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PubMed2006

Spatial modeling in ecology: the flexibility of eigenfunction spatial analyses.

Recently, analytical approaches based on the eigenfunctions of spatial configuration matrices have been proposed in order to consider explicitly spatial predictors. The present study demonstrates the usefulness of eigenfunctions in spatial modeling applied to ecological problems and shows equivalencies of and differences between the two current implementations of this methodology. The two approaches in this category are the distance-based (DB) eigenvector maps proposed by P. Legendre and his colleagues, and spatial filtering based upon geographic connectivity matrices (i.e., topology-based; CB) developed by D. A. Griffith and his colleagues. In both cases, the goal is to create spatial predictors that can be easily incorporated into conventional regression models. One important advantage of these two approaches over any other spatial approach is that they provide a flexible tool that allows the full range of general and generalized linear modeling theory to be applied to ecological and geographical problems in the presence of nonzero spatial autocorrelation.

Animals↗

PubMed1990

The effects of temporal modulation and spatial location on the perceived spatial frequency of visual patterns.

The perceived spatial frequency of a visual pattern can increase when a pattern drifts or is presented at a peripheral visual field location, as compared with a foveally viewed, stationary pattern. We confirmed previously reported effects of motion on foveally viewed patterns and of location on stationary patterns and extended this analysis to the effect of motion on peripherally viewed patterns and the effect of location on drifting patterns. Most central to our investigation was the combined effect of temporal modulation and spatial location on perceived spatial frequency. The group data, as well as the individual sets of data for most observers, are consistent with the mathematical concept of separability for the effects of temporal modulation and spatial location on perceived spatial frequency. Two qualitative psychophysical models suggest explanations for the effects. Both models assume that the receptive-field sizes of a set of underlying psychophysical mechanisms monotonically change as a function of temporal modulation or visual field location, whereas the perceptual labels attached to a set of channels remain invariant. These models predict that drifting or peripheral viewing of a pattern will cause a shift in the perceived spatial frequency of the pattern to a higher apparent spatial frequency.

Adult↗

PubMed2003

Head-only exposure to GSM 900-MHz electromagnetic fields does not alter rat's memory in spatial and non-spatial tasks.

Over the last decade, exposure to high frequency (2450 MHz) electromagnetic fields (EMFs) has been found to induce performance deficit in rodents in spatial memory tasks. As concern was expressed about potential biological effects of mobile communication microwaves, studies testing the effects of signals such as GSM were required. In a previous study, using head-only exposure to 900 MHz GSM EMF, we could not demonstrate any behavioural deficit in two simple learning tasks. The present study aimed at extending these results with more complex spatial learning tasks and a non-spatial task. In a first experiment, rats were trained in a radial-arm maze with a 10-s confinement between each visited arm. In a second experiment, a 15-min intra-trial delay was introduced after four visited arms. In a third experiment, non-spatial memory was tested in an object recognition task. In all experiments, performance of the head-only exposed rats (1 and 3.5 W/kg) was compared with that of sham and control rats. In the first experiment, a slightly improved performance was found after 3.5 W/kg exposure, a result that was not observed in the delay-task. In the third experiment, although some effects on exploratory activity were found, recognition memory was unaffected in exposed rats. Altogether, this set of experiments provides no evidence indicating that spatial and non-spatial memory can be affected by a 45-min head-only exposure to 900 MHz GSM EMF.

Animals↗

PubMed1999

Effects of lesions to the glutamatergic afferents to the nucleus accumbens in the modulation of reactivity to spatial and non-spatial novelty in mice.

The purpose of this study was to compare the effects of selective lesions of the three main sources of limbic afferents to the nucleus accumbens-fornix, prelimbic cortex and amygdala-with those induced by N-methyl-D-aspartate receptor blockage in this structure, in a non-associative task designed to estimate the ability of rodents to encode spatial and non-spatial relationships between discrete stimuli. The task consists of placing mice in an open field containing five objects and, after three sessions of habituation, examining their reactivity to object displacement (spatial novelty) and object substitution (object novelty). Focal administrations of the competitive N-methyl-D-aspartate antagonist DL-2-amino-5-phosphonopentanoic acid (0.1 microg/side) induced a selective impairment in the ability of mice to react to the spatial change. Lesions to the different structures affect the response of mice to spatial and non-spatial novelty in different ways. In particular, while fornix lesions induced a decrease in re-exploration of the displaced objects, prelimbic cortex lesions enhanced the exploration of both displaced and non-displaced objects. Finally, the basolateral amygdala lesions did not induce any impairment in the detection of the displaced objects but decreased the latencies to approach novel objects. It is concluded that N-methyl-D-aspartate receptor blockage in the nucleus accumbens subsumes the effects of the three lesions. Some hypotheses on the role of glutamatergic transmission in the accumbens on information processing are briefly discussed.

