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PubMed1996

Hyperacuity for spatial localization of contrast-modulated patterns.

The acuity for localizing the position of a grating and other first order patterns which are defined directly by the luminance distribution, is much higher than the resolution for such gratings. This well-described phenomenon usually is referred to as hyperacuity, and is regarded as a cortical function which is not limited by the optics and the sampling properties of the eye. Second order patterns which can be defined by the distribution of local contrast gained some interest because they require more complex processing mechanisms than first order patterns. We investigated how well gratings and bars which are exclusively defined by the variation of the local contrast of static random dot patterns can be localized in space. In this case localization acuity does not reach the precision which is known for first order patterns. However, the localization of contrast-modulated patterns can be almost one order of magnitude better than second order grating resolution, and therefore reaches into the hyperacuity range. In combination with findings for motion-defined or stereo-defined patterns it is concluded that the brain mechanisms responsible for the localization of features in the visual scene have not only access to first order information which is available immediately from the retinal image, but in addition, to second order information which has to be extracted from the retinal intensity distribution by some sort of nonlinear processing.

Adult↗
PubMed1984

The effect of eccentricity and colour on negativity in pattern onset visual evoked potentials.

The effects of stimulus size, eccentricity and colour on the amplitudes of N100 and N130 were investigated in pattern onset VEPs. For black-and-white pattern stimulation, the first set of stimuli was derived from a full dartboard pattern. Central stimulation of various extents was produced by patterns with reduced number of outer rings and for eccentric stimuli a number of central rings were removed from the full pattern. It was found that amplitude of N100 was maximal in VEPs to central stimuli and that it was greatly reduced when eccentric stimulation was applied. The amplitude of N130 showed no significant change in relation to the type of stimulus. When checkerboard stimuli of identical configuration were used for black-and-white pattern stimulation instead of dartboards, systematic changes in peak latencies of N100 were observed in relation to check size. In VEPs to centrally presented small checks the emergence of an early negative peak preceding N100 was recorded at 75 msec. In VEPs to coarse checkerboards presented centrally N100 was often observed with a delayed peak latency of 110 msec. Changes in N130 were not regular when checkerboards with different check sizes were presented centrally. For eccentric checkerboard stimulation, both negative peaks N100 and N130 were revealed. Their peak latencies were similar to those observed in the case of dartboard paracentral stimulation. In VEPs to patterns projected through red or blue filters, regular changes were observed in both negative peaks. Introduction of the red filter led to enhancement of the N100 amplitude in VEPs to dartboard and to checkerboards with fine checks, but it caused no effect on N100 in the VEPs to coarse checkerboards. Introduction of the blue filter led to a decrease in the N100 amplitude in VEPs to dartboard and fine checkerboards and to a slight increase of N100 in VEPs to coarse checkerboards. Changes in N130 were observed only when the blue filter was introduced and they corresponded to those which take place when the level of illumination changes from photopic to mesopic.

Color Perception↗
PubMed2003

Perceived complexity and the grouping effect in band patterns.

Symmetry properties have been shown to determine the perceived complexity of certain patterns. We used a paired-comparison method to obtain judgments of relative complexity for a family of two-dimensional regular patterns called band patterns. Although the complexity of these patterns is well predicted by their symmetry properties we were unable to explain an interaction observed between two of these properties for our experimental patterns. We discuss the implications of our results for two predominant approaches to the perceived complexity of patterns. Neither approach takes into account that the presence of grouping sometimes makes it difficult to perceive a relationship within the pattern that would--were it not for the grouping--simplify it. We conclude that grouping can mask simplicity and that this phenomenon is crucial to the understanding of perceived complexity.

Form Perception↗
PubMed2005

Restoring partly occluded patterns: a neural network model.

This paper proposes a neural network model that has an ability to restore missing portions of partly occluded patterns. It is a multi-layered hierarchical neural network, in which visual information is processed by interaction of bottom-up and top-down signals. Memories of learned patterns are stored in the connections between cells. Occluded parts of a pattern are reconstructed mainly by top-down signals from higher stages of the network, while the unoccluded parts are reproduced mainly by signals from lower stages. The restoration progresses successfully, even if the occluded pattern is a deformed version of a learned pattern. The model tries to complete even an unlearned pattern by interpolating and extrapolating visible edges. Resemblance of local features to other learned patterns are also utilized for the restoration.

