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PubMedDate not supplied

Effect of aging on vertical visual tracking and visual-vestibular interaction.

We investigated the effect of aging on vertical smooth pursuit, small-field optokinetic nystagmus (OKN), the vestibulo-ocular reflex (VOR), and visual-vestibular interactions (VVI). Telescopic spectacles were used to magnify the visual effects of head movements and accentuate the demand on VVI. Eleven normally sighted young subjects (age 30 +/- 6 y, mean +/- SD), and 9 normally sighted elderly subjects (age 70 +/- 8 y) were studied. Three types of stimulus motion were used: 1) predictable single sinusoidal frequencies from 0.8 to 3.2 Hz, 2) poorly predictable motion consisting of a sum of multiple harmonics of a 0.4 Hz fundamental, and 3) unpredictable velocity impulses. Tracking gains declined with frequency and stimulus unpredictability but were always greater for young than elderly subjects. Pursuit gain was always less than OKN gain for subjects tested under comparable conditions of frequency and velocity. In both subject groups, pursuit and OKN tracking exhibited phase lags at higher frequencies, particularly for poor predictable motion. Tracking phase lags were greater for pursuit than OKN and were consistently greater in the elderly than in young subjects. In young subjects, stimulus dimming using a 2 log neutral density filter reduced tracking gains and increased phase lags. In both young and elderly subjects, VOR gain was < 1.0 at low frequencies and increased slightly with increasing frequency. Visually enhanced VOR gain during normal vision was the ideal value of 1.0 at all frequencies in both subject groups. During wearing of telescopic spectacles, the young subjects exhibited marked gain enhancement that was greatest at lower frequencies and greater during predictable than unpredictable motion. Young subjects were able to suppress the VOR by fixation of real or imaginary targets moving with the head; this suppression was better at the lowest frequencies and for predictable motion. Phase errors were substantial for significant VVI in young subjects but were minimal in the elderly. Visual enhancement of VOR gain, as well as suppression by real and imaginary head-fixed targets, were attenuated in the elderly subjects. During rotations in which young subjects wore 4x telescopic spectacles, 2 log unit dimming of the visual environment reduced gain and increased phase lags. The deficiencies in VVI exhibited by elderly subjects are attributable both to deficits in the visual tracking component, as well as to nonvisual mechanisms, because even changes in mental set are less effective in modifying gain in older subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1980

Regional variation in the representation of the visual field in the visual cortex of the Siamese cat.

In Siamese cats, many ganglion cell fibers from the temporal retina misproject to the contralateral hemisphere; as a result, each lateral geniculate nucleus contains an abnormally large representation of the ipsilateral visual field. The manner in which the visual cortex processes this aberrant visual information has been examined in several previous studies. In some Siamese cats, the region of the 17/18 border was found to contain an extensive, systematic map of the ipsilateral field, while in other animals no such map was found, and the 17/18 border appeared to represent the zero meridian of azimuth (as in normal cats). These results have led to the suggestion that there are two distinct types of Siamese cat ("Boston" and "Midwestern") which can be distinguished on the basis of cortical topography and the anatomical organization oif the geniculocortical pathway. In the present study, we have recorded from four Siamese cats in order to examine the visual field map in the region of the 17/18 border; in each cat we recorded at anterior coronal levels corresponding to the representation of the lower visual field, and also at more posterior levels near the horizontal meridian representation. In all of the animals we found that the anterior penetrations (corresponding to mean receptive field elevations inferior to -7 degrees) yielded 15-20 degrees of ipsilateral field representation at the 17/18 border; however, the posterior, horizontal meridian penetrations (with mean elevations from +1 degrees to -4 degrees) showed excursions of only about 5 degrees into the ipsilateral field. This large difference in the representation of azimuth was not due to rotation of the eyes during our recording sessions. The finding of appreciable differences in the amount of ipsilateral field represented at different anterior-posterior levels of the same animal might lead to the suggestion that there are not two distinct populations (or types) of Siamese cat with regard to the cortical map of the ipsilateral field. Rather, we raise the possibility that Siamese cats form one population in which there is a continuous variation in the extent of ipsilateral field represented in the cortex.

