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PubMed1995

Olfactory-visual associative learning in monkeys depends on intrahemispheric olfactory-visual interaction.

Three Cynomolgus monkeys (Macaca fasicularis) learned a series of food-visual conditional discrimination problems. In each problem, 1 of 2 possible food items was presented at the beginning of each trial and acted as an instruction cue as to which of 2 visually distinct stimulus objects the monkey must displace on that trial to obtain a further food reward. Following surgical disconnection of olfactory-visual intrahemispheric interaction, the monkeys were unable to use olfactory properties of the food items to guide visual choices. These results show both that olfactory differences between foodstuffs are a powerful olfactory stimulus, which can enter into cross-modal association with visual stimuli, and that this association depends on an intrahemispheric pathway of olfactory-visual interaction.

Afferent Pathways↗

PubMed1999

The cortical visual area V6: brain location and visual topography.

The brain location and topographical organization of the cortical visual area V6 was studied in five hemispheres of four awake macaque monkeys. Area V6 is located in the caudal aspect of the superior parietal lobule (SPL). It occupies a 'C'-shaped belt of cortex whose upper branch is in the depth of the parieto-occipital sulcus (POS) and lower one is in the depth of the medial parieto-occipital sulcus (POM), with the medial surface of the brain as a zone of junction between the two branches. Area V6 contains a topographically organized representation of the contralateral visual field up to an eccentricity of at least 80 degrees. The lower visual field representation is located dorsally, in the ventral part of POS, and the upper field ventrally, in the dorsal wall of POM. The representation of the horizontal meridian forms the posterior border of V6. It is adjacent to area V3 in POS as well as in the caudal part of POM, on the ventral convexity of the brain. The lower vertical meridian forms the anterior border of V6, adjacent to area V6A. The upper vertical meridian is in the depth of POM. The representation of the central visual field is not magnified relative to that of the periphery. The central visual field (below 20-30 degrees of eccentricity) is represented in the medial-most aspect of the annectant gyrus, in the lateral part of the posterior bank of POS. The visuotopic organization of area V6 suggests a role in the analysis of the flow field resulting from self-motion, in selecting targets during visual searching as well as in the control of arm-reaching movements towards non-foveated targets.

Animals↗

PubMed1983

Visual receptive fields and response properties of neurons in human temporal lobe and visual pathways.

Recordings were made from depth electrodes placed in medial temporal and occipital lobes for the localization of seizure foci in patients with medically intractable psychomotor epilepsy. Electrodes were located in the amygdala and at three rostrocaudal levels of the hippocampal formation including the posterior hippocampal gyrus, which lies medial to the portion of the geniculostriate pathway which passes through the temporal lobe. 1. Approximately 10 per cent of single units recorded from microelectrodes chronically implanted in medial temporal sites were visually responsive. Some of the units in the posterior hippocampal gyrus displayed receptive field characteristics similar to those reported in lower primates, including circular or linear shape, monocular or binocular response, variable (1 to 10 deg) receptive field size, retinotopic organization and sustained or transient response. 2. Visually responsive units were also recorded from lateral geniculate nucleus, pulvinar nucleus and occipital cortex, and their basic response form and latencies compared with the short latency visually responsive cells in medial temporal lobe. 3. The heterogeneity of receptive field characteristics in the medial temporal lobe is consistent with the existence of more than one visual input to this region, while their retinotopic relationship differentiates these receptive fields from those of units studied in the inferior temporal lobe of lower primates. 4. Properties of visual pathways in this region are discussed in relation to several types of temporal lobe function and to memory. Recordings from these neurons offer a rare opportunity for comparison of central visual response properties and receptive field characteristics of humans with those reported in animal studies.

Adult↗

PubMed1996

Feasibility of a visual prosthesis for the blind based on intracortical microstimulation of the visual cortex.

