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At least 1,099 records · Page 61Linked to original sources
PubMed2002

Orientation and color columns in monkey visual cortex.

The literature on orientation and color columns in monkey visual cortex is reviewed. The orientation column model most consistent with existing data is one containing 'stripes' of alternating positive and negative orientation 'singularities' (cytochrome oxidase blobs) which run along the centers of ocular dominance (OD) columns, with horizontal and vertical orientations alternating at interblob centers. Evidence is summarized suggesting that color is mapped continuously across the monkey's primary visual cortex, with the ends of the spectrum located at 'red' and 'blue' cytochrome oxidase blobs and extra-spectral purple located between adjacent red and blue blobs in the same OD column. In the orientation column model, the 'linear zones' of Obermayer and Blasdel have the appearance of the lines on a pumpkin. A pinwheel model of color columns, consistent with existing data, includes spectral and extra-spectral colors as spokes. Spectral iso-color lines run across iso-orientation lines in linear zones, while extra-spectral iso-color lines occupy the 'saddle points' of Obermayer and Blasdel. The color column model accounts for closure of the perceptual color circle, as proposed by Isaac Newton in 1704, but does not account for color opponency.

Animals↗
PubMed1996

Sleeping position, orientation, and proximity in bedsharing infants and mothers.

The impact of mother-infant bedsharing on infant sleeping position, orientation, and proximity to the mother was assessed in 12 breast-feeding Latino mother-infant pairs. Six routinely bedsharing and six routinely solitary-sleeping pairs slept 3 nights in the sleep laboratory. The first night matched the routine home condition, followed by 1 bedsharing night and 1 solitary-sleeping night in random order. During bedsharing infants were never placed prone, regardless of their routine sleeping condition. On the bedsharing night, mothers and infants spent most of the night oriented toward each other; seven of 12 infants remained oriented toward their mothers the entire night. While sleeping in a face-to-face orientation, most pairs slept most of the time less than 30 cm apart with appreciable amounts of time at less than 20 cm. This orientation and proximity should facilitate sensory exchanges between mother and infant which, we hypothesize, influence the infant's sleep physiology and nocturnal behavior. We conclude that bedsharing minimizes the use of the prone infant sleeping position, probably in part to facilitate breast feeding. By promoting nonprone positions, bedsharing may protect some infants from sudden infant death syndrome (SIDS), since prone sleeping is a known risk factor for SIDS. The large percentage of the night that mothers spent oriented toward their infants suggests that a higher degree of maternal vigilance may also result from bedsharing.

Breast Feeding↗
PubMed1992

Subcortical mechanisms in orientation sensitivity of cat visual cortical cells.

The orientation biases seen in the responses of neurones of the dorsal lateral geniculate nucleus (dLGN) can be reduced by the local application of the GABA antagonist, bicuculline methiodide. This fact was exploited to investigate whether these biases are important for cortical orientation selectivity by measuring the orientation sensitivity of cortical cells before and during iontophoretic administration of bicuculline in the topographically corresponding region of the dLGN. This procedure led to a significant reduction in the orientation sensitivity of the cortical cell. The results suggest that subcortical orientation biases are at least partly responsible for the orientation sensitivity seen at the level of the striate cortex.

Animals↗
PubMed2003

Sensitivity to horizontal and vertical disparity and orientation preference in areas V1 and V2 of the monkey.

It has been suggested that cells are most sensitive to disparities along the axis orthogonal to their orientation preference. To test this assumption we studied the orientation preference of 73 cells sensitive to retinal disparity, 44 from V1 and 29 from V2. Orientation preference and disparity sensitivity were not related in tuned excitatory and tuned inhibitory cells. We found 18 near/far cells with orientation preference. Of these, 10 (56%) had a preferred orientation less than 30% away from the orthogonal to the disparity axis whereas the remaining eight cells (44%) exceeded this value. Our data suggests that the neural mechanisms for encoding retinal disparities present in dynamic random dot stereograms may not be related to the preferred orientation of the cell.

Animals↗
PubMed1982

Functional implications of cross-orientation inhibition of cortical visual cells. I. Neurophysiological evidence.

