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At least 613 records · Page 34Linked to original sources

PubMed2005

Oriented multiscale spatial filtering and contrast normalization: a parsimonious model of brightness induction in a continuum of stimuli including White, Howe and simultaneous brightness contrast.

The White effect [Perception 8 (1979) 413] cannot be simply explained as due to either brightness contrast or brightness assimilation because the direction of the induced brightness change does not correlate with the amount of black or white border in contact with the gray test patch. This has led some investigators to abandon spatial filtering explanations not only for the White effect but for brightness perception in general. Offered instead are explanations based on a variety of junction analyses and/or perceptual organization schemes which in the case of the White effect are usually based on T-junctions. Recently, Howe [Perception 30 (2001) 1023] challenged T-junction based explanations with a novel variation of White's effect in which the T-junctions were constant while the brightness effect was eliminated or reversed, and proposed an alternative explanation in terms of illusory contours. The present study argues that an analysis at the level of illusory contours is not necessary and that a much simpler spatial filtering based explanation is sufficient. Brightness induction was measured in a set of stimuli chosen to illustrate the relationship between the Howe stimulus [Perception 30 (2001) 1023], the White stimulus [Perception 8 (1979) 413] and the classical simultaneous brightness contrast (SBC) stimulus. The White stimulus and the SBC stimulus occupy opposite ends of a continuum of stimuli in which the Howe stimulus is the mid-point. The psychophysical measurements were compared with the predictions of the oriented difference-of-Gaussians (ODOG) computational model of Blakeslee and McCourt [Vision Research 39 (1999) 4361]. The ODOG model parsimoniously accounted for both the direction and relative magnitude of the brightness effects suggesting that more complex mechanisms are not required to explain them.

Contrast Sensitivity↗

PubMed1999

Neuronal response sensitivity to bidirectional off-vertical axis rotations: a dimension of imbalance in the bilateral vestibular nuclei of cats after unilateral labyrinthectomy.

In decerebrate cats after acute hemilabyrinthectomy, the response sensitivity of extracellularly recorded vestibular nuclear neurons on the lesioned and labyrinth-intact sides were examined quantitatively during constant velocity off-vertical axis rotations with an aim to elucidate the functional contribution of otolithic inputs to the ipsilateral and contralateral vestibular nuclei. The bidirectional response sensitivity, delta, was determined as the ratio of the gain during clockwise to that during counterclockwise rotations. A continuum of response sensitivity was identified: one-dimensional neurons showed symmetrically bidirectional response patterns, while two-dimensional neurons showed asymmetrically bidirectional patterns that in some cases approached unidirectional patterns with change in velocity. The proportion of two-dimensional neurons was significantly increased after acute hemilabyrinthectomy. Two-dimensional neurons that responded only to one direction of rotation in at least one of the velocities tested were described as unidirectional neurons. This unidirectional response pattern was observed in one-third of the entire neuronal population studied, but not in cats with both labyrinths intact, thus suggesting that such prominent broadly tuned responses are normally masked by converging otolithic inputs from the contralateral side. These neurons were found in higher proportion on the lesioned side than on the labyrinth-intact side. Among the 70% of unidirectional neurons that exhibited bidirectional response at some velocities and unidirectional response at others, prominent shifts in delta values (i.e. between 0/infinity and finite values) with velocity can be computed for each neuron. The shifts in delta values correlated with large shifts in the response dynamics and spatial orientation as the response pattern changed with velocity. The response orientations of the unidirectional neurons pointed in all directions on the horizontal plane. When all the two-dimensional neurons (i.e. both the unidirectionally and bidirectionally responsive ones) were pooled, imbalances in the distribution of the response orientations and in response gain were found between the ipsilateral-side-down/head-down half-circle and the contralateral-side-down/head-up half-circle on the labyrinth-intact side, but not on the lesioned side. These results, derived from spatiotemporal processing of gravitational signals, reveal a novel dimension of imbalance between neuronal populations in the two vestibular nuclear complexes after acute lesion of one labyrinth. This feature would provide, on the one hand, deranged cues of spatial orientation and direction during slow head excursions and, on the other, a framework for the dynamic behavioral deficits associated with hemilabyrinthectomy.

