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PubMed1999

Orientation topography of layer 4 lateral networks revealed by optical imaging in cat visual cortex (area 18).

The functional specificity of corticocortical connections with respect to the topography of orientation selectivity was studied by optical imaging of intrinsic signals and bulk injections of fluorescent latex beads (green and red) and biocytin into layer 4. The distributions of retrogradely labelled cells and anterogradely labelled axon terminals were histologically reconstructed from all cortical laminae, and the resulting anatomical maps compared with the optically imaged functional maps. Layer 4 injections produced extensive horizontal labelling up to 2-3 mm from the injection centres albeit without the clear patchy pattern described after layer 2/3 injections (Gilbert & Wiesel 1989, J. Neurosci., 9, 2432-2442; Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618). The functional (orientation) distribution of the labelled projections was analysed according to laminar location and lateral spread. With regard to the former, no major difference in the orientation topography between supragranular- (upper tier), granular- (middle tier) and infragranular (lower tier) layers was seen. Laterally, proximal and distal projections were distinguished and further dissected into three orientation categories, iso- (+/- 30 degrees ), oblique- (+/- 30-60 degrees ) and cross-orientations (+/- 60-90 degrees ) with respect to the orientation preference at the injection sites. The majority of distal connections (retrograde and anterograde) was equally distributed across orientations (35.4% iso-, 33.7% oblique-, and 30.9% cross-orientations) that are equivalent with a preponderance to dissimilar orientations (oblique- and cross-orientations, 64.6%). In one case, distal excitatory and inhibitory connections could be morphologically distinguished. For both categories, a marked bias to dissimilar orientations was found (excitatory, 63.7%; inhibitory, 86.6%). Taken together, these results suggest that the long-range layer 4 circuitry has a different functional role from that of the iso-orientation biased (52.9%, Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618) layer 2/3 circuitry, and is perhaps involved in feature difference-based mechanisms, e.g. figure ground segregation.

Animals↗
PubMed2001

The integration of orientation information in the motion correspondence problem.

We examine how differently oriented components contribute to the discrimination of motion direction along a horizontal axis. Stimuli were two-frame random-dot kinematograms that were narrowband filtered in spatial frequency. On each trial, subjects had to state whether motion was to the left or the right. For each stimulus condition, Dmax (the largest displacement supporting 80% correct direction discrimination performance) was measured. In experiment 1, Dmax was measured for orientationally narrowband stimuli as a function of their mean orientation. Dmax was found to increase as the orientation of the stimuli became closer to the axis of motion. Experiment 2 used isotropic stimuli in which some orientation bands contained a coherent motion signal, and some contained only noise. When the noise band started at vertical orientations and increased until only horizontal orientations contained a coherent motion signal, Dmax increased slightly. This suggests that near-vertical orientations interfere with motion perception at large displacements when they contain a coherent motion signal. When the noise band started at horizontal and increased until only vertical orientations contained the motion signal, Dmax decreased steadily. This implies that Dmax depends at least partly on the most horizontal motion signal in the stimulus. These results were contrasted with two models. In the first, the visual system utilises the most informative orientations (nearest horizontal). In the second, all available orientations are used equally. Results supported an intermediate interpretation, in which all orientations are used but more informative ones are weighted more heavily.

Discrimination, Psychological↗
PubMed2005

Relationship between contrast adaptation and orientation tuning in V1 and V2 of cat visual cortex.