Afferent Pathways↗

PubMed2004

Dissociation of function between the dorsal and the ventral hippocampus in spatial learning abilities of the rat: a within-subject, within-task comparison of reference and working spatial memory.

Lesions restricted to the dorsal, but not the ventral, hippocampus severely impair the formation of spatial memory. This dissociation was first demonstrated using the water maze task. The present study investigated whether the dorsal and the ventral hippocampus are involved differentially in spatial reference and spatial working memory using a four-baited/four-unbaited version of the eight-arm radial maze task. This test allows the concurrent evaluation of reference and working memory with respect to the same set of spatial cues, and thereby enables a within-subjects within-task comparison between the two forms of memory functions. Rats with N-methyl-d-aspartic acid-induced excitotoxic lesions of the dorsal hippocampus, ventral hippocampus or both were compared with sham and unoperated controls. We showed that dorsal lesions were as effective as complete lesions in severely disrupting both reference and working spatial memory, whereas rats with ventral lesions performed at a level comparable with controls. These results lend further support to the existence of a functional dissociation between the dorsal and the ventral hippocampus, with the former being preferentially involved in spatial learning.

Animals↗

PubMed2004

[Spatial spectra of neural electric activities and their application in study of visual spatial selective attention].

In this paper, the spatial spectra of neural electric activities and their primary application to visual spatial selective attention are presented. Based on the spherical harmonic spectra inversion by equivalent distributed dipole layer technique, novel latitude spectra S(1) and longitudinal spectra S(m) are defined as the description of spatial spectra of brain electric activities. When the latitude and longitudinal spectra are applied to the event-related potentials (ERP) of spatial selective attention to the right and left visual fields, the temporal structures of spatial spectra of all temporal sample points show meaningful delay and amplitude differences of components between 100 ms and 200 ms for attended and unattended stimulus conditions. These facts indicate that the latitude and longitudinal spatial spectra concept is useful in study of cognitive brain research.

Attention↗

PubMed2001

Evidence for a relationship between place-cell spatial firing and spatial memory performance.

The rat hippocampus contains place cells whose firing is location-specific. Although many properties of place cells have been uncovered, little is known about their actual contribution to the animal's spatial performance. In this study, we addressed this issue by recording place cells while rats solved a continuous spatial alternation task in which they had to alternate between the two arms of a Y-maze to get a food reward in the third (goal) arm. By manipulating the information available to the animals, we induced the cells to establish their fields in locations that were out of register relative to their standard position, thus making them inconsistent with the learned spatial task. When this happened, the rats' performance in the alternation task was markedly decreased. In addition, the nature of the behavioral errors during inconsistent field placements also changed dramatically in a way that was highly indicative of the rats' spatial disorientation. These results suggest that there is a functional relationship between the spatial firing patterns of place cells and the spatial behavior of the rat, thus strengthening the idea that these cells are part of a navigational system.

Animals↗

PubMed1990

The effects of spatial phase on reaction time to spatially filtered images.

Many studies of visual perception have used periodic stimuli such as sine-wave gratings and checkerboard patterns. It is well known that reaction time (RT) to such stimuli increases with increasing spatial frequency and decreasing contrast. While this is the case with periodic stimuli it is not clear that these relationships obtain for aperiodic stimuli such as natural scenes. A digitized image of an object (a vase) was submitted to two-dimensional Fourier analysis. Four pairs of spatial frequency band-limited images were created for each image. Each pair consisted of a normal-phase (NP) and a scrambled-phase (SP) version, with the magnitude spectrum and space-averaged luminance the same within each pair. Filter band-widths were 1 octave wide. Manual RT was measured for onset and offset of each spatially filtered image. Mean RT for SP images increased significantly with increasing spatial frequency, while no other significant differences were found with the NP images. This suggests that the temporal processing of complex, aperiodic images is influenced by the spatial frequency and contrast of local regions within the image, rather than by the space-averaged contrast of the entire image, and cannot be predicted by global estimates of contrast and spatial frequency.

Adult↗

PubMed2006

Effect of spatial frequency of stimulus on focal macular ERGs in monkeys : fmacERG dependence on the spatial-frequency.