Simple and complex cells of striate cortex of anaesthetized and paralysed cats were stimulated with two superimposed one-dimensional grating stimuli of different orientations to investigate inhibitory effects of non-optimally oriented stimuli. We confirmed that a stimulus of orientation orthogonal to a cell's long axis significantly reduces the cell's discharge rate. Further experiments revealed the following. (i) The inhibition was typically stronger for simple than for complex cells. (ii) It is very broadly tuned for orientation, all orientations outside the cell's tuning band having a comparable inhibitory effect. (iii) Similarly, it is broadly tuned for spatial frequency. These last two results suggest that the inhibition arises not from a single cell but from a pool of cells. (iv) The pattern of the discharge of the inhibition in response to stimulation by phase-reversed sinusoidal gratings is consistent with the notion that the inhibition arises from complex cells. A second series of recordings of stimulation by visual noise patterns demonstrated how 'cross-orientation inhibition' prevents simple cells from responding to two-dimensional visual noise while allowing them to respond to comparable one-dimensional noise patterns. We suggest that this mechanism may serve to render simple cells selectively sensitive to one-dimensional stimuli, such as the contours or borders of visual objects.

Action Potentials↗
PubMed2004

Lunar orientation in a beetle.

Many animals use the sun's polarization pattern to orientate, but the dung beetle Scarabaeus zambesianus is the only animal so far known to orientate using the million times dimmer polarization pattern of the moonlit sky. We demonstrate the relative roles of the moon and the nocturnal polarized-light pattern for orientation. We find that artificially changing the position of the moon, or hiding the moon's disc from the beetle's field of view, generally did not influence its orientation performance. We thus conclude that the moon does not serve as the primary cue for orientation. The effective cue is the polarization pattern formed around the moon, which is more reliable for orientation. Polarization sensitivity ratios in two photoreceptors in the dorsal eye were found to be 7.7 and 12.9, similar to values recorded in diurnal navigators. These results agree with earlier results suggesting that the detection and analysis of polarized skylight is similar in diurnal and nocturnal insects.

Animals↗
PubMed1975

The interaction of stars and magnetic field in the orientation system of night migrating birds. I. Autumn experiments with European Warblers (gen. Sylvia).

In the autumn migration periods of 1971, 1972, and 1973 the orientation behavior in registration cages of Sylvia communis, S. borin and S. cantillans was analyzed to find out what relative importance the birds assign to information from the stars and from the magnetic field for direction finding. We obtained the following results: 1. Under clear sky in the local earth's magnetic field (Control) the warblers showed directional preferences that corresponded to their expected migratory direction based on ringing recoveries. 2. When magnetic north was turned by 120 degrees to ESE (Test), all three species preferred on clear nights their migratory direction according to the magnetic field, in spite of contradicting information from the stars. 3. In a partly compensated magnetic field, which could not be used for orientation any more, no significant directional preference could be observed, although the stars were visible. Dividing these data into two groups according to whether the birds had been tested in Control or Test previously, we found a tendency for the directions selected here to depend upon the north direction of the magnetic field during the bird's previous tests. From this and from the observation that the concentration of orientation behavior decreases in the absence of stars, we derive the following orientational model: The magnetic field provides the primary directional information for migrating birds. The stars do not contain directional information in themselves, but they can become secondary sources of orientation when information from the magnetic field has been transferred to them previously. The importance of this mechanism lies in making it easier for the birds to maintain their migratory direction. The ecological advantages of such a system are discussed and critically compared to the other models of star orientation.

Animals↗
PubMed1994

Does practice in orientation discrimination lead to changes in the response properties of macaque inferior temporal neurons?

We trained two rhesus monkeys in a task in which they had to judge whether or not two successively presented gratings differed in orientation. In a first experiment, we trained a monkey for only a restricted set of orientations and then recorded from the temporal cortical visual area (TE) while he made discriminations at trained and untrained orientations. Although this orientation-selective practice induced a marked anisotropy in his behavioural performance, this was not matched by a similar anisotropy in single-cell response properties. In a second experiment, we compared the response properties of TE cells in two monkeys before and after practice in the discrimination of small orientation differences. The training had no effect on either the responsiveness or the orientation tuning. We did, however, observe alterations in the pattern of response modulations induced by the behavioural context. However, these changes with practice, although present in both monkeys, were not consistent from animal to animal. The relevance of these findings for the functional significance of behavioural context dependencies of TE cells, as well as for the plasticity of TE responses, is discussed.

