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At least 847 records · Page 47Linked to original sources
PubMed1978

Early development of visual cortical cells in normal and dark-reared kittens: relationship between orientation selectivity and ocular dominance.

1. 535 units were recorded in the primary visual cortex in twelve normally reared and fifteen dark-reared kittens aged between 8 and 50 days. These results were pooled with a previous study of 582 units recorded from thirty-five kittens reared in similar conditions. 2. These 1117 cells were classified into four functional classes of neurones: (a) visually unresponsive cells, (b) non-specific cells which were sensitive to spots or slits of light moving in any direction, (c) immature cells which were preferentially activated by a rectilinear stimulus but unselective regarding its precise orientation and (d) specific cells that appeared to be as selective for orientation as the simple or complex cells in the adult cat. 3. The results confirm that cells having the same orientation-specific response properties as adult cortical visual neurones are present in the earliest stages of post-natal development, independently of visual experience. However, to maintain and develop these specific cells after the third week of post-natal life, visual experience is necessary. 4. The ocular dominance of visual cells is not constant from the earliest stages of development. A significant increase in binocularly driven neurones occurs with age. 5. Before 3 weeks of age, whatever the rearing conditions, there are more specific cells coding horizontal and vertical orientations than those coding oblique orientations. These 'horizontal and vertical detectors' are preferentially driven by the contralateral eye. 5. After 4 weeks of age, specific neurones are found at all orientations in normally reared kittens. At this stage of development the ocular dominance is independent of orientation preference, of the functional class of neurones considered and of the rearing conditions. The proportion of binocularly driven cells is slightly below adult standard. 7. A hypothesis of differential plasticity is proposed: contralateral, monocular 'horizontal and vertical detectors' are supposed to be stable; they would remain so until they become binocular. Binocular cells, for which competition between two inputs occurs, are the labile units which can be despecified or specified under the control of visual experience.

Action Potentials↗
PubMedDate not supplied

Receptive field properties of near neighbor orientation selective neurons in the visual cortex: a modeling study.

The primary visual cortex is organized into clusters of cells having similar receptive fields (RFs). A purely feedforward model has been shown to produce realistic simple cell receptive fields. The modeled cells capture a wide range of receptive field properties of orientation selective cortical cells. We have analyzed the responses of 78 nearby cell pairs to study which RF properties are clustered. Orientation preference shows strongest clustering. Orientation tuning width (hwhh) and tuning height (spikes/sec) at the preferred orientation are not as tightly clustered. Spatial frequency is also not as tightly clustered and RF phase has the least clustering. Clustering property of orientation preference, orientation tuning height and width depend on the location of cells in the orientation map. No such location dependence is observed for spatial frequency and RF phase. Our results agree well with experimental data.

Animals↗
PubMed2004

Early alcohol exposure induces persistent alteration of cortical columnar organization and reduced orientation selectivity in the visual cortex.

Fetal alcohol syndrome (FAS) is a major cause of learning and sensory deficits in children. The visual system in particular is markedly affected, with an elevated prevalence of poor visual perceptual skills. Developmental problems involving the neocortex are likely to make a major contribution to some of these abnormalities. Neuronal selectivity to stimulus orientation, a functional property thought to be crucial for normal vision, may be especially vulnerable to alcohol exposure because it starts developing even before eye opening. To address this issue, we examined the effects of early alcohol exposure on development of cortical neuron orientation selectivity and organization of cortical orientation columns. Ferrets were exposed to ethanol starting at postnatal day (P) 10, when the functional properties and connectivity of neocortical neurons start to develop. Alcohol exposure ended at P30, just before eye opening at P32. Following a prolonged alcohol-free period (15-35 days), long-term effects of early alcohol exposure on cortical orientation selectivity were examined at P48-P65, when orientation selectivity in normal ferret cortex has reached a mature state. Optical imaging of intrinsic signals revealed decreased contrast of orientation maps in alcohol- but not saline-treated animals. Moreover, single-unit recordings revealed that early alcohol treatment weakened neuronal orientation selectivity while preserving robust visual responses. These findings indicate that alcohol exposure during a brief period of development disrupts cortical processing of sensory information at a later age and suggest a neurobiological substrate for some types of sensory deficits in FAS.

Action Potentials↗
PubMed2002

Motor facilitation while observing hand actions: specificity of the effect and role of observer's orientation.

