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PubMed2003

Visual-spatial ability correlates with efficiency of hand motion and successful surgical performance.

BACKGROUND: This study examines the influence of visual-spatial ability and manual dexterity on surgical performance across 3 levels of expertise. METHODS: Dental students, surgical residents, and staff surgeons completed standardized tests of manual dexterity and visual-spatial ability and were assessed objectively while performing the rigid fixation of an anterior mandible on bench model simulations. Outcome variables included expert assessment of technical performance and efficiency of hand motion during the procedure (recorded using electromagnetic sensors). RESULTS: Visual-spatial scores correlated significantly with surgical performance scores within the group of dental students (r=.40 to.73), but this was not the case for residents or staff surgeons. For all groups, manual dexterity did not correlate with hand motion parameters. There were no differences between groups in visual-spatial ability or manual dexterity, but highly significant differences were seen in surgical performance scores (P<.001), in that surgeons outperformed residents, who in turn outperformed students. CONCLUSIONS: Among novices, visual-spatial ability is associated with skilled performance on a spatially complex surgical procedure. However, advanced trainees and experts do not score any higher on carefully selected visual-spatial tests, suggesting that practice and surgical experience may supplant the influence of visual-spatial ability over time. Thus, the use of these tests for the selection of residents is not currently recommended; they may be of more use in identifying those novice trainees (ie, those with lower test scores) who might benefit most from brief supplementary instruction on specific technical tasks.

Clinical Competence↗
PubMed2002

Suppressive and facilitatory spatial interactions in amblyopic vision.

Amblyopic vision is characterized by reduced spatial resolution, and inhibitory spatial interactions ("crowding") that extend over long distances. The present paper had three goals: (1) To ask whether the extensive crowding in amblyopic vision is a consequence of a shift in the spatial scale of analysis. To test this we measured the extent of crowding for targets that were limited in their spatial frequency content, over a large range of target sizes and spatial frequencies. (2) To ask whether crowding in amblyopic vision can be explained on the basis of contrast masking by remote flanks. To test this hypothesis 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 comprised of Gabor features, thus allowing us to control the feature contrast, spatial frequency and orientation. (3) To examine the relationship between the suppressive and facilitatory interactions in amblyopic contrast detection and "crowding". Our results show that unlike the normal fovea [Levi, Klein, & Hariharan, Journal of Vision 2 (2002a) 140] crowding in amblyopia is neither scale invariant, nor is it attributable to simple contrast masking. Rather, our results suggest that suppressive spatial interactions in amblyopic vision extend over larger distances than in normal foveal vision, similar to peripheral vision of non-amblyopic observers [Levi, Hariharan, & Klein, Journal of Vision 2 (2002b) 167], for targets of the same size. Observers can easily detect the features that comprise our targets (Gabor patches) under conditions where crowding is strong. Thus, our speculation is that crowding occurs because the target and flanks are combined or pooled at a second stage that is coarse in the amblyopic visual system, following the stage of feature extraction. In amblyopic vision, this pooling takes place over a large spatial distance.

Adult↗
PubMed2003

Spatial frequency processing in inferred PC- and MC-pathways.

The goal of this study was to investigate the role of inferred parvocellular (PC) and magnocellular (MC) pathways in spatial contrast sensitivity. Localized, spatially narrow-band patterns (sixth derivatives of Gaussians, D6s) were presented at various peak spatial frequencies. When the D6 appeared on a pulsed luminance pedestal (Pulsed-Pedestal Paradigm), the spatial contrast sensitivity showed a band-pass shape with good contrast sensitivity at medium spatial frequencies. When the D6 appeared on a steady luminance pedestal (Steady-Pedestal Paradigm), the spatial contrast sensitivity showed a low-pass shape with decreased sensitivity at high spatial frequencies. The band-pass CSF was interpreted as reflecting PC-pathway mediation; the lower spatial frequency region of the low-pass CSF as reflecting MC-pathway mediation.

Contrast Sensitivity↗
PubMed2003

Utilisation of spatial frequency information in face search.

