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PubMed2006

Spatial variation in demography and population growth rate: the importance of natal location.

1. Understanding the pattern and magnitude of spatial variation in demography and population growth rate (lambda) is key to understanding the structure and dynamics of natural populations. However, such spatial variation is challenging to quantify. We use>20 years of individual life-history data to quantify small- and large-scale spatial variation in demography and lambda within a single population of red-billed choughs Pyrrhocorax pyrrhocorax on Islay, Scotland. Critically, we demonstrate a major importance of an individual's natal rather than current location in driving observed spatial variation. 2. Breeding success (the number of offspring fledged per breeding attempt) varied among individual chough nest sites but did not vary on a larger spatial scale across Islay. 3. The proportion of fledglings observed to survive to recruiting age varied markedly among individual nest sites and also varied more widely across Islay. Spatial capture-mark-recapture models defined two discrete geographical regions where fledgling survival differed significantly: choughs fledged in region 'BGE' were more likely to survive than choughs fledged in region 'CNSW' as both subadults and adults. 4. The asymptotic lambda attributable to breeding attempts in region BGE exceeded unity, and exceeded that attributable to breeding attempts in region CNSW. Relatively productive and unproductive regions therefore exist within this population. 5. Spatial variation in adult survival was better explained by an individual's natal region than the region where that individual settled to breed. Spatial variation in lambda would consequently have remained undetected had survival been measured across resident breeders rather than across individuals fledged in each region. Furthermore, breeding success was a weak predictor of a nest site's estimated productivity of recruits. 6. We therefore describe marked spatial variation in demography and lambda within a single population of a territorial vertebrate, mediated partly by long-term links between an individual's natal location and its subsequent life-history. Life-long monitoring of individuals of known origin may therefore be necessary to identify accurately subpopulations of intrinsically high and low lambda.

Animals↗
PubMed1992

Short-term retention of spatial information.

Four experiments investigated the recall of a subspan set of spatial locations over short intervals of 5 and 15 s. The intervals were filled by one of three activities: simple tapping, repeated tapping at spatial targets and backwards counting. Spatial tapping, which decreases spatial memory span, led to further small but significant errors in recall, as did backward counting. These errors were larger than those found with simple tapping over the same intervals. Backwards counting led to further decreases in recall performance if it was also present during encoding, but this was not the case for spatial tapping. Spatial tapping had little effect on recall of three digits, whereas backwards counting had a large effect, which was much larger than that found with spatial memory items in any condition. The results are interpreted in terms of the use of place-keeping functions in spatial memory sequences, which may not be specific to spatial material.

Female↗
PubMed1993

Spatial facilitation and depression within one motor nerve terminal of frogs.

1. Perfused macropatch electrodes were used to stimulate and simultaneously measure release from two sites on the same terminal of the frog cutaneous pectoris muscle. 2. It was found that release occurring at one site often affected release at an adjacent site 50 microns away, either enhancing it ('spatial facilitation') or depressing it ('spatial depression'). Spatial facilitation (or depression) was defined as the release produced by a test pulse at the second site (test electrode) when preceded by a pulse at the first site (prepulse electrode) divided by the release produced by the test pulse alone. 3. Spatial facilitation varied with the time interval between the prepulse and the test pulse. Peak spatial facilitation, which on the average was 2.14, occurred with an interval of 1-3 ms. With longer intervals spatial facilitation decayed with a time constant between 3-6 ms. When the time interval between the prepulse and the test pulse was zero (no delay), the release after the test pulse was always depressed. 4. When Ca2+ was omitted from the perfusate of the prepulse electrode, spatial facilitation was abolished. When a brief hyperpolarizing pulse followed the depolarizing prepulse with zero delay spatial facilitation was also abolished. 5. Electrotonic spread or Ca2+ diffusion within the axon terminal are excluded as coupling agents for spatial facilitation. It is suggested that the coupling agent may possibly be related to a hypothetical release-promoting factor.

Animals↗
PubMed2002

Magnetoencephalographically directed review of high-spatial-resolution surface-coil MR images improves lesion detection in patients with extratemporal epilepsy.

