The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform
Dale Purves - One of the best experts on this subject based on the ideXlab platform.
-
Temporal events in cyclopean vision
Proceedings of the National Academy of Sciences of the United States of America, 1996Co-Authors: Timothy J. Andrews, Leonard E. White, Devin Binder, Dale PurvesAbstract:Abstract The majority of neurons in the primary visual cortex of primates can be activated by stimulation of either eye; moreover, the monocular receptive fields of such neurons are located in about the same region of visual space. These well-known facts imply that Binocular Convergence in visual cortex can explain our cyclopean view of the world. To test the adequacy of this assumption, we examined how human subjects integrate Binocular events in time. Light flashes presented synchronously to both eyes were compared to flashes presented alternately (asynchronously) to one eye and then the other. Subjects perceived very-low-frequency (2 Hz) asynchronous trains as equivalent to synchronous trains flashed at twice the frequency (the prediction based on Binocular Convergence). However, at higher frequencies of presentation (4-32 Hz), subjects perceived asynchronous and synchronous trains to be increasingly similar. Indeed, at the flicker-fusion frequency (approximately 50 Hz), the apparent difference between the two conditions was only 2%. We suggest that the explanation of these anomalous findings is that we parse visual input into sequential episodes.
-
Temporal events in cyclopean vision (perceptionyprimary visual cortexytimeyf licker-fusion)
1996Co-Authors: Timothy J. Andrews, Devin Binder, E. White, Dale PurvesAbstract:The majority of neurons in the primary visual cortex of primates can be activated by stimulation of either eye; moreover, the monocular receptive fields of such neurons are located in about the same region of visual space. These well-known facts imply that Binocular Convergence in visual cortex can explain our cyclopean view of the world. To test the adequacy of this assumption, we examined how human subjects integrate Binocular events in time. Light f lashes presented synchronously to both eyes were compared to f lashes presented alternately (asynchronously) to one eye and then the other. Subjects perceived very-low-frequency (2 Hz) asynchronous trains as equivalent to synchronous trains f lashed at twice the frequency (the prediction based on Binocular Convergence). However, at higher frequencies of presentation (4-32 Hz), subjects perceived asynchronous and synchronous trains to be increasingly similar. Indeed, at the f licker-fusion frequency ('50 Hz), the apparent difference between the two conditions was only 2%. We suggest that the explanation of these anomalous findings is that we parse visual input into sequential episodes.
M. Beth Bazin - One of the best experts on this subject based on the ideXlab platform.
-
Prevalence and reporting of near-point Binocular Convergence and acuity vision deficits in potential research participants
Behavior Research Methods, 2008Co-Authors: Patrick A. Ament, Darcy K. Robbins, Callie J. Brockman, Raeanna Hawkins, Susan Lake, M. Beth BazinAbstract:Visual abilities at near-point distances of 200 self-reported normal vision college students were assessed. Results show that normal visual functioning with no deficits is the exception. The most common visual deficits observed involved Binocular lateral posture and fusion Convergence deficits. Binocular and monocular acuity deficits also had high prevalence rates, although not as prevalent as the Binocular Convergence deficits. In addition, 1,340 articles published in four major journals from the years 1997–2004 were examined to ascertain the extent to which authors report the visual capabilities of their participants. Reporting of research participant visual abilities by authors using visual stimuli in experiments appears to be lacking. The results are discussed in terms of the potential impact that visual deficits may have on results obtained in experiments in which visual stimuli are used and the importance of reporting the visual assessment tests and procedures used to assess the visual abilities of potential participants.
Klaus-peter Hoffmann - One of the best experts on this subject based on the ideXlab platform.
-
Tiermodelle für das optokinetische System des Menschen
Klinische Monatsblatter fur Augenheilkunde, 1999Co-Authors: Claudia Distler, Klaus-peter HoffmannAbstract:Background We compare the neuronal and behavioural consequences of abnormal visual experience during early infancy for the optokinetic system of cat and monkey with the neuroopthalmological results in man. Material and methods Optokinetic eye movements were recorded with the search coil method and electrooculography. In addition, the response properties of single neurons in the visual cortex and pretectum of anesthetized and paralyzed cats and monkeys were determined in electrophysiological experiments. Results Our data show that monocular deprivation and strabismus lead to an increase of asymmetry of monocular optokinetic nystagmus and a decrease in gain of slow phase optokinetic eye movements during monocular stimulation as well as to a significant decrease of Binocular Convergence in the oculomotor system of both cat and monkey. Although these changes are basically similar in both species they are not identical. These differential effects may be explained by structural differences. Conclusions Assuming a similar neuronal substrate for the optokinetic system in all primates the monkey represents a more suitable animal model for the human visual system than the cat.