Previous studies investigating the response properties of neurons in the primary visual cortex of cats and primates have shown that prolonged exposure to optimally oriented, high-contrast gratings leads to a reduction in responsiveness to subsequently presented test stimuli. We recorded from 119 neurons in cat V1 and V2 and found that in a high proportion of cells contrast adaptation also occurs for gratings oriented orthogonal to a neuron's preferred orientation, even though this stimulus did not elicit significant increases in spiking activity. Approximately 20% of neurons adapted equally to all orientations tested and a further 46% showed at least some adaptation to orthogonally oriented gratings, whereas 20% of neurons did not adapt to orthogonal gratings. The magnitude of contrast adaptation was positively correlated with adapting contrast, but was not related to the spiking activity of the cells. Highly direction selective neurons produced stronger adaptation to orthogonally oriented gratings than other neurons. Orientation-related adaptation was correlated with the rate of change of orientation tuning in consecutive cells along electrode penetrations that traveled parallel to the cortical layers. Nonoriented adaptation was most common in areas where orientation preference changed rapidly, whereas orientation-selective adaptation was most common in areas where orientation preference changed slowly. A minority of neurons did not show contrast adaptation (14%). No major differences were found between units in different cortical layers, V1 and V2, or between complex and simple cells. The relevance of these findings to the current understanding of adaptation within the context of orientation column architecture is discussed.

Action Potentials↗
PubMed1984

Direction and orientation selectivity of neurons in visual area MT of the macaque.

We recorded from single neurons in the middle temporal visual area (MT) of the macaque monkey and studied their direction and orientation selectivity. We also recorded from single striate cortex (V1) neurons in order to make direct comparisons with our observations in area MT. All animals were immobilized and anesthetized with nitrous oxide. Direction selectivity of 110 MT neurons was studied with three types of moving stimuli: slits, single spots, and random-dot fields. All of the MT neurons were found to be directionally selective using one or more of these stimuli. MT neurons exhibited a broad range of direction-tuning bandwidths to all stimuli (minimum = 32 degrees, maximum = 186 degrees, mean = 95 degrees). On average, responses were strongly unidirectional and of similar magnitude for all three stimulus types. Orientation selectivity of 89 MT neurons was studied with stationary flashed slits. Eighty-three percent were found to be orientation selective. Overall, orientation-tuning bandwidths were significantly narrower (mean = 64 degrees) than direction-tuning bandwidths for moving stimuli. Moreover, responses to stationary-oriented stimuli were generally smaller than those to moving stimuli. Direction selectivity of 55 V1 neurons was studied with moving slits; orientation selectivity of 52 V1 neurons was studied with stationary flashed slits. In V1, compared with MT, direction-tuning bandwidths were narrower (mean = 68 degrees). Moreover, V1 responses to moving stimuli were weaker, and bidirectional tuning was more common. The mean orientation-tuning bandwidth in V1 was also significantly narrower than that in MT (mean = 52 degrees), but the responses to stationary-oriented stimuli were of similar magnitude in the two areas. We examined the relationship between optimal direction and optimal orientation for MT neurons and found that 61% had an orientation preference nearly perpendicular to the preferred direction of motion, as is the case for all V1 neurons. However, another 29% of MT neurons had an orientation preference roughly parallel to the preferred direction. These observations, when considered together with recent reports claiming sensitivity of some MT neurons to moving visual patterns (39), suggest specific neural mechanisms underlying pattern-motion sensitivity in area MT. These results support the notion that area MT represents a further specialization over area V1 for stimulus motion processing. Furthermore, the marked similarities between direction and orientation tuning in area MT in macaque and owl monkey support the suggestion that these areas are homologues.

Animals↗
PubMed1985

Orientation sensitivity of the cat assessed from evoked potentials: central and peripheral contributions.