In previous studies the utilisation of spatial frequency information in face perception has been investigated by using static recognition tasks. In this study we used a visual search task, which requires eye movements and fast identification of previously learned facial photographs. Using Fourier phase randomisation, spatial information was selectively removed without changing the amplitude spectrum of the image. Fourier phase was randomised within one-octave wide bands of nine different centre spatial frequencies (2-32 c/face width, 0.63-10.1 c/deg). In a control condition no randomisation was used. All stimuli had similar contrast. Search times and eye movements during the search were measured. The removal of spatial information by phase randomisation at medium spatial frequencies resulted in a considerable increase of search times. In the main experiment the maximum of the search times occurred between 8 and 11 c/face width. The number of eye fixations behaved similarly. In an additional experiment with a threefold viewing distance the search times increased and the maximum of the search times shifted slightly to lower object spatial frequencies (5.6-8 c/face width). This suggests that the band of spatial frequencies used in face search is not completely scale invariant. The results show that information most important to face search is located at a limited band of mid spatial frequencies. This is consistent with earlier studies, in which non-dynamical face recognition tasks and low-contrast stimuli have been used.

Adult↗
PubMed1997

Independent coding across spatial scales in moving fractal images..

We compared observers' ability to discriminate the direction of apparent motion using images which varied in their spatial characteristic; white or flat spectrum noise, and 1/f noise which has an amplitude spectrum characteristic of natural scenes. The upper spatial limit for discrimination (dmax) was measured using a two-flash random dot kinematogram (RDK), which consisted either of a pair of bandpass filtered images or of a bandpass filtered image and its broadband counterpart. Six bandpass central frequencies were used, ranging from 0.25 to 5.66 cyc/deg. Subjects could perform the direction discrimination task for all six central frequencies in both the bandpass-bandpass and bandpass-broadband sequences for the 1/f images, and dmax values were found to be approximately equal in these two conditions at all spatial scales. However, for the white noise images, direction discrimination was not possible at the lowest central frequencies in the bandpass-broadband task. These data show that information from a wide range of spatial scales is equally salient to the human motion system in images whose amplitude spectra fall as 1/f. However, for white noise images, information at the higher spatial frequencies is more salient and dominates performance in the direction discrimination task. These results are consistent with a model in which spatial frequency filters in the input lines of motion detectors have octave constant spatial frequency bandwidths and equal peak sensitivity. In line with a number of recent studies, this suggests that the spatial properties of motion sensitive cells are matched to the statistical properties of natural scenes.

Contrast Sensitivity↗
PubMed1997

Contrast and spatial-frequency requirements for emmetropization in chicks.

This study examined the contrast and spatial-frequency requirements for emmetropization in chicks. Chicks were form deprived from hatching either constantly or had this treatment interrupted with 20 min of "visual stimulation" each day. Visual stimulation comprised exposure to either a normal cage environment (i.e., normal vision) or environments that were restricted in either their spatial contrast or spatial-frequency composition. Constant form deprivation resulted in high myopia (e.g. -11.8 D after 5 days), with refractive changes being much smaller in chicks allowed 20 min of normal vision each day (e.g. -3.4D). The restricted contrast environments (contrast range: 9-78%) were generally only slightly less effective than the normal cage environment in preventing form-deprivation myopia. However, in the case of restricted spatial-frequency environments, both the intermediate (0.86 cycles deg-1) and mixed spatial-frequency environments significantly reduced the form deprivation response, while both the high (4.3 cycles deg-1) and low spatial-frequency (0.086 cycles deg-1) stimuli, as well as the composites of these, were less effective in preventing form-deprivation myopia. This spatial-frequency dependence did not vary when, instead of white light, monochromatic illumination was used to eliminate chromatic aberration, although all groups showed more myopia under this condition. It is assumed that the observed inhibitory effects on form-deprivation myopia reflect the adequacy of the visual information presented during the period of visual stimulation for emmetropization in chicks. In this context, the data imply a mid-spatial-frequency tuning in the current study and a low contrast threshold which was not reached for this emmetropization process. Finally, the data hint that chromatic aberration may have some role as a cue to defocus in emmetropization.