PURPOSE: To determine whether (a) interictal magnetoencephalographic (MEG) epileptiform activity corresponds to anatomic abnormalities at magnetic resonance (MR) imaging, (b) high-spatial-resolution MR imaging depicts lesions in regions without MEG spike activity, (c) MEG-directed review of high-spatial-resolution MR images enables detection of abnormalities not apparent on conventional MR images, and (d) MEG information results in a greater number of diagnosed lesions at re-review of conventional MR images. MATERIALS AND METHODS: Twenty patients with neocortical epilepsy were evaluated with MEG, conventional brain MR imaging with a head coil, and high-spatial-resolution MR imaging with either a surface coil (n = 17) or a high-spatial-resolution birdcage coil (n = 3). Abnormal MEG foci were compared with corresponding anatomic areas on conventional and high-spatial-resolution MR images to determine the presence (concordance) or absence (discordance) of anatomic lesions corresponding to foci of abnormal MEG activity. RESULTS: Forty-four epileptiform MEG foci were identified. Twelve foci (27%) were concordant with an anatomic abnormality at high-spatial-resolution MR imaging, and 32 foci (73%) were discordant. Results of high-spatial-resolution MR imaging were normal in eight patients, and 23 lesions were detected in the remaining 12 patients. Twelve lesions (52%) were concordant with abnormal MEG epileptiform activity, and 11 (48%) were discordant (ie, there was normal MEG activity in the region of the anatomic abnormality). At retrospective reevaluation of conventional MR images with MEG guidance, four occult gray matter migration lesions that had initially been missed were observed. An additional patient with MEG-concordant postoperative gliosis was readily identified with high-spatial-resolution MR images but not with conventional MR images. CONCLUSION: Review of MEG-localized epileptiform areas on high-spatial-resolution MR images enables detection of epileptogenic neocortical lesions, some of which are occult on conventional MR images.

Adult↗
PubMed1984

Spatial filter characteristics of optic nerve fibers in California ground squirrel (Spermophilus beecheyi).

The spatial response properties of single optic nerve fibers in the California ground squirrel (Spermophilus beecheyi) were investigated. Results are reported for each of several response classes. Resolution limits determined for 165 spectrally nonopponent optic nerve fibers ranged from 0.1 to 4.2 cycles/degree (c/d), with a mean resolution limit of 1.49 c/d. Directionally selective units possessed the highest resolution limits (mean = 1.91 c/d.) Sustained and transient units possessed mean resolution limits of 1.44 and 1.09 c/d, respectively. The correlation between response and sensitivity measures of spatial tuning was examined for 29 units. Optimal spatial frequency and spatial frequency bandwidth estimates derived from the two measures were highly correlated. As measured from response functions, optimal spatial frequencies of 97 spectrally nonopponent units ranged from 0.1 to 2.2 c/d (mean = 0.44 c/d). Directionally selective units possessed the highest optimal spatial frequencies (mean = 0.60 c/d). Mean optimal spatial frequencies for sustained and transient units were 0.32 and 0.27 c/d, respectively. Mean half-amplitude response bandwidth for 96 optic nerve fibers was 2.80 octaves. Directionally selective units were narrowly tuned, possessing a mean half-amplitude bandwidth of 1.99 octaves. Sustained and transient units had mean half-amplitude response bandwidths of 3.56 and 2.80 octaves, respectively. The response bandwidths of directionally selective optic nerve fibers were highly negatively correlated with optimal spatial frequency; no significant correlation between these measures existed for sustained or transient units. Peak contrast sensitivity in 88 optic nerve fibers ranged from 3.0 to 55.0. Mean contrast sensitivity was 16.7 and did not differ between fiber response classes. Peak contrast sensitivity was not correlated with optimal spatial frequency. Poststimulus time histograms of unit responses to sinusoidal luminance modulation revealed that some sustained units modulate their discharge rates around spontaneous levels and show predominant Fourier amplitude at the fundamental frequency. Transient units possess low levels of spontaneous discharge and respond abruptly to the passage of grating half-cycles, resulting in a characteristically dispersed spectrum of Fourier amplitude. Directionally selective units respond to sinusoidal luminance gratings with an elevation of maintained firing rate and possess moderate Fourier amplitudes corresponding to the fundamental and second harmonic frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Spatial and temporal properties of neurons of the lateral suprasylvian cortex of the cat.