To estimate contour-orientation sensitivity of the cat and the degree to which precortical processing contributes to such estimates, the amplitude of visually evoked potentials (VEP) recorded from the visual cortex of cats in response to a visual stimulus (S2) presented at various intervals after presentation of another visual stimulus (S1) was measured under several conditions. Recordings were made when both stimuli were presented through one eye (monoptic condition) or when S1 was presented to one eye and S2 to the other (dichoptic condition). In some experiments, simultaneous recordings were made from the optic tract and visual cortex. The stimuli were pairs of sinusoidal gratings with a spatial frequency of 0.5 cycles/deg and of various orientations. Each stimulus was presented by stepping the grating contrast from 0.0 (adapting field) to 0.5 for 50 ms. The intervals between the presentation of the two test stimuli (S1 and S2) was varied from 0 to 1,550 ms, and on different trials the orientation of the S2 grating relative to that of S1 was varied from 0 to 90 degrees. Results showed that under monoptic conditions, the VEP to the second stimulus (S2) was reduced by presentation of the first stimulus (S1) when the interstimulus interval was less than 200 ms, whereas under dichoptic conditions, the response to S2 was reduced with interstimulus intervals less than 75 ms. The response reduction was always in a forward direction (e.g., reduced S2 response), increased in magnitude with decreases in the interstimulus interval, and was larger under monoptic conditions than under dichoptic conditions. The response reduction produced monoptically was orientation selective in that it was greatest when the orientation of S1 and S2 was the same, and it recovered by half when the orientation differed by 6 to 15 degrees (orientation half-band pass). In some cortical recordings, the orientation-selective response reduction was superimposed on a response reduction that was not selective for S2 orientation. Stimultaneous recording in the optic tract also showed a response reduction of S2 response that was not orientation selective, suggesting that precortical neural elements contribute to the cortical VEP. With dichoptic stimulus presentation an orientation-nonspecific response reduction was obtained. We hypothesized that binocular inhibitory effects, resulting from disparate retinal input, produced this surprising finding. The results demonstrate that the VEP recorded at the cortex can be used to estimate orientation sensitivity, but that response interactions in peripheral (precortical) neural elements can contribute to such estimates.

Animals↗
PubMed1994

Three-dimensional eye, head, and chest orientations after large gaze shifts and the underlying neural strategies.

1. The fixation orientations adopted by the eye, head, and chest were examined when all three were allowed to participate in gaze shifts to visual targets. The objective was to discover whether there are invariant, neurally determined laws governing these orientations that might provide clues to the processes of perception and motor control. This is an extension of the classical studies of eye-only saccades that determined that there is only one eye orientation for each gaze direction (Donders' law) and that the rotations necessary to take the eye from a reference orientation to all other orientations adopted are about axes that lie in a plane (Listing's law). 2. The three-dimensional orientations of the static eyes, head, and chest were measured after each gaze shift to a visual target, the targets having been fixed at positions ranging from 0 to 135 degrees to the left and right of center and 45 degrees up and down. These measurements were taken of seven human subjects by means of the search coil technique with coils attached to the sternum, head, and right eye. Orientations were plotted as quaternion vectors so that those orientations obeying Donders' law formed a surface and those obeying Listing's law formed a plane. 3. The orientations adopted by the eye, head, and chest were found to be a small subset of those possible under the biomechanical and task-imposed constraints. Thus there is a neurally implemented restriction, specifically of the rotation of the eye relative to space (i.e., the orientation variable es) and to the head (eh); also of the rotation of the head relative to space (hs) and to the chest (hc), and the rotation of the chest relative to space (cs). Plotted as quaternion vectors, the data for each orientation variable formed a characteristic surfacelike shape. In the case of es, hs, and hc these were twisted surfaces, whereas for eh the surface was planar and for cs it was nearly linear. Thus to a first approximation each of the orientation variables conformed to Donders' law. 4. The eye adopted a pointing (gaze) direction that has the ratio of vertical to horizontal components generally greater than one when fixating each of the corner targets. The chest, by contrast, moved almost entirely in the horizontal direction, whereas the head performed an intermediate role. 5. The es-, hs-, and hc-fitted surfaces and cs-fitted lines were titled remarkably little from the vertical axis (i.e., the gravity direction) despite larger tilts being possible.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2001

Object orientation agnosia: a failure to find the axis?