Animals↗

PubMed2004

A qualitative analysis of the mini mental state examination on Alzheimer's disease patients treated with cholinesterase inhibitors.

The improvement in cognitive performances due to cholinesterase inhibitors (ChEls) is not homogeneous among Alzheimer's disease (AD) subjects. Aim of this study is to evaluate whether a specific pattern of change in mini mental state examination (MMSE) could be observed in AD subjects after 9-month treatment with ChEls. From September 2000 to September 2002, 99 subjects enrolled in the CRONOS project. They have never been previously treated with ChEls. All of them completed both the 3- and the 9-month follow-up. The multidimensional assessment included MMSE, activity of daily living (ADL), instrumental activity of daily living (IADL), somatic health status, according to design of the CRONOSproject. The MMSE was analyzed both as a total score and disaggregated in 11 items. All subjects were divided in 2 groups according to the degree of change in MMSE total score from baseline to the 9th month. Subjects with a change </= -1 were defined as non-responders(NR), whereas those with a change >0 as responders (R). At start, no statistically significant differences were found between the 2 groups. MMSE score was significantly higher in the R group both at 3 (p < 0.0001) and 9 months (p < 0.0001), while functional status (ADL and IADL) was significantly lower in NR group at 9 months (p = 0.025; p =0.018, respectively). In MMSE qualitative analysis of 3-month, NR significantly worsened in temporal (p </= 0.05) and spatial orientation (p </= 0.001), and in delayed recall items (p </= 0.0005) in comparison to their counterpart. At 9-month the differences between the 2 groups were observed also for registration (p < 0.001), attention (p </= 0.0005), obeying oral commands (p < 0.0005), reading and obeying commands (p </= 0.0005), writing a sentence (p </= 0.0005) and copying a design (p </= 0.05). In a multivariate regression model, after adjustment for demographic (age, education, gender) and clinical factors (duration of disease), only the change at 3 months in 5 MMSE items (temporal and spatial orientation,delayed recall, obeying an oral command and reading and obeying command) is associated with global cognitive change observed at 9 months. Data suggest that the change in cognitive performances of AD subjects treated with ChEls involves few and specific MMSE items at 3-month, while it tend to generalize to almost all the others at 9-month treatment.

Aged↗

PubMed2004

Posture, head stability, and orientation recovery during vestibular regeneration in pigeons.

Compensatory behavior such as oculomotor, gaze, and postural responses that occur during movement largely depend upon a functioning vestibular system. In the present study, the initial loss and subsequent recovery of postural and head stability in pigeons undergoing vestibular regeneration were examined. Adult pigeons were trained to manipulate a straight run chamber to peck an illuminated key for fluid reward. Six behavioral measures assessing performance, posture, and head stability were quantified. These included run latency, steps (walking), path negotiation (lane changes), gaze saccades, head bobs, and head shakes. Once normative values were obtained for four birds, complete lesion of all receptor cells and denervation of the epithelia in the vestibular endorgans were produced using a single intralabyrinthine application of streptomycin sulfate. Each bird was then tested at specific times during regeneration and the same behavioral measures examined. At 7 days post-streptomycin treatment (PST), all birds exhibited severe postural and head instability, with tremors, head shakes, staggering, and circling predominating. No normal trial runs, walking, gaze saccades, or head bobs were present. Many of these dysfunctions persisted through 3-4 weeks PST. Gradually, tremor and head shakes diminished and were replaced with an increasing number of normal head bobs during steps and gaze saccades. Beginning at 4 weeks PST, but largely inaccurate, was the observed initiation of directed steps, less staggering, and some successful path negotiation. As regeneration progressed, spatial orientation and navigation ability increased and, by 49 days PST, most trials were successful. By 70 days PST, all birds had recovered to pretreatment levels. Thus, it was observed that ataxia must subside, coincident with normalized head and postural stability prior to the recovery of spatial orientation and path navigation recovery. Parallels in recovery were drawn to hair cell regeneration and afferent responsiveness, as inferred from present results and those in other investigations.

Animals↗

PubMed1999

Structural requirements for marbox function in transcriptional activation of mar/sox/rob regulon promoters in Escherichia coli: sequence, orientation and spatial relationship to the core promoter.

