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At least 235 records · Page 13Linked to original sources
PubMed1999

On the human left ventricular shape.

The geometry of the heart plays a major role in cardiac function. The purpose of this study was to characterize analytically the geometric properties of the left ventricular (LV) three-dimensional (3D) shape, while excluding the effects of aspect ratio and size. Two groups of human hearts were studied by Cine-CT. The first group was composed of 10 healthy volunteers and the second of 9 pathological hearts. The hearts were scanned from apex to base. The endocardial borders of each LV scan were traced and used to reconstruct the 3D LV at end-diastole (ED) and end-systole (ES). Using a special normalized helical shape descriptor, denoted "geometrical cardiogram" (GCG), the typical 3D normal ED and ES shapes were determined. These typical shapes were then analytically approximated via a discrete cosine transform (DCT). The shape of each LV was then investigated for its correspondence to five analytically defined shapes: (i) a cone, (ii) a sphere, including all ellipsoidal shapes, (iii) a cylinder, (iv) a truncated ellipsoid, and (v) the DCT approximation of the normal LV shape. The results indicate that the normal LV shape can be well approximated by using only seven coefficients of the DCT. Conicity was the only geometrical feature which did not change from ED to ES in the normal group of hearts. The most prominent shape difference between normal and abnormal hearts was the significantly reduced conicity of the latter. Conicity is an important feature of LV geometry. The possible contribution of the conical shape to LV ejection efficiency is also discussed.

Adult↗
PubMed1984

Fourier analysis of the shape of normal and transformed epithelial cells derived from human transitional epithelium.

The aim of this paper is to show the possibility of objective mathematical description of changes occurring in the shape of cells in the process of transformation. The evaluation of the changes in cell shape of the chosen cell lines differing in transformation grade was performed by the use of Fourier analysis of the shape. Any two-dimensional contour can be described with specific accuracy in a mathematical manner using the closed form Fourier series of cosines. The components forming the analysed shape, called harmonics, are independent and uncorrelated measures of their contribution to the total shape. The shape of each cell can be represented by the spectrum of harmonic amplitudes. To quote the paper by Healy-Williams and Williams (1981): "The observed shape is partitioned into series, where gross shape, as elongation or triangularity, is measured by the harmonic amplitudes of the lower harmonic order and increasingly fine scaled surface sculpture is measured at higher orders". The statistically evaluated results allow the objective comparison of the cell shapes of several compared cell lines differing in transformation grades. Malignant transformation is supposed to be a multistep process. The different grades of transformation could be defined by several parameters as changes in the morphology of the cells, their ability to compete with fibroblasts, their life span, their angiogenic potency, their invasiveness in vitro and their tumorigenicity in nude mice. In this paper several human urothelial cell lines of normal and tumor origin differing in their transformation grade (TGr I-III) were compared by the use of Fourier analysis of their shape. TGr I cultures have finite life span but do not need intermittent collagenase treatment to prevent fibroblast overgrowth. TGr II cultures acquire infinite growth potential, here defined as capacity to survive at least 70 passages. They are neither tumorigenic nor invasive. TGr III cultures show infinite growth transformation, increased angiogenicity and ability to invade normal host tissue in vitro. They produce progressively growing tumors in nude mice. The following human uroepithelial cell lines differing in the degree of transformation were studied and compared by statistical evaluation of the harmonic amplitudes describing mathematically the cell shape: Two cell lines derived from human transitional cell carcinoma (TCC): 1. Hu 1703S classified as TGr I, 2. Hu 1703He classified as TGr III. It was found that these two cell lines differ in all harmonics. Two cell lines derived from morphological normal human bladder epithelium: 3. HCV-29 classified as TGr II.(ABSTRACT TRUNCATED AT 400 WORDS)

Carcinoma, Transitional Cell↗
PubMed2002

Perceptual segregation of overlapping shapes activates posterior extrastriate visual cortex in man.

Objects in natural scenes are rarely seen in isolation, but are usually overlapping or partially occluding other objects. To recognize individual objects, the visual system must be able to segregate overlapping objects from one another. Evidence from lesions in humans and monkeys suggest that perceptual segregation of occluded or overlapping objects involves extrastriate visual cortex. In monkeys, area V4 has been shown to play an important role in recognizing occluded or poorly salient shapes. In humans, a retinotopic homologue of ventral V4 (V4v) has been described, but it is not known whether this area is also functionally homologous to area V4 in monkeys. In this study, we tried to localize the visual cortical regions involved in perceptual segregation of overlapping shapes using positron emission tomography (PET). Regional cerebral blood flow (rCBF) was measured in seven subjects while they discriminated the relative areas of simultaneously presented rectangular shapes. In the control condition, the shapes were displayed without overlaps; in a second condition, the shapes overlapped each other partially. In a third condition, the shapes did not overlap but had been reduced in salience by adding random noise to the stimuli. Contrasting the overlapping shape condition with the control condition identified a single region in the left posterior lateral occipital cortex. The rCBF in this region also increased, though more weakly, during discrimination of shapes embedded in noise, relative to the control condition. The region activated by segregation of overlapping shapes was located in the posterior occipital cortex close to the anterior border of area V2, near the average location of human V4v as determined by retinotopic mapping studies. The activation of this region of extrastriate visual cortex by a task that involved segregation of overlapping shapes is consistent with monkey V4 and human V4v being functionally homologous. We conclude that discrimination of overlapping shapes involves in particular a region of extrastriate visual cortex located in the left lateral occipital cortex and that this region may correspond to human V4v.