-
Retinal slip neurons in the nucleus of the optic tract and dorsal terminal nucleus in cats with congenital strabismus.
Journal of neurophysiology, 1996Co-Authors: Claudia Distler, Klaus-peter HoffmannAbstract:1. Visual response properties of neurons in the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic tract (DTN) were electrophysiologically investigated in five congenitally strabismic cats and compared with normal adult cats and 3- to 4-wk-old kittens. 2. As in normal cats, NOT-DTN cells of strabismic cats preferred horizontal ipsiversive stimulus movement. However, NOT-DTN neurons in strabismic cats altered their activity to a lesser amount per degree change of stimulus direction than do normal adult cats. In addition, NOT-DTN cells in strabismic cats exhibited a broader directional tuning, i.e., they increase their activity to a broader range of directions than control NOT-DTN cells. 3. Spontaneous activity and activity difference between preferred and nonpreferred direction were significantly lower in NOT-DTN neurons of strabismic cats than in normal adult cats and resembled that found in 3-wk-old kittens. Maximal stimulus-related activity was lower than in normal adult cats but higher than in kittens. 4. Visual latencies to onset of movement in the preferred direction were indistinguishable in strabismic and in normal adult cats. Visual latencies to onset of movement in the nonpreferred direction, however, were shorter in strabismic cats than in normal adult cats. 5. The average velocity tuning curve of NOT-DTN cells in strabismic cats was very flat without a well-defined optimal stimulus velocity. Thus it closely resembled data from 3-wk-old kittens. 6. Binocular Convergence was significantly altered to a stronger dominance of the contralateral eye in NOT-DTN of strabismic cats. This reduction of Binocular neurons was less pronounced than in cats with artificially induced strabismus or in 3-wk-old kittens. 7. In conclusion, the data presented here for retinal slip neurons in the NOT-DTN of strabismic cats closely resemble those from 3-wk-old kittens where no functional cortical input to the NOT-DTN is present. However, the elevated stimulus-driven activity and the still relatively high degree of Binocularity give a clear indication of a functional, albeit weak and abnormal, cortical input to the NOT-DTN in these naturally strabismic cats.
R D Freeman - One of the best experts on this subject based on the ideXlab platform.
-
Neural mechanisms for processing Binocular information I. Simple cells.
Journal of neurophysiology, 1999Co-Authors: A Anzai, I Ohzawa, R D FreemanAbstract:The visual system integrates information from the left and right eyes and constructs a visual world that is perceived as single and three dimensional. To understand neural mechanisms underlying this process, it is important to learn about how signals from the two eyes interact at the level of single neurons. Using a sophisticated receptive field (RF) mapping technique that employs binary m-sequences, we have determined the rules of Binocular interactions exhibited by simple cells in the cat's striate cortex in relation to the structure of their monocular RFs. We find that Binocular interaction RFs of most simple cells are well described as the product of left and right eye RFs. Therefore the Binocular interactions depend not only on Binocular disparity but also on monocular stimulus position or phase. The Binocular interaction RF is consistent with that predicted by a model of a linear Binocular filter followed by a static nonlinearity. The static nonlinearity is shown to have a shape of a half-power function with an average exponent of approximately 2. Although the initial Binocular Convergence of signals is linear, the static nonlinearity makes Binocular interaction multiplicative at the output of simple cells. This multiplicative Binocular interaction is a key ingredient for the computation of interocular cross-correlation, an algorithm for solving the stereo correspondence problem. Therefore simple cells may perform initial computations necessary to solve this problem.
Wolf Singer - One of the best experts on this subject based on the ideXlab platform.
-
Monocularly induced 2-deoxyglucose patterns in the visual cortex and lateral geniculate nucleus of the cat: I. Anaesthetized and paralysed animals.