Action observation enhances cortico-spinal excitability. Here we tested the specificity of this effect and the role played by the orientation of the observer. Ten normal subjects observed video clips of right hand performing three different finger movements (thumb ab-/adduction, index ab-/adduction, index extens-/flexion) in two different orientations (Away, i.e., natural hand-orientation facing out from the observer; or Toward, i.e., unnatural hand-orientation facing toward the observer). Motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) were recorded from the abductor pollicis brevis (APB) and the first dorsal interosseus (FDI) muscles. Movement direction of the index finger was recorded using force transducers. Facilitation of MEP size was significantly greater for APB during observation of thumb movements and for FDI during observation of index finger movements. Facilitation of MEP size was significantly greater when the hand presented on screen was facing out from and corresponding to that of the observer (Away orientation). The direction of the index finger movement evoked by TMS shifted toward extension/flexion versus ab-/adduction matching the observed movement. Our results give further evidence that observation of a movement enhances motor output to the muscles involved in the movement and facilitates the observed action. In addition, we provide novel evidence about the high degree of specificity of this observation-induced motor cortical modulation. The degree of modulation depends on hand orientation. The modulation is maximal when the observed action corresponds to the orientation of the observer.

Adult↗
PubMed2002

Learning and adaptation in a recurrent model of V1 orientation selectivity.

Learning and adaptation in the domain of orientation processing are among the most studied topics in the literature. However, little effort has been devoted to explaining the diverse array of experimental findings via a physiologically based model. We have started to address this issue in the framework of the recurrent model of V1 orientation selectivity and found that reported changes in V1 orientation tuning curves after learning and adaptation can both be explained with the model. Specifically, the sharpening of orientation tuning curves near the trained orientation after learning can be accounted for by slightly reducing net excitatory connections to cells around the trained orientation, while the broadening and peak shift of the tuning curves after adaptation can be reproduced by appropriately scaling down both excitation and inhibition around the adapted orientation. In addition, we investigated the perceptual consequences of the tuning curve changes induced by learning and adaptation using signal detection theory. We found that in the case of learning, the physiological changes can account for the psychophysical data well. In the case of adaptation, however, there is a clear discrepancy between the psychophysical data from alert human subjects and the physiological data from anesthetized animals. Instead, human adaptation studies can be better accounted for by the learning data from behaving animals. Our work suggests that adaptation in behaving subjects may be viewed as a short-term form of learning.

Adaptation, Physiological↗
PubMed2004

Haphazard wiring of simple receptive fields and orientation columns in visual cortex.

The receptive fields of simple cells in visual cortex are composed of elongated on and off subregions. This spatial arrangement is widely thought to be responsible for the generation of orientation selectivity. Neurons with similar orientation preferences cluster in "columns" that tile the cortical surface and form a map of orientation selectivity. It has been proposed that simple cell receptive fields are constructed by the selective pooling of geniculate receptive fields aligned in space. A recent analysis of monosynaptic connections between geniculate and cortical neurons appears to reveal the existence of "wiring rules" that are in accordance with the classical model. The precise origin of the orientation map is unknown, but both genetic and activity-dependent processes are thought to contribute. Here, we put forward the hypothesis that statistical sampling from the retinal ganglion cell mosaic may contribute to the generation of simple cells and provide a blueprint for orientation columns. Results from computer simulations show that the "haphazard wiring" model is consistent with data on the probability of monosynaptic connections and generates orientation columns and maps resembling those found in the cortex. The haphazard wiring hypothesis could be tested by measuring the correlation between the orientation map and the structure of the retinal ganglion cell mosaic of the contralateral eye.

Animals↗
PubMed1986

Cat area 17. III. Response properties and orientation anisotropies of corticotectal cells.

The receptive field properties of antidromically identified corticotectal (CT) cells in area 17 were explored in the paralyzed, anesthetized cat. To compare these with another population of infragranular cells, we also examined the receptive field properties of cells in layer 6. Sixty percent of our sample of CT cells showed increased response to increased stimulus length (length summation) and were classified as standard complex cells. The other 40% showed little or no length summation, were generally end stopped, and were classified as special complex cells. Standard and special complex CT cells have complementary orientation anisotropies: the distribution of orientation preferences of standard complex cells is biased toward obliquely oriented stimuli, whereas special complex cells are biased toward horizontally and vertically oriented stimuli. The receptive fields of the cells in our sample were primarily along the horizontal meridian so we cannot determine if these anisotropies are defined relative to the vertical meridian or relative to the meridian passing through the receptive field. The effects of these anisotropies in preferred orientation are minimized by the broad orientation tuning of CT cells. There was no simple relationship between the direction bias of CT cells and the reported direction bias of tectal cells. In contrast to the heterogeneity of corticotectal cells, layer 6 cells uniformly showed strong length summation, tight orientation tuning, and little spontaneous activity.