Neurons in the posteromedial lateral suprasylvian cortex (PMLS) of cats were recorded extracellularly to investigate their response to stimulation by bars and by sinusoidal gratings. Two general types of cells were identified: those that modulated in synchrony with the passage of drifting bars and gratings and those that responded with an unmodulated increase in discharge. Both types responded to contrast reversed gratings with a modulation of activity: the cells that modulated to drifting gratings modulated to the first harmonic of contrast reversed gratings (at appropriate spatial phase and frequency), whereas those that did not modulate to drifting gratings always modulated to the second harmonic of contrast reversed gratings. No cell had a clear null point. Nearly all cells were selective for spatial frequency. The preferred frequency ranged from 0.1 to 1 cycles per degree (cpd), and selectivity bandwidths (full width at half height) were around two octaves. Preferred spatial frequency was not correlated with receptive field size, but bandwidth and receptive field size were positively correlated. Preferred spatial frequency decreased with eccentricity, at about 0.05 octaves/deg. The response of all cells increased as a function of grating contrast up to a saturation level. The contrast threshold for response to a grating of optimal parameters was approximately 1% for most cells and the saturation contrast approximately 10%. The contrast gain was approximately 25 spikes/s per log unit of contrast. All cells were tuned for temporal frequency, preferring frequencies from approximately 3 to 10 Hz, with a selectivity bandwidth approximately 2 octaves. For some cells, the spatial selectivity did not depend on the temporal frequency and vice versa. Others were spatiotemporally coupled, with the preferred temporal frequency being lower at high than at low spatial frequencies, and the preferred spatial frequency lower at high than at low temporal frequencies. Previous results showing broad velocity tuning to a bar were replicated and found to be predictable from the combined spatial and temporal tuning of PMLS cells and the Fourier spectrum of a bar. Preferred temporal frequency steadily decreased with eccentricity, at 0.025 octaves/deg. The results for PMLS cells are compared with those of other visual areas. Acuity and spatial preference and selectivity bandwidth is comparable to all areas except area 17, where they are a factor of about two higher. Temporal selectivity in PMLS is as fine as observed in other areas. The possibility that PMLS cells may be involved with motion detection and detection of motion in depth is discussed.

Animals↗
PubMed1987

The effects of contrast on visual orientation and spatial frequency discrimination: a comparison of single cells and behavior.

We have compared the effects of contrast on human psychophysical orientation and spatial frequency discrimination thresholds and on the responses of individual neurons in the cat's striate cortex. Contrast has similar effects on orientation and spatial frequency discrimination: as contrast is increased above detection threshold, orientation and spatial frequency discrimination performance improves but reaches maximum levels at quite low contrasts. Further increases in contrast produce no further improvements in discrimination. We measured the effects of contrast on response amplitude, orientation and spatial frequency selectivity, and response variance of neurons in the cat's striate cortex. Orientation and spatial frequency selectivity vary little with contrast. Also, the ratio of response variance to response mean is unaffected by contrast. Although, in many cells, response amplitude increases approximately linearly with log contrast over most of the visible range, some cells show complete or partial saturation of response amplitude at medium contrasts. Therefore, some cells show a clear increase in slope of the orientation and spatial frequency tuning functions with increasing contrast, whereas in others the slopes reach maximum values at medium contrasts. Using receiver operating characteristic analysis, we estimated the minimum orientation and spatial frequency differences that can be signaled reliably as a response change by an individual cell. This analysis shows that, on average, the discrimination of orientation or spatial frequency improves with contrast at low contrasts more than at higher contrasts. Using the optimal stimulus for each cell, we estimated the contrast threshold of 48 neurons. Most cells had contrast thresholds below 5%. Thresholds were only slightly higher for nonoptimal stimuli. Therefore, increasing the contrast of sinusoidal gratings above approximately 10% will not produce large increases in the number of responding cells. The observed effects of contrast on the response characteristics of nonsaturating cortical cells do not appear consistent with the psychophysical results. Cells that reach their maximum response at low-to-medium contrasts may account for the contrast independence of psychophysical orientation and spatial frequency discrimination thresholds at medium and high contrasts.