The feasibility of producing a visual prosthesis for the blind using intracortical microstimulation (ICMS) of the visual cortex was studied in a 42-year-old woman who had been totally blind for 22 years secondary to glaucoma. Thirty-eight microelectrodes were implanted in the right visual cortex, near the occipital pole, for a period of 4 months. Percepts reported as small spots of light, called phosphenes, were produced with 34 of the 38 implanted microelectrodes. Threshold currents for phosphene generation with trains of biphasic pulses were as low as 1.9 microA, and most of the microelectrodes had thresholds below 25 microA. Phosphene brightness could be modified with stimulus amplitude, frequency and pulse duration. Repeated stimulation over a period of minutes produced a gradual decrease in phosphene brightness. Phosphenes did not flicker. The apparent size of phosphenes ranged from a "pin-point' to a "nickel' (20 mm diameter coin) held at arm's length. Phosphene size usually decreased as stimulation current was increased but increased slightly as the train length (TL) was increased. At levels of stimulation near threshold, the phosphenes were often reported to have colours. As the stimulation level was increased, the phosphenes generally became white, greyish or yellowish. Individual phosphenes appeared at different distances from the subject. When two phosphenes were simultaneously generated, the apparent distances of the individual phosphenes sometimes changed to make them appear to be at about the same distance. When three or more phosphenes were simultaneously generated, they became coplanar. Except for rare occasions, phosphenes extinguished rapidly at the termination of the stimulation train. When stimulation TLs were increased beyond 1 s, phosphenes usually disappeared before the end of the train. The duration of phosphene perception could be increased by interrupting a long stimulation train with brief pauses in stimulation. Intracortical microelectrodes spaced 500 microns apart generated separate phosphenes, but microelectrodes spaced 250 microns typically did not. This two-point resolution was about five times closer than has typically been achieved with surface stimulation. With some individual microelectrodes, a second closely spaced phosphene was sometimes produced by increasing the stimulation current. Phosphenes moved with eye movements. When up to six phosphenes were simultaneously elicited, they all moved with the same relative orientation during eye movements. All phosphenes were located in the left hemi-field with the majority above the horizontal meridian. There was a clustering of most of the phosphenes within a relatively small area of visual space. The potentially greater microelectrode density and lower power requirements of ICMS compared with surface stimulation appears encouraging for a visual prosthesis. However, further studies with blind subjects are required to optimize stimulation parameters and test complex image recognition before the feasibility of a visual prosthesis based on ICMS can be established.

Adult↗

PubMedDate not supplied

Estimates of the net excitatory currents evoked by visual stimulation of identified neurons in cat visual cortex.

The action potential discharge response of single neurons to both visual stimulation and injections of current were obtained during intracellular recordings in cat visual cortex in order to estimate the net excitatory current arriving at the soma during visual stimulation. Of 45 neurons recorded intracellularly, 19 pyramidal neurons and one basket cell were labelled with horseradish peroxidase. The discharge of all neurons adapted to constant current. For 40 neurons, a single exponential provided a good fit to the adapting discharge (r2 = 0.73 +/- 0.03) for all current intensities. Superficial layer neurons were significantly faster adapting [P < 0.001, mean (+/- SEM) time constant of adaptation = 11.5 +/- 1.3 ms; n = 20] than deep layer neurons (mean time constant of adaptation = 51.4 +/- 6.4 ms; n = 10). The percentage adaptation of the spike frequency, %(peak - adapted rate)/peak, was determined from the fitted exponential. Superficial layer neurons adapted significantly more strongly (P < 0.01, mean = 67 +/- 3%) than deep layer neurons (mean = 51 +/- 5%). The mean firing frequency in response to a current step of 320 ms duration had a linear relationship to the amplitude of the injected current (slope 66 spikes/s/nA; origin zero, mean r2 = 0.94; n = 33). This relationship provided a means of estimating the net peak excitatory current generated by visual stimuli. The estimated mean peak somatic current during the passage of a bar across the receptive field was 1.1 nA and the average current for the duration of the visually evoked discharge was 0.64 nA (n = 17). The transfer response of real and model neurons was obtained by differentiating the discharge response to a step input current and was then used to predict the output of the neuron following an arbitrary input. When these transfer responses were convolved with known input signals in model neurons, the predicted output was close to the simulated response of the model neuron to the same input waveforms. The transfer response was calculated for eight real neurons. Estimates of the net excitatory current arriving at the soma during visual stimulation was obtained by deconvolution. The mean peak somatic current for these neurons was 0.62 nA.

Action Potentials↗

PubMed1976

The visual evoked response to word stimuli in the visual fields.