Animals↗
PubMed2000

Dynamic properties of recurrent inhibition in primary visual cortex: contrast and orientation dependence of contextual effects.

A fundamental feature of neural circuitry in the primary visual cortex (V1) is the existence of recurrent excitatory connections between spiny neurons, recurrent inhibitory connections between smooth neurons, and local connections between excitatory and inhibitory neurons. We modeled the dynamic behavior of intermixed excitatory and inhibitory populations of cells in V1 that receive input from the classical receptive field (the receptive field center) through feedforward thalamocortical afferents, as well as input from outside the classical receptive field (the receptive field surround) via long-range intracortical connections. A counterintuitive result is that the response of oriented cells can be facilitated beyond optimal levels when the surround stimulus is cross-oriented with respect to the center and suppressed when the surround stimulus is iso-oriented. This effect is primarily due to changes in recurrent inhibition within a local circuit. Cross-oriented surround stimulation leads to a reduction of presynaptic inhibition and a supraoptimal response, whereas iso-oriented surround stimulation has the opposite effect. This mechanism is used to explain the orientation and contrast dependence of contextual interactions in primary visual cortex: responses to a center stimulus can be both strongly suppressed and supraoptimally facilitated as a function of surround orientation, and these effects diminish as stimulus contrast decreases.

Animals↗
PubMed2005

Biases in attentional orientation and magnitude estimation explain crossover: neglect is a disorder of both.

Crossover refers to a pattern of performance on the line bisection test in which short lines are bisected on the side opposite the true center of long lines. Although most patients with spatial neglect demonstrate crossover, contemporary theories of neglect cannot explain it. In contrast, we show that blending the psychophysical construct of magnitude estimation with neglect theory not only explains crossover, but also addresses a quantitative feature of neglect that is independent of spatial deficits. We report a prospective validation study of the orientation/estimation hypothesis of crossover. Forty subjects (17 patients with and without neglect following unilateral brain injury and 23 normal controls) completed four experiments that examined crossover using line bisection, line bisection with cueing, and reproducing line lengths from both memory and a standard. Replicating earlier findings, all except one subject group exhibited crossover on the standard line bisection test, all groups showed a spontaneous preference to orient attention to one end of the lines, and all groups overestimated the length of short lines and underestimated long lines. Biases in attentional orientation and magnitude estimation are exaggerated in patients with neglect. The truly novel finding of this study occurred when, after removing the line from the bisection task, the direction of crossover was completely reversed in all subject groups depending on where attention was oriented. These findings are consistent with our hypothesis of crossover: (1) crossover is a normal component of performance on line bisection; (2) crossover results from the interplay of biases in attentional orientation and magnitude estimation; and (3) attentional orientation predicts the direction of crossover, whereas a disorder of magnitude estimation, not previously emphasized in neglect, accounts for the quantitative changes in length estimation that make crossover more obvious in neglect subjects. Paradoxically, we observed that the traditional line bisection test is suboptimal for exploring crossover because lines elicit spontaneous orientation responses from subjects that confound experimental manipulations of attention. We conclude that attentional orientation and magnitude estimation are necessary and sufficient to explain crossover and that bias in magnitude estimation is a core component of neglect.

Adult↗
PubMed1997

Singularities in primate orientation maps.

We report the results of an analysis of orientation maps in primate striate cortex with focus on singularities and their distribution. Data were obtained from squirrel monkeys and macaque monkeys of different ages. We find the approximately 80% of singularities that are nearest neighbors have the opposite sign and that the spatial distribution of singularities differs significantly from a random distribution of points. We do not find evidence for consistent geometric patterns that singularities may form across the cortex. Except for a different overall alignment of orientation bands and different periods of repetition, maps obtained from different animals and different ages are found similar with respect to the measures used. Orientation maps are then compared with two different pattern models that are currently discussed in the literature: bandpass-filtered white noise, which accounts very well for the overall map structure, and the field analogy model, which specifies the orientation map by the location of singularities and their properties. The bandpass-filtered noise approach to orientation patterns correctly predicts the sign correlations between singularities and accounts for the deviations in the spatial distribution of singularities away from a random dot pattern. The field analogy model can account for the structure of certain local patches of the orientation map but not for the whole map. Neither of the models is completely satisfactory, and the structure of the orientation map remains to be fully explained.

Aging↗
PubMed2001

Reference frame for rapid visual processing of line orientation.

Detection of a uniquely oriented line element in a background field of uniformly oriented line elements depends on the orientation of the background field. Is the orientational reference frame for this anisotropy entirely dependent on the orientations of structures outside the line-element display, the spatial regularity of the stimulus elements, and the direction of gravity? The effects of these potential cues were investigated in target-detection experiments with brief displays. The anisotropy was found whether or not gravitational or visual cues defined an orientational reference frame. Stimulus orientation may be coded with respect to the retina or body axis in rapid visual processing.