Algorithms↗
PubMed2006

Cellular pattern formation during retinal regeneration: a role for homotypic control of cell fate acquisition.

A dominant mechanism of cellular patterning in the growing fish retina is control of cell fate acquisition by negative feedback signals arising from differentiated cells. We tested the ability of a computational model of this pattern formation mechanism to simulate cellular patterns in regenerated goldfish retina. The model successfully simulated quantitative features of in vivo regenerated patterns, indicating that regenerating retina has access to and utilizes patterning mechanisms that are operational during normal growth. The atypical patterns of regenerated retina could arise in part from regenerative progenitors that, compared to normal growth progenitors, are less responsive to the feedback patterning signals.

Animals↗
PubMed2004

HyBMP5-8b, a BMP5-8 orthologue, acts during axial patterning and tentacle formation in hydra.

Developmental gradients play a central role in axial patterning in hydra. As part of the effort towards elucidating the molecular basis of these gradients as well as investigating the evolution of the mechanisms underlying axial patterning, genes encoding signaling molecules are under investigation. We report the isolation and characterization of HyBMP5-8b, a BMP5-8 orthologue, from hydra. Processes governing axial patterning are continuously active in adult hydra. Expression patterns of HyBMP5-8b in normal animals and during bud formation, hydra's asexual form of reproduction, were examined. These patterns, coupled with changes in patterns of expression in manipulated tissues during head regeneration, foot regeneration as well as under conditions that alter the positional value gradient indicate that the gene is active in two different processes. The gene plays a role in tentacle formation and in patterning the lower end of the body axis.

Amino Acid Sequence↗
PubMed2004

Differences in expression pattern and function between zebrafish hoxc13 orthologs: recruitment of Hoxc13b into an early embryonic role.

Vertebrate Hox genes are generally believed to initiate expression at the primitive streak or early neural plate stages. The timing and spatial restrictions of the Hox expression patterns during these stages correlate well with their demonstrated role in axial patterning. Here we demonstrate that one zebrafish hoxc13 ortholog, hoxc13a, has an expression pattern in the developing tail bud that is consistent with the gene playing a role in axial patterning. However, the second hoxc13 ortholog, hoxc13b, is maternally expressed and is detectable in every cell of early cleavage embryos through gastrulae. In addition, both transcript and protein are detectable at these stages. At 19 h post fertilization (hpf), hoxc13b expression is up-regulated in the tail bud, becoming restricted to the tail bud by 24 hpf. Importantly, by 24 hpf, hoxc13b morphants show a specific developmental delay, which can be rescued by co-injecting synthetic capped hoxc13a or hoxc13b message. These data suggest some functional divergence due to altered expression patterns of the two hoxc13 orthologs after duplication. Further characterization of the hoxc13b morphant delay reveals that it is biphasic in nature, with the first phase of the delay occurring before gastrulation, suggesting a new role for vertebrate Hox genes before their conserved role in axial patterning. The extent of the delay does not change through 20 hpf; however, an additional delay emerges at this time. Notably, this second phase of the delay correlates with hoxc13b expression pattern becoming restricted to the tail bud.

Amino Acid Sequence↗
PubMedDate not supplied

Pattern adaptation and cross-orientation interactions in the primary visual cortex.

The responsiveness of neurons in the primary visual cortex (V1) is substantially reduced after a few seconds of visual stimulation with an effective pattern. This phenomenon, called pattern adaptation, is uniquely cortical and is the likely substrate of a variety of perceptual after-effects. While adaptation to a given pattern reduces the responses of V1 neurons to all subsequently viewed test patterns, this reduction shows some specificity, being strongest when the adapting and test patterns are identical. This specificity may indicate that adaptation affects the interaction between groups of neurons that are jointly activated by the adapting stimulus. We investigated this possibility by studying the effects of adaptation to visual patterns containing one or both of two orientations--the preferred orientation for a cell, and the orientation orthogonal to it. Because neurons in the primary visual cortex are sharply tuned for orientation, stimulation with orthogonal orientations excites two largely distinct populations of neurons. With intracellular recordings of the membrane potential of cat V1 neurons, we found that adaptation to the orthogonal orientation alone does not evoke the hyperpolarization that is typical of adaptation to the preferred orientation. With extracellular recordings of the firing rate of macaque V1 neurons, we found that the responses were not reduced by adaptation to the orthogonal orientation alone nearly as much as by adaptation to the preferred orientation. In the macaque we also studied the effects of adaptation to plaids containing both the preferred and the orthogonal orientations. We found that adaptation to these stimuli could modify the interactions between orientations. It increased the amount of cross-orientation suppression displayed by some cells, even turning some cells that showed cross-orientation facilitation when adapted to a blank stimulus into cells that show cross-orientation suppression. This result suggests that pattern adaptation can affect the interaction between the groups of neurons tuned to the orthogonal orientations, either by increasing their mutual inhibition or by decreasing their mutual excitation.