A dissociation between the ability to recognize misoriented objects and to determine their orientation has been reported in a small number of patients with vascular lesions. In this article, we describe a 57-year-old man with probable Alzheimer' s disease who shows the same dissociation. Neuroimaging findings indicated marked hypometabolism in the posterior cortical regions, particularly the postero-superior parietal lobes. Clinically, the patient had good object recognition accompanied by severely impaired spatial abilities. The experimental investigations comprised a variety of tasks in which he identified misoriented objects, evaluated the orientation of single objects, or discriminated the orientation of simultaneously presented items. Results revealed that his object recognition was independent of orientation and was largely mediated by salient features. With respect to orientation judgements, the patient displayed a profound inability to judge the orientation of nonupright objects, but remarkably intact (though largely implicit) knowledge of the upright orientation. Strikingly, his orientation judgements were also more accurate for upside-down objects than for other orientations (i.e., 90 degrees ). We interpret these results as evidence that judgements about object orientation are facilitated when the orientation of the principal axis of the object matches that of an internal representation. We propose that the inability to determine other orientations may be due to the failure of an "axis-finding" mechanism implemented in the posterior parietal lobes, that translates between object-centered and eye-centered coordinates appropriate for guiding visual scanning.

Agnosia↗
PubMed1997

Orientation tuning of the spatial-frequency-tuned mechanisms of the red-green channel.

Significant orthogonal masking for color stimuli [Invest. Ophthalmol. Visual Sci. 34, 782 (No. 405-54) (1993)] but not for achromatic stimuli [J. Opt. Soc. Am. A 1, 226 (1984)] under sustained presentation led us to investigate the orientation tuning of the spatial-frequency- (SF-) tuned color mechanisms. The Red-Green channel was isolated from the achromatic channel by the minimum flicker technique and from the Yellow-Blue channel by the hue cancellation technique. Contrast sensitivity functions, threshold elevation versus mask orientation curves (measured by orientation masking), and threshold elevation versus mask contrast curves were measured by the method of constant stimuli and a two-interval forced-choice technique on two normal observers. Test targets were spatially localized (D6), vertical color patterns, and masks were sinusoidal color patterns oriented 15 degrees-90 degrees from the vertical in 15 degrees steps and had the same SF's as those of test patterns. Mask contrasts were varied between 1.2% and 60%. The orientation tuning curves of the SF-tuned color mechanisms were extracted by obtaining the best fit to contrast sensitivity and threshold elevation data simultaneously at a given SF with use of the masking model. Results show that threshold elevations depend on test SF, mask SF, mask orientation, and mask contrast. Half-bandwidths at half-height (with respect to 15 degrees from the vertical) of threshold elevation versus mask orientation curves range from 90 degrees to 29 degrees depending on SF's. The slopes of threshold elevation versus mask contrast curves range from 0.76 to 0.29 on octave-octave coordinates depending on SF's. Orientation half-bandwidths at half-height of orientation tuning curves of the SF-tuned color mechanisms (1) range from 79 degrees to 28 degrees and (2) average from 68 degrees to 30 degrees for SF's 0.063-8 cycles per degree (cpd). Data suggest that the orientation tuning curves of the SF-tuned chromatic mechanisms are broader (except at 2 cpd) than those of the achromatic mechanisms (orientation half-bandwidths: 32 degrees-15 degrees for 0.5-11.3 cpd [J. Opt. Soc. Am. A 1, 226 (1984)]); moreover, the orientation bandwidths are SF dependent.

Algorithms↗
PubMed1995

Consistent improvement in sphincterotome orientation with manual grooming.

BACKGROUND: During ampullary cannulation with standard sphincterotomes, wire orientation is frequently to the right of 0 and can not always be rotated to the 12 o'clock ideal. It is not known if the presence of a wire guide alters a sphincterotome's orientation or if grooming in a standardized manner improves the orientation in the majority of cases. METHODS: The intra-ampullary range of orientation of a double channel sphincterotome was prospectively evaluated before and after catheter grooming in 25 patients undergoing ERCP. The range of orientation was also measured with and without an indwelling biliary wire guide in 14 cases. RESULTS: The maximal right orientation of the untrained sphincterotomes was 35 +/- 16 degrees; with a wire guide it was 33 +/- 22 degrees. Maximal left orientation was 17 +/- 16 degrees, wire guided it remained 19 +/- 14 degrees. Manual grooming shifted the mean maximal left orientation of the sphincterotomes to -37 +/- 28 degrees (p < 0.0001), permitting 80% of groomed sphincterotomes to achieve a 0 (12 o'clock) orientation and 100% to orient 10 degrees or less from zero. CONCLUSIONS: The presence of the wire guide did not alter the orientation of the sphincterotome. Because manual grooming reliably improved the orientation of double-channel sphincterotomes, it should be routinely performed before their use.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed2005

How effective for fold recognition is a potential of mean force that includes relative orientations between contacting residues in proteins?