Adult↗
PubMed1993

Methods for computer assisted analysis of lymphoid cell shape and motility, including Fourier analysis of cell outlines.

Locomotion of lymphocytes and other leukocytes is an essential feature of the immune system, and therefore the evaluation of the locomotor behaviour of a lymphocyte population is part of its functional analysis. Paradoxically, the locomotor status of leukocytes is usually assessed on the basis of static information, by counting the number of spherical versus non-spherical cells. In this paper we describe two methods for the measurement of shape changes in microscopic images of lymphoid cells. First we computed a simple shape change factor, coined incongruence factor, based on the degree of non-overlap of the contours of the cell at the beginning and at the end of a 1 min time interval. Second we have used Fourier analysis of the cell outline: a function describing the undulations of the cell outline is broken down into sinusoidal 'waves' of increasing frequency, each with its corresponding amplitude. The amplitude values for the first ten frequencies produced a satisfactory mathematical description of lymphoid cell shapes, and the change of these amplitudes over a 1 minute time interval produced a quantitative description of the shape alterations of the cells. We have used five approaches to evaluate the shape and shape changes in the following populations of mouse lymphoma cells: a constitutively low-motile T lymphoma cell line (BW5147), a high-motile hybridoma (BW-O-Li1) either on plastic or on a precultured fibroblast-like monolayer, BW-O-Li1 cells after penetration through the monolayer, and BW-O-Li1 cells after treatment with cytochalasin B. We compare the results from direct visual evaluation of cell shape, from computer assisted assessment of sphericity and from Fourier analysis of cell shape at one moment, with the two methods for quantitative shape change analysis. All approaches revealed a clear distinction between spherical low-motile populations, and non-spherical high-motile cells. Moreover, the incongruence factor proved to be a reliable single parameter of active cell deformation. In addition, the Fourier analysis of cell outlines produced useful measures of static shape and of dynamic shape change, at any user-defined level of accuracy.

Animals↗
PubMed2006

Neural basis of shape representation in the primate brain.

Visual shape recognition--the ability to recognize a wide variety of shapes regardless of their size, position, view, clutter and ambient lighting--is a remarkable ability essential for complex behavior. In the primate brain, this depends on information processing in a multistage pathway running from primary visual cortex (V1), where cells encode local orientation and spatial frequency information, to the inferotemporal cortex (IT), where cells respond selectively to complex shapes. A fundamental question yet to be answered is how the local orientation signals (in V1) are transformed into selectivity for complex shapes (in IT). To gain insights into the underlying mechanisms we investigated the neural basis of shape representation in area V4, an intermediate stage in this processing hierarchy. Theoretical considerations and psychophysical evidence suggest that contour features, i.e. angles and curves along an object contour, may serve as the basis of representation at intermediate stages of shape processing. To test this hypothesis we studied the response properties of single units in area V4 of primates. We first demonstrated that V4 neurons show strong systematic tuning for the orientation and acuteness of angles and curves when presented in isolation within the cells' receptive field. Next, we found that responses to complex shapes were dictated by the curvature at a specific boundary location within the shape. Finally, using basis function decoding, we demonstrated that an ensemble of V4 neurons could successfully encode complete shapes as aggregates of boundary fragments. These findings identify curvature as a basis of shape representation in area V4 and provide insights into the neurophysiological basis for the salience of convex curves in shape perception.

Animals↗
PubMed1988

Priming effects between two-dimensional shapes.

The role of reference frames in shape perception was examined by investigating priming effects between two-dimensional shapes. Ambiguous shapes and shapes with an unambiguous axis were used, and primes and targets could be orientationally transformed so that for ambiguous shapes, different axes aligned with the vertical. Reliable priming effects were established that were dependent on the structural similarity of primes and targets, the informativeness of the prime, and the interval between the stimuli. Most interestingly, with short interstimulus intervals, differential priming effects were found between ambiguous shapes and unambiguous shapes when an orientational transformation aligned different axes in the ambiguous shape with the vertical. The result was interpreted as demonstrating that priming was determined by the similarity of the frame-based descriptions of primes and targets. The finding occurred irrespective of the informativeness of the prime, suggesting that it reflects obligatory processes in shape perception. Further data showed that under some circumstances prespecifying the orientation of a shape also facilitated its processing; this provided direct evidence that shapes are represented relative to a perceptual reference frame.

Adult↗
PubMed2005

Light-induced shape-memory polymers.