Animals↗
PubMed2004

The orientation and dynamics of cell division within the plane of the developing vertebrate retina.

The orientation of a dividing cell within the plane of the tissue plays an essential role in regulating cell fate in a range of developing structures. To assess its potential role in the developing vertebrate retina we used standard confocal microscopy of fixed tissue and time-lapse confocal imaging of living tissue to examine the orientation of cell division and mitotic spindle rotation within the plane of the retinal neuroepithelium. Based on the study of three rat strains and chick, we report in contrast to recent findings that during the main phase of cell production (E18-P4 in the rat and E6-E11 in the chick) dividing cells are randomly orientated with respect to key anatomical landmarks as well as the orientation of their dividing neighbours. Results from live imaging of neonatal rat retinae support these findings and suggest that unlike the developing cortex, in which metaphase plates often rotate extensively before coming to rest in anaphase, retinal mitotic spindle rotations prior to cell division are minimal. Furthermore, the orientation of metaphase entry largely defines that which is finally adopted during anaphase. Hence, the dynamics of metaphase progression through to anaphase in the retina appear to differ markedly from the brain, and cell divisions within the plane of the tissue are randomly orientated. These results contribute to a growing body of evidence that suggests that the current paradigm with respect to asymmetric division derived from the study of invertebrates cannot be generalized to the developing vertebrate nervous system.

Anaphase↗
PubMed1995

Hair cell orientation patterns on the saccules of juvenile and adult toadfish, Opsanus tau.

Saccules from 10 adult (five female, five male) toadfish (Opsanus tau) 13.5-26 cm standard length, were examined for individual/sexual variation in the hair cell orientation pattern. In addition, saccules from two juveniles (5 and 6 cm standard length) were compared with those of the adults to determine whether maturational differences exist in the hair cell orientations. The hair cell orientation pattern is unlike any reported previously for this species or its congener, O. beta. There are no major differences between the hair cell orientations of males and females, nor between the juveniles and the adults. A slight individual variation is present in the proportion of hair cells oriented in a particular direction in a specific area of the sensory epithelium. Potential ramifications of this hair cell orientation pattern are discussed with regard to development and auditory processing.

Age Factors↗
PubMed1989

Is elicitation of the autonomic orienting response associated with allocation of processing resources?

Two experiments investigated whether elicitation of the autonomic orienting response is associated with active allocation of processing resources as indexed by the slowing of reaction time to secondary task probes. In Experiment 1, 75 college student subjects performed a dual task consisting of a primary auditory orienting task and a concurrent secondary visual reaction time task. The primary orienting task included task-relevant tones presented to one ear and task-irrelevant tones presented to the other ear. The last trial of the primary task included an unexpected novel tone presented binaurally. The secondary task consisted of a series of brief light flashes presented at critical times throughout the primary task; the reaction time of the subjects' motor responses to these flashes was measured. Consistent with the resource allocation view of orienting, the results demonstrated that resources were allocated during the primary task tones and the novel tone, and this allocation was greater during the early trials than the late trials of the primary task. However, a directional dissociation was observed in that resource allocation was greater during the task-irrelevant tone whereas autonomic orienting responses were larger to the task-relevant tone. Experiment 2 replicated all of these effects and demonstrated that the directional dissociation was sensitive to the predictability and ease of discrimination between the task-relevant and task-irrelevant tones. Taken together, these findings indicate that the relationship between resource allocation and autonomic orienting is a reliable but complex one in need of further research.

Adult↗
PubMed1998

Development of spatial memory and spatial orientation in preschoolers and primary school children.

