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PubMed1988

Sex differences in the lateralization of spatial abilities: a spatial component analysis of extreme group scores.

Sex differences in the cerebral lateralization of two discrete components of spatial processing were investigated in high and low ability males and females using the dual-task paradigm. In the first phase of the experiment, the results indicated a pattern of right hemispheric control for a spatial visualization component, regardless of sex and ability level. In the processing of the spatial orientation component of spatial ability, high ability males and females showed left hemispheric lateralization, whereas low ability males and females displayed right hemispheric control. In the second phase of this study, it was observed that high ability females and low ability males may use a verbal mediation strategy in processing spatial visualization tasks. No verbal mediation effects were found for the spatial orientation component.

Adult↗
PubMed2004

Active navigation and orientation-free spatial representations.

In this study, we examined the orientation dependency of spatial representations following various learning conditions. We assessed the spatial representations of human participants after they had learned a complex spatial layout via map learning, via navigating within a real environment, or via navigating through a virtual simulation of that environment. Performances were compared between conditions involving (1) multiple- versus single-body orientation, (2) active versus passive learning, and (3) high versus low levels of proprioceptive information. Following learning, the participants were required to produce directional judgments to target landmarks. Results showed that the participants developed orientation-specific spatial representations following map learning and passive learning, as indicated by better performance when tested from the initial learning orientation. These results suggest that neither the number of vantage points nor the level of proprioceptive information experienced are determining factors; rather, it is the active aspect of direct navigation that leads to the development of orientation-free representations.

Adolescent↗
PubMed2000

On asymmetries in cross-modal spatial attention orienting.

In a previous study, Ward (1994) reported that spatially uninformative visual cues orient auditory attention but that spatially uninformative auditory cues fail to orient visual attention. This cross-modal asymmetry is consistent with other intersensory perceptual phenomena that are dominated by the visual modality (e.g., ventriloquism). However, Spence and Driver (1997) found exactly the opposite asymmetry under different experimental conditions and with a different task. In spite of the several differences between the two studies, Spence and Driver (see also Driver & Spence, 1998) argued that Ward's findings might have arisen from response-priming effects, and that the cross-modal asymmetry they themselves reported, in which auditory cues affect responses to visual targets but not vice versa, is in fact the correct result. The present study investigated cross-modal interactions in stimulus-driven spatial attention orienting under Ward's complex cue environment conditions using an experimental procedure that eliminates response-priming artifacts. The results demonstrate that the cross-modal asymmetry reported by Ward (1994) does occur when the cue environment is complex. We argue that strategic effects in cross-modal stimulus-driven orienting of attention are responsible for the opposite asymmetries found by Ward and by Spence and Driver (1997).

Adolescent↗
PubMedDate not supplied

A comparison of inhibition in orientation and spatial frequency selectivity of cat visual cortex.

Neurones in the visual cortex are highly selective for orientation and spatial frequency of visual stimuli. There is strong neurophysiological evidence that orientation selectivity is enhanced by inhibitory interconnections between columns in the cortex which have different orientation sensitivities, an idea which is supported by experiments using neuropharmacological manipulation or complex visual stimuli. It has also been proposed that selectivity for spatial frequency is mediated in part by a similar mechanism to that for orientation, although evidence for this is based on special use of visual stimuli, which hampers interpretation of the findings. We have therefore examined selectivity for both orientation and spatial frequency using a technique which allows direct inferences about inhibitory processes. Our method uses microiontophoresis of an excitatory amino acid to elevate maintained discharge of single neurones in the visual cortex. We then present visual stimuli both within and outside the range of orientations and spatial frequencies which cause a cell to respond with increased discharge. Our results show that orientations presented on either side of the responsive range usually produce clear suppression of maintained discharge. In marked contrast, spatial frequencies shown to either side of the responsive range have little or no effect on maintained activity. We conclude that there is an intracortical organization of inhibitory connections between cells tuned to different orientations but not different spatial frequencies.

Animals↗
PubMed2003

Conjugacy of torsional eye movements in response to a head tilt paradigm.