Anisotropy↗
PubMed1994

Finding perceptually dominant orientations in natural textures.

An algorithm for detecting orientation in texture is developed and compared with results of humans detecting orientation in the same textures. The algorithm is based on the steerable filters of Freeman and Adelson (IEEE Trans. PAMI 13, 891-906, 1991), orientation-selective filters derived from derivatives of Gaussians. The filters are applied over multiple scales and their outputs non-linearly contrast-normalized. The data for humans were collected from forty subjects who were asked to identify 'the minimum number of dominant orientations' they perceived, and the 'strength' with which they perceived each orientation. Test data consisted of 111 grey-level images of natural textures taken from the Brodatz album, a standard collection used in computer vision and image processing. Results show that the computer and humans chose at least one of the same dominant orientations on 95 of the natural textures. Of these textures, 74 were also in 100% agreement on the location of all the dominant orientations chosen by both humans and computer. Disagreements are analyzed and possible causes are discussed. Some apparent limitations in the current filter shapes and sizes are illustrated, as well as some (surprisingly small) effects believed to be caused by semantic recognition and gestalt grouping.

Algorithms↗
PubMed2005

The time course of the oblique effect in orientation judgments.

It is well known that maximal sensitivity to subtle orientation differences around a cardinal axis exceeds that around an oblique axis. In principle, this oblique effect in orientation sensitivity could either be constant across stimulus durations or could evolve as stimulus durations increase. To distinguish between these possibilities, we asked participants to judge subtle (4 deg) angular differences between pairs of gratings that were presented for various durations and masked to limit neural persistence. When the gratings were presented successively and for just 8.33 ms each, the ability to judge subtle (4 deg) orientation differences was already reliably better than chance, but comparable around cardinal and oblique axes. The oblique effect emerged only at subsequent stimulus durations, and increased across the tens of milliseconds after reliable (if modest) orientation sensitivity had occurred. These additional tens of milliseconds appear to be necessary but not sufficient for the oblique effect, which was absent at these durations when the stimuli were presented simultaneously rather than successively. Relative to simultaneously presented stimuli, successively presented stimuli generated a reduction in oblique orientation sensitivity, not an enhancement in cardinal orientation sensitivity. We believe the data suggest that the oblique effect in orientation sensitivity is a dynamic phenomenon that can be influenced by the neural events occurring between two successively presented stimuli.

Form Perception↗
PubMed2006

Orientation coding: a specific deficit in Williams syndrome?

Williams syndrome (WS) is a rare genetic disorder with a unique cognitive profile in which verbal abilities are markedly stronger than visuospatial abilities. This study investigated the claim that orientation coding is a specific deficit within the visuospatial domain in WS. Experiment 1 employed a simplified version of the Benton Judgement of Line Orientation task and a control, length-matching task. Results demonstrated comparable levels of orientation matching performance in the group with WS and a group of typically developing (TD) controls matched by nonverbal ability, although it is possible that floor effects masked group differences. A group difference was observed in the length-matching task due to stronger performance from the control group. Experiment 2 employed an orientation-discrimination task and a length-discrimination task. Contrary to previous reports, the results showed that individuals with WS were able to code by orientation to a comparable level as that of their matched controls. This demonstrates that, although some impairment is apparent, orientation coding does not represent a specific deficit in WS. Comparison between Experiments 1 and 2 suggests that orientation coding is vulnerable to task complexity. However, once again, this vulnerability does not appear to be specific to the population with WS, as it was also apparent in the TD controls.

Adolescent↗
PubMed2005

Prior classical olfactory conditioning improves odour-cued flight orientation of honey bees in a wind tunnel.

Odours are key cues used by the honey bee in various situations. They play an important role in sexual attraction, social behaviour and location of profitable food sources. Here, we were interested in the role of odours in orientation at short distance, for instance the approach flight to a floral patch or in close proximity to the hive entrance. Using a newly designed wind tunnel, we investigated the orientation behaviour of the bee towards two different odours: a social odour and a floral component, linalool. We then tested the effect of prior olfactory conditioning (conditioning of the proboscis extension reflex) on subsequent flight orientation. We showed that both stimuli induced orientated behaviour (orientated flights, circling around the odour source) in up to 70% of the worker bees, social odour being slightly more attractive than the linalool. We found thereafter that orientation performance towards the floral compound can be significantly enhanced by prior classical olfactory learning. This type of information transfer, from a Pavlovian associative context to an orientation task, might allow future foragers to acquire, within the hive, relevant information about the odours and food they will encounter during their later foraging bouts.