The present study addresses the question of what kind of information children use when orientating in new environments, if given proximal and distal landmarks, and how spatial memory develops in the investigated age groups. Ten 5-year-old, ten 7-year-old and ten 10-year-old children were presented with the 'Kiel Locomotor Maze', containing features of the Radial Arm Maze and the Morris Water Maze, in order to assess spatial memory and orientation. Children had to learn to approach baited locations only. Task difficulty was equated with respect to the children's age. Training was given until the children reached criterion. During testing, the maze configuration and response requirements were systematically altered, including response rotation, cue rotation, cue deletion and response rotation with cue deletion in order to assess the spatial strategies used by the children. During training and testing, working-memory errors (WM), reference-memory errors (RM) and working-reference memory errors (WR) were recorded. As expected, no difference between age groups appeared during training, thus confirming comparable task difficulty across age groups. During testing, age groups differed significantly with regard to the orientation strategy used. The 5-year-olds were bound to a cue strategy, orientating towards local, proximal cues. The 10-year-olds mastered all tasks, thus displaying a place strategy, being able to use distal cues for orientation, and were even able to do so after being rotated 180 degrees. The 7-year-olds proved to be at an age of transition: five of them were bound to a cue strategy, five children were able to adopt a place strategy. The differences in the orientation strategies used by children of different age groups was reflected by the sum of errors they made, also by RM. WM were found to be rare, especially in older children. We conclude that preschoolers use a cue strategy, that the development of place strategies occurs during primary school age and seems to be complete by the age of 10 years.

Age Factors↗
PubMed1996

A linear model fails to predict orientation selectivity of cells in the cat visual cortex.

1. Postsynaptic potentials (PSPs) evoked by visual stimulation in simple cells in the cat visual cortex were recorded using in vivo whole-cell technique. Responses to small spots of light presented at different positions over the receptive field and responses to elongated bars of different orientations centred on the receptive field were recorded. 2. To test whether a linear model can account for orientation selectivity of cortical neurones, responses to elongated bars were compared with responses predicted by a linear model from the receptive field map obtained from flashing spots. 3. The linear model faithfully predicted the preferred orientation, but not the degree of orientation selectivity or the sharpness of orientation tuning. The ratio of optimal to non-optimal responses was always underestimated by the model. 4. Thus non-linear mechanisms, which can include suppression of non-optimal responses and/or amplification of optimal responses, are involved in the generation of orientation selectivity in the primary visual cortex.

Animals↗
PubMed2004

Correlation of local and global orientation and spatial frequency tuning in macaque V1.

Visual cortical neurones display a variety of visual properties. Among those that emerge in the primary visual cortex V1 are sharpening of selectivity for spatial frequency and for orientation. The selectivity for these stimulus attributes can be measured around the peak of the tuning function, usually as bandwidth. Other selectivity measures take into account the response across a broader range of stimulus values. An example of such a global measure is the circular variance of orientation tuning. Here we introduce a similar measure in the spatial frequency domain that takes into account the shape of the tuning curve at frequencies lower than the peak, called the low-spatial frequency variance. Our recent studies with dynamic stimuli suggest that the selectivity for spatial frequency and orientation is strongly correlated with the degree of suppression at low spatial frequencies and off-axis orientations. Here we extend the study of the global tuning to stimulus conditions that measure the response of cells to the presentation of drifting sinusoidal grating stimuli for periods of a few seconds. We find that under such steady-state stimulus conditions there is a strong correlation between the global selectivity measures, orientation circular variance and low spatial frequency variance. Consistent with previous studies, there is a weaker correlation between the local tuning measures, orientation and spatial frequency bandwidth. These results support the idea that there are multiple factors that contribute to tuning and that suppression observed in dynamic experiments is also likely to contribute to the global selectivity for steady-state stimuli.

Animals↗
PubMed2005

Stimulation of non-classical receptive field enhances orientation selectivity in the cat.

We have investigated how the nonclassical receptive field (nCRF) affects dynamic orientation selectivity of cells in the primary visual cortex (V1) in anaesthetized and paralysed cats using the reverse correlation method. We found that tuning to the orientation of the test stimulus depends on the size of the stimulation area. A significant sharpening of orientation tuning was induced by nCRF stimulation, with the magnitude of the effect increasing with the size of stimulation. The effect of the nCRF on the temporal dynamics of orientation tuning was also investigated by examining the tuning over a range of delays from stimulus onset. We found small but detectable changes in both the preferred orientation and the bandwidth of tuning over time when the classical receptive field (CRF) was stimulated alone. Stimulation in nCRF significantly increased the magnitude of these temporal changes. Thus, nCRF stimulation not only enhances the overall orientation selectivity, but also enriches the temporal dynamics of cortical neurones, which may increase the computational power of the visual cortex in information processing.