Animals↗
PubMed1998

The effect of complex motion pattern on speed perception.

We recently reported a new motion illusion where dots in expanding random dot patterns appear to move faster than those in rotation patterns despite having the same physical speed distributions. In the current paper, we compared expansion and rotation motion to translational motion and found that the perceived dot speed in translation patterns was between that of expansion and rotation. We also explored contraction motion and found subjects perceived dots in contracting patterns as moving slightly faster than those in expanding patterns and much faster than those in rotating patterns. Finally, we found that stimulus presentation order in a trial plays an important role in determining the magnitude of the speed illusion--the effect is greater when the subjectively faster stimulus is viewed second (e.g., expansion after rotation). The dependence on stimulus order is greatest when comparing complex motion patterns with large subjective speed differences. This phenomenon is unlikely to be explained in terms of channel fatigue or adaptation.

Humans↗
PubMed2004

Blood vessel patterning at the embryonic midline.

The reproducible pattern of blood vessels formed in vertebrate embryos has been described extensively, but only recently have we obtained the genetic and molecular tools to address the mechanisms underlying these processes. This review describes our current knowledge regarding vascular patterning around the vertebrate midline and presents data derived from frogs, zebrafish, avians, and mice. The embryonic structures implicated in midline vascular patterning, the hypochord, endoderm, notochord, and neural tube, are discussed. Moreover, several molecular signaling pathways implicated in vascular patterning, VEGF, Tie/tek, Notch, Eph/ephrin, and Semaphorin, are described. Data showing that VEGF is critical to patterning the dorsal aorta in frogs and zebrafish, and to patterning the vascular plexus that forms around the neural tube in amniotes, is presented. A more complete knowledge of vascular patterning is likely to come from the next generation of experiments using ever more sophisticated tools, and these results promise to directly impact on clinically important issues such as forming new vessels in the human body and/or in bioreactors.

Animals↗
PubMed1999

Flat foot functional evaluation using pattern recognition of ground reaction data.

OBJECTIVE: Main purpose of this study was to apply quantitative gait analysis and statistical pattern recognition as clinical decision-making aids in flat foot diagnosis and post-surgery monitoring. DESIGN: Statistical pattern recognition techniques were applied to discriminate between normal and flat foot populations through ground reaction force measurements; ground reaction forces time course was assumed as a sensible index of the foot function. BACKGROUND: Gait analysis is becoming recognized as an important clinical tool in orthopaedics, in pre-surgery planning, post-surgery monitoring and in a posteriori evaluation of different treatment techniques. Statistical pattern recognition techniques have been utilized with success in this field to identify the most significant variables of selected motor functions in different pathologies, and to design classification rules and quantitative evaluation scores. METHODS: Ground reaction forces were recorded during free speed barefoot walks on 28 healthy subjects, and 28 symptomatic flexible flat foot children selected for surgical intervention. A new feature selection algorithm, based on heuristic optimization, was applied to select the most discriminant ground reaction forces time samples. A two-stage pattern recognition system, composed by three linear feature extractors, one for each ground reaction force component, and a linear classifier, was designed to classify the feet of each subject using the selected features. The output of the classifier was used to define a functional score. RESULTS: The classifier assigned the ground reaction force patterns performed by each subject into the right class with an estimated error of 15%, corresponding to an assignment error for each subject's foot of 9%. The most discriminant ground reaction forces time samples selected are in full agreement with the pathophysiology of the symptomatic flexible flat foot. The obtained score was utilized to monitor the 1 and 2 years post-operative functional recovery of two differently treated subgroups of 32 flexible flat foot subjects. CONCLUSIONS: Statistical pattern recognition techniques are promising tools for clinical gait analysis; the obtained score provides important functional information that could be used as a further aid in the clinical evaluation of flat foot and different surgical treatment techniques. RELEVANCE: Symptomatic flexible flat foot surgical decision making is frequently difficult because of the lack of objective criteria to assess functional abnormalities of the foot/ankle complex. Gait analysis and statistical pattern recognition can give us parameters with which to characterize "functional" flat foot. Moreover, we can objectively follow up the recovery of the foot/ankle complex function after surgical treatment.

