processing abilities in early infancy. The available range of data and experimental techniques are now sufficiently refined that many clinical issues are currently being addressed. The purpose of this review is to document the evolution of scientific studies since Harter's seminal work. The selection of protocols presented focuses on those with either current clinical applications or those which hold promise for future applications in the evaluation and treatment issues of abnormal visual development.

Albinism, Ocular↗

PubMed1991

The flanker compatibility effect as a function of visual angle, attentional focus, visual transients, and perceptual load: a search for boundary conditions.

When subjects must respond to a relevant center letter and ignore irrelevant flanking letters, the identities of the flankers produce a response compatibility effect, indicating that they are processed semantically at least to some extent. Because this effect decreases as the separation between target and flankers increases, the effect appears to result from imperfect early selection (attenuation). In the present experiments, several features of the focused attention paradigm were examined, in order to determine whether they might produce the flanker compatibility effect by interfering with the operation of an early selective mechanism. Specifically, the effect might be produced because the paradigm requires subjects to (1) attend exclusively to stimuli within a very small visual angle, (2) maintain a long-term attentional focus on a constant display location, (3) focus attention on an empty display location, (4) exclude onset-transient flankers from semantic processing, or (5) ignore some of the few stimuli in an impoverished visual field. The results indicate that none of these task features is required for semantic processing of unattended stimuli to occur. In fact, visual angle is the only one of the task features that clearly has a strong influence on the size of the flanker compatibility effect. The invariance of the flanker compatibility effect across these conditions suggests that the mechanism for early selection rarely, if ever, completely excludes unattended stimuli from semantic analysis. In addition, it shows that selective mechanisms are relatively insensitive to several factors that might be expected to influence them, thereby supporting the view that spatial separation has a special status for visual selective attention.

Attention↗

PubMedDate not supplied

VEP acuity, FPL acuity, and visual behavior of visually impaired children.

Forced-choice preferential-looking (FPL) and pattern-visual-evoked potential (VEP) acuity tests were conducted with 42 children with bilateral moderate to severe visual impairment (age, 4 months to 9 years). Within this group of children, FPL acuity testing was more successful than VEP acuity testing (98% versus 64%). Mean FPL acuity was better than mean VEP acuity (20/155 vs 20/290, P less than .002). For the children who completed both FPL and VEP acuity tests, an acuity difference score (FPL minus VEP) was derived, and compared to difference scores based on normative data. Significant differences were found between visually impaired (VI) and control difference scores (P less than .001). Difference scores of VI were larger than and opposite in sign to the control scores. Rating scores of visual behaviors supported the concurrent validity of the FPL acuities (P = .01), but not the VEP acuities.

Child↗

PubMed2005

Comparison of visual evoked potentials, automated perimetry and frequency-doubling perimetry in early detection of glaucomatous visual field loss.

The present study compares frequency-doubling perimetry (FDP), automated perimetry (AP) and visual evoked potentials (VEP) for their ability to diagnose early glaucoma. In present study 224 patients of Clinic for Eye Diseases, Clinical Hospital "Sestre Milosrdnice" that had diagnosis of open angle glaucoma and glaucomatous visual field loss proven by automated static perimetry on only one eye were performing all three tests. Visual evoked potentials, automated perimetry and frequency-doubling perimetry were performed four times in each patient with six months period in between testing. Significant difference was proven between frequency-doubling perimetry and automated perimetry in favor for FDP in early detection of glaucomatous field loss. There was no significant difference between FDP and VEP neither between VEP and AP measurements. The results of this study indicate that frequency-doubling perimetry is significantly better method for early detection of glaucomatous visual field loss than automated static perimetry.

Automation↗

PubMed1976

Visually evoked response. Use in neurologic evaluation of posttraumatic subjective visual complaints.