The promoters of the mar/sox/rob regulon of Escherichia coli contain a binding site (marbox) for the homologous transcriptional activators MarA, SoxS and Rob. In spite of data from footprinting studies, the marbox has not been precisely defined because of its degeneracy and asymmetry and seemingly variable location with respect to the -10 and -35 hexamers for RNA polymerase (RNP) binding. Here, we use DNA retardation studies and hybrid promoters to identify optimally binding 20 bp minimal marboxes from a number of promoters. This has yielded a more defined marbox consensus sequence (AYnGCACnnWnnRYYAAAYn) and has led to the demonstration that some marboxes are inverted relative to others. Using transcriptional fusions to lacZ, we have found that only one marbox orientation is functional at a given location. Moreover, the functional orientation is determined by marbox location: marboxes that are 15 or more basepairs upstream of the -35 hexamer are oriented opposite those closer to the -35 hexamer. Marbox orientation and the spacing between marbox and signals for RNP binding are critical for transcriptional activation, presumably to align MarA with RNP.

Bacterial Proteins↗

PubMedDate not supplied

[Shadow optic. An endoscope with optimized ligth].

Modern endoscopes use a single mid-frontal illumination source that yields an unnatural flat image. At the University of Tübingen, in collaboration with Gimmi GmbH (Tuttlingen, Germany), a new concept endoscope has been developed with an additional light source: the shadow optic. With the aid of a secondary light source along the axis of the endoscope, a shadow is obtained which gives an impression of spatial depth. The aim of the study was to assess this new endoscope objectively, focusing on the speed and safety of the surgical act. The shadow optic was used in an experimental setting by 20 probands, each of whom performed five different standardized procedures of increasing difficulty five times, with and without shadow optic in randomized sequence, making a total of 1000 experiments. The procedures consisted in spatial orientation tests, structure-surrounding maneuvers, tissue clamping, needle puncture and suturing. The evaluation criteria were the time required to perform the procedures and the number of predefined errors as determined by electronic control. In each procedure, the time needed to perform the experiments was shorter with the shadow optic, reductions of up to 18% being recorded, and the number of errors was up to 54% lower compared to the experiments conducted with the traditional endoscope. The results of the study demonstrate that, as a result of the more natural spatial view conditions, the procedures were performed faster and with greater precision when the shadow optic was used. The endoscopic imaging with the shadow optic makes for better spatial orientation and a more natural and manageable image.

Endoscopes↗

PubMed1986

Learner drivers with spina bifida and hydrocephalus: the relationship between perceptual-cognitive deficit and driving performance.

This study investigated the relationship between perceptual-cognitive skills and driving performance in a group of eleven learner drivers disabled by spina bifida and hydrocephalus. Perceptual-cognitive skills assessed include figure-ground discrimination, visual scanning/tracking, spatial orientation, language, reasoning and memory ability. Following ten hours driving tuition in suitably adapted cars, driving performance in off-road manoeuvres and in-traffic situations was measured. Results showed that the perceptual-cognitive skills of this group were in the low average or below average range compared to a non-handicapped population. Spearman Rank Order Correlations between clinical tests and driving performance indicated that although certain tests correlated with off-road manoeuvres, no perceptual measures were reliable indicators of in-traffic driving. There were indications that practical measures of spatial orientation and reasoning ability may be more relevant to some aspects of driving than tested perceptual skills. Memory for road signs, landmarks and routes was also investigated. Accurate retention seemed more dependent on general reasoning ability than tested aspects of memory functioning. It is suggested that as clinically tested perceptual skills do not seem to be reliable indicators of driving performance, an individual's test results should not be used to deter him from learning to drive.

Adolescent↗

PubMedDate not supplied

Prospective study of brief neuropsychological measures to assess crash risk in older primary care patients.