The visual evoked response (VER) has been considered an objective indicator of visual and perceptual processing, although as yet there is no clear evidence of a relationship between visual recognition and electrophysiological activity. The present study was performed to determine whether VER's can provide indications of differences in responses to word stimuli presented in different parts of the visual field. Additionally, evidence was sought as to whether the left and right hemispheres process visual information symmetrically. In 20 adult subjects with normal binocular vision, VER's were recorded simultaneously from left and right hemispheres in response to the repeated presentation of a three-letter word in each of 7 visual field locations. VER's of any subject in response to one stimulus site were consistent and repeatable; intersubject variation was large. For subject comparison, amplitude of VER was the measured response. No significant or consistent amplitude characteristics were identified that related to recognition of the stimulus. From comparison of responses to the different field locations, central stimulation (at 0 degrees) evoked the largest peak-to-trough amplitude (X=8.21 uV+/- 2.56). Amplitudes tended to be larger at 4 degrees than at 2 degrees from center; left field stimulation tended to give larger amplitudes than right field; however, these trends were larger than from the left, this difference was not valid since 11 subjects had larger right hemisphere responses, whereas 9 had larger amplitudes from the left hemisphere. Thus, the study suggests that the VER reflects some net electrical activity from the recording sites that may be traced to an external sensory stimulus and shows that this activity is symmetrical for each hemisphere.

Adult↗

PubMed1989

Functional development of the visual system in normal and protein-deprived rats. IX. Visual evoked response in young rats.

Changes in latencies of the visual evoked response (VER) during early post-natal development were examined in protein-deprived (PD) rats. The evoked response to light-flash stimulation was recorded in the dorsal lateral geniculate nucleus (dLGN) and on the surface of the visual cortex. In control rats, latencies of the cortical VER decreased rapidly up to 20 days and slowly thereafter. In PD rats, the latencies of the cortical VER were increased by 10-15 ms at 17 days; the developmental decrease was delayed by approximately 3 days. After 20 days, PD rats also went into a phase with slow decrease of the latencies, and the onset latency of the cortical VER was still increased by some 10 ms at 26/27 days. At this age, PD rats showed an increase in the latencies of the VER in the dLGN which was of similar magnitude to that in the cortical VER, indicating that alterations were more marked in the peripheral parts of the visual system at this stage of development. The findings are in agreement with previous studies indicating that there is a delay of visual system development in PD rats before 20 days. A maturational event which turns rapid into slow development at approximately 20 days in both C and PD rats turns this delay into a distortion of development. The delays and distortions of visual system development may be one causative factor for the functional deficit present in the visual cortex of adult PD rats.

Animals↗

PubMedDate not supplied

Dichoptic visual masking reveals that early binocular neurons exhibit weak interocular suppression: implications for binocular vision and visual awareness.

Visual masking effects are illusions in which a target is rendered invisible by a mask, which can either overlap or not overlap the target spatially and/or temporally. These illusions provide a powerful tool to study visibility and consciousness, object grouping, brightness perception, and much more. As such, the physiological mechanisms underlying the perception of masking are critically important to our understanding of visibility. Several models that require cortical circuits have been proposed previously to explain the mysterious spatial and timing effects associated with visual masking. Here we describe single-unit physiological experiments from the awake monkey that show that visual masking occurs in at least two separate and independent circuits, one that is binocular and one that is monocular (possibly even subcortical), without feedback from higher-level visual brain areas. These and other results together fail to support models of masking that require circuits found only in the cortex, but support our proposed model that suggests that simple ubiquitous lateral inhibition may itself be the fundamental mechanism that explains visual masking across multiple levels in the brain. We also show that area V1 neurons are dichoptic in terms of excitation, but monoptic in terms of inhibition. That is, responses within area V1 binocular neurons reveal that excitation to monocular targets is inhibited strongly only by masks presented to the same eye, and not by masks presented to the opposite eye. These results lead us to redefine the model for the first stage of binocular processing in the visual system, and may be crucial to interpreting the effects of other similar binocular and dichoptic stimulation paradigms, such as the binocular rivalry family of illusions.

Action Potentials↗

PubMed1990

Visual mechanisms and predictors of far field visual task performance.

Visual mechanisms involved in target detection, recognition, and tracking were examined. Relationships were analyzed in the context of simulated combat, focusing on the short-range air defense weapon operator. Objectives were to identify visual ability interrelations, predictors of performance, and interactions with cuing, target characteristics, and experience. Good predictors included visual acuity, contrast sensitivity, resting focus, near focal point, and blur interpretation. Many of these abilities interacted with the independent variables, producing differential effects on performance. Visual abilities logically grouped into three principal components: active accommodation predicted target detection and identification; passive accommodation predicted detection and acquisition; and image interpretation predicted acquisition, identification, and tracking. Results supported the three visual subsystems hypothesis, based on neurophysiological evidence of pathways in the brain corresponding to specific visual functions.

Adult↗

PubMed1990

Fresnel prisms improve visual perception in stroke patients with homonymous hemianopia or unilateral visual neglect.