Evaluation of subjective visual complaints unassociated with objective signs is a frequent problem in neurologic and ophthalmic practice. The visually evoked response (VER) is an important tool for separating the functional from the organic in patients claiming visual disturbance. In visual complaints associated with late posttraumatic epileptic activity, the VER can demonstrate an abnormality even in asymptomatic intervals. In complaints due to concussion, it demonstrates disorganized evoked responses initially and later a return of the normal resonse. It shows an abnormality in the occipital lobes during and after transient compression of the vertebral artery. A normal VER excludes all but trivial involvement of the visual system, symptomatic claims of the patient notwithstanding.

Adult↗

PubMed2003

Origin of the vertebrate visual cycle: genes encoding retinal photoisomerase and two putative visual cycle proteins are expressed in whole brain of a primitive chordate.

The absorption of light by rhodopsin leads to the cis-to-trans isomerization of the chromophore to generate all-trans-retinal. In the visual cycle, the resultant all-trans-retinal is converted back into the 11-cis-retinal. In the mammalian eye, the retinal pigment epithelium (RPE) plays an essential role in the visual cycle. We have identified cDNA clones encoding three putative visual cycle proteins, homologs of mammalian retinal G-protein-coupled receptor (RGR), cellular retinaldehyde-binding protein (CRALBP) and beta-carotene 15,15'-monooxygenase (BCO)/RPE65 in a primitive chordate, ascidian Ciona intestinalis. The mRNAs for these proteins are specifically expressed in the central nervous system during embryonic development. In the larva, the transcripts were widely distributed in the brain vesicle and visceral ganglion. Since visual pigment, Ci-opsin1, is solely expressed in photoreceptor cells, the visual cycle in this primitive chordate may take place in two compartments, which are coupled into a cycle by the direct flow of retinoids though the intercellular matrix. The Ci-opsin3, an ascidian homolog of mammalian RGR, was expressed in HEK 293S cells and purified after binding of retinal. The chromophore of Ci-opsin3 is in an all-trans-retinal and it is isomerized to an 11-cis-form upon absorption of light. Mammalian CRALBP and BCO/RPE65 are believed to play critical roles in the process of reisomerization of all-trans-retinoid to 11-cis-retinoid in RPE. The present data suggest that isomerization of all-trans-retinoid to 11-cis-retinoid occurs in the brain vesicle and visceral ganglion of a primitive chordate.

Amino Acid Sequence↗

PubMed2005

Multiple sensitive periods in human visual development: evidence from visually deprived children.

Psychophysical studies of children deprived of early visual experience by dense cataracts indicate that there are multiple sensitive periods during which experience can influence visual development. We note three sensitive periods within acuity, each with different developmental time courses: the period of visually-driven normal development, the sensitive period for damage, and the sensitive period for recovery. Moreover, there are different sensitive periods for different aspects of vision. Relative to the period of visually driven normal development, the sensitive period for damage is surprisingly long for acuity, peripheral vision, and asymmetry of optokinetic nystagmus, but surprisingly short for global motion. A comparison of results from unilaterally versus bilaterally deprived children provides insights into the complex nature of interactions between the eyes during normal visual development.

Adolescent↗

PubMed2006

Inhibiting the transient choroidal thickening response using the nitric oxide synthase inhibitor l-NAME prevents the ameliorative effects of visual experience on ocular growth in two different visual paradigms.