BACKGROUND: Practicing primary care physicians often encounter the difficult clinical situation of evaluating the older driver. We wanted to investigate the relation between self-reported driving behavior, neuropsychological measures, and crash risk to inform the development of a test battery that could predict unsafe driving behavior and was feasible for use by primary care physicians. METHODS: This study was a prospective follow-up of 107 drivers aged 65 years and older recruited from a primary care setting in 1995. Tests of attention, visual information processing, spatial orientation, and general mental status were administered at baseline. At baseline and after 2 years of follow-up, patients were asked about their driving history using the driving questionnaire. Risk for reported crashes in the follow-up period was assessed in relation to baseline driving history and measures of cognition. RESULTS: Baseline self-reports of driving habits and attitudes were associated with an increased risk of reporting a crash after 2 years of follow-up (relative risk ratio = 5.31; 95% confidence interval [CI], 0.63, 44.63). In addition, baseline tests of attention, visual information processing, and spatial orientation were associated with an increased risk of reporting motor vehicle crash at follow-up. For example, respondents with poor performance on the Trail Making Test-part A, were almost four times more likely to report a crash at follow-up (risk ratio = 3.15; 95% CI, 0.76, 13.07). CONCLUSION: Although our conclusions are tempered by small sample size, this preliminary study suggests that brief cognitive tests and simple questions about driving habits warrant further investigation as indicators of crash risk with potential utility for assessing older drivers in primary care.

Accidents, Traffic↗

PubMed1988

Ground-based training for the stimulus rearrangement encountered during spaceflight.

Approximately 65-70% of the crew members now experience motion sickness of some degree during the first 72 h of orbital flight on the Space Shuttle. Lack of congruence among signals from spatial orientation systems leads to sensory conflict, which appears to be the basic cause of space motion sickness. A project to develop training devices and procedures to preadapt astronauts to the stimulus rearrangements of microgravity is currently being pursued. The preflight adaptation trainers (PATs) are intended to: demonstrate sensory phenomena likely to be experienced in flight, allow astronauts to train preflight in an altered sensory environment, alter sensory-motor reflexes, and alleviate or shorten the duration of space motion sickness. Four part-task PATs are anticipated. The trainers are designed to evoke two adaptation processes, sensory compensation and sensory reinterpretation, which are necessary to maintain spatial orientation in a weightless environment. Recent investigations using one of the trainers indicate that self-motion perception of linear translation is enhanced when body tilt is combined with visual surround translation, and that a 270 degrees phase angle relationship between tilt and surround motion produces maximum translation perception.

Adaptation, Physiological↗

PubMedDate not supplied

Looking around: 35 years of oculomotor modeling.

Eye movements have attracted an unusually large number of researchers from many disparate fields, especially over the past 35 years. The lure of this system stemmed from its apparent simplicity of description, measurement, and analysis, as well as the promise of providing a "window in the mind." Investigators in areas ranging from biological control systems and neurological diagnosis to applications in advertising and flight simulation expected eye movements to provide clear indicators of what the sensory-motor system was accomplishing and what the brain found to be of interest. The parallels between compensatory eye movements and perception of spatial orientation have been a subject for active study in visual-vestibular interaction, where substantial knowledge has accumulated through experiments largely guided by the challenge of proving or disproving model predictions. Even though oculomotor control has arguably benefited more from systems theory than any other branch of motor control, many of the original goals remain largely unfulfilled. This paper considers some of the promising potential benefits of eye movement research and compares accomplishments with anticipated results. Four topics are considered in greater detail: (i) the definition of oculomotor system input and output, (ii) optimization of the eye movement system, (iii) the relationship between compensatory eye movements and spatial orientation through the "internal model," and (iv) the significance of eye movements as measured in (outer) space.

Aerospace Medicine↗

PubMed2003

Testosterone-induced muscle hypertrophy is associated with an increase in satellite cell number in healthy, young men.

Testosterone (T) supplementation in men induces muscle fiber hypertrophy. We hypothesized that T-induced increase in muscle fiber size is associated with a dose-dependent increase in satellite cell number. We quantitated satellite cell and myonuclear number by using direct counting and spatial orientation methods in biopsies of vastus lateralis obtained at baseline and after 20 wk of treatment with a gonadotropin-releasing hormone agonist and a 125-, 300-, or 600-mg weekly dose of T enanthate. T administration was associated with a significant increase in myonuclear number in men receiving 300- and 600-mg doses. The posttreatment percent satellite cell number, obtained by direct counting, differed significantly among the three groups (ANCOVA P < 0.000001); the mean posttreatment values (5.0 and 15.0%) in men treated with 300- and 600-mg doses were greater than baseline (2.5 and 2.5%, respectively, P < 0.05 vs. baseline). The absolute satellite cell number measured by spatial orientation at 20 wk (1.5 and 4.0/mm) was significantly greater than baseline (0.3 and 0.6/mm) in men receiving the 300- and 600-mg doses (P < 0.05). The change in percent satellite cell number correlated with changes in total (r = 0.548) and free T concentrations (r = 0.468). Satellite cell and mitochondrial areas were significantly higher and the nuclear-to-cytoplasmic ratio lower after treatment with 300- and 600-mg doses. We conclude that T-induced muscle fiber hypertrophy is associated with an increase in satellite cell number, a proportionate increase in myonuclear number, and changes in satellite cell ultrastructure.