Animals↗
PubMed1999

On the relationship between the spatial channels for luminance and disparity processing.

To determine the relationship between the spatial channels for luminance and shape-from-stereo-disparity processing we measured disparity modulation sensitivity as a function of disparity spatial frequency for sinusoidal modulations of a field of Gabor micropatterns of differing luminance spatial frequency. We first examine the effects of contrast, spatial bandwidth and element density and show that it is only the last of these which is critical for the shape of the disparity modulation threshold function. We show that the shape of this function depends on the luminance spatial frequency of the surface that is modulated in depth. Specifically, low corrugation frequencies enjoy a greater scale support from the early luminance spatial filters than do high corrugation frequencies. The results are consistent with higher spatial frequency disparity channels receiving a greater input from higher spatial frequency luminance channels.

Contrast Sensitivity↗
PubMed1999

Optimal spatial frequencies for discrimination of motion direction in optic flow patterns.

Spatial frequency tuning functions were measured for direction discrimination of optic flow patterns. Three subjects discriminated the direction of a curved motion path using computer generated optic flow patterns composed of randomly positioned dots. Performance was measured with unfiltered patterns and with patterns that were spatially filtered across a range of spatial frequencies (center spatial frequencies of 0.4, 0.8, 1.6, 3.2, 6.4, and 9.6 c/deg). The same subjects discriminated the direction of uniform, translational motion on the fronto-parallel plane. The uniform motion patterns were also composed of randomly positioned dots, that were either unfiltered or filtered with the same spatial filters used for the optic flow patterns. The peak spatial frequency was the same for both the optic flow and uniform motion patterns. For both types of motion, a narrow band (1.5 octaves) of optimal spatial frequencies was sufficient to support the same level of performance as found with unfiltered, broadband patterns. Additional experiments demonstrated that the peak spatial frequency for the optic flow patterns varies with mean image speed in the same manner as has been reported for moving sinusoidal gratings. These findings confirm the hypothesis that the outputs of the local motion mechanisms thought to underlie the perception of uniform motion provide the inputs to, and constrain the operation of, the mechanism that processes self motion from optic flow patterns.

Computer Graphics↗
PubMed1999

Spatial-frequency bandwidth of perceived contrast.

The aim of this study was to investigate the spatial-frequency bandwidth of perceived suprathreshold contrast. It has been shown that for grating stimuli contrast detection thresholds depend on spatial frequency, grating area and the number of orientation components. However, suprathreshold contrast perception exhibits contrast constancy, i.e. suprathreshold contrast matches are independent of these stimulus parameters. To study whether contrast constancy applies to spatial-frequency bandwidth, contrast matching was performed and detection thresholds were measured for spatial noise stimuli at various bandwidths centred at 2 c/deg. At high contrast levels, contrast matches were nearly independent of stimulus spatial-frequency bandwidth up to about 6 octaves, even though detection thresholds increased with bandwidth. Thus, a broad band of spatial frequencies contributed to perceived suprathreshold contrast. The requisites for this are contrast constancy with respect to spatial frequency, and integration of contrast information across different spatial frequencies so that the effective bandwidth of the system is broad.

Computer Graphics↗
PubMed2001

Effects of hippocampal lesions on repeated acquisition of spatial discrimination in pigeons.

Anatomical studies of avian hippocampus suggest this structure is a counterpart of that of mammals, and allometric studies of food storing birds support the idea that the avian hippocampus has spatial cognitive functions. In the present study, the spatial cognitive function of hippocampus in pigeons was examined by lesion experiments. Pigeons were trained on either a spatial discrimination, or a spatial discrimination with an added color cue, using a repeated acquisition procedure. In the spatial task, the pigeons were trained to discriminate the position of three keys. Each time the subjects reached the criterion, they were trained on different discriminations in which one out of two previously incorrect keys became the correct key. In the task with color added, each key had its own color, so the subject had both spatial and color cues for the discrimination. The hippocampal lesions disturbed the acquisition of the spatial discrimination, but not in the task in which color cues were added. These results suggest that the avian hippocampus have a crucial role in acquisition of spatial discriminations.