Animals↗

PubMed1982

Subclinical visual field defects in multiple sclerosis. Demonstration and quantification with automated perimetry, and comparison with visually evoked potentials.

Fourteen patients with definite but inactive multiple sclerosis (MS) and 17 normal controls were examined with the automated perimeter octopus. Most of the patients had subclinical visual field defects, typically consisting of patchy, shallow scotomata located mostly in an area of between 15 degrees and 30 degrees eccentricity. In 8 patients, more than 15% of the tested visual field of at least one eye was abnormal. The severity and extent of the defects was unrelated to a history of optic neuritis. When visually evoked potentials (VEPs) of these subjects were examined using a reversing pattern, no correlation was found in the MS patients between prolonged VEP latencies and the location, depth or extent of visual field defects. Since subclinical visual field defects may be found in MS patients with normal VEP latencies, automated perimetry can be helpful in diagnosing some cases.

Adolescent↗

PubMed2001

Primary visual cortex and memory. Retinal position specificity and lack of size constancy at early stages of learning a visual memory task in the macaque.

Two monkeys were trained in a novel version of a delayed match-to-sample (DMS) task. They were required to fixate on a small spot at the center of the monitor and distinguish whether two gratings presented one after the other with delays up to 1.5 s in a specific visual field location were similar or not. It was found that such learning fails to transfer readily to other retinal locations. In fact, the learning was sensitive even to very small retinal displacements of the visual stimuli. Such acute retinal position specificity implies that at least a component of the learning in this particular memory task occurs at an early visual area such as the striate cortex, which has a fine-grain topographical representation. Furthermore, at early stages of learning the DMS task, when the monkeys had not generalized the learning to stimuli of different sizes, they failed to show size constancy. That is, when the display was placed at a different distance but with the same absolute size, the performance dropped. The performance was almost fully restored when, at the new display location, stimuli were changed to fit the original retinal size. This indicates that a crucial component of the learning does occur at a site even prior to size constancy. These results show that, under certain situations, an early visual area such as the primary visual cortex may be involved even in complex behaviours such as a memory task as more than just a feature-detecting area or a relay station.

Animals↗

PubMed2005

[Conventional techniques of visual field examination Part 2: confrontation visual field testing -- kinetic perimetry].

Evaluation of visual field findings is an essential ophthalmological task. Applying psychophysical principles enables noninvasive (topo-)diagnosis in cases of unexplained visual loss or suspected lesions of the visual pathway. Furthermore, any kind of expert opinion or ability test critically depends on adequate visual field findings. Repeated examinations allow functional follow-up of a disease and assessment of therapeutic efficiency. This paper explicitly focuses on conventional strategies since these are widespread, easily accessible, standardized, and well established in everyday practice over years. Standardized white-on-white perimetry with moving targets (kinetic perimetry) is the major topic of this paper (part 2) in addition to "rough"/preliminary confrontation visual field testing. This review series is aimed at imparting basic concepts in perimetry and psychophysics to ophthalmologists and also addresses interested physicians from other disciplines.

Eye Movements↗

PubMed2005

Progression of visual field defects and visual loss in trabeculectomized eyes.