We randomly assigned 39 patients with stroke and homonymous hemianopia or unilateral visual neglect to treatment with 15-diopter plastic press-on Fresnel prisms (n = 18) or to serve as controls (n = 21). Baseline evaluations of visual perception and activities-of-daily-living (ADL) function were similar for both groups. After 4 weeks, the prism-treated group performed significantly better than controls on the following: (1) Motor Free Visual Perception Test; (2) Line Bisection Task; (3) Line Cancellation Task; (4) Harrington Flocks Visual Field Screener; and (5) Tangent Screen Examination. There was no significant difference in Barthel ADL assessment at 4 weeks. Thus, treatment with 15-diopter Fresnel prisms improves visual perception test scores but not ADL function in stroke patients with homonymous hemianopia or unilateral visual neglect.

Aged↗

PubMed2006

Use of multifocal visual evoked potential tests in the objective evaluation of the visual field in pediatric epilepsy surgery.

OBJECT: To evaluate objectively the visual fields of patients with pediatric epilepsy who are uncooperative with perimetry and in whom postoperative visual field deficits are expected, the authors investigated the usefulness of the multifocal visual evoked potential (VEP) method. METHODS: Normal waves in multifocal VEP were determined in 21 healthy children (21 eyes) 6 to 15 years of age (mean 11.4 years). Responses from eight sites in each child were divided into four quadrants (superior and inferior temporal and superior and inferior nasal). In each quadrant, two response waves were grouped and averaged. The peak latency and amplitude at approximately 100 msec were used for assessment. In three cases involving patients with epilepsy, multifocal VEP measurements were also recorded and compared with the peak latency and amplitude in the healthy children. In these children, no significant differences were observed in the peak latency of amplitude among four quadrants using one-way analysis of variance. In each patient, multifocal VEP tests showed abnormal waves in the quadrant corresponding to the lesion demonstrated in neuroradiological images. This result was useful in the treatment of choice and the postoperative evaluation. CONCLUSIONS: Multifocal VEP tests can be useful in evaluating the visual field of children objectively. They can also be valuable in assessing preoperative visual field defects and revealing changes in the visual field after treatment.

Adolescent↗

PubMed2002

[Visual perception of Japanese characters and complicated figures: developmental changes of visual P300 event-related potentials].

In order to evaluate developmental change of visual perception, the P300 event-related potentials (ERPs) of visual oddball task were recorded in 34 healthy volunteers ranging from 7 to 37 years of age. The latency and amplitude of visual P300 in response to the Japanese ideogram stimuli (a pair of familiar Kanji characters or unfamiliar Kanji characters) and a pair of meaningless complicated figures were measured. Visual P300 was dominant at parietal area in almost all subjects. There was a significant difference of P300 latency among the three tasks. Reaction time to the both kind of Kanji tasks were significantly shorter than those to the complicated figure task. P300 latencies to the familiar Kanji, unfamiliar Kanji and figure stimuli decreased until 25.8, 26.9 and 29.4 years of age, respectively, and regression analysis revealed that a positive quadratic function could be fitted to the data. Around 9 years of age, the P300 latency/age slope was largest in the unfamiliar Kanji task. These findings suggest that visual P300 development depends on both the complexity of the tasks and specificity of the stimuli, which might reflect the variety in visual information processing.

Adolescent↗

PubMed1989

[Visually evoked potentials and visual acuity of the young child].

Interest in the development of visual acuity in young infants is increasing. At this age a reliable estimation of visual function is hazardous. This paper highlights the role of flash- and pattern evoked visual potentials. Flash evoked potentials are valuable in following development and/or recovery of visual acuity intra-individually as well as in providing an estimation of sensitiveness to light. Pattern evoked potentials may give an estimation of maturation of the visual system: these potentials also give an objective measurement of visual acuity.

Child, Preschool↗

PubMed1994

[A.R.G.U.S. A model for an interactive visual field and visual pathway atlas].

A.R.G.U.S. is a data base that connects visual field defects directly with possible lesion sites that are presented graphically. By means of a touch screen or "mouse," scotomata can be depicted on a VDU, while on a second monitor the computer program simultaneously shows the resulting defects in the visual pathway. It is possible to page through different sections of the visual pathway; the lesion is probably located in the section where the affected fibers lie the closest to each other and where the non-affected fibers are the farthest apart. Additionally, the VDU depicting the visual pathway can show the surrounding anatomic structures in the form of brain sections. Even in these sections, lesions can be superimposed interactively; the resulting scotomata are simultaneously depicted on the "visual field VDU." Anatomic and functional details can be displayed by touching the structure of interest. If necessary, a video clip can be activated in the same way. New anatomic findings can be considered by modifying the course of the fibers of the visual pathway. This new technique is especially helpful in distributing comprehensive neuro-ophthalmological knowledge.