Animals↗
PubMed2002

Chronic ethanol consumption induces tolerance to the spatial memory impairing effects of acute ethanol administration in rats.

A large number of studies in rats have investigated the effects of acute and chronic ethanol administration on performance on many spatial learning and memory tasks. However, no study has addressed the problem of whether chronic ethanol consumption induces tolerance to acute ethanol-induced spatial memory deficits. In this study, we analyzed the behavioral effects of acute ethanol administration on spatial memory and locomotor activity in rats chronically intoxicated by ethanol. Male Sprague-Dawley rats were given as their only available liquid source a 10% (v/v) aqueous ethanol solution for 2 weeks before behavioral testing and during the 1-week behavioral testing period. They were treated intraperitoneally with 1.5 g/kg of ethanol 30 min before daily training in the Morris water maze, a spatial memory task sensitive to hippocampal damage. Our results demonstrate that learning and spatial memory of ethanol-consuming animals were not altered compared with control rats. Chronic ethanol consumption had no effect on spatial reference memory in terms of either the distance traveled to find the hidden platform during the acquisition phase of the experiment, or the time spent in the training quadrant during the retention trial. Acute ethanol administration impaired spatial memory in control rats and this impairment was reversed in chronic ethanol-consuming animals, revealing that chronic ethanol consumption did induce tolerance to the spatial memory deficits induced by acute ethanol injection, although plasma ethanol levels did not differ between the two groups. In contrast, chronic ethanol consumption did not induce tolerance to the acute ethanol-induced stimulatory locomotor activity measured in the same animals. Our results, therefore, indicate that chronic ethanol consumption induces tolerance to the cognitive impairing effects, but not to the locomotor stimulatory effects of acute ethanol administration in rats, suggesting that these two behavioral effects of ethanol do not share a common mechanism in the CNS.

Alcohol Drinking↗
PubMed2002

Tracking the time-course of attentional involvement in spatial working memory: an event-related potential investigation.

Spatial working memory is a cognitive brain mechanism that enables the temporary maintenance and manipulation of spatial information. Recent neuroimaging and behavioral studies have led to the proposal that directed spatial attention is the mechanism by which location information is maintained in spatial working memory. Yet it is unclear whether attentional involvement is required throughout the period of active maintenance or is only invoked during discrete task-phases such as mnemonic encoding. In the current study, we aimed to track the time-course of attentional involvement during spatial working memory by recording event-related brain potentials (ERPs) from healthy volunteers. In Experiment 1, subjects performed a delayed-recognition task. Each trial began with the presentation of a brief stimulus (S1) that indicated the relevant location that subjects were to maintain in working memory. A 4.8-5.3 sec delay interval followed during which a single task-irrelevant probe was presented. The delay interval concluded with a test item (S2) to which subjects made a response indicating whether the S2-location was the same as the S1-memory location. To determine if attention was differentially engaged during discrete phases of the trial, task-irrelevant probes were presented early (400-800 msec following S1-offset) or late (2600-3000 msec following S1-offset) during the delay interval. Sensory-evoked ERPs (P1 and N1) elicited by these irrelevant probes showed attention-like modulations with greater amplitude responses for probes occurring at the S1-memory locations in comparison to probes presented at other locations. This pattern was obtained for both early- and late-delay probes. Probe-evoked activity during delayed-recognition trials was similar to activity observed when spatial attention was explicitly focused on a location in visual space (Experiment 2). These results are consistent with a model of spatial working memory in which perceptual level selective attention is utilized throughout the entire period of active maintenance to keep relevant spatial information in mind.

Adolescent↗
PubMed2004

A secreted form of the beta-amyloid precursor protein (sAPP695) improves spatial recognition memory in OF1 mice.