We estimate the statistical distribution of relative orientations between contacting residues from a database of protein structures and evaluate the potential of mean force for relative orientations between contacting residues. Polar angles and Euler angles are used to specify two degrees of directional freedom and three degrees of rotational freedom for the orientation of one residue relative to another in contacting residues, respectively. A local coordinate system affixed to each residue based only on main chain atoms is defined for fold recognition. The number of contacting residue pairs in the database will severely limit the resolution of the statistical distribution of relative orientations, if it is estimated by dividing space into cells and counting samples observed in each cell. To overcome such problems and to evaluate the fully anisotropic distributions of relative orientations as a function of polar and Euler angles, we choose a method in which the observed distribution is represented as a sum of delta functions each of which represents the observed orientation of a contacting residue, and is evaluated as a series expansion of spherical harmonics functions. The sample size limits the frequencies of modes whose expansion coefficients can be reliably estimated. High frequency modes are statistically less reliable than low frequency modes. Each expansion coefficient is separately corrected for the sample size according to suggestions from a Bayesian statistical analysis. As a result, many expansion terms can be utilized to evaluate orientational distributions. Also, unlike other orientational potentials, the uniform distribution is used for a reference distribution in evaluating a potential of mean force for each type of contacting residue pair from its orientational distribution, so that residue-residue orientations can be fully evaluated. It is shown by using decoy sets that the discrimination power of the orientational potential in fold recognition increases by taking account of the Euler angle dependencies and becomes comparable to that of a simple contact potential, and that the total energy potential taken as a simple sum of contact, orientation, and (phi,psi) potentials performs well to identify the native folds.

Journal Article↗
PubMed1981

The sensitivity of binocular rivalry suppression to changes in orientation assessed by reaction-time and forced-choice techniques.

Binocular rivalry was induced between two orthogonal square-wave gratings of the same spatial frequency, luminance, contrast, and field size, presented dichoptically. One of the gratings could be instantly replaced by a third grating differing only in orientation. In one experiment subjects were required to respond as soon as an orientation change was noticed, and to withhold response to catch trials (no orientation change). When orientation changes were made to the visible grating, reaction time was found to be a U-shaped function of the magnitude of orientation change. When orientation changes were made to the grating undergoing binocular-rivalry suppression, an overall increase in reaction time was found with the increase being greater for large orientation changes (an asymmetrical U-shaped function). In another experiment subjects were required to detect the direction of a change in orientation in a two-alternative forced-choice procedure. Thresholds were thus obtained for 75% correct performance. It was found that thresholds for orientation changes made to the visible and invisible fields were identical from 20 degrees to 70 degrees orientation change. Outside this range thresholds were higher when orientation changes were made to the field suppressed by binocular rivalry. It is argued that the orientation functions obtained in the two experiments may represent incomplete suppression of either form or transient information during binocular rivalry.

Adaptation, Ocular↗
PubMed1989

Electrophoresis of DNA in oriented agarose gels.

