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At least 1,621 records · Page 90Linked to original sources
PubMed1995

A spatial oculomotor memory-task performance produces a task-related slow shift in human electroencephalography.

Electroencephalographic (EEG) deflections in humans related to the performance of memory-guided saccades were studied in this work. The EEG deflections were recorded during 2 spatial oculomotor delayed response tasks in which the subject was instructed to make a saccade either to the right or to the left depending on the spatial location of the cue which had been shown in the beginning of the delay period. The EEG deflections were compared to those recorded during a control task in which the subject also made a saccade to the right or to the left after a delay but the requirement to keep spatial information actively in mind was minimized. A slow delay-related shift was recorded during all task conditions. The slow shift was positive in the most frontal and negative in the more posterior recording sites. The negative slow shift in the more posterior recording sites was larger in the memory tasks than in the control task. Since the memory and the control tasks differed mainly in their requirement to hold spatial information in mind it is suggested that the difference in the magnitude of slow shifts between the memory and the control tasks reflects neural activity related to spatial working memory. But although the oculomotor responses in all tasks were similar, the preparatory activities for the impending eye movements may not have been similar and in addition to working memory may have contributed to the observed differences in the slow shifts.

Adult↗
PubMed1987

The development of landmarks in spatial memory: the role of differential experience.

To assess how differential experience with objects in a spatial array might serve to establish relative landmarks within the array, first and fifth graders learned models of a town and farm under two conditions. In a homogeneous condition, all elements in the array were visited an equal number of times. In a landmark condition, the relative landmark status of an element was established by distributing the same total number of visits unequally across the elements. The effects of such landmarks on spatial memory were assessed both in reconstructions of the entire array and by pairwise distance estimations. The landmark condition led to a general improvement in spatial recall accuracy as well as providing a relative landmark within the array to help organize the space. The results suggest that different levels of experience (controlling for overall experience and object salience) can establish elements as relative landmarks in spatial memory. Although there was clear developmental improvement in spatial memory, the specific landmark effects were similar for both first and fifth graders.

Attention↗
PubMed1990

Spatial and molecular aspects of estrogen and progesterone receptor expression in human uteri and uterine carcinomas.

The expression of steroid hormone receptors as molecules reflecting processes of development and differentiation in the human uterine tissue was analysed in a spatial distinct fashion: tissue samples were excised at the fundus and at different, spatially distinct positions of the uterus. They were analysed for concentrations of cytosolic estrogen and progesterone receptors in supernatants from frozen sections using an isoelectric focusing technique. The spatial and molecular distinct, qualitative and quantitative pattern of their expression in the human uterus and uterine adenocarcinomas were studied by sectioning tissue sample from the functionalis through the basalis of the endometrium until reaching deep myometrial parts of the tissue: (1) Specific spatial patterns of estrogen and progesterone receptor levels were detectable throughout the menstrual cycle. (2) For proliferative endometrium from the functionalis to the basalis of the endometrium, the content of both cytosolic receptor species increased up to 6-fold. (3) Differences detectable were less pronounced in the myometrial part of the tissue. (4) Differences of steroid receptor concentrations measured in the endometrium at different uterine positions were highest between fundus and corpus of the endometrium. (5) Maximal differences were detectable around ovulation. (6) After secretory transformation of the organ, specific patterns were still detectable, however quantitative differences were less pronounced. (7) Additionally, quantitative differences measurable were accompanied by variations of molecular properties of the progesterone receptor as demonstrated in an isoelectric focusing gel. (8) In endometrial adenocarcinomas, not only significant quantitative alterations in steroid receptor content were measured, but also a significantly changed spatial pattern of receptor concentrations, also a change of the molecular properties of the progesterone receptor was resolved if these tumor parameters were compared to those detected in the normal tissue of the same organ surrounding the tumor.

Adenocarcinoma↗
PubMed1991

Spatial and temporal patterning distinguishes the locomotor activating effects of dizocilpine and phencyclidine in rats.