The beta-amyloid precursor protein (APP) plays a central role in Alzheimer's disease (AD) and appears to be a multifunctional protein. Secreted forms of APP (sAPP) have memory-enhancing effects in certain behavioral paradigms. To investigate sAPP's role in spatial memory processes, we adapted a spatial recognition task and evaluated (1) the performance of OF1 mice after massed training (single 15-min acquisition session) and distributed training (three 5-min acquisition sessions), (2) the decline of spatial recognition performance by introducing different delays (5min, 1, 3, and 24h) between the acquisition and retention phases, and (3) the effects of sAPP(695) on spatial recognition memory. In the present study, mice selectively reacted to a change in the spatial configuration of five objects. Indeed, 3min post-acquisition, mice performed similarly in the massed and distributed versions of the task, by re-exploring the two displaced objects only, whereas mice exposed to the same spatial configuration did not. Additionally, all mice did react to a novel object in a subsequent object recognition phase. Mice detected object displacements 5min, 1h, or 3h post-acquisition, but no more at a 24h-delay. Finally, mice treated with sAPP(695) intracerebroventricularly at a dose of 0.5pg/4microL/mouse, 20-min pre-acquisition or 5-min post-acquisition, still reacted to a spatial change in objects position 24h post-acquisition, in marked contrast to NaCl-treated mice. Our data demonstrate that sAPP(695) significantly improves a form of spatial memory, and confirms the hypothesis of an action of this protein on early memory processes.

Amyloid beta-Protein Precursor↗
PubMed2001

Abnormal executive function in attention deficit hyperactivity disorder: the effect of stimulant medication and age on spatial working memory.

OBJECTIVE: This study sought to examine the factors associated with spatial working memory and the use of strategies to impairments in spatial working memory in children with attention deficit hyperactivity disorder (ADHD). The developmental trajectories for spatial working memory in medicated and medication naïve children with ADHD were investigated. In addition, the effect of psychostimulant medication on deficits in spatial working memory was examined. METHOD: A cross-sectional study compared performance between 21 psychostimulant medicated children with ADHD, 27 medication naïve children with ADHD and 26 matched control subjects on computerized tests of spatial memory and spatial working memory. RESULTS: Compared with the controls, performance in medication naïve children with ADHD was significantly worse on the spatial working memory task. There was no difference in performance between the medicated children with ADHD and the control subjects on this same task, despite the ongoing symptoms of ADHD in the former group. The pattern of normal and abnormal performance in the ADHD groups was age-independent. CONCLUSIONS: Deficits in executive functions related to spatial working memory do occur in children with ADHD, although the magnitude of these deficits is not related to the child's age or the level of ADHD symptoms. These deficits were not present in the current sample of children who were receiving psychostimulant medication.

Age Factors↗
PubMedDate not supplied

Spatial receptive-field structure of cat retinal W cells.

We have used frequency-domain methods to characterize the spatial receptive-field structure of cat retinal W cells. For most ON- and OFF-center tonic and phasic W cells, measurements of responsivity to drifting gratings at various spatial frequencies could be adequately described by a difference-of-Gaussians (DOG) function, consistent with the presence of center and surround mechanisms that are approximately Gaussian in shape and whose signals are combined additively. Estimates of the responsivity of the center mechanisms of tonic and phasic W cells were similar, but both were significantly lower than the corresponding values for X or Y cells. The width of the center mechanisms of tonic W cells, phasic W cells, and Y cells did not differ significantly from each other, but all were significantly larger than the width of X-cell centers. Surround parameters did not vary significantly among the four groups of ganglion cells. Measurements of contrast gain in both tonic and phasic W cells gave values that were significantly lower than in X or Y cells. Virtually all of the phasic W cells in our sample displayed evidence of spatial non-linearities in their receptive fields, in the form of either d.c. responses to drifting sine-wave gratings or second harmonic responses to counterphased gratings. The spatial resolution of the mechanism underlying these nonlinearities was typically higher than that of the center mechanism of these cells. Most tonic W cells exhibited linear spatial summation, although a subset gave strong second harmonic responses to counterphased gratings. Spatial-responsivity measurements for most ON-OFF and directionally selective W cells were not adequately described by DOG functions. These cells did, however, show evidence of spatial nonlinearities similar to those seen in phasic W cells. Suppressed-by-contrast cells gave both modulated and unmodulated responses to drifting gratings which both appeared to involved rectification, but which differed from each other in both spatial resolution and contrast gain. These data confirm earlier reports that the receptive fields of tonic and most ON- or OFF-center phasic W cells appear to include classical center and surround mechanisms. However, the receptive fields of some phasic cells, as well as ON-OFF and directionally selective W cells may have quite different structures. Our results also suggest that phasic, ON-OFF, directionally selective, suppressed-by-contrast, and a subset of tonic W cells may all receive nonlinear inputs with characteristics similar to those described in the receptive fields of retinal Y cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Spatial sign preprocessing: a simple way to impart moderate robustness to multivariate estimators.