Algorithms↗
PubMed1999

Reaction-diffusion microtubule concentration patterns occur during biological morphogenesis.

Reaction-diffusion processes can lead to a macroscopic concentration pattern from an initially homogeneous solution, and thus provide a physical-chemical mechanism for biological pattern formation and morphogenesis. The central prediction of reaction-diffusion theory is that the patterns contain periodic concentration variations in some of the reactives. Microtubules assembled in vitro spontaneously self-organise and form stationary striped macroscopic structures. In agreement with reaction-diffusion theory. Here we show, in agreement with reaction-diffusion theory, that these preparations contain substantial microtubule concentration variations. Similar striped microtubule patterns arise during Drosophila embryogenesis. A characteristic of these patterns is their dependence on sample dimensions. In Drosophila eggs shortened by ligation, we found that the microtubule pattern varied with egg fragment length in the same way as the in vitro microtubule pattern varied with sample length, and as expected from theory. This is evidence that reaction-diffusion structures occur during Drosophila morphogenesis.

Animals↗
PubMed1996

msh may play a conserved role in dorsoventral patterning of the neuroectoderm and mesoderm.

Many of the mechanisms that govern the patterning of the Drosophila neuroectoderm and mesoderm are still unknown. Here we report the sequence, expression, and regulation of the homeobox gene msh, which is likely to play an important role in the early patterning events of these two tissue primordia. msh expression is first observed in late blastoderm embryos and occurs in longitudinal bands of cells that are fated to become lateral neuroectoderm. This expression is under the control of dorsoventral axis-determination genes and depends on dpp-mediated repression in the dorsal half of the embryo and on fib-(EGF-) mediated repression ventrally. The bands of msh expression define the cells that will form the lateral columns of proneural gene expression and give rise to the lateral row of SI neuroblasts. This suggests that msh may be one of the upstream regulators of the achaete-scute (AS-C) genes and may play a role that is analogous to that of the homeobox gene vnd/NK2 in the medial sector of the neuroectoderm. During neuroblast segregation, msh expression is maintained in a subset of neuroblasts, indicating that msh, like vnd/NK2, could function in both dorsoventral patterning of the neuroectoderm and neuroblast specification. The later phase of msh expression that occurs after the first wave of neuroblast segregation in defined ectodermal and mesodermal clusters of cells points to similar roles of msh in patterning and cell fate specification of the peripheral nervous system, dorsal musculature, and the fat body. A comparison of the expression patterns of the vertebrate homologs of msh, vnd/NK2, and AS-C genes reveals striking similarities in dorsoventral patterning of the Drosophila and vertebrate neuroectoderm and indicates that genetic circuitries in neural patterning are evolutionarily conserved.

Age Factors↗
PubMed1999

Sonic hedgehog (SHH) specifies muscle pattern at tissue and cellular chick level, in the chick limb bud.

Development of the musculature in chick limbs involves tissue and cellular patterning. Patterning at the tissue level leads to the precise arrangement of specific muscles; at the cellular level patterning gives rise to the fibre type diversity in muscles. Although the data suggests that the information controlling muscle patterning is localised within the limb mesenchyme and not in the somitic myogenic precursor cells themselves, the mechanisms underlying muscle organisation have still to be elucidated. The anterior-posterior axis of the limb is specified by a group of cells in the posterior region of the limb mesenchyme, called the zone of polarizing activity (ZPA). When polarizing-region cells are grafted to the anterior margin of the bud, they cause mirror-image digit duplications to be produced. The effect of ZPA grafts can be reproduced by application of retinoic acid (RA) beads and by grafting sonic hedgehog (SHH)-expressing cells to the anterior margin of the limb. Although most previous studies have looked at changes of the skeletal patterning, ZPA and RA also affect muscle patterning. In this report, we investigated the role of SHH in tissue and cellular patterning of forearm wing muscles. Ectopic application of a localised source of SHH to the anterior margin of the wing, leading to complete digit duplication, is able to transform anterior forearm muscles into muscles with a posterior identity. Moreover, the ectopic source of SHH induces a mirror image duplication of the normal posterior muscles fibre types in the new posterior muscles. The reorganisation of the slow fibres can be detected before muscle mass cleavage has started; suggesting that the appropriate fibre type arrangement is in place before the splitting process can be observed.