It is generally accepted that the increase in choroidal thickness in response to myopic defocus in chicks acts to move the retina towards the image plane. It may also constitute part of the signal cascade in the visual regulation of eye growth. To test this, we used the nitric oxide synthase inhibitor l-NAME to inhibit the defocus induced choroidal thickening under two different visual conditions, and looked at the effects on ocular growth rate. Exp. 1: Deprivation/Vision: chicks were monocularly deprived of form vision with translucent diffusers from day 6 to day 9. In the middle of each day the diffusers were removed for 2 h. One group received an intravitreal injection of 30 microl l-NAME (16 micromole; n=12) prior to the vision, a second group received injections of physiological saline (n=11). Exp. 2: Recovery/Vision: chicks were made myopic by form deprivation from day 6 to day 10. On days 11 to 14 the diffusers were removed for 2 h per day for 4 days to allow eyes to "recover" from the myopia. One group received an injection of l-NAME prior to vision (n=8), the other saline (n=6). Refractive errors were measured with a refractometer at the start (days 6 and 11) and end (days 10 and 15, respectively) of both experiments. Ocular dimensions were measured with high frequency A-scan ultrasonography at the start and end, and on the third experimental day immediately before and after the period of vision. Choroidal retinoic acid synthesis was measured by HPLC. Finally, NO production and scleral proteoglycan synthesis were measured in eyes wearing positive lenses 6 and 24h after an injection of l-NAME. l-NAME prevented the transient vision-induced choroidal thickening in both experiments. Furthermore, l-NAME inhibited the protective effect of brief daily vision: eyes became significantly more myopic than saline controls (exp. 1: -9 D vs -2.7D; exp. 2: -0.9 D vs +4.3 D; p<0.005 for both) and grew faster (change in lens-sclera: exp. 1: 295 vs 158 microm; exp. 2: 147 vs 39 microm; p<0.05 for both). Notably, l-NAME inhibited the growth of the anterior chamber (exp. 1: 88 vs 185 microm; exp. 2: 147 vs 254 microm; p<0.01 for both). Injections of l-NAME after the periods of vision had no effect on growth at the back of the eye, but still had an inhibitory effect on the anterior chamber. Retinoic acid levels in the drug-injected choroids were significantly decreased compared to controls. In eyes responding to positive lenses, l-NAME inhibited NO synthesis and disinhibited scleral glycosaminoglycan synthesis 6h after the injection. In summary, preventing the transient vision-induced increases in choroidal thickness altered ocular growth rate in a consistent manner under two different visual conditions, in both preventing the vision-induced reduction in growth rate. This supports the hypothesis that visually-induced changes in choroidal thickness play a role in the visual regulation of ocular growth.

Animals↗

PubMed1989

Interaction of visual and non-visual signals in the initiation of smooth pursuit eye movements in primates.

The initiation of smooth pursuit eye movements (PEM) by visual and non-visual signals was analysed in humans and monkeys. While PEM latency ranged around 150 ms when a purely visual target was provided, it often dropped to about 0 ms, or even became negative, when target movement was coupled to the subject's arm; this suggests that signals about the intention to move the arm can be evaluated for PEM control. Eye movements always started in the visually correct direction, independent of the sign of coupling between arm and target; from this we conclude that intentional signals are not mere triggers, but also convey directional information. Short-latency PEM trials were intermixed with those characterized by normal latencies, which often resulted in bimodal latency distributions; this suggests that visual and intentional signals compete for the control of PEM.

Animals↗

PubMed1999

Tumor Treatment Response Based on Visual and Quantitative Changes in Global Tumor Glycolysis Using PET-FDG Imaging. The Visual Response Score and the Change in Total Lesion Glycolysis.