The spatial sign is a multivariate extension of the concept of sign. Recently multivariate estimators of covariance structures based on spatial signs have been examined by various authors. These new estimators are found to be robust to outlying observations. From a computational point of view, estimators based on spatial sign are very easy to implement as they boil down to a transformation of the data to their spatial signs, from which the classical estimator is then computed. Hence, one can also consider the transformation to spatial signs to be a preprocessing technique, which ensures that the calibration procedure as a whole is robust. In this paper, we examine the special case of spatial sign preprocessing in combination with partial least squares regression as the latter technique is frequently applied in the context of chemical data analysis. In a simulation study, we compare the performance of the spatial sign transformation to nontransformed data as well as to two robust counterparts of partial least squares regression. It turns out that the spatial sign transform is fairly efficient but has some undesirable bias properties. The method is applied to a recently published data set in the field of quantitative structure-activity relationships, where it is seen to perform equally well as the previously described best linear model for these data.

Journal Article↗
PubMed2005

Spatial variability and uncertainty in ecological risk assessment: a case study on the potential risk of cadmium for the little owl in a Dutch river flood plain.

This paper outlines a procedure that quantifies the impact of different sources of spatial variability and uncertainty on ecological risk estimates. The procedure is illustrated in a case study that estimates the risks of cadmium for a little owl (Athene noctua vidalli) living in a Dutch river flood plain along the river Rhine. A geographical information system (GIS) was used to quantify spatial variability in contaminant concentrations and habitats. It was combined with an exposure and effect model that uses Monte Carlo simulation to quantify parameter uncertainty. Spatial model uncertainty was assessed by the application of two different spatial interpolation methods (classification and kriging) and foraging ranges. The results of the case study show that parameter uncertainty is the main type of uncertainty influencing the risk estimate, and to a lesser extent spatial variability, while spatial model uncertainty was of minor importance. Compared to the deterministically calculated hazard index for the little owl (0.9), inclusion of spatial variability resulted in a median hazard index that can vary between 0.8 and 1.4. It is concluded that a single estimator for a whole flood plain may over- or underestimate risks for specific parts within the flood plain. Further research that expands the procedure presented in this paper is necessary to improve the incorporation of spatial factors in ecological risk assessment.

Animals↗
PubMed1995

Shifting and focusing auditory spatial attention.

Auditory spatial attention was investigated by manipulating spatial and temporal relations between an auditory spatial cue and an auditory target. The principal findings were that performance improved as time available to shift attention to a cued spatial position increased, accurate spatial cues facilitated performance more than inaccurate cues, performance was virtually identical for shifts of attention ranging from 0 degrees and 180 degrees, and performance declined as the distance of an unexpected target from a cued spatial location increased. The experiments provided evidence that auditory attention may be allocated to a specific location in response to an auditory spatial cue and that the time required to shift attention does not appear to depend on the distance of the shift. Furthermore, the findings suggest that the spatial distribution of auditory attention may be described most accurately by a gradient model in which attentional resources decline gradually with distance from a focal point.

Attention↗