PURPOSE: To evaluate progression of visual field (VF) defects and development of visual impairment (low vision and blindness) after trabeculectomy. METHODS: We evaluated retrospectively 138 eyes of 138 consecutive patients over 40 years of age with primary open-angle glaucoma (POAG) or exfoliation glaucoma (EG) operated on by trabeculectomy without antimetabolites. The mean follow-up period was 3.5 years (range 2-5). In 83 eyes, pre- and postoperative VF measured by the same technique were compared to detect progression. Visual acuities (VA) were recorded as Snellen decimal notations. VA of <0.3 to 0.05 was defined as low vision and VA of <0.05 or VF constricted to less than 20 degrees in diameter as blindness. RESULTS: In 34 (41%) of 83 eyes with comparable fields, VF defects progressed because of glaucoma. In logistic regression analysis, severity of preoperative VF loss (P=0.0047) and use of preoperative oral anti-glaucomatous medication (P=0.047) correlated significantly with VF progression. In univariate analysis, also initial intraocular pressure (IOP) reduction after surgery (P=0.023) and IOP reduction from preoperative to last postoperative examination (P=0.036) were significantly smaller in eyes with VF progression. Defect progression did not, however, correlate significantly with the last IOP (P=0.58). Six eyes (4.3%) were blind due to glaucoma preoperatively and 14 eyes (10.1%) at the last follow-up. Visual impairment correlated with the severity of initial VF loss (P=0.008). CONCLUSIONS: Progression of VF defects and development of visual impairment due to glaucoma was fairly common despite trabeculectomy. Both were associated with severity of initial VF defect. In this series, no significant correlation appeared between defect progression and the last IOP, but association between stability of VF and the amount of IOP reduction after surgery indicate that a lower target IOP level particularly in eyes with initially severe VF defect would, however, be needed.

Adult↗

PubMed1987

Visual discrimination in the absence of visual cortex.

Normal rats and rats with devascularization lesions ranging from subtotal removals of striate cortex (Area 17) to complete removal of neocortex were trained in a horizontal/vertical stripe discrimination for a liquid reinforcer. Subgroups of animals were identified on the basis of size and location of lesion (with particular reference to striate cortex) as Subtotal, Striate, Posterior and Decorticate. Some animals in all of the lesion groups were able to acquire the discrimination, but there was a direct relationship between lesion size and number of training trials. Those animals which reached criterion on the original discrimination were trained on a second horizontal/vertical discrimination under either transfer or reversal conditions using 'rotated obliques' stimuli. Performance on this second discrimination indicated that animals from all lesion groups had been using visual stimuli based on stripe orientation in the original problem. Members of all lesion groups solved the rotated obliques problem under the transfer condition, though the speed and completeness with which they did so was again inversely related to lesion size. These data show high levels of visual competence in the absence of visual cortex even when stimuli thought to detect form discrimination are used and thus reinforce the view that superior colliculus may be a more significant visual area for the rat than was previously assumed. They also support other observations that animals do not use residual visual capacities without extensive experience and appropriate motivation.

Animals↗

PubMed2004

The relationship between visually evoked cerebral blood flow velocity responses and visual-evoked potentials.

A noninvasive assessment of neurovascular coupling would be of great importance. For this reason, we simultaneously studied graded responses of visually evoked cerebral blood flow (CBF) velocity responses (VEFR) and visual-evoked potentials (VEP) to visual contrasts. The records were made from 30 healthy volunteers aged 38.0 +/- 9.6 years. The stimulus was a black-and-white checkerboard with visual contrasts (VC) of 1%, 10%, and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler, and the VEP were recoded from the scalp from occipital leads. To test the relationship between the VEFR and the VEP, a linear regression analysis was performed. We found that the VEFR at 100% VC were 36% higher than those at 10% VC (P < 0.01). The VEFR at 10% VC were 81% higher than those at 1% VC (P < 0.01). The VEP at 100% VC were 76% higher than those at 10% VC (P < 0.01). The VEP at 10% VC were 184% higher than those at 1% VC (P < 0.01). The linear regression showed a significant, moderate association between the VEP and the VEFR (r = 0.66, P < 0.01). The analysis of the regression slopes (b = 0.48 in older subjects vs. b = 0.58 in younger subjects) between two different age subgroups (P < 0.01) did not show any significant difference (P = 0.035). We concluded that a simultaneous recording of VEFR and VEP to graded visual contrasts could allow an assessment of neurovascular coupling.

Adult↗

PubMed1999

Effects of blocking non-N-methyl-D-aspartate receptors on visual responses of neurons in the cat visual cortex.