PURPOSE: To determine the effect of the spatial frequency of a small grating stimulus centered on the macula on the focal macular ERGs (fmacERGs) of monkeys. METHODS: fmacERGs were recorded from eight eyes of four adult monkeys (Macaca fuscata). The spatial frequency of the stimulus was changed from 0.25 to 8 cycles/degree. The luminance of the light bars was 10 cd/m(2), and the contrast was 95%. The stimulus was flashed on and off with an on duration of 100 ms and an off duration of 150 ms (4 Hz). The stimulus was centered on the fovea and subtended 12.7 degrees at the cornea. The luminance of the steady light-adapting background was 3.5 cd/m(2). The location of the stimulus on the retina was monitored throughout the recordings. The effects of the spatial frequency of the stimulus on the amplitudes and implicit times of the a-waves, b-waves, and oscillatory potentials (OPs) were determined. fmacERGs were also recorded following intravitreal tetrodotoxin (TTX). RESULTS: The amplitudes of the a- and b-waves did not change with changes in the spatial frequency of the stimulus. The OPs, on the other hand, responded best to the lowest spatial frequency, and the OPs after the first two were attenuated at intermediate and higher frequencies (Wilcoxon signed-rank test: P < 0.05). TTX reduced all OP wavelets in monkeys. CONCLUSIONS: The OPs of the photopic macular ERGs are affected by the spatial frequency of the stimulus and are reduced by TTX, consistent with their being generated by inner retinal neurons.

Adaptation, Ocular↗

PubMed1992

Spatial recognition and spatial order memory in patients with dementia of the Alzheimer's type.

Patients diagnosed as having mild or moderate primary degenerative dementia of the Alzheimer's type (PDDAT), and normal elderly subjects were tested for spatial order and a spatial recognition memory. Results for spatial order memory indicated that compared to normal elderly subjects, patients with mild PDDAT showed an impaired memory only for the last serial positions. In contrast, with respect to spatial recognition memory, patients with mild PDDAT showed an impaired memory only for the early serial positions. Patients with moderate PDDAT were impaired on all serial positions for both spatial order and spatial recognition memory. Based on comparable deficit patterns seen in animals and patients with hippocampal and parietal cortex lesions, it is suggested that memory deficits displayed by PDDAT patients might be a function of underlying pathology in the hippocampus and parietal cortex.

Aged↗

PubMed1988

Spatial frequency and orientation tuning of spatial visual mechanisms in human albinos.

A masking paradigm was used to measure the spatial frequency and orientation tuning of spatial mechanisms in the albino visual system. Threshold elevation curves obtained in this manner at test spatial frequencies of 0.25 cycles/deg (cpd), 0.50 cpd, and 1 cpd have the same shape as curves obtained from normal subjects at test frequencies two octaves higher. Additional masking studies showed that contrast processing in albinos obeys the same compressive power law as in normals. Thus, spatial mechanisms in albino central vision have normal spatial frequency and orientation bandwidths. As central cones in the albino are spaced 3-4 times further apart than in the normal fovea, these results support the hypothesis that monocular spatial vision in albinos is primarily limited by this increased receptor spacing. It is hypothesized that this, in turn, is the result of arrested development of the albino retina.

Adult↗

PubMed1994

The coding of spatial position by the human visual system: effects of spatial scale and retinal eccentricity.

In this study we investigate the nature of the computations that underlie the encoding of spatial position by the human visual system. Specifically, we explore the relationship between alignment accuracy and retinal eccentricity for stimuli where local luminance, local contrast, and orientation cues do not underlie performance. Spatial scale is especially important for such a comparison because of the well documented spatial inhomogeneity of the human visual field. The results suggest that the relationship between spatial localization and eccentricity is invariant with spatial scale if accuracy and eccentricity are expressed in terms of the stimulus envelope size. We show that the photoreceptor disarray does not determine the limit to performance for this task, the limit is post-receptoral and can be modelled in terms of a positional uncertainty within the early filters located before the response envelope has been extracted. This uncertainty varies with eccentricity in a similar way within each spatial array.

Contrast Sensitivity↗

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↗

PubMed2005

Visuo-spatial processing in Parkinson's disease: evidence for diminished visuo-spatial sketch pad and central executive resources.

A dual-task study compared the visuo-spatial sketch pad and central executive components of working memory as potential cognitive mechanisms of visuo-spatial dysfunction in Parkinson's disease. Mildly to moderately affected Parkinsonian patients (n = 15) and controls (n = 15) performed the Corsi blocks task concurrently with tasks designed to load on the visuo-spatial sketch pad (spatial tapping) or the central executive (random interval repetition). Patients performed more poorly in both concurrent task conditions, implicating a reduction in both visuo-spatial sketch pad and central executive resources. The impact of the concurrent tasks varied with disease severity, with the central executive deficit prominent at disease onset, but the visuo-spatial sketch pad deficit becoming apparent only in the moderate stages of the illness.