Oriented agarose gels were prepared by applying an electric field to molten agarose while it was solidifying. Immediately afterwards, DNA samples were applied to the gel and electrophoresed in a constant unidirectional electric field. Regardless of whether the orienting field was applied parallel or perpendicular to the eventual direction of electrophoresis, the mobilities of linear and supercoiled DNA molecules were either faster (80% of the time) or slower (20% of the time) than observed in control, unoriented gels run simultaneously. The difference in mobility in the oriented gel (whether faster or slower) usually increased with increasing DNA molecular weight and increasing voltage applied to orient the agarose matrix. In perpendicularly oriented gels linear DNA fragments traveled in lanes skewed toward the side of the gel; supercoiled DNA molecules traveled in straight lanes. If the orienting voltage was applied parallel to the direction of electrophoresis, both linear and supercoiled DNA molecules migrated in straight lanes. These effects were observed in gels cast from different types of agarose, using various agarose concentrations and two different running buffers, and were observed both with and without ethidium bromide incorporated in the gel. Similar results were observed if the agarose was allowed to solidify first, and the orienting electric field was then applied to the gel for several hours before the DNA samples were added and electrophoresed. The results suggest that the agarose matrix can be oriented by electric fields applied to the gel before and probably during electrophoresis, and that orientation of the matrix affects the mobility and direction of migration of DNA molecules. The skewed lanes observed in the perpendicularly oriented gels suggest that pores or channels can be created in the matrix by application of an electric field. The oriented matrix becomes randomized with time, because DNA fragments in oriented and unoriented gels migrated in straight lanes with identical velocities 24 hours later.

DNA↗
PubMed2006

Simultaneous constraints on pre- and post-synaptic cells couple cortical feature maps in a 2D geometric model of orientation preference.

The most prominent feature of mammalian striate cortex (V1) is the spatial organization of response preferences for the position and orientation of elementary visual stimuli. Models for the formation of cortical maps of orientation and 'retinotopic' position typically rely on a combination of Hebbian or correlation-based synaptic plasticity, and constraints on the distribution of synaptic weights. We consider a simplified model of orientation and retinotopic specificity based on the geometry of the feed-forward synaptic weight distribution from an 'unoriented' layer of cells to a first weakly oriented layer. We model the feed-forward weight distribution as a system of planar Gaussian receptive fields each elongated in the direction matching the preferred orientation of the postsynaptic cell. Under the constraint of presynaptic weight normalization (each cell in the oriented layer receives the same net synaptic weight) and a uniform retinotopic map (displacement of centres of mass of receptive fields in the unoriented layer is strictly proportional to the displacement of the corresponding cells in the oriented layer), we find that imposing a pattern of orientation preference forces the system to violate postsynaptic weight normalization (each cell in the unoriented layer no longer sends forth the same net synaptic weight). We study this deviation from uniformity of the postsynaptic weight, and find that the deviation has a distinct form in the vicinity of the 'pinwheel' singularities of the orientation map. We show that uniform synaptic coverage of the unoriented layer can be restored by introducing a distortion in the retinotopic locations of the receptive fields. We calculate, to first order in the relative elongation of the receptive fields, the retinotopic distortion vector field. Both the pattern of postsynaptic weight non-uniformity and the corrective retinotopic distortion vector field fail to possess the reflection symmetry commonly assumed to relate orientation singularities with topological index +/- pi. Hence, we show that 'right-handed' and 'left-handed' orientation singularities are funda-mentally distinct anatomical structures when full 2D synaptic architecture is taken into account. Finally, we predict specific patterns of retinotopic distortion that should obtain in the vicinity of +/- pi-fold orientation singularities, if uniform pre- and post-synaptic weight constraints are strongly enforced.

Algorithms↗
PubMed2004

Facet orientation in the thoracolumbar spine: three-dimensional anatomic and biomechanical analysis.