PURPOSE: Vertically skewed eye movements are induced by head tilt toward the shoulder (roll). Because vertical and torsional eye movements are tightly coupled both mechanically and neuronally, the purpose of the present study was to investigate the conjugacy of torsional eye movements during the Bielschowsky head tilt test (BHTT). Furthermore, the purpose was to investigate the influence of different visual and viewing condition on torsional conjugacy. The issue has clinical relevance in interpreting the outcome of the BHTT. METHODS: Eye movement recordings were performed using the infrared three-dimensional video-oculography (3D-VOG) technique. Objective cycloposition of 20 healthy individuals was measured in presumed primary position and in head tilt positions of 15 degrees, 30 degrees, and 45 degrees to the right and left, respectively. The same paradigm was performed under three different viewing conditions: binocularly without spatial orientation and both binocularly and monocularly with spatial orientation. The stimulus used with spatial orientation was a photographic picture of a historic building, whereas the stimulus with no spatial cues consisted of concentric circles. RESULTS: Consistent excyclovergence occurred in all subjects in head tilt. The relative amount increased with head tilt, regardless of the visual stimulus. Maximum excyclovergence was 0.7 degrees in 45 degrees head tilt during monocular fixation. Binocular viewing enhanced the torsion conjugacy by means of vergence stability (SD), whereas spatial visual cues improved the torsional conjugacy only slightly. CONCLUSIONS: Consistent excyclovergence was induced in head tilt. A vestibular origin seems to provide a plausible explanation of the induced torsional disconjugacy, whereas visual feed-back seems plausible in explaining the better conjugacy in binocular viewing.

Adult↗
PubMed1984

Contrast sensitivity loss in multiple sclerosis. Selectivity by eye, orientation, and spatial frequency measured with the evoked potential.

Multiple sclerosis can produce highly selective losses in visual function. Psychophysical studies have demonstrated contrast sensitivity deficits for spatial frequencies or for stimulus orientations. Using real-time lock-in retrieval of the visual evoked potential, the authors measured contrast sensitivity in 15 cases with probable or definite multiple sclerosis and acuities of 20/40 or better. Sine-wave grating contrast threshold determinations for three spatial frequencies (1, 4, and 8 cycles/deg) and four orientations (0, 45, 90, and 135 deg) revealed contrast deficits in at least one spatial frequency and orientation in every case. In most cases the visual losses were spotty or multifocal, and not the same in both eyes. Some cases with highly selective patterns of orientation or spatial frequency losses were observed and are discussed in terms of involvement of cortical functional architecture in the disease.

Adult↗
PubMed2006

Anisotropic local contrast normalization: the role of stimulus orientation and spatial frequency bandwidths in the oblique and horizontal effect perceptual anisotropies.

Visual ability for sine waves and other narrowband stimuli shows an oblique effect--worst performance at obliques, best at horizontal and vertical orientations. Recently, we have shown that with broadband stimuli (either 1/f(alpha) visual noise or natural scenes), performance for detecting oriented content is worst at horizontal, best at the obliques, and intermediate at vertical orientations (a "horizontal effect"). This horizontal effect has been explained by a cortical contrast normalization model that is both local (over orientation and spatial frequency) and anisotropic (due to a numerical bias of neurons with different preferred orientations). Here, the bandwidth of content at which an oblique effect or horizontal effect occurs was assessed in two suprathreshold matching experiments conducted with 1/f(alpha) noise stimuli filtered with a triangle increment function of varied bandwidth (16 levels of orientation and spatial frequency bandwidth). The results provided further support for the local anisotropic normalization model in that an oblique effect was observed when a fairly small range of orientations and high spatial frequencies were tested and the horizontal effect was observed for broadband increments > or = 20 degrees orientation bandwidth and > or = 1-octave in frequency. At intermediate spatial frequency and orientation increment bandwidths, a blend of the two anisotropies was observed.

Adult↗
PubMed1978

The role of frontal and parietal cortex in cognitive processing: tests of spatial and sequence functions.

Normal monkeys and monkeys with resection of anterior frontal or posterior parietal cortex were trained to press a panel next to a green panel as a test of extrapersonal spatial orientation and to press a panel next to their own prior press as a test of personal spatial orientation. All monkeys also learned two sets of sequence problems in which the solutions were made independent of spatial location by randomly shifting the locations of the stimuli after each response within a trial. The Parietal Group was significantly impaired on the extrapersonal 'next-to' task but not the more difficult personal 'next-to' task. The Frontal Group was impaired on both the personal and the extrapersonal 'next-to' tasks but only when the relevant cues shifted spatial locations from trial to trial. The performance of the Parietal Group completely overlapped that of the Normal Group on the sequence problems regardless of the level of testing sophistication the monkeys had attained. In contrast, the Frontal Group demonstrated a significant impairment in learning sequences but only when the monkeys were naive. Once they became sophisticated they learned each sequence at a normal rate. Their poor performance was attributed to the lack of stability in the spatial location of the stimuli. The data support the view that a distinction between personal and extrapersonal spatial orientation is relevant to posterior parietal function but indicate that neither sequencing per se nor personal spatial orientation or spatial memory per se is dependent on intact frontal functioning. Rather, the frontal cortex is involved with a higher-order control essential to allow the monkey to perceive the reliable aspects of stimuli contained in a stimulus context full of unreliable noise and to further allow for flexible response pattern appropriate to the demands of a variable context.