Animals↗
PubMed1990

Afferent bases of spatial- and temporal-frequency processing by neurons in the cat's posteromedial lateral suprasylvian cortex: effects of removing areas 17, 18, and 19.

1. We investigated whether spatial- and temporal-frequency processing by neurons in the cat's posteromedial lateral suprasylvian (PMLS) extrastriate cortex depends on inputs from ipsilateral areas 17, 18, and 19 (visual cortex; VC) or occurs in parallel with those cortical areas. 2. Single neurons were recorded in PMLS cortex of normal adult cats and adult cats that had ipsilateral VC removed within 24 h before recording. Receptive-field properties were characterized, and responses to sine-wave gratings of different spatial frequencies, contrasts, and temporal frequencies were measured and Fourier analyzed. 3. As in previous studies, removing inputs from VC led to a reduction in the proportion of direction-selective PMLS cells. In addition there were statistically significant reductions in response amplitude and variability, although signal-to-noise ratios were unchanged. Contrast sensitivity also was reduced at all spatial frequencies. Spatial resolution was reduced slightly; however, this reduction appears to be secondary to the overall reduction in response amplitude and sensitivity. 4. The shape of the spatial-frequency contrast-sensitivity functions and the distribution of optimal spatial frequencies were unaffected by removing inputs from VC. In addition, once response threshold was reached, the slope of the contrast-response function (contrast gain) at the optimal spatial frequency was similar for PMLS cells in normal cats and cats with a VC lesion. 5. When tested at the optimal spatial frequency, temporal-frequency bandwidths, high and low temporal-frequency cutoffs, and optimal temporal frequencies were similar for PMLS cells in normal cats and cats with VC removed. 6. The results thus indicate that inputs from VC are important for the elaboration of direction selectivity and affect response amplitude and contrast sensitivity among PMLS neurons. However, visual-cortical inputs have little or no influence on spatial- and temporal-frequency processing by PMLS neurons. These properties depend on inputs from other cortical areas or the thalamus and are processed in parallel with areas 17, 18, and 19.

Animals↗
PubMedDate not supplied

Spatial processing in the primate auditory cortex.

Spatial localization of auditory stimuli is dependent on the cerebral cortex, yet it remains unclear how cortical activity gives rise to spatial percepts. It has recently been proposed that spatial information is processed serially within the primate auditory cortex, initially in the primary auditory cortex (AI) through the auditory areas caudal to AI, particularly the caudomedial (CM) and caudolateral fields, and onward to the parietal lobe. The activity of single neurons in AI and CM supports this hypothesis, where a greater percentage of CM neurons are sensitive to the spatial location of acoustic stimuli than AI neurons, and the spatial sensitivity of CM neurons extends across a broader range of the stimulus spectrum compared to AI neurons. Further, populations of CM neurons are better able to predict sound localization ability than are populations of AI neurons. We have recently explored the effects of stimulus intensity on both sound localization performance and the spatial sensitivity of auditory cortical neurons. The preliminary results of these experiments again indicate that spatial information is serially processed between AI and the caudal fields. The effects of visual stimulation on auditory localization have also been investigated. Under the appropriate circumstances, visual stimuli can "capture" the spatial location of auditory stimuli in both humans and monkeys. This perceptual illusion suggests that there is a plastic shift in auditory spatial perception. Where the representation of this shift resides is unknown, although two likely candidates are the multimodal regions of the parietal lobe and the superior temporal sulcus.

Acoustic Stimulation↗
PubMed2002

Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking.