STUDY DESIGN: Thoracolumbar facet orientations were measured and analyzed. OBJECTIVES: To establish a comprehensive database for facet orientation in the thoracolumbar vertebrae and to determine the normal human condition. SUMMARY OF BACKGROUND DATA: Most studies on facet orientation have based their conclusions on two-dimensional measurements, in small samples or isolated vertebrae. The amount of normal asymmetry in facet orientation is poorly addressed. METHODS: Transverse and longitudinal facet angles were measured directly from 240 human vertebral columns (males/females, blacks/whites). The specimens' osteologic material is part of the Hamann-Todd Osteological Collection housed at the Cleveland Museum of Natural History (Cleveland, OH). A total of 4,080 vertebrae (T1-L5) from the vertebral columns of individuals 20 to 80 years of age were measured, using a Microscribe three-dimensional apparatus (Immersion Co., San Jose, CA). Data were recorded directly on computer software. Statistical analysis included paired t tests and analysis of variance. RESULTS.: Facet orientation is independent of gender, age, and ethnic group. Asymmetry in facet orientation is found in the thorax. All thoracolumbar facets are positioned in an oblique plane. In the transverse plane, all facets from T1 to T11 are positioned with an anterior inclination of approximately 25 degrees to 30 degrees from the frontal plane. The facets of T12-L2 are oriented closer to the midsagittal plane of the vertebral body (mean range, 25.89 degrees-33.87 degrees), while the facets of L3-L5 are oriented away from that plane (mean range, 40.40 degrees-56.30 degrees). Facet transverse orientation at the thoracolumbar junction is highly variable (approximately 80% with approximately 101 degrees and approximately 20% with 35 degrees). All facets are oriented more vertically from T1 (approximately 150 degrees) to L5 (approximately 170 degrees). The facet sagittal orientations of the lumbar zygoapophyseal joints are not equivalent. CONCLUSIONS.: Asymmetry in facet orientation is a normal characteristic in the thorax.

Adult↗
PubMed2006

Multisensory activation of the intraparietal area when classifying grating orientation: a functional magnetic resonance imaging study.

Humans can judge grating orientation by touch. Previous studies indicate that the extrastriate cortex is involved in tactile orientation judgments, suggesting that this area is related to visual imagery. However, it has been unclear which neural mechanisms are crucial for the tactile processing of orientation, because visual imagery is not always required for tactile spatial tasks. We expect that such neural mechanisms involve multisensory areas, because our perception of space is highly integrated across modalities. The current study uses functional magnetic resonance imaging during the classification of grating orientations to evaluate the neural substrates responsible for the multisensory spatial processing of orientation. We hypothesized that a region within the intraparietal sulcus (IPS) would be engaged in orientation processing, regardless of the sensory modality. Sixteen human subjects classified the orientations of passively touched gratings and performed two control tasks with both the right and left hands. Tactile orientation classification activated regions around the right postcentral sulcus and IPS, regardless of the hand used, when contrasted with roughness classification of the same stimuli. Right-lateralized activation was confirmed in these regions by evaluating the hemispheric effects of tactile spatial processing with both hands. In contrast, visual orientation classification activated the left middle occipital gyrus when contrasted with color classification of the same stimuli. Furthermore, visual orientation classification activated a part of the right IPS that was also activated by the tactile orientation task. Thus, we suggest that a part of the right IPS is engaged in the multisensory spatial processing of grating orientation.

Adult↗
PubMed1992

Orientation selectivity, preference, and continuity in monkey striate cortex.

Maps of orientation preference and selectivity, inferred from differential images of orientation (Blasdel, 1992), reveal linear organizations in patches, 0.5-1.0 mm across, where orientation selectivities are high, and where preferred orientations rotate linearly along one axis while remaining constant along the other. Most of these linear zones lie between the centers of adjacent ocular dominance columns, with their short iso-orientation slabs oriented perpendicular, in regions enjoying the greatest binocular overlap. These two-dimensional linear zones are segregated by one- and zero-dimensional discontinuities that are particularly abundant in the centers of ocular dominance columns, and that are also correlated with cytochrome oxidase-rich zones within them. Discontinuities smaller than 90 degrees extend in one dimension, as fractures, while discontinuities greater than 90 degrees are confined to points, in the form of singularities, that are generated when orientation preferences rotate continuously through +/- 180 degrees along circular paths. The continuous rotations through 180 degrees imply that direction preferences are not organized laterally in striate cortex. And they also ensure that preferences for all orientations converge at each singularity, with perpendicular orientations represented uniquely close together on opposite sides. The periodic interspersing of linear zones and singularities suggests that orientation preferences are organized by at least two competing schemes. They are optimized for linearity, along with selectivity and binocularity, in the linear zones, and they are optimized for density near singularities. Since upper-layer neurons are likely to have similarly sized dendritic fields in all regions (Lund and Yoshioka, 1991), those in the linear zones should receive precise information about narrowly constrained orientations, while those near singularities should receive coarse information about all orientations--very different inputs that suggest different perceptual functions.