Animals↗
PubMed1999

The effect of conformation of the acyloxyalkoxy-based cyclic prodrugs of opioid peptides on their membrane permeability.

In an earlier study using Caco-2 cells, an in vitro cell culture model of the intestinal mucosa, we have shown that the acyloxyalkoxy-based cyclic prodrugs 3 and 4 of the opioid peptides [Leu5]-enkephalin(1, H-Tyr-GLY-Gly-Phe-Leu-OH) and DADLE(2, H-Tyr-D-Ala-Gly-Phe-D-Leu-OH), respectively, were substrates for apically polarized efflux systems and therefore less able to permeate the cell monolayers than were the opioid peptides themselves. In an attempt to explain how structure may influence the recognition of these cyclic prodrugs as substrates by the apically polarized efflux systems, we have determined the possible solution conformations of 3 and 4 using spectroscopic techniques (2D-NMR, CD) and molecular dynamics simulations. Spectroscopic as well as computational studies indicate that cyclic prodrug 4 exhibits a major and a minor conformer in a ratio of 3:2 where both conformers exhibit gamma and beta-turn structures. Spectroscopic, as well as molecular dynamics, studies indicate that the difference between the two conformers involves a cis/trans inversion occurring at the amide bond between the promoiety and Tyr1. The major conformer has a trans amide bond between the promoiety and Tyr1, whereas the minor conformer has a cis amide bond. The spectroscopic data indicate that cyclic prodrug 3 has a structure similar to that of the major conformer in cyclic prodrug 4. It has recently been reported that a particular arrangement of polar groups and spatial separation distances is required for substrate recognition by P-glycoprotein. When the conformation of the acyloxyalkoxy linker was investigated in the major and minor conformers of cyclic prodrug 4, with respect to distances between the polar functional groups, this ideal fixed spatial orientation was observed. Interestingly this same spatial orientation of polar functional groups was not observed for other cyclic prodrugs prepared by our laboratory using different chemical linkers (coumarinic acid and phenylpropionic acid) but the same opioid peptides that had previously been shown not to be substrates for the apically polarized efflux systems. Therefore, we hypothesize that the structure and/or the flexibility of the acyloxyalkoxy linker itself allows cyclic prodrugs 3 and 4 to adopt conformations that permit ideal arrangement of polar groups in the linker and their fixed spatial orientation. This possibly induces the substrate activity of cyclic prodrugs 3 and 4 for the apically polarized efflux systems.

Biological Transport↗
PubMed1992

Perception of motion and position relative to the earth. An overview.

Results of the five experiments are consistent with the following generalizations. Canal-mediated turn perception (pitch, roll, or yaw) in earth-horizontal or earth-vertical plane, is suppressed in direct relationship to the magnitude of a linear acceleration vector lying in the plane of a responding canal when the magnitude of the linear vector is constant or increasing and when its direction is either fixed or rotating in the same direction as the concomitant canal signal. Canal-mediated turn perception (pitch, roll, or yaw) is not suppressed by a coplanar linear vector that is counterrotating relative to the canal signal. Change in perceived attitude (pitch, roll, or yaw) is very sluggish in the absence of concordant canal information; attitude change may not be an immediate otolith-mediated perceptual event but a slowly developing perception dependent upon cognitive appreciation of an immediate otolith angular position signal. Otolith phasic neural units, unreinforced by appropriate canal signals, may contribute more to a brief linear velocity component in perception than to rate of attitude change. Otolith-mediated attitude perception within a given earth-vertical plane can be distorted by strong coplanar angular velocity canal information. Once distorted, return to veridical attitude perception can be gradual because, in the absence of complimentary canal or visual information, recovery is dependent upon relatively slow cognitive appreciation of a prevailing otolith position signal. Several attractive hypotheses relating to the dynamics of attitude perception can only be tested by substantially more data on the dynamics of spatial orientation perception. Most of our objectives cannot be achieved without models that yield valid prediction of the dynamics of spatial orientation perception. All of the observations in these experiments were carried out in darkness, or, in the simulated catapult experiment, without external visual reference. Various forms of visual information will change the dynamics of spatial orientation perception. My discussion has been limited to consideration of the vestibular system, as though the canal and otolith systems completely controlled the dynamics of spatial orientation perceptions. Obviously other partners in the dynamics of postural control, including vision, proprioception, and expectation, must be included in this challenging field of research. Dedication to stereotyped ideas about objectivity in the 20th century has hindered advancement of knowledge on the dynamics of spatial orientation perception relative to rate of progress achieved by several scientists of the 18th and 19th centuries, who provided word pictures of perceived motions and tilts along with descriptions of the motions that engendered the pictures.(ABSTRACT TRUNCATED AT 400 WORDS)

Gravitation↗
PubMed2005

Specific recognition of the collagen triple helix by chaperone HSP47: minimal structural requirement and spatial molecular orientation.