A behavioral pattern monitor was used to assess the effects of dizocilpine (MK-801) and phencyclidine on the spatial and temporal patterns of locomotion and investigatory behavior in rats. The monitor provided both quantitative measures of crossovers, rearings and holepokes and qualitative measurement of the spatial and temporal patterns of locomotion. Dizocilpine (0.004-0.5 mg/kg) and phencyclidine (0.25-5.0 mg/kg) produced similar, dose-dependent increases in locomotor activity. At small doses, dizocilpine and phencyclidine increased investigatory holepokes, while at larger doses, both drugs significantly decreased the number of holepokes. Rearings were reduced similarly by the larger doses of each drug. Both dizocilpine and phencyclidine produced perseverative spatial patterns of locomotion, especially at larger doses. However, the locomotor patterns produced by these drugs were found to be dissimilar in spatial quality. After phencyclidine, animals frequently circled the perimeter of the monitor chamber or moved repetitively in horseshoe or figure-8 patterns. By contrast, rats given dizocilpine completed small rotations about either end of the chamber. Pretreatment with a small dose (0.02 mg/kg) of haloperidol, prior to either dizocilpine (0.5 mg/kg) or phencyclidine (5.0 mg/kg) had no effect on the increase in locomotor activity or the decreases in investigatory holepokes produced by the drugs. However, haloperidol altered the effects of phencyclidine on the spatial and temporal patterns of locomotion, suggesting that sigma receptors or other haloperidol-sensitive binding sites, may influence the quality but not the quantity of phencyclidine-induced hyperactivity.

Animals↗
PubMed1990

Contrast sensitivity and low spatial frequency discrimination in hemi-neglect patients.

Contrast sensitivity for sinusoidal gratings of different spatial frequencies and low spatial frequency discrimination of high contrast squarewave gratings were measured in 26 right brain damaged patients, 15 of whom showed symptoms of spatial hemi-neglect. No difference was present between neglect and non-neglect patients in either task. A difference in contrast sensitivity restricted to low spatial frequencies was present between controls and patients, independent of neglect. Overall, results indicated that spatial vision at threshold and suprathreshold levels is not selectively impaired in patients with hemi-neglect, a finding consistent with theories which postulate a post-perceptual locus of impairment in this syndrome.

Aged↗
PubMed1996

Memory for spatial location is affected in Parkinson's disease.

Are the striato-frontal neuronal circuits implicated in learning of item-specific spatial coordinates? To answer this question, we compared the performance of 20 patients with Parkinson's disease to that of 14 controls matched for age, global cognitive efficiency and mood, on a visuo-spatial learning task with little involvement of motor and constructive functions, allowing control of encoding and comparison of free recall, cued recall and recognition. Compared to controls, patients showed a severe memory impairment for visuo-spatial location of pictures, contrasting with relative preservation of verbal memory, and mild difficulties in perceptive visuo-spatial and executive functions. These results implicate striato-frontal neuronal circuits in memory for spatial location.

Aged↗
PubMed1991

Tetrahydroaminoacridine alleviates medial septal lesion-induced and age-related spatial reference but not working memory deficits.

This study examined the effects of tetrahydroaminoacridine (THA, an anticholinesterase) on water-maze (WM) spatial reference (stable platform location during training) and spatial working memory (reversal of platform location) learning in young intact/medial septal (MS)-lesioned and aged rats. THA (1 or 3 mg/kg, IP) had no effect on reference or working memory performance of young intact rats. MS lesions decreased cholineacetyltransferase activity in the hippocampus and also impaired spatial reference and working memory. THA at 3 mg/kg stabilized MS lesion-induced reference memory performance deficit (path length increase), but was ineffective at 1 mg/kg. THA had no effect on the working memory performance of MS-lesioned rats. Aged rats were impaired in spatial reference and working memory tasks. THA at 3 mg/kg partially stabilized the age-induced spatial reference memory deficits, but was ineffective at 1 mg/kg. THA at either 1 or 3 mg/kg did not alleviate the age-related deficit in the working memory version of WM. The present results suggest that some of the age-related WM deficits may be related to the degeneration of the MS-hippocampus cholinergic system and that THA may be effective in stabilizing the reference memory deficits induced by hippocampal cholinergic dysfunction.

Aging↗
PubMed1996

Differential environmental modulations on locomotor activity, exploration and spatial behaviour in young and old rats.

The effects of environmental enrichment on motor activity, exploration and spatial performances were studied in young and old rats. Both young (4 mo old) and old (22 mo old) rats were housed from weaning to testing either in standard or in enriched conditions. All rats were submitted successively to spontaneous alternation test and to object exploration test. Results show that locomotion is decreased by age and enrichment but that the quality of exploration expressed by corrected alternation scores or by the response to spatial change is improved by enrichment sometimes in old, sometimes in young rats. Enrichment tends to accelerate the acquisition of spatial informations in young rats, but it does not succeed to restore the reactivity to spatial change of old rats in the object exploration test. These results, although they do not rule out a persistance of a continued behavioural plasticity during aging, also support the idea that the beneficial effects of environmental stimulations do not succeed to restore high cognitive function, such as the capacity to have a spatial representation, in old animals.