To elucidate the function of non-N-methyl-D-aspartate types of glutamate receptors in the primary visual cortex of the adult cat, we studied the effects of the iontophoretically applied glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and D-amino-5-phosphonovalerate. Antagonists were applied with ejecting currents that selectively blocked non-N-methyl-D-aspartate receptors. Among 93 cells in which stable recordings were obtained, 6-cyano-7-nitroquinoxaline-2,3-dione reduced the visual response in all cells. The average response magnitude during 6-cyano-7-nitroquinoxaline-2,3-dione administration was reduced to 11.7% of the control (average ejecting current: 41.2 nA). The effect of 6-cyano-7-nitroquinoxaline-2,3-dione was obvious throughout all cortical layers. The effect of D-amino-5-phosphonovalerate on the visual response was tested in 14 cells and it was also effective in blocking the visual response: the average response magnitude during D-amino-5-phosphonovalerate administration was 45.0% of the control (average ejecting current: 41.4 nA). The effect of 6-cyano-7-nitroquinoxaline-2,3-dione on the response was compared in individual cells at both high and low firing rates in order to determine whether a differential effect exists on the level of firing activity of cells due to secondary inactivation of voltage-dependent N-methyl-D-aspartate receptors. However, no indication of response dependency on firing rate was seen with 6-cyano-7-nitroquinoxaline-2,3-dione. We suggest that excitatory transmission at the geniculocortical and corticocortical synapses seems to be strongly dependent on non-N-methyl-D-aspartate receptors throughout the primary visual cortex of the adult cat, and that both non-N-methyl-D-aspartate and N-methyl-D-aspartate type glutamate receptors function additively.

2-Amino-5-phosphonovalerate↗

PubMedDate not supplied

Video-rate and continuous visual stimuli do not produce equivalent response timings in visual cortical neurons.

Video cathode ray tube (CRT) technology has proven to be extremely valuable for performing research in the visual system. However, the image on a CRT monitor is not constant, but consists of a series of brief pulses. This has implications for any study that explores the responses of neurons in the visual system on short time scales. In particular, there is no unambiguous time point at which a visual stimulus presented via CRT may be said to have ended. Recordings from single units in visual cortical area V1 of an awake primate demonstrate that, when studying changes in response timing on the order of 10 ms or less, stimuli delivered at video frame rates do not duplicate the effects seen with stimuli that have continuous functions of luminance versus time. Additionally, there does not seem to be any clear method of comparing the results obtained with video-rate stimuli with results obtained with continuous-time stimuli that holds for all conditions. These effects are especially critical when exploring the time course of the neuronal responses to the ending of a visual stimulus (off-response). Our findings cast doubt upon the recently reported result that off-responses have consistently shorter latencies than on-responses.

Animals↗

PubMed2000

Visual electrophysiology in children with tumours affecting the visual pathway. Case reports.

In 9 children (8-14 years of age) with orbital, suprasellar or postchiasmal tumours, visual loss was studied by visual electrophysiology in relation to ophthalmologic and neuroimaging findings. Pattern electroretinography (PERG) and pattern visual evoked potentials (PVEP) to full and half-field pattern-reversal stimulation were recorded and PERG and PVEP changes were related to the tumour location. PERG wave P50 attenuation was found associated with the central retinal dysfunction in the child with orbital rhabdomyosarcoma; PVEP wave P100 delay was associated with the optic nerve dysfunction in a child with retrobulbar chondrosarcoma and in a child with optic nerve glioma; PVEP wave P100 asymmetry was associated with the crossed fibers dysfunction in a child with hypothalamic germinoma, and PVEP wave P100 uncrossed asymmetry was associated with postchiasmal dysfunction in children with postchiasmal tumours (one with pilocytic astrocytoma and two with angioma). On the other hand, normal PERG suggested that there was no central retinal dysfunction in a child with pleomorphic adenoma of the lacrimal gland, and normal PVEP to full and half-field stimulation excluded visual pathway dysfunction at the chiasm in a child with suprasellar arachnoidal cyst. Follow-up was useful in indicating whether visual dysfunction was progressive or not. We conclude that PERG and PVEP findings contributed to understanding whether the dysfunction originated was at the retina, in the optic nerve, chiasm or postchiasmal pathway.