Action Potentials↗
PubMed1991

Early orientation of attention toward the half space ipsilateral to the lesion in patients with unilateral brain damage.

Posner has suggested that unilateral spatial neglect could be due to a difficulty in disengaging attention from its current focus to orient it toward the neglected half space. Clinical and experimental data suggest, however, that this disengaging difficulty could be only one aspect of a more complex disturbance also characterized by an early automatic orienting of attention toward the half space ipsilateral to the lesion. To test this hypothesis, two different investigations in unselected groups of patients with right and left brain-damage were carried out. The first investigation, to evaluate forms of lateral orienting of attention severe enough to provoke an overt gaze deviation, consisted of the systematic assessment of the phenomenon of "magnetic gaze attraction". The second investigation, to detect milder forms of automatic orienting of attention, analysed the temporal sequence followed in identifying the pictures represented in an "Overlapping Figures task", to see if patients tended to identify first figures lying in the half space ipsilateral to the lesion. In both investigations results consistently showed: a) that patients with right brain damage tend to orient attention automatically toward the ipsilateral half space more than patients with left brain damage; b) that this tendency is tightly linked to the presence of behavioural manifestations of hemi-neglect. These results are therefore consistent with the hypothesis that hemi-neglect is a multi-component syndrome with an early orienting of attention toward the half space ipsilateral to the lesion as the first of these components.

Analysis of Variance↗
PubMed2005

Tilt aftereffect and adaptation-induced changes in orientation tuning in visual cortex.

The tilt aftereffect (TAE) is a visual illusion in which prolonged adaptation to an oriented stimulus causes shifts in subsequent perceived orientations. Historically, neural models of the TAE have explained it as the outcome of response suppression of neurons tuned to the adapting orientation. Recent physiological studies of neurons in primary visual cortex (V1) have confirmed that such response suppression exists. However, it was also found that the preferred orientations of neurons shift away from the adapting orientation. Here we show that adding this second factor to a population coding model of V1 improves the correspondence between neurophysiological data and TAE measurements. According to our model, the shifts in preferred orientation have the opposite effect as response suppression, reducing the magnitude of the TAE.

Adaptation, Physiological↗
PubMed2004

Influence of contrast on orientation and temporal frequency tuning in ferret primary visual cortex.

Neurons in primary visual cortex are highly sensitive to the contrast, orientation, and temporal frequency of a visual stimulus. These three stimulus properties can be varied independently of one another, raising the question of how they interact to influence neuronal responses. We recorded from individual neurons in ferret primary visual cortex to determine the influence of stimulus contrast on orientation tuning, temporal-frequency tuning, and latency to visual response. Results show that orientation-tuning bandwidth is not affected by contrast level. Thus neurons in ferret visual cortex display contrast-invariant orientation tuning. Stimulus contrast does, however, influence the structure of orientation-tuning curves as measures of circular variance vary inversely with contrast for both simple and complex cells. This change in circular variance depends, in part, on a contrast-dependent change in the ratio of null to preferred orientation responses. Stimulus contrast also has an influence on the temporal-frequency tuning of cortical neurons. Both simple and complex cells display a contrast-dependent rightward shift in their temporal frequency-tuning curves that results in an increase in the highest temporal frequency needed to produce a half-maximum response (TF(50)). Results show that the degree of the contrast-dependent increase in TF(50) is similar for cortical neurons and neurons in the lateral geniculate nucleus (LGN) and indicate that subcortical mechanisms likely play a major role in establishing the degree of effect displayed by downstream neurons. Finally, results show that LGN and cortical neurons experience a contrast-dependent phase advance in their visual response. This phase advance is most pronounced for cortical neurons indicating a role for both subcortical and cortical mechanisms.

Action Potentials↗