Algorithms↗
PubMed1989

Organized arrangement of orientation-sensitive relay cells in the cat's dorsal lateral geniculate nucleus.

We studied the physiological orientation biases of over 700 relay cells in the cat's dorsal lateral geniculate nucleus (LGNd). Relay cells were sampled at regular intervals along horizontally as well as vertically oriented electrode penetrations in a fashion analogous to that used previously in studies of visual cortex (Hubel and Wiesel, 1962). The strengths of the orientation biases and the distributions of the preferred orientations were determined for different classes of relay cells, relay cells in different layers of the LGNd, and relay cells subserving different parts of the visual field. We find that, at the population level, LGNd cells exhibit about the same degree of orientation bias as do the retinal ganglion cells providing their inputs (see also Soodak et al., 1987). Also, as in the retina (Levick and Thibos, 1982; Leventhal and Schall, 1983), most LGNd cells tend to prefer stimuli oriented radially, i.e., parallel to the line connecting their receptive fields to the area centralis projection. However, the radial bias in the LGNd is weaker than in the retina. Moreover, there is a relative overrepresentation of cells preferring tangentially oriented stimuli in the LGNd but not in the retina. As a result of the overrepresentation of cells preferring radial and tangential stimuli, the overall distribution of preferred orientations varies in regions of the LGNd subserving different parts of the visual field. Reconstructions of our electrode penetrations provide evidence that, unlike in the retina, cells having similar preferred orientations are clustered in the LGNd. This clustering is apparent for all cell types and in all parts of laminae A and A1. The tendency to cluster according to preferred orientation is evident for cells preferring radially, intermediately, and tangentially oriented stimuli and thus is not simply a reflection of the radial bias evident among retinal ganglion cells at the population level. It is already known that cells having inputs from different eyes, on-center, off-center, X-, Y-, W-type, and color-sensitive ganglion cells are distributed nonrandomly in the LGNd of cats and monkeys (for review, see Rodieck, 1979; Stone et al., 1979; Lennie, 1981; Stone, 1983). The finding that relay cells having similar preferred orientations are also distributed nonrandomly suggests that the initial sorting of virtually all properties segregated in visual cortex may begin in the LGNd.

Animals↗
PubMed1983

Relationship between preferred orientation and receptive field position of neurons in cat striate cortex.

It has been known for two decades that neurons in mammalian visual cortex respond selectively to stimuli falling on the retina at a particular angular orientation (Hubel and Wiesel, '62). Recent evidence suggests that most cat retinal ganglion cells (Levick and Thibos, '82) and relay cells (Vidyasagar and Urbas, '82) in the cat's dorsal lateral geniculate nucleus are also orientation selective. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis, most retinal ganglion cells have oriented dendritic fields (Leventhal and Schall, '83) and respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick an Thibos, '82). This relationship is strongest close to the horizontal meridian (the visual streak) of the retina (Leventhal and Schall, '83). To determine if a relationship between preferred orientation and polar angle exists in visual cortex, the preferred orientations and receptive field positions of 768 striate cortical neurons were studied. As in the retina, a systematic relationship exists between preferred orientation and visual field position in area 17. In parts of striate cortex 15--80 degrees from the area centralis projection there is a strong tendency for cells to respond best to lines oriented radially. In regions 4--15 degrees from the area centralis projection this relationship appears weaker. In regions subserving the central 4 degrees of visual angle no such relationship exists. Throughout area 17 the relationship between preferred orientation and polar angle is strongest in regions subserving the horizontal meridian.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