Acyclic Monoterpenes↗
PubMed2001

Magnetic compass orientation in the blind mole rat Spalax ehrenbergi.

The blind mole rat Spalax ehrenbergi is a solitary, subterranean rodent that digs and inhabits a system of branching tunnels, with no above-ground exits, which it never leaves unless forced to. To survive, the mole rat must be able to orient efficiently in its tunnel system. The sensory channels available for spatial orientation in the subterranean environment are restricted in comparison with those existing above ground. This study examined the possibility that the mole rat is able to perceive and use the earth's magnetic field to orient in space. Experiments were performed using a device constructed from a pair of electromagnetic 'Helmholtz coils', which create a magnetic field whose direction and strength can be altered. In the first experiment, we tested a group of mole rats (N=33) in an eight-armed maze under the earth's natural magnetic field to determine whether they have directional preferences for the location of their sleeping nest, food chamber and toilet site. A second group of mole rats (N=30) was tested for their directional preference after the earth's magnetic field had been experimentally shifted by 180 degrees. We found that the first group exhibited a significant preference (P<0.001) to build both their sleeping nest and their food store in the southern sector of the maze, whereas the second group shifted the location of their nests (P<0.01) and food store (P<0.05), to the northern sector of the maze, corresponding to the shift in the magnetic field. In the second experiment, we tested whether the magnetic compass orientation found in the first experiment depends on a light stimulus by testing a group of mole rats in the eight-armed maze under total darkness. No significant difference in directional preference between light and dark test conditions was observed. It can be concluded, therefore, that, in contrast to some amphibians and birds, magnetic compass orientation in the mole rat is independent of light stimulation. In the third experiment, we examined whether mole rats (N=24) use the earth's magnetic field as a compass cue to orient in a labyrinth. In the first stage (trials 1-13), the animals were trained to reach a goal box at the end of a complex labyrinth until all individuals had learned the task. In the second stage (trial 14), half the trained mole rats underwent another labyrinth trial under the earth's natural magnetic field, while the other half were tested under a magnetic field shifted by 180 degrees. We found a significant decrease (P<0.001) in performance of the mole rats tested under the shifted magnetic field compared with the group tested under the natural magnetic field. The findings from these experiments prove that the mole rat is able to perceive and use the earth's magnetic field to orient in space.

Animals↗
PubMed1985

Relationship between spatial-frequency and orientation tuning of striate-cortex cells.

If striate cells had the receptive-field (RF) shapes classically attributed to them, their preferred spatial frequencies would vary considerably with orientation. Other models of RF shape would predict a greater independence between orientation and spatial-frequency tuning. We have examined this by recording the responses of cat striate-cortex cells to a wide range of different spatial-frequency and orientation combinations. In almost all cells studied, peak orientation did not consistently vary with spatial frequency, but the majority of cells showed some change in peak spatial-frequency tuning with orientation. The amount of change in peak spatial frequency tended to be greater for cells that were narrowly tuned for orientation. However, cells narrowly (and also very broadly) tuned for spatial frequency tended to show considerable independence of spatial-frequency and orientation tuning, and in all but a few cells the degree of change was less than predicted by the classic RF model. Such cells were found to fire only to patterns whose local spatial spectra fell within a compact, restricted, roughly circular two-dimensional spatial-frequency region. We conclude that the two-dimensional RF shape of striate cells more closely approximates that predicted by a two-dimensional Gabor model or by a Gaussian-derivative model than it does the classic shape based on the output of geniculate cells with aligned RF's.

Animals↗
PubMed1990

Motion detection in the presence of local orientation changes.

To investigate the orientation selectivity of motion detectors, we measured the perception of horizontal apparent motion of dense patterns of line elements with randomized orientation. Horizontal motion of these displays became invisible when the simultaneous rotation of the line elements exceeded a critical rate (pc). The value of pc increased for higher horizontal velocities, approximately according to a square-root relation. In a direct test of orientation selectivity, the discrimination of horizontal motion direction disappeared when the orientation change per horizontal jump exceeded 30 deg. Thus, for the perception of the global flow the orientation change should not exceed a critical angle during the traverse of a critical distance. The critical distance increases according to a square-root relation as a function of horizontal velocity. These results strongly suggest that bilocal motion detectors are involved in horizontal motion detection and that these detectors are selective for orientation. The properties of these detectors, such as the orientation sensitivity that is reported in this paper, seem highly relevant to the perception of coherent motion.

Humans↗