Spatial interactions are a critical and ubiquitous feature of spatial vision. These interactions may be inhibitory (reducing sensitivity as occurs in crowding) or facilitatory (enhancing sensitivity). In this work, we had four goals. 1. To test the hypothesis that foveal crowding depends on target size by measuring the extent of crowding for novel targets that were limited in their spatial frequency content. We used a large range of target sizes and spatial frequencies. 2. To assess whether the critical spatial frequency model (Hess, Dakin, & Kapoor, 2000) provides a general model for foveal crowding. To test this model, we measured crowding for a direction-identification task that did not require judging the orientation of the gap. 3. To test the hypothesis that foveal crowding is simply contrast masking by remote flanks we measured and compared crowding in a direction-identification experiment with masking by remote flanks in a detection experiment. In each of the experiments, our targets and flanks were composed of Gabor features, thus allowing us to control the feature contrast, spatial frequency, and orientation. 4. To assess the relationship between suppressive and facilitatory spatial interactions in foveal vision. Our results show that (1) foveal crowding is proportional to feature size over the more than 50-fold range of target sizes that we examined. Over this large range, foveal crowding is scale invariant. Our results also show it is the size of the envelope (SD) rather than the carrier (SF) that determines the extent of crowding in the fovea. 2. Crowding that occurs in the direction-identification task is quite similar to crowding where orientation information is available. Thus we conclude that the critical spatial frequency model does not provide a general explanation for foveal crowding. 3. Threshold elevation for crowding is similar to threshold elevation for masking as predicted by our test-pedestal model. Thus we conclude that foveal crowding is simple contrast masking. 4. Based on our comparison of threshold changes in crowding and masking, we conclude that in foveal vision, the suppressive spatial interactions due to nearby flanks are similar in the two tasks. However, the facilitatory interactions are quite different. In the crowding task, we find very little evidence for facilitation by flankers, whereas in the detection task, we find strong facilitation. We suggest that facilitation of detection by remote flanks may be, at least in part, a consequence of uncertainty reduction.

Contrast Sensitivity↗
PubMed2002

Primacy of spatial information in guiding target selection for pursuit and saccades.

Previous studies have examined the facilitative effects of prior spatial information on target selection for saccadic eye movements. More recently, studies have shown that prior spatial information also influences target selection for smooth pursuit. However, direct comparisons of the effects of prior information on target selection for pursuit and saccades have not been made. To this end, we provided different classes of prior information and measured their effects on target selection for pursuit and saccades. In Experiment 1, we assessed the relative effects of spatial cues (indicating the target stimulus' initial location) and color cues (indicating the target stimulus' color) on eye movement latencies. In Experiment 2, we assessed the effects of motion cues (indicating the target stimulus' direction of motion) in addition to spatial cues. For both pursuit and saccades, we found that spatial cues reduced eye movement latencies more than color cues (Experiment 1). Spatial cues also reduced eye movement latencies more than motion cues (Experiment 2), even for pursuit, despite the fact that stimulus motion is essential for the generation of pursuit eye movements. These results indicate that both pursuit and saccades are affected to a greater degree by spatial information than motion or color information. We suggest that the primacy of spatial information for both pursuit and saccades reflects the importance of spatial attention in selecting the stimulus target for both eye movements.

Adolescent↗
PubMed2004

Tissue-specific spatial organization of genomes.

BACKGROUND: Genomes are organized in vivo in the form of chromosomes. Each chromosome occupies a distinct nuclear subvolume in the form of a chromosome territory. The spatial positioning of chromosomes within the interphase nucleus is often nonrandom. It is unclear whether the nonrandom spatial arrangement of chromosomes is conserved among tissues or whether spatial genome organization is tissue-specific. RESULTS: Using two-dimensional and three-dimensional fluorescence in situ hybridization we have carried out a systematic analysis of the spatial positioning of a subset of mouse chromosomes in several tissues. We show that chromosomes exhibit tissue-specific organization. Chromosomes are distributed tissue-specifically with respect to their position relative to the center of the nucleus and also relative to each other. Subsets of chromosomes form distinct types of spatial clusters in different tissues and the relative distance between chromosome pairs varies among tissues. Consistent with the notion that nonrandom spatial proximity is functionally relevant in determining the outcome of chromosome translocation events, we find a correlation between tissue-specific spatial proximity and tissue-specific translocation prevalence. CONCLUSIONS: Our results demonstrate that the spatial organization of genomes is tissue-specific and point to a role for tissue-specific spatial genome organization in the formation of recurrent chromosome arrangements among tissues.

Animals↗
PubMed2005

A context-sensitive approach to anonymizing spatial surveillance data: impact on outbreak detection.