Aging↗
PubMed1996

Spatial and visual discrimination learning in CD1 mice: partial analogy between the effect of lesions to the hippocampus and the amygdala.

CD1 mice with dorsal hippocampal and central amygdaloid lesions were submitted to three radial eight-arm maze tasks requiring various degrees of spatial and nonspatial information processing. The results show that, on the standard version of the radial maze, only hippocampal lesions disrupted performance. In the spatial four-baited path task, both hippocampal and amygdaloid lesions increased the errors and modified the patterns of arm choice. Finally, on the visually cued four-baited path task, the two lesions did not affect any quantitative aspect of performance but a strong and unexpected effect of amygdaloid lesions on the patterns of arm choice was found. Taken together, the results indicate i) an effect of hippocampal lesions in all situations that require performing a spatial discrimination, and ii) an effect of amygdaloid lesions in all situations that require distinguishing between baited and unbaited arms, whatever the modality--spatial or visual--being relevant for discriminating the two sets of arms. The analogy between the effects of hippocampal and amygdaloid lesions specifically observed in the spatial four-baited path task suggests that these two limbic areas can exert a similar control on performance in tasks involving mapping operations based upon the discrimination of rewarded and nonrewarded reinforced locations.

Amygdala↗
PubMed1983

The role of area centralis in the spatial vision of the cat.

Spatial contrast sensitivity was measured over a 6 log unit luminance range in two cats before and after bilateral 4-5 deg radius argon laser lesions were placed in area centralis. The lesions reduced high luminance contrast sensitivity by approximately 0.3-0.4 log units at the low and middle spatial frequencies and by 0.5-1.0 log unit at the highest spatial frequencies. The loss of visual acuity was 0.4 octave in the cat with the smaller lesions and 0.8 octave in the cat whose lesions were larger. At lower luminance, little loss in contrast sensitivity was seen and no change was detectable at scotopic luminance levels. Visual acuity, on the other hand, was decreased at higher scotopic conditions, but unaffected at the lowest luminance levels tested (16 X 10(-6) cd/m2). These data indicate that area centralis plays an important role in detecting both high and low spatial frequencies under high luminance conditions but contributes only to spatial resolution at low luminance levels. This result is consistent with known anatomical and physiological properties of the cat area centralis.

Animals↗
PubMed1984

Spatial summation in visual noise.

Contrast thresholds were measured for sinusoidal gratings, with Gaussian spatial and temporal envelopes, as a function of spatial extent in the presence and absence of dynamic white noise. Spatial frequencies ranged from 0.5 to 32 c/deg. Efficiency is defined as the ratio of the ideal's contrast-energy threshold to that of the observer under study, each at the same performance level. For spatial frequencies from 0.5 to 8 c/deg, efficiencies for gratings in noise ranged from 8 to 30% for widths less than one cycle, but dropped rapidly as the width was increased beyond one cycle. Spatial summation of gratings in noise resembles the performance of a cross-correlator whose template is matched to a signal about 1 cycle wide (between 1/e points). The psychometric function slope is consistent with this idea.

Form Perception↗
PubMed1984

Spatial frequency tuning in the visual evoked potential elicited by sine-wave gratings.

This investigation examined the onset response of the transient visually evoked potential elicited by the appearance-disappearance of sine-wave gratings at various levels of spatial frequency, suprathreshold contrast, and stimulus duration. The response was most easily characterized by two negative-positive complexes that were differentially tuned to spatial frequency. The earlier complex peaked at high spatial frequencies while the later complex peaked at low spatial frequencies. For both complexes, amplitude showed only slight variations across three-octave ranges of contrast and duration. Latency was curvilinearly related to spatial frequency, decreased with increasing contrast, and showed no apparent change as a function of duration.

Adult↗
PubMed1984

Adaptive processes controlling sensitivity of short-wave cone pathways to different spatial frequencies.

The sensitivity of the short-wave cone pathways was measured with violet interference gratings on monochromatic adapting fields. Spectral field sensitivity functions for test gratings of 2, 4 and 8 c/deg approximately matched Stiles' pi 3 function, which presumably reflects light-adaptation of the short-wave cones. Previous work had suggested that field sensitivity varies as a function of test spatial frequency, but this now seems an artifact of spatial adaptation. (The present study shows the pathway is highly susceptible to spatial adaptation induced by fine patterns.) For various spatial frequencies that affect the short-wave pathway, signals also pass through a cancellate adaptation site where signals from the short-wave and the middle- and long-wave cones act in opposition. Transient inputs in either opponent direction polarize or desensitize the opponent site. Additional transient inputs of the opposite sign then reduce the polarization and increase sensitivity. Such effects were demonstrated with test gratings as high as 12 c/deg. Transient effects at the opponent site are particularly evident at higher spatial frequencies.