Adult↗

PubMed1994

Induced motion and the visual vertical: effects of frame size.

Induced visual motion and the rod-and-frame effect have both been explained in terms of changes in the observer's spatial orientation. Accordingly, we examined the effects of large and small visual frames on the two phenomena in the present experiment, testing 8 male and 8 female undergraduates. During induced motion, subjects noted the perceived motion of a stationary central point of light and then moved this light back to its apparent original location. For the visual vertical, subjects aligned two points of light to indicate the perceived vertical in the presence of straight and tilted frames. As predicted, the larger frames generated more induced motion and greater displacement of the visual vertical. These results may have occurred because the larger frame had a greater effect on the subjects' spatial orientation, perhaps due to the more extensive involvement of the peripheral, or ambient, visual system.

Adult↗

PubMed2003

Mental object rotation in Parkinson's disease.

Deficits in visual-spatial ability can be associated with Parkinson's disease (PD), and there are several possible reasons for these deficits. Dysfunction in frontal-striatal and/or frontal-parietal systems, associated with dopamine deficiency, might disrupt cognitive processes either supporting (e.g., working memory) or subserving visual-spatial computations. The goal of this study was to assess visual-spatial orientation ability in individuals with PD using the Mental Rotations Test (MRT), along with other measures of cognitive function. Non-demented men with PD were significantly less accurate on this test than matched control men. In contrast, women with PD performed similarly to matched control women, but both groups of women did not perform much better than chance. Further, mental rotation accuracy in men correlated with their executive skills involving mental processing and psychomotor speed. In women with PD, however, mental rotation accuracy correlated negatively with verbal memory, indicating that higher mental rotation performance was associated with lower ability in verbal memory. These results indicate that PD is associated with visual-spatial orientation deficits in men. Women with PD and control women both performed poorly on the MRT, possibly reflecting a floor effect. Although men and women with PD appear to engage different cognitive processes in this task, the reason for the sex difference remains to be elucidated.

Aged↗

PubMed2006

Perception of longitudinal body axis in microgravity during parabolic flight.

It has been proposed that an internal representation of body vertical has a prominent role in spatial orientation. This investigation investigated the ability of human subjects to accurately locate their longitudinal body axis (an imaginary straight body midline running from head to toes) while free-floating in microgravity. Subjects were tested in-flight, as well as on ground in normal gravity in both the upright and supine orientations to provide baseline measurements. The subjects wore a goggle device and were in total darkness. They used knobs to rotate two luminous lines until they were parallel to the subjective direction of their longitudinal body axis, in the roll (right/left) and the pitch (forward/backward) planes. Results showed that the error between the perceived and the objective direction of the longitudinal body axis was significantly larger in microgravity than in normal gravity. This error in this egocentric frame of reference is presumably due to the absence of somatosensory cues when free-floating. Mechanical pressure on the chest using an airbag reduced the error in perception of the longitudinal body axis in microgravity, thus improving spatial orientation.

Adult↗

PubMed2005

Neurovestibular and sensorimotor studies in space and Earth benefits.