The unique folding of procollagens in the endoplasmic reticulum is achieved with the assistance of procollagen-specific molecular chaperones. Heat-shock protein 47 (HSP47) is an endoplasmic reticulum-resident chaperone that plays an essential role in normal procollagen folding, although its molecular function has not yet been clarified. Recent advances in studies on the binding specificity of HSP47 have revealed that Arg residues at Yaa positions in collagenous Gly-Xaa-Yaa repeats are critical for its interactions (Koide, T., Takahara, Y., Asada, S., and Nagata, K. (2002) J. Biol. Chem. 277, 6178-6182; Tasab, M., Jenkinson, L., and Bulleid, N. J. (2002) J. Biol. Chem. 277, 35007-35012). In the present study, we further examined the client recognition mechanism of HSP47 by taking advantage of systems employing engineered collagen model peptides. First, in vitro binding studies using conformationally constrained collagen-like peptides revealed that HSP47 only recognized correctly folded triple helices and that the interaction with the corresponding single-chain polypeptides was negligible. Second, a binding study using heterotrimeric model clients for HSP47 demonstrated a minimal requirement for the number of Arg residues in the triple helix. Finally, a cross-linking study using photoreactive collagenous peptides provided information about the spatial orientation of an HSP47 molecule in the chaperone-collagen complex. The obtained results led to the development of a new model of HSP47-collagen complexes that differs completely from the previously proposed "flying capstan model" (Dafforn, T. R., Della, M., and Miller, A. D. (2001) J. Biol. Chem. 276, 49310-49319).

Amino Acid Sequence↗
PubMed1985

Detection and identification of near-threshold visual patterns.

For a number of visual dimensions--spatial frequency, orientation, spatial position, and direction of motion (at velocities higher than 1 or 2 deg/sec)--experimental results at near-threshold contrasts can be explained by assuming that multiple mechanisms selectively sensitive along that dimension exist and have labeled outputs. For the temporal-position dimension, analogous experimental results can be explained by assuming that each mechanism's output at a particular time depends only on the recent past and is labeled. For the eye-of-origin dimension, however, although the evidence suggests selectively sensitive mechanisms (at least at some spatial and temporal frequencies), these mechanisms seem not to have labeled outputs. For the temporal-frequency dimension (at any fixed spatial frequency), evidence suggests that there are not narrowly tuned mechanisms although there may be very broadly tuned ones.

Attention↗
PubMedDate not supplied

Visual cortex neurons in monkeys and cats: detection, discrimination, and identification.

A descriptive function method was used to measure the detection, discrimination, and identification performance of a large population of single neurons recorded from within the primary visual cortex of the monkey and the cat, along six stimulus dimensions: contrast, spatial position, orientation, spatial frequency, temporal frequency, and direction of motion. First, the responses of single neurons were measured along each stimulus dimension, using analysis intervals comparable to a normal fixation interval (200 ms). Second, the measured responses of each neuron were fitted with simple descriptive functions, containing a few free parameters, for each stimulus dimension. These functions were found to account for approximately 90% of the variance in the measured response means and response standard deviations. (A detailed analysis of the relationship between the mean and the variance showed that the variance is proportional to the mean.) Third, the parameters of the best-fitting descriptive functions were utilized in conjunction with Bayesian (optimal) decision theory to determine the detection, discrimination, and identification performance for each neuron, along each stimulus dimension. For some of the cells in monkey, discrimination performance was comparable to behavioral performance; for most of the cells in cat, discrimination performance was better than behavioral performance. The behavioral contrast and spatial-frequency discrimination functions were similar in shape to the envelope of the most sensitive cells; they were also similar to the discrimination functions obtained by optimal pooling of the entire population of cells. The statistics which summarize the parameters of the descriptive functions were used to estimate the response of the visual cortex as a whole to a complex natural image. The analysis suggests that individual cortical neurons can reliably signal precise information about the location, size, and orientation of local image features.

Animals↗
PubMed2005

Design-based stereology in neuroscience.