"Functional" tumor treatment response parameters have been developed to measure treatment induced biochemical changes in the entire tumor mass, using positron emission tomography (PET) and [F-18] fludeoxyglucose (FDG). These new parameters are intended to measure global changes in tumor glycolysis. The response parameters are determined by comparing the pre- and posttreatment PET-FDG images either visually from the change in image appearance in the region of the tumor, or quantitatively based on features of the calibrated digital PET image. The visually assessed parameters are expressed as a visual response score (VRS), or visual response index (VRI), as the estimated percent response of the tumor. Visual Response Score (VRS) is recorded on a 5 point response scale (0-4): 0: no response or progression; 1: 1-33%; 2: >33%-66%; 3: >66%-99%; and 4: >99%, estimated response, respectively. The quantitative changes are expressed as total lesion glycolysis TLG or as the change in TLG during treatment, also called deltaTLG or Larson-Ginsberg Index (LGI), expressed as percent response. The volume of the lesion is determined from the PET-FDG images by an adaptive thresholding technique. This response index is computed as, deltaTLG (LGI) = {[(SUV(ave))(1) * (Vol)(1) - (SUV(ave))(2) * (Vol)(2)]/[(SUV(ave))(1) * (Vol)(1)]} * 100. Where "1" and "2" denote the pre- and posttreatment PET-FDG, scans respectively. Pre- and posttreatment PET-FDG scans were performed on a group of 41 locally advanced lung (2), rectal (17), esophageal (16) and gastric (6) cancers. These patients were treated before surgery with neoadjuvant chemo-radiation. Four experienced PET readers determined individual VRS and VRI blinded to each other as well as to the clinical history. Consensus VRS was obtained based on a discussion. The interobserver variability captured by intraclass correlation coefficient was 89.7%. In addition, reader reliability was assessed for the categorized VRS using Kendall's coefficient of concordance for ordinal data and was found to be equal to 85% This provided assurance that these response parameters were highly reproducible. The correlation of deltaTLG with % change in SUV(ave) and % change in SUV(max), as widely used parameters of response, were 0.73 and 0.78 (P <.0001) respectively. The corresponding correlation of VRI were 0.63 and 0.64 (P <.0001) respectively. Both deltaTLG and VRI showed greater mean changes than SUV maximum or average (59.7% and 76% vs. 46.9% and 46.8%). We conclude that VRS and deltaTLG are substantially correlated with other response parameters and are highly reproducible. As global measures of metabolic response, VRS, VRI and deltaTLG (LGI) should provide complementary information to more commonly used PET response parameters like the metabolic rate of FDG (MRFDG), or the standardized uptake value (SUV), that are calculated as normalized per gram of tumor. These findings set the stage for validation studies of the VRS and deltaTLG as objective measures of clinical treatment response, through comparison to the appropriate gold standards of posttreatment histopathology, recurrence free survival, and disease specific survival in well characterized populations of patients with locally advanced cancers.

Journal Article↗

PubMed2005

Auditory-visual speech perception and auditory-visual enhancement in normal-hearing younger and older adults.

OBJECTIVE: The purpose of the present study was to examine the effects of age on the ability to benefit from combining auditory and visual speech information, relative to listening or speechreading alone. In addition, the study was designed to compare visual enhancement (VE) and auditory enhancement (AE) for consonants, words, and sentences in older and younger adults. DESIGN: Forty-four older adults and 38 younger adults with clinically normal thresholds for frequencies of 4 kHz and below were asked to identify vowel-consonant-vowels (VCVs), words in a carrier phrase, and semantically meaningful sentences in auditory-only (A), visual-only (V), and auditory-visual (AV) conditions. All stimuli were presented in a background of 20-talker babble, and signal-to-babble ratios were set individually for each participant and each stimulus type to produce approximately 50% correct in the A condition. RESULTS: For all three types of stimuli, older and younger adults obtained similar scores for the A condition, indicating that the procedure for individually adjusting signal-to-babble ratios was successful at equating A scores for the two age groups. Older adults, however, had significantly poorer performance than younger adults in the AV and V modalities. Analyses of both AE and VE indicated no age differences in the ability to benefit from combining auditory and visual speech signals after controlling for age differences in the V condition. Correlations between scores for the three types of stimuli (consonants, words, and sentences) indicated moderate correlations in the V condition but small correlations for AV, AE, and VE. CONCLUSIONS: Overall, the findings suggest that the poorer performance of older adults in the AV condition was a result of reduced speechreading abilities rather than a consequence of impaired integration capacities. The pattern of correlations across the three stimulus types indicates some overlap in the mechanisms mediating AV perception of words and sentences and that these mechanisms are largely independent from those used for AV perception of consonants.

Acoustic Stimulation↗

PubMed2004

Will visual discomfort among visual display unit (VDU) users change in development when moving from single vision lenses to specially designed VDU progressive lenses?