Artificial Intelligence↗

PubMed1995

Functional magnetic resonance imaging of the primary visual cortex: evaluation of human afferent visual system.

The authors evaluated signal changes in the human primary visual cortex during visual stimulation using functional magnetic resonance imaging (MRI) scanner at 1.5 Tesla. Experiments were performed on 10 normal volunteers and 2 patients with homonymous hemianopsia. In the normal volunteers, a signal increase was observed on the bilateral primary visual cortex during hemifield stimulation. In one patient with homonymous hemianopsia after cerebral infarction, the signal change was clearly decreased on the affected side. In the other patient, who was recovering from multiple sclerosis to an almost normal visual field, the fMRI results were within normal limits. These results suggest that it is possible to map noninvasively the activation of the visual stimulation with a clinical MRI system, and that this test might be useful as an objective method of visual field examination.

Adult↗

PubMed1998

[The usefulness of visual evoked potentials for the evaluation of visual pathways in children and adolescents with selected neuro-ophthalmological syndromes. (Summary of the doctor of medicine degree dissertation)].

OBJECTIVES: Much study and care have been devoted to evaluated lesions of the visual pathway in children and adolescents with different neuroophthalmological disorders. The aim of the study was to determine the usefulness of visual evoked potentials (VEP) for evaluation of visual pathway in young patients with cerebral palsy, sclerosis multiplex and subacute sclerosing panencephalitis. MATERIAL AND METHODS: During the research 63 healthy children and 78 pathological ones, between 5 and 18 years of age, were studied. First ophthalmological examination was performed and next VEPs were recorded. For poorly cooperative children, a flash on TV screen was used as a stimulus, and for normal mental children a pattern-reversal black and white checkboard was used. The comparison of VEP in normal healthy subjects and pathological ones was the last part of the investigation to evaluate visual system of patients. RESULTS: In all groups of patients, both with visual complains and without them, pathological results of VEP were found. The pathology of VEP were connected with shape, amplitudes and latencies of the peaks N75, P100, N145. CONCLUSIONS: The VEP is a good and objective method of diagnosis in neuroophthalmological patients, which supplies extra information about lesions of visual pathway. It allows to detect subclinical lesions. It is a noninvasive and painless diagnostical method and it can be repeated a few times in various periods of illness and even in poorly cooperative patients.

Adolescent↗

PubMed1985

The application of flash visual evoked potentials during operations on the anterior visual pathways.

Flash visual evoked potentials (F-VEP's) have been recorded in fifteen patients (thirty eyes) with anterior visual pathway compression lesions before, during and after the operation in relation to clinical visual testing. A grading system for the wide variety of abnormal F-VEP's has been established, based on changes in forty patients (eighty eyes). No significant correlation between change in F-VEP and visual acuity or visual field has been demonstrated. Intraoperative F-VEP's have been found to be sensitive to halothane and to surgical manipulation of the optic nerve and/or chiasm during dissection of the tumour. The technique is considered a useful means of identifying the optic pathway during operation and may assist in prevention of optic damage if the transphenoidal approach is used.

Adult↗

PubMed1976

Modification of visual function by early visual experience.

Physiological experiments, involving recording from the visual cortex in young kittens and monkeys, have given new insight into human developmental disorders. In the visual cortex of normal cats and monkeys most neurones are selectively sensitive to the orientation of moving edges and they receive very similar signals from both eyes. Even in very young kittens without visual experience, most neurones are binocularly driven and a small proportion of them are genuinely orientation selective. There is no passive maturation of the system in the absence of visual experience, but even very brief exposure to patterned images produces rapid emergence of the adult organization. These results are compared to observations on humans who have "recovered" from early blindness. Covering one eye in a kitten or a monkey, during a sensitive period early in life, produces a virtually complete loss of input from that eye in the cortex. These results can be correlated with the production of "stimulus deprivation amblyopia" in infants who have had one eye patched. Induction of a strabismus causes a loss of binocularity in the visual cortex, and in humans it leads to a loss of stereoscopic vision and binocular fusion. Exposing kittens to lines of one orientation modifies the preferred orientations of cortical cells and there is an analogous "meridional amblyopia" in astigmatic humans. The existence of a sensitive period in human vision is discussed, as well as the possibility of designing remedial and preventive treatments for human developmental disorders.

Amblyopia↗