Adaptation, Ocular↗
PubMed1984

Spatial mapping of monkey V1 cells with pure color and luminance stimuli.

We recorded the responses of single macaque striate cortical cells to color-varying and luminance-varying patterns. We show that (a) the vast majority of primate striate cells respond to pure color stimuli, in addition to responding to luminance-varying stimuli (b) in general, simple cells are color-selective whereas complex cells respond to multiple color regions, (c) most cortical cells show bandpass spatial frequency tuning to pure color-varying gratings, with various cells tuned to each of a wide range of spatial frequencies and (d) the peak spatial frequency and bandwidth of most striate cells is the same for color as for luminance-varying gratings; when they differ, cells tend to be more broadly tuned and peak at lower spatial frequencies for color (e) complex cells, on the average, respond to higher spatial frequencies than do simple cells.

Animals↗
PubMed1987

Scale invariant features of differential spatial displacement discrimination.

For a configuration of three blobs, with Gaussian spatial contrast profiles, at threshold luminance contrast, differential spatial displacement discrimination thresholds were determined. The blobs were arranged one above the other, at equal spatial intervals. Thresholds were determined for displacements of the middle blob both orthogonal to and along the axis joining the outer two blobs. Thresholds for both tasks were obtained as a function of both the resolution and the separation of the blobs. The thresholds for both tasks increased linearly with decreasing resolution (increasing blur), for a constant ratio of the resolution parameter and the separation of the outer two blobs. At all levels of resolution there are two blob-separation regimes, in which different strategies are used to compute differential spatial displacements. Independent of the level of resolution, transition between those regions occurs when the separation of the outer two blobs is a constant multiple (approx. 25) of their blur parameter. We interpret these results as further evidence for a scale-invariant mechanism for differential spatial displacement computation.

Adult↗
PubMed1988

Aging, senile miosis and spatial contrast sensitivity at low luminance.

The purpose of this study was to determine how aging affects spatial contrast sensitivity at low light levels and to examine whether senile miosis, which reduces retinal illuminance in the aged eye, underlies any observed sensitivity loss. Contrast thresholds for targets having a range of spatial frequencies were measured in young (n = 13, M age = 24) and older (n = 11, M age = 73) adults who were free from identifiable ocular pathology. Measurements were carried out at three luminance levels spanning a three log unit range. Results indicated that older adults' loss in contrast sensitivity not only increased with increasing spatial frequency, but also became more pronounced with decreases in luminance level. Additional threshold measurements where pupil diameter was varied indicated that senile miosis was not responsible for older adults' loss in spatial vision at any level tested. Rather, older adults' miotic pupil tended to have a positive effect on their spatial vision in that it slightly improved their contrast sensitivity.

Adult↗
PubMed1988

Effects of blur and eccentricity on differential spatial displacement discrimination.

Differential spatial displacement discrimination thresholds were determined for stimuli consisting of blobs with Gaussian spatial and temporal contrast envelopes. The stimuli were presented at detection threshold luminance contrast. The tasks were similar to the two-point discrimination acuity task and the three-dot alignment hyperacuity task. Thresholds were determined as a function of eccentricity along the horizontal meridian of the visual field (from 45 degrees nasal to 65 degrees temporal). The spatial spread or blur parameter of the blobs was adopted as a scale parameter. The results show that the performance of the visual system in differential spatial displacement discrimination tasks becomes progressively more homogeneous for a progressive increase in the blur parameter of the stimuli. Scaling (i) the three-blob alignment results with estimates of the cortical magnification factor and (ii) the two-blob separation discrimination results with their corresponding neural blur parameter shows an impressive isotropy and blur scale-invariance for the mechanisms mediating differential spatial displacement discrimination across the visual field. These results are interpreted in terms of a scaled sampling lattice model of the visual system, in combination with an automatic scale-selection mechanism.

Adult↗
PubMed1989

Spatial frequency discrimination at different orientations.

Hirsch and Hylton (1984) have reported a meridional anisotropy for spatial frequency discrimination with a periodicity containing both square and hexagonal components. We measured the difference limen for spatial frequency for sine-wave gratings whose orientations varied over a 180 deg range and whose nominal spatial frequency varied between 2.5 and 10.0 c.deg.-1. Although some periodicity was evident at the lowest spatial frequency, it was not consistent between observers and it did not contain a hexagonal component. At the higher spatial frequencies there was no evidence for any meridional anisotropy.

Adult↗