This review summarizes what has been learned from studies of human neurovestibular system in weightless conditions, including balance and locomotion, gaze control, vestibular-autonomic function and spatial orientation, and gives some examples of the potential Earth benefits of this research. Results show that when astronauts and cosmonauts return from space flight both the peripheral and central neural processes are physiologically and functionally altered. There are clear distinctions between the virtually immediate adaptive compensations to weightlessness and those that require longer periods of time to adapt. However, little is known to date about the adaptation of sensory-motor functions to long-duration space missions in weightlessness and to the transitions between various reduced gravitational levels, such as on the Moon and Mars. Results from neurovestibular research in space have substantially enhanced our understanding of the mechanisms and characteristics of postural, gaze, and spatial orientation deficits, analogous to clinical cases of labyrinthine-defective function. Also, space neurosciences research has participated in the development and application of significant new technologies, such as video recording and processing of three-dimensional eye movements and posture, hardware for the unencumbered measurement of head and body movement, and procedures for investigating otolith function on Earth. In particular, devices such as centrifugation or off-vertical axis rotation could enhance clinical neurological testing because it provides linear acceleration which specifically stimulates the otolith organs in a frequency range close to natural head and body movement.

Earth, Planet↗

PubMed1981

Spontaneous reference systems in individuals.

In a series of five experiments the referencing function of spatial structures was investigated. The problem was (a) to determine whether subjects' effective frames of reference and their object figures could be experimentally identified, (b) to determine whether the analyses developed for this purpose were adequate, and (c) to determine some conditions of frames of reference. Graduate and undergraduate students were asked to reconstruct and to recall multiply-embedded figures viewed earlier. In these figures the spatial orientation of the figure elements was manipulated. Both reconstruction and recall errors were analyzed to identify subjects' effective frames of reference and their object figures. A single-subject design was used throughout. Frames of reference and their objects could be identified in Exp. 1. This experiment also showed the appropriateness of the analyses. Exp. 2 indicated that embedding figures provide one condition for identifying frames of reference. Exps. 3 to 5 demonstrated that changes in element figures, measurement, and reduction of trials and number of elements did not eliminate frames of reference. Differences in types of frames of reference were found. These differences were interpreted to indicate that some subjects use content, others formal schema (referents) to evaluate spatial orientation.

Adult↗

PubMed2001

Effects of dentate nucleus lesions on spatial and postural sensorimotor learning in rats.

The role of the dentate nucleus on spatial orientation, assessed by the Morris water maze test, and on postural sensorimotor performance, assessed by vertical grid, suspended wire, and rotorod tests, was investigated. Bilateral electrolytic lesions of the dentate nucleus slowed down the acquisition of the hidden platform task of the Morris water maze, without affecting long-term retention, the probe trial, and the visuomotor guidance necessary for swimming toward a visible goal. In addition, reversal learning was impaired in the submerged platform condition. The lesions did not affect any of the motor performance scores. The selective impairment seen during acquisition of the hidden platform task is similar to that previously reported in rats with combined lesions of the cerebellar hemispheres and dentate, indicating a specific role for this region in spatial orientation.

Animals↗

PubMedDate not supplied

Vestibulo-ocular response of human subjects seated in a pivoting support system during 3 Gz centrifuge stimulation.

The vestibulo-ocular reflex (VOR) and spatial orientation perceptions were recorded in 15 subjects during 3 Gz centrifuge runs. These data were obtained to study two issues: (1) to gain insight into reports of asymmetrical disorientation and disturbance during acceleration and deceleration of centrifuge runs like those used to train pilots on the procedures to counteract G-induced loss of consciousness (G-LOC); (2) to study the effects of sustained vertical linear acceleration on the vestibular system. The centrifuge angular velocity profile consisted of a 19 s angular acceleration to 3 Gz that was sustained for 5 min during a period of constant angular velocity, and a 19 s deceleration to 1 Gz. The runs were repeated three times with the subject facing the motion and three times with the subject's back to the motion. The VOR and spatial orientation perceptions from the eight subjects who completed all six runs were analyzed. The total VOR response during acceleration and deceleration was composed of interacting angular (AVOR) and linear components (LVOR). Asymmetries in pitch orientation perception between centrifuge acceleration and decleration were not matched by asymmetries in the total VOR slow phase velocity. During the constant velocity high-G phase of the run, sustained up-beating LVOR (Lz nystagmus) was present in 14 of the 15 subjects. Significant individual differences in Lz nystagmus were found, but the maximum Lz response in our 15 subjects was probably of insufficient magnitude to degrade visual scan of cockpit instruments. Mean magnitudes ranged from 0 to 10 deg/s at 90 s from onset of centrifuge run.

Adult↗