Quantitative morphology of the CNS has recently undergone major developments. In particular, several new approaches, known as design-based stereologic methods, have become available and have been successfully applied to neuromorphological research. However, much confusion and uncertainty remains about the meaning, implications, and advantages of these design-based stereologic methods. The objective of this review is to provide some clarification. It does not comprise a full description of all stereologic methods available. Rather, it is written by users for users, provides the reader with a guided tour through the relevant literature. It has been the experience of the authors that most neuroscientists potentially interested in design-based stereology need to analyze volumes of brain regions, numbers of cells (neurons, glial cells) within these brain regions, mean volumes (nuclear, perikaryal) of these cells, length densities of linear biological structures such as vessels and nerve fibers within brain regions, and the cytoarchitecture of brain regions (i.e. the spatial distribution of cells within a region of interest). Therefore, a comprehensive introduction to design-based stereologic methods for estimating these parameters is provided. It is demonstrated that results obtained with design-based stereology are representative for the entire brain region of interest, and are independent of the size, shape, spatial orientation, and spatial distribution of the cells to be investigated. Also, it is shown that bias (i.e. systematic error) in results obtained with design-based stereology can be limited to a minimum, and that it is possible to assess the variability of these results. These characteristics establish the advantages of design-based stereologic methods in quantitative neuromorphology.

Animals↗
PubMedDate not supplied

A neural network model of chemotaxis predicts functions of synaptic connections in the nematode Caenorhabditis elegans.

The anatomical connectivity of the nervous system of the nematode Caenorhabditis elegans has been almost completely described, but determination of the neurophysiological basis of behavior in this system is just beginning. Here we used an optimization algorithm to search for patterns of connectivity sufficient to compute the sensorimotor transformation underlying C. elegans chemotaxis, a simple form of spatial orientation behavior in which turning probability is modulated by the rate of change of chemical concentration. Optimization produced differentiator networks capable of simulating chemotaxis. A surprising feature of these networks was inhibitory feedback connections on all neurons. Further analysis showed that feedback regulates the latency between sensory input and behavior. Common patterns of connectivity between the model and biological networks suggest new functions for previously identified connections in the C. elegans nervous system.

Action Potentials↗
PubMed2006

Functions of the left superior frontal gyrus in humans: a lesion study.

The superior frontal gyrus (SFG) is thought to contribute to higher cognitive functions and particularly to working memory (WM), although the nature of its involvement remains a matter of debate. To resolve this issue, methodological tools such as lesion studies are needed to complement the functional imaging approach. We have conducted the first lesion study to investigate the role of the SFG in WM and address the following questions: do lesions of the SFG impair WM and, if so, what is the nature of the WM impairment? To answer these questions, we compared the performance of eight patients with a left prefrontal lesion restricted to the SFG with that of a group of 11 healthy control subjects and two groups of patients with focal brain lesions [prefrontal lesions sparing the SFG (n = 5) and right parietal lesions (n = 4)] in a series of WM tasks. The WM tasks (derived from the classical n-back paradigm) allowed us to study the impact of the SFG lesions on domain (verbal, spatial, face) and complexity (1-, 2- and 3-back) processing within WM. As expected, patients with a left SFG lesion exhibited a WM deficit when compared with all control groups, and the impairment increased with the complexity of the tasks. This complexity effect was significantly more marked for the spatial domain. Voxel-to-voxel mapping of each subject's performance showed that the lateral and posterior portion of the SFG (mostly Brodmann area 8, rostral to the frontal eye field) was the subregion that contributed the most to the WM impairment. These data led us to conclude that (i) the lateral and posterior portion of the left SFG is a key component of the neural network of WM; (ii) the participation of this region in WM is triggered by the highest level of executive processing; (iii) the left SFG is also involved in spatially oriented processing. Our findings support a hybrid model of the anatomical and functional organization of the lateral SFG for WM, according to which this region is involved in higher levels of WM processing (monitoring and manipulation) but remains oriented towards spatial cognition, although the domain specificity is not exclusive and is overridden by an increase in executive demand, regardless of the domain being processed. From a clinical perspective, this study provides new information on the impact of left SFG lesions on cognition that will be of use to neurologists and neurosurgeons.

Adult↗
PubMed1995

In defense of traditional views of spatial disorientation and loss of situation awareness: a reply to Navathe and Singh's "An operational definition of spatial disorientation".

In a recent article in Aviation, Space, and Environmental Medicine, Navathe and Singh proposed new "operational" definitions for spatial disorientation (SD) and loss of situation(al) awareness (LSA). The major feature of their new scheme was to treat the two phenomena as distinct, with SD attributable to physiologically based (peripheral) illusions and LSA to psychological (central) factors. The present commentary argues in favor of traditional views of SD that consider spatial orientation to be a subset of overall situation awareness.

Awareness↗