The European journal of neuroscience, 1993Co-Authors: Siegrid Löwel, Wolf SingerAbstract:Extending previous investigations of the topographic relationship between ocular dominance and orientation columns in the cat visual cortex the two systems were visualized with transneuronally transported [3H]proline and with activity-dependent uptake of [14C]2-deoxyglucose, respectively. In addition, we used the 2-deoxyglucose method for a functional assay of both columnar systems. To this end, cats were injected with [3H]proline in the right eye. Two weeks later, they were stimulated monocularly through this eye by presenting contours of only a single orientation in the left and contours of many different orientations in the right visual hemifield while 2-deoxyglucose was injected. The patterns of increased 2-deoxyglucose uptake and of terminal labelling were analysed in flat-mount sections of the visual cortices and in frontal sections of the lateral geniculate nuclei. In the lateral geniculate nucleus, regions of increased 2-deoxyglucose uptake are in register with the [3H]proline-labelled laminae of the open eye. In the visual cortex, the hemispheres stimulated with many different orientations showed a rather homogeneous accumulation of 2-deoxyglucose over the entire extent and throughout all layers of area 17. The hemispheres stimulated with a single orientation displayed columnar patterns of orientation domains essentially similar to those obtained with Binocular presentation of a single orientation. In particular and despite monocular stimulation, regions of increased 2-deoxyglucose uptake were neither in register with the [3H]proline-labelled terminals of the increased 2-deoxyglucose uptake were neither in register with the [3H]proline-labelled terminals of the stimulated eye in layer IV nor confined to columns of neural tissue above and below these terminals. The maximal horizontal offset between the termination sites of thalamic afferents and activated orientation columns was in the order of 400 microns. These findings suggest several conclusions. (i) In the cat visual cortex, Binocular Convergence seems to occur so early in cortical processing that monocular stimulation with many orientations leads to a rather homogeneous activation of cortical tissue. (ii) From the termination zones of geniculate afferents activity is apparently distributed already within layer IV to the respective orientation columns. (iii) This horizontal spread of activity could be assured by target cells with radially extending dendrites and/or tangentially oriented fibres.
-
Monocularly Induced 2-Deoxyglucose Patterns in the Visual Cortex and Lateral Geniculate Nucleus of the Cat: II. Awake Animals and Strabismic Animals
European Journal of Neuroscience, 1993Co-Authors: Siegrid Löwel, Wolf SingerAbstract:In the course of experiments studying the organization of ocular dominance columns in the visual cortex of cats, we noticed that--contrary to common belief--labelling with 2-deoxyglucose after monocular stimulation failed to induce a pattern of ocular dominance columns but resulted in a rather homogenous 2-deoxyglucose uptake throughout area 17 in anaesthetized and paralysed animals. We wondered whether 2-deoxyglucose columns could be obtained in awake animals and/or in strabismic animals, which have a more pronounced segregation of ocular dominance columns. To this end, we investigated 2-deoxyglucose patterns after monocular stimulation in three groups of animals: (i) in awake normally reared cats, (ii) in awake strabismic cats and (iii) in anaesthetized and paralysed strabismic cats. Additionally, we labelled ocular dominance columns with intraocular [3H]proline injections. In all cats, monocular stimulation induced 2-deoxyglucose patterns that were in precise register with the proline-labelled ocular dominance columns in layer IV. Regions of increased 2-deoxyglucose uptake extended in a columnar fashion through all cortical layers. In contrast to normally reared animals, in strabismic cats, the expression of 2-deoxyglucose labelled ocular dominance columns was not abolished by anaesthesia or paralysis. However, there was a difference between the 2-deoxyglucose patterns in the awake normally reared cats and the strabismic animals. In the former, the patches of 2-deoxyglucose labelling were smaller and occupied less territory than the afferents of the stimulated eye in layer IV. Together with the results of the previous study, these data indicate that in awake normally reared and in awake and anaesthetized strabismic cats, but not in anaesthetized and paralysed normally reared animals, monocular stimulation activates selectively neurons in columns that are in register with the termination sites of afferents from the stimulated eye. This suggests the existence of a mechanism in normally reared animals which restricts cortical activation after monocular stimulation to territories that are in register with the afferents from the stimulated eye. This mechanism appears to be effective only when the animals are awake and actively exploring their environment. This and the fact that the active columns were narrower than the terminal fields of the stimulated eye suggest an active inhibitory process, perhaps related to mechanisms of selective attention. The observation that ocular dominance columns persist in strabismic cats even under anaesthesia can be accounted for by the lack of Binocular Convergence in these animals.