OBJECTIVE: The use of spatially based methods and algorithms in epidemiology and surveillance presents privacy challenges for researchers and public health agencies. We describe a novel method for anonymizing individuals in public health data sets by transposing their spatial locations through a process informed by the underlying population density. Further, we measure the impact of the skew on detection of spatial clustering as measured by a spatial scanning statistic. DESIGN: Cases were emergency department (ED) visits for respiratory illness. Baseline ED visit data were injected with artificially created clusters ranging in magnitude, shape, and location. The geocoded locations were then transformed using a de-identification algorithm that accounts for the local underlying population density. MEASUREMENTS: A total of 12,600 separate weeks of case data with artificially created clusters were combined with control data and the impact on detection of spatial clustering identified by a spatial scan statistic was measured. RESULTS: The anonymization algorithm produced an expected skew of cases that resulted in high values of data set k-anonymity. De-identification that moves points an average distance of 0.25 km lowers the spatial cluster detection sensitivity by less than 4% and lowers the detection specificity less than 1%. CONCLUSION: A population-density-based Gaussian spatial blurring markedly decreases the ability to identify individuals in a data set while only slightly decreasing the performance of a standardly used outbreak detection tool. These findings suggest new approaches to anonymizing data for spatial epidemiology and surveillance.

Algorithms↗
PubMed2005

Impaired spatial coding within objects but not between objects in prosopagnosia.

BACKGROUND: Patients with prosopagnosia from occipitotemporal lesions have impaired perception of the configuration of facial features. This may be an example of impaired "within-object" spatial coding, which others propose to be distinct from "between-object" spatial coding. OBJECTIVE: To determine whether the prosopagnosic deficit in perceiving spatial configuration was specific to within-face and not between-face spatial coding and whether the deficit was face-selective or extended to objects other than faces. METHODS: Six prosopagnosic patients were tested using an oddity paradigm in which they detected which of three simultaneously seen stimuli was an altered target. In the "within-face" task, the target face had altered interocular distance or mouth position. In the "between-face" task, the target face was located farther away from the other two. In the "within-object" task, the stimulus was a two-dot pattern, and the target pattern had altered interdot distance. RESULTS: Spatial judgments were impaired within faces for all six patients and within the two-dot pattern for five of six patients. However, all six had normal between-face spatial perception. CONCLUSIONS: Impaired perception of spatial relations in prosopagnosia is selective to the spatial structure within individual objects and spares the perception of spatial location of objects. It is not specific to faces. It reveals a process involved in analyzing object structure, consistent with the patients' deficits in recognizing facial identity, and illustrates a different type of "visuospatial" defect.

Adult↗
PubMed2002

Girls' spatial abilities: charting the contributions of experiences and attitudes in different academic groups.

BACKGROUND: Gender-related differences in spatial abilities favouring males are well established but have also generated a great deal of controversy. Cross-cultural research, meta-analyses and training studies could show the influence of socio-cultural and experiential factors on spatial-test performance. However, little is known about how experiences and gender-role stereotypes mediate performance differences in this area. AIM: The relationship between specific experiences (spatial activities, computer experience), achievement-related attitudes, and spatial abilities, i.e., mental-rotation ability was investigated with males and females in different academic subgroups. SAMPLE: The sample comprised 112 female and 71 male undergraduates, majoring in arts, humanities and social sciences, sports, psychology and computational visualistics. METHODS: A redrawn version of the Vandenberg and Kuse Mental Rotations Test (MRT) was administered and the participants completed a questionnaire about their spatial activities, computer experience, self-ratings regarding everyday spatial abilities, and attitudes towards mathematics and physics. RESULTS: Mental Rotations Test performance was mainly affected by academic programme and gender, but the effect size of gender differences varied. It was largest with students majoring in arts, humanities and social sciences and smallest with those majoring in computational visualistics. Data analyses revealed statistically significant correlations with spatial activities and computer experience only for females. The relationship between test performance and scales of achievement-related self-concept also depended on gender. CONCLUSIONS: Compared to males, females' spatial abilities are extremely vulnerable to and thus modifiable through attitudinal and experiential factors. This has considerable consequences for intervention programmes that could help to overcome the gender gap in spatial abilities.