Animals↗
PubMed2003

Perception of temporally interleaved ambiguous patterns.

BACKGROUND: Continuous viewing of ambiguous patterns is characterized by wavering perception that alternates between two or more equally valid visual solutions. However, when such patterns are viewed intermittently, either by repetitive presentation or by periodic closing of the eyes, perception can become locked or "frozen" in one configuration for several minutes at a time. One aspect of this stabilization is the possible existence of a perceptual memory that persists during periods in which the ambiguous stimulus is absent. Here, we use a novel paradigm of temporally interleaved ambiguous stimuli to explore the nature of this memory, with particular regard to its potential impact on perceptual organization. RESULTS: We found that the persistence of a perceptual configuration was robust to interposed visual patterns, and, further, that at least three ambiguous patterns, when interleaved in time, could undergo parallel, stable time courses. Then, using an interleaved presentation paradigm, we established that the occasional reversal in one pattern could be coupled with that of its interleaved counterpart, and that this coupling was a function of the structural similarity between the patterns. CONCLUSIONS: We postulate that the stabilization observed with repetitive presentation of ambiguous patterns can be at least partially accounted for by processes that retain a recent perceptual interpretation, and we speculate that such memory may be important in natural vision. We further propose that the interleaved paradigm introduced here may be of great value to gauge aspects of stimulus similarity that appeal to particular mechanisms of perceptual organization.

Adolescent↗
PubMed2003

Gender dependent EMGs of runners resolved by time/frequency and principal pattern analysis.

A promising approach for the analysis of surface electromyograms is to use wavelets to determine the spectral distribution of the signal intensity at any time. The authors have recently proposed using non-linearly scaled wavelets to obtain intensity patterns, which reflect the spectral distribution at any given time point. Further analysis of intensity-patterns is greatly facilitated by representing them as linear combinations of a base set of principal-patterns. The weight with which each principal-pattern contributes to the intensity-pattern can be represented on a set of orthogonal axes that span a previously introduced pattern space. The purpose of the present study was to show how to use pattern space to discriminate and classify male and female runners based on the electromyograms of five muscles of the limb. The results showed that there were significant gender specific differences, which allowed more than a 95% correct classification of the subjects as males or females. Classification was possible irrespective of the shod condition while running. Gender specific differences occurred at well-defined time periods during the movement. Common to both genders was that spectral changes did not parallel the changes in total signal intensity.

Electromyography↗
PubMed1984

Test-retest reliability and differential patterns of score change on the group embedded figures test.

Retest reliability of the Group Embedded Figures Test (GEFT) was examined under three different intervals between test and retest, all with an interpolated cognitive task. Despite a significant increase in the group mean score from test to retest in all three experiments, retest reliability coefficients were high, .78-.92. There was also a suggestion that reliability increased with duration of delay. Examination of individual patterns of test-retest score change revealed four patterns: consistent field dependent (FD), consistent field independent (FI), unclassifiable (UNCL), and latent field independent (FIL), whose retest scores took them from the FD range to the FI range. The latter two patterns accounted for the significant retest improvement. Relative frequencies of subjects in each pattern were relatively constant over the three experiments. Subjects in the pattern categories also differed with respect to score on number series completion tests, suggesting that the four patterns reflect more general individual differences in analytic ability. It was concluded that the GEFT is a reliable test, but suggestions for a more error-free classification procedure based on a test-retest score pattern is proposed. Implications of the findings for intervention studies of cognitive style are also noted.

Adolescent↗
PubMed1980

Perceptual interpretation of complex line patterns.

Leeuwenberg's coding system for the representation of line pattern interpretations is tentatively applied to the interpretation of complex line patterns, that is, line patterns with intersecting lines. Perceptually preferred interpretations of complex line patterns can only be predicted correctly if two requirements are met: (a) The codes of line patterns should contain information about the objects represented by the line patterns, not about the line patterns as drawings; and (b) effects of the gestalt law of good continuation have to be taken into account.

Adult↗