Adolescent↗

PubMed1999

Covariation of activity in visual and prefrontal cortex associated with subjective visual perception.

Visual areas of the occipitotemporal pathway are thought to be essential for the conscious perception of objects, but the contribution of other cortical regions and the neural mechanisms leading to the awareness of a visual stimulus remain unclear. By using functional MRI in humans exposed to bistable viewing conditions, subjective visual perception was related to covariation of activity in multiple extrastriate ventral, parietal, and prefrontal cortical areas. The coordination of activity among these regions was not linked to external sensory or motor events; rather, it reflected internal changes in perception and varied in strength with the frequency of perceptual events, suggesting that functional interactions between visual and prefrontal cortex may contribute to conscious vision. Because similar cortical systems have been implicated in short-term memory and motor planning, the results also imply that related neural processes may underlie visual awareness and the organization of voluntary behavior contingent on sensory cues.

Adult↗

PubMed2005

Detrimental effects of irrelevant speech on serial recall of visual items are reflected in reduced visual N1 and reduced theta activity.

The term irrelevant sound effect (ISE) describes an empirically robust finding in which serial recall performance of visual items is reduced by irrelevant speech. At present little is known about its neurophysiological basis. Although some previous neuroelectric studies have concentrated on responses elicited by irrelevant background sound, whether the processing of visually presented to-be-remembered digits itself is affected by irrelevant speech has yet to be studied. An experiment (n = 20) was conducted in which serial recall performance for visually presented digits was tested during exposure to either irrelevant speech, continuous white noise or silence while measuring EEG activity. White noise was chosen as a control condition, because it constitutes auditory stimulation while leaving serial recall performance unimpaired. In addition to replicating the detrimental behavioural effect of irrelevant speech, an analogous speech-specific early decrease ( approximately 160 ms) in the visual ERP (N1) and subsequently a reduced theta response (4-6 Hz; 400-800 ms) at right prefrontal electrodes were observed. Although irrelevant sound presentation was restricted to the visual presentation phase, power spectra reveal that the weaker theta response for speech persisted in a silent retention phase before serial recall. Based on such data we propose re-evaluating the role attention plays in explaining the ISE.

Adaptation, Physiological↗

PubMed1992

Visually evoked oscillations of membrane potential in cells of cat visual cortex.

In response to visual stimulation, cells of the cat visual cortex fire rhythmically at frequencies between 30 and 60 hertz. This rhythmic firing can be synchronized among cells in widespread areas of the visual cortex. The visual stimulus conditions under which this process occurs suggest that the synchronization may contribute to the integration of information across broadly displaced parts of the visual field. An intricate mechanism must control the regularity of firing and its synchronization. In vivo whole-cell patch recordings from cells in area 17 have now shown that robust oscillations of membrane potential underlie the regularity of firing seen extracellularly. In the cells studied, the characteristics of the oscillations of membrane potential suggest that such oscillations are produced by rhythmic activity in synaptic inputs. These rhythmic synaptic inputs form the most likely mechanism for the synchronization of activity in neighboring cortical cells.

Animals↗

PubMed2006

Visual FMRI responses in human superior colliculus show a temporal-nasal asymmetry that is absent in lateral geniculate and visual cortex.

Eye patching has revealed enhanced saccadic latencies or attention effects when orienting toward visual stimuli presented in the temporal versus nasal hemifields of humans. Such behavioral advantages have been tentatively proposed to reflect possible temporal-nasal differences in the retinotectal pathway to the superior colliculus, rather than in the retinogeniculate pathway or visual cortex. However, this has not been directly tested with physiological measures in humans. Here, we examined responses of the human superior colliculus (SC) to contralateral visual field stimulation, using high spatial resolution fMRI, while manipulating which hemifield was stimulated and orthogonally which eye was patched. The SC responded more strongly to visual stimulation when eye-patching made this stimulation temporal rather than nasal. In contrast, the lateral geniculate nucleus (LGN) plus retinotopic cortical areas V1-V3 did not show any temporal-nasal differences and differed from the SC in this respect. These results provide the first direct physiological demonstration in humans that SC shows temporal-nasal differences that LGN and early visual cortex apparently do not. This may represent a temporal hemifield bias in the strength of the retinotectal pathway, leading to a preference for the contralateral hemifield in the contralateral eye.