Adolescent↗
PubMed1985

Uncertainty relation for resolution in space, spatial frequency, and orientation optimized by two-dimensional visual cortical filters.

Two-dimensional spatial linear filters are constrained by general uncertainty relations that limit their attainable information resolution for orientation, spatial frequency, and two-dimensional (2D) spatial position. The theoretical lower limit for the joint entropy, or uncertainty, of these variables is achieved by an optimal 2D filter family whose spatial weighting functions are generated by exponentiated bivariate second-order polynomials with complex coefficients, the elliptic generalization of the one-dimensional elementary functions proposed in Gabor's famous theory of communication [J. Inst. Electr. Eng. 93, 429 (1946)]. The set includes filters with various orientation bandwidths, spatial-frequency bandwidths, and spatial dimensions, favoring the extraction of various kinds of information from an image. Each such filter occupies an irreducible quantal volume (corresponding to an independent datum) in a four-dimensional information hyperspace whose axes are interpretable as 2D visual space, orientation, and spatial frequency, and thus such a filter set could subserve an optimally efficient sampling of these variables. Evidence is presented that the 2D receptive-field profiles of simple cells in mammalian visual cortex are well described by members of this optimal 2D filter family, and thus such visual neurons could be said to optimize the general uncertainty relations for joint 2D-spatial-2D-spectral information resolution. The variety of their receptive-field dimensions and orientation and spatial-frequency bandwidths, and the correlations among these, reveal several underlying constraints, particularly in width/length aspect ratio and principal axis organization, suggesting a polar division of labor in occupying the quantal volumes of information hyperspace.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Involvement of the anterior cingulate cortex in the expression of remote spatial memory.

Although the hippocampus plays a crucial role in the formation of spatial memories, as these memories mature they may become additionally (or even exclusively) dependent on extrahippocampal structures. However, the identity of these extrahippocampal structures that support remote spatial memory is currently not known. Using a Morris water-maze task, we show that the anterior cingulate cortex (ACC) plays a key role in the expression of remote spatial memories in mice. To first evaluate whether the ACC is activated after the recall of spatial memory, we examined the expression of the immediate early gene, c-fos, in the ACC. Fos expression was elevated after expression of a remote (1 month old), but not recent (1 d old), water-maze memory, suggesting that ACC plays an increasingly important role as a function of time. Consistent with the gene expression data, targeted pharmacological inactivation of the ACC with the sodium channel blocker lidocaine blocked expression of remote, but spared recent, spatial memory. In contrast, inactivation of the dorsal hippocampus disrupted expression of spatial memory, regardless of its age. We further showed that inactivation of the ACC blocked expression of remote spatial memory in two different mouse strains, after training with either a hidden or visible platform in a constant location, and using the AMPA receptor antagonist CNQX. Together, our data provide evidence that circuits supporting spatial memory are reorganized in a time-dependent manner, and establish that activity in neurons intrinsic to the ACC is critical for processing remote spatial memories.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2003

The impact of spatial structure on the accuracy of contour maps of small data sets.

Spatial analysis of insect counts provides important information about how insect species respond to the heterogeneity of a given sampling space. Contour mapping is widely used to visualize spatial pest distribution patterns in anthropogenic environments, and in this study we outlined recommendations regarding semivariogram analysis of small data sets (N < 50). Second, we examined how contour maps based upon linear kriging were affected by the spatial structure of the given data set, as error estimation of contour maps appears to have received little attention in the entomological domain. We used weekly trap catches of the warehouse beetle, Trogoderma variabile, and the accuracy assessment was based upon data sets that had either a random spatial structure or were characterized by asymptotic spatial dependence. Asymptotic spatial dependence (typically described with a semivariogram analysis) means that trap catches at locations close to each other are more similar than trap catches at locations further apart. Trap catches were poorly predicted for data sets with a random spatial structure, while there was a significant correlation between observed and predicted trap catches for the spatially rearranged data sets. Therefore, for data sets with a random spatial structure we recommend visualization of the insect counts as scale-sized dots rather than as contour maps.

Animals↗