Aged↗

PubMed2004

An experimental characterization of elastographic spatial resolution: analysis of the trade-offs between spatial resolution and contrast-to-noise ratio.

An experimental study of the spatial resolution in elastography was conducted. Models that involved two cylindrical inclusions arranged as a wedge were used to characterize the axial and lateral resolution of the axial strain elastograms. A study of the dependence of the spatial resolution on several factors such as the algorithmic parameters, the applied strain and the modulus contrast was performed. The axial resolution was found to show a linear dependence with respect to the algorithmic parameters, namely the window length and the window shift used for strain estimation. The lateral resolution showed a weak dependence on the algorithmic parameters. A weak dependence of the spatial resolution on factors such as the modulus contrast and the applied strain was found. The trade-offs between the spatial resolution and the elastographic contrast-to-noise ratio (CNR(e)) were then analyzed. A nonlinear trade-off between the CNR(e) and the axial and lateral resolution was shown for conventional strain estimation techniques, with the CNR(e) improving at a more than linear rate with respect to a linear degradation in the resolution. This study provided an experimental framework for characterizing the spatial resolution in elastography and facilitating a comparison of the CNR(e) with spatial resolution.

Elasticity↗

PubMed2003

Preserved use of spatial cues for sound segregation in a case of spatial deafness.

Auditory spatial cues contribute to sound localisation and to sound object segregation. We have investigated these capacities in a patient (NM) who complained having difficulties to localise sounds in everyday life after a right temporo-parieto-frontal ischemic lesion. Two groups of tasks were used, in which spatial dimension was simulated by interaural time differences (ITD): (i) active localisation of stationary or moving sound targets, and (ii) sound segregation on the basis of spatial cues. This latter included a spatial release from masking paradigm and two ITD diotic tasks. NM failed to localise stationary and moving sounds: she perceived all the stimuli at the centre of the head, and could not differentiate stationary from moving targets. In contrast, NM was able to use ITD cues to segregate simultaneous sound sources in the spatial-release-from-masking paradigm and in ITD diotic tasks.These results suggest that sound localisation and sound object segregation based on spatial cues do not rely on the same mechanisms.

Adult↗

PubMed1996

Rats perform better on spatial than brightness delayed matching-to-sample water-escape due to an unlearned bias to use spatial cues.

Rats readily acquire water-escape spatial delayed matching-to-sample (DMTS) tasks and show excellent performance with retention intervals as long as 120 m (17). They also acquire the task more readily with a 5-min retention interval (RI) than with a 1-min RI (16). To determine if these observations are unique to spatial DMTS, or are also true of nonspatial water-escape DMTS, 75-day-old rats were compared on acquisition and subsequent retention of spatial and brightness DMTS. A larger proportion of the rats tested on the spatial problem were able to acquire the task, made fewer acquisition errors, and demonstrated better retention when tested at RIs of 1, 5, 15, 30, 60, and 120 min than did the rats tested on the brightness problem. Acquisition RI did not affect the rate of acquisition on either task. Examination of perserveration errors, the occurrence of intrusions, and position-congruent performance (escape platform in the same physical location on both runs of a trial) revealed that the choices of brightness-trained rats were often more influenced by spatial than brightness cues, suggesting that rats have an unlearned bias to use spatial cues in water-escape DMTS tasks.

Animals↗

PubMed1997

Dissociation of spatial reference memory, spatial working memory, and hippocampal mossy fiber distribution in two rat strains differing in emotionality.

Rats of the inbred strains DA/Han and BDE/Han were compared on two complex spatial learning tasks, a spatial reference memory task in a 16-unit multiple T-maze and a spatial working memory task in an eight-arm radial-maze. In addition, sizes of hippocampal mossy fiber terminal fields were measured. BDE rats showed marked superiority in multiple T-maze learning whereas DA rats outperformed BDE rats on the radial-maze task. DA rats had significantly larger intra- and infrapyramidal mossy fiber terminal fields (IIP-MF). This is consistent with findings from other studies suggesting that large IIP-MF are related to excellent spatial radial-maze learning, but it also indicates that size of IIP-MF is correlated with processing of a specific type of spatial information rather than with overall spatial abilities. BDE rats had more extended suprapyramidal mossy fiber projections (SP-MF) and a larger hilus. Rats of both strains differed in exploratory behaviour and emotionality: DA rats revealed little freezing and had a high rearing activity, whereas BDE rats showed frequent freezing and reared rarely. Results suggest that IIP-MF are involved with flexible expression of memory, updating environmental information and parallel processing whereas SP-MF might be linked to processing of familiar information. Presumably, emotional factors contribute to performance differences.

Animals↗