PURPOSE: Three types of progressive additions lenses (PAL) specially designed for VDU-work and one single vision lens were compared in a prospective field study. The aim was to investigate if these progressive lenses created a difference in the development of visual discomfort compared to single vision lenses when working on an optimized VDU-workstation. METHODS: The study had a prospective, parallel group design, with four groups of VDU-workers. Approximately 40 subjects in each group, selected after careful task analysis with special attention towards the visual angles and distances to the work tasks. The groups were followed over one year. A questionnaire concerning visual conditions, working conditions, discomfort in different body areas, the status of the subjects' optometric corrections, psychological factors both at work and at home, amount, frequency and duration of VDU-work etc. was filled in before the intervention, after six months and after one year. No other contact was made with the subjects. The VDU-lenses included were Interview (Essilor), Gradal RD (Zeiss) and Technica (American Optical). Pain intensity and duration were assessed on a 100 mm Visual Analogue Scale (VAS) before the intervention, and six and twelve months after the intervention. All subjects were given a complete optometric examination. RESULTS: Only small changes in the development of headache and visual discomfort were registered. However, the subjective evaluation of area of clear vision and overall satisfaction was significantly improved for the Interview and Gradal RD lens (p < 0.05). There were no significant changes for Technica and single vision lenses. CONCLUSION: Lens designs that cover viewing distances from near and out to approximately 2 meters work well compared to lens designs trying to cover greater range of clear vision. When tasks analysis shows that single vision correction may be used, this is still an acceptable solution.

Computer Terminals↗

PubMedDate not supplied

LOD map--A visual interface for navigating multiresolution volume visualization.

In multiresolution volume visualization, a visual representation of level-of-detail (LOD) quality is important for us to examine, compare, and validate different LOD selection algorithms. While traditional methods rely on ultimate images for quality measurement, we introduce the LOD map--an alternative representation of LOD quality and a visual interface for navigating multiresolution data exploration. Our measure for LOD quality is based on the formulation of entropy from information theory. The measure takes into account the distortion and contribution of multiresolution data blocks. A LOD map is generated through the mapping of key LOD ingredients to a treemap representation. The ordered treemap layout is used for relative stable update of the LOD map when the view or LOD changes. This visual interface not only indicates the quality of LODs in an intuitive way, but also provides immediate suggestions for possible LOD improvement through visually-striking features. It also allows us to compare different views and perform rendering budget control. A set of interactive techniques is proposed to make the LOD adjustment a simple and easy task. We demonstrate the effectiveness and efficiency of our approach on large scientific and medical data sets.

Algorithms↗

PubMed1989

The meaning of visual impairment to visually impaired adults.

The purpose of this study was to explore the subjective meaning of visual impairment in the context of day to day life to adults whose visual impairment began in their adult years. Information was elicited through interviews from 25 people whose visual impairment ranged from an inability to see ordinary print to no light perception. Hermeneutics, as elaborated by Ricoeur, was used in the interpretation of the texts (transcribed interviews). A core variable, adjusting to a visual impairment, and five distinct categories, each with subcategories, emerged from the data. The meaning of visual impairment was derived from the manner in which the categories interrelated with the process of adjusting.

Adaptation, Psychological↗

PubMed1986

Persistent behavioural blindness after early visual deprivation and active visual rehabilitation: a case report.

Early long lasting binocular deprivation results in behavioural blindness in both man and experimental animals. However, few reported cases show that visual rehabilitation may improve visual behaviour. A 34-year-old man who had experienced 30 years of binocular deprivation due to bilateral cataracts received visual rehabilitation for one year. The rehabilitation included training in eye-hand co-ordination, recognition of objects, evaluation of distance and size, and mobility training. Despite signs of recovery of visual functions the patient never started to use vision in his normal life. The negative outcome of the rehabilitation is partly attributed to the patient's motivational problems and to the relatively short rehabilitation time. Visual rehabilitation may be successful when started immediately after the corrective operation on the eyes when the level of motivation is also high.

Adult↗