Adult↗

PubMed1987

The deafferented visual cortex: neuronal activity and visual evoked potentials.

The callosal transfer of information to the visual cortex following its unilateral deafferentation from its geniculate input was studied in both hemispheres. Deafferentation was performed in adult cats by sectioning the optic tract. Action potentials of single cortical cells and visual evoked potentials were recorded from area 17-18 boundary in acute and chronic operated cats. In the deafferented hemisphere, cortical cells were usually visually inactive. However, some recovery of function took place in this hemisphere in the chronic cats, as expressed by the increase in the proportion of S-cells. In the intact hemisphere diminution of responsiveness and reduction of selectivity to the stimulus orientation and direction were found. The responsiveness and selectivity level in the intact hemisphere increased with postoperative time. The ocular dominance distribution in this hemisphere was similar to that of our normal control cats. The characteristics of the visual evoked potentials were in keeping with the hemispheric dominance of the cortical cells found in the experimental cats. It was concluded that a plasticity related mechanism is involved in the recovery of callosal activation of visual cortical cells following deafferentation.

Animals↗

PubMedDate not supplied

Constriction of the visual field of children after early visual deprivation.

PURPOSE: We measured the extent of the monocular visual fields of children deprived of normal visual experience and examined the influence of the timing and duration of deprivation, of whether deprivation was monocular or binocular, of having patched the fellow eye, and of optical factors. METHODS: The Goldmann perimeter and a 6.4' stimulus of either 31.8 cd/m2 (target 12e) or of 318 cd/m2 (target 14e) were used to test 44 children treated for a dense and central cataract in one (n = 25) or both (n = 31) eyes that developed before 6 years of age. Then, the influence of optical factors was assessed in two adults treated for a late-onset, unilateral cataract and in two children treated for unilateral congenital cataract. RESULTS: Compared with age norms or the normal fellow eye, all children treated for cataract showed a restricted field, especially temporally, even when deprivation began as late as 6 years of age and lasted less than 6 months. The restrictions were larger than those shown by the adults who developed cataracts. The restrictions were larger after longer deprivation and monocular deprivation than after binocular deprivation. However, children who regularly patched the fellow nondeprived eye and, therefore, experienced less interocular competition, exhibited smaller restrictions temporally. Neither visual acuity nor optical factors could account for all of the restrictions in the deprived children. CONCLUSIONS: The development of the visual field is vulnerable to the effects of deprivation, especially to unilateral deprivation and to long deprivation. The losses likely reflect alterations in the visual pathways subserving peripheral vision.

Adult↗

PubMed2006

[Comparison of objective assessment using the sweep pattern visual evoked response acuity (SPVERA) and illiterate E visual acuity].

OBJECTIVE: To compare the vision objectively assessed by SPVERA with the illiterate E Acuity in normal subjects. METHODS: The effect of artificially induced image defocusing on visual acuities (Vas) measured by SPVEP and illiterate E chart measurement was studied in 14 normal subjects. SPVEP was recorded using vertical gratings of 8 different spatial frequencies ranging from 0.235 9 to 30.203 2 c/deg. The responses were averaged and displayed through the discrete Fourier transform on the monitor display. SPVERA was determined by extrapolating the PVER amplitude -spatial frequency function to baseline. SPVERA was compared with illiterate E visual acuity measured under the same conditions of optical defocus. RESULTS: With moderate defocusing (<+1.0 diopter (D),VA > 0.42), the SPVERA were equal to or poorer than the illiterate E visual acuity. With more defocus (> +2.0 diopter (D), VA < 0.3),the SPVERA became better than the illiterate E chart Visual Acuity. The correlation between the two acuities was r2 = 0.919. CONCLUSION: SPVERA and the illiterate E visual acuity correlated to a certain degree. We conclude that the SPVERA is effective in estimating vision objectively.

Adult↗