Materials are said to show a shape-memory effect if they can be deformed and fixed into a temporary shape, and recover their original, permanent shape only on exposure to an external stimulus. Shape-memory polymers have received increasing attention because of their scientific and technological significance. In principle, a thermally induced shape-memory effect can be activated by an increase in temperature (also obtained by heating on exposure to an electrical current or light illumination). Several papers have described light-induced changes in the shape of polymers and gels, such as contraction, bending or volume changes. Here we report that polymers containing cinnamic groups can be deformed and fixed into pre-determined shapes--such as (but not exclusively) elongated films and tubes, arches or spirals--by ultraviolet light illumination. These new shapes are stable for long time periods, even when heated to 50 degrees C, and they can recover their original shape at ambient temperatures when exposed to ultraviolet light of a different wavelength. The ability of polymers to form different pre-determined temporary shapes and subsequently recover their original shape at ambient temperatures by remote light activation could lead to a variety of potential medical and other applications.

Journal Article↗
PubMedDate not supplied

Adaptation and constraint in the evolution of Drosophila melanogaster wing shape.

We have taken advantage of parallel instances of natural selection on body size in Drosophila melanogaster to investigate constraints and adaptation affecting wing shape. Using recently developed techniques for statistical shape analysis, we have examined variation in wing shape in similar body size clines on three continents. Gender-related shape differences were constant among all populations, suggesting that gender differences represent a developmental constraint on wing shape. In contrast, the underlying shape varied significantly between continents and shape change within each cline (i.e., between small and large body size populations) also varied between continents. Therefore, variation at these two levels presumably results from either drift or natural selection. Functional considerations suggest that shape variation between the continents is unlikely to be adaptive. However, cline-related shape change, which we show has a significant allometric component, may be adaptive. The overall range of wing shape variation, across a large range of wing size, is extremely small, and the possibility that wing shape is subject to stabilizing selection (or canalization) is discussed.

Adaptation, Physiological↗
PubMed1979

Development of the perception of invariants: substance and shape.

Three experiments investigated the perception of substance and shape as invariant properties of objects by three-month-old infants. In experiment 1, infants were habituated to two differently shaped objects undergoing a rigid motion. After habituation of the infants, the objects were presented undergoing a different rigid motion, or undergoing a deforming motion, or undergoing the same rigid motion. Habituation was maintained to the new rigid motion, indicating that the two rigid motions were perceived as sharing an invariant property. Dishabituation, on the other hand, occurred when a deforming motion followed a rigid one. In experiment 2, infants were habituated to one shape undergoing two different rigid motions. After habituation, the shape was changed but the same two motions continued. Dishabituation occurred, compared to a group with no shape change, indicating that shape is distinguished as an invariant property over two rigid motions. In experiment 3, habituation to a shape undergoing two rigid motions was followed by a new shape presented motionless, or the same shape presented motionless. Cessation of motion did not prevent recognition of shape as invariant. Two properties of an object, substance and shape, thus appear to be detectable as invariant in an event sequence, an instance of "phenomenal doubling" at an early age.

Child Development↗
PubMed1993

Perceptual frames of reference and two-dimensional shape recognition: further examination of internal axes.

Three experiments on the perception of simple four-sided two-dimensional shapes are reported. In the first experiment subjects were given a paper-and-pencil test in which they had to consider each of a set of shapes in turn. They were instructed to draw in what they considered to be the most salient axis of each of the shapes ie a line that they felt most naturally went with the shape. The results showed a significant tendency to draw an axis of symmetry if one was present. However, when presented with instances of a shape that was elongated but possessed no symmetries they failed to consistently draw any particular axis. A further, speeded classification, task revealed that for this shape explicit axis information appeared not to influence performance. In contrast, such information clearly affected performance with a shape that did possess a salient axis of symmetry and elongation. Indeed this axis was shown to be integral with the contour of the shape when a final classification experiment was carried out. The axis of elongation of the other shape acted as a characteristic which was separable from the contour. The results are discussed in relation to accounts of shape perception which assume that a necessary stage in the perception of shape is the derivation of an axis-based structural description.

Adolescent↗
PubMed2005

Ultrasonographic tissue characteristics of mushroom-shaped uveal melanoma.

PURPOSE: To evaluate the ultrasonographic tissue characteristics of mushroom-shaped versus dome-shaped uveal melanoma and to compare them with the tumor vasculature. METHODS: We examined clinically and ultrasonically 18 dome-shaped and 11 mushroom-shaped uveal melanomas (29 consecutive patients; mean age 57 years) and compared their normalized A-scan patterns. Using histological sections from a different set of patients (12 dome- and 17 mushroom-shaped tumors), we calculated the percentage of area covered by blood vessels. RESULTS: A-scans of dome-shaped tumors presented low homogeneous reflectivity, whereas the heads of mushroom-shaped tumors had high and irregular reflectivity (p < 0.001). The reflectivity of their bases was low and similar to dome-shaped tumors. The blood vessel area in the histological sections was significantly larger in the heads of mushroom-shaped tumors (0.88 +/- 0.14%), compared both to their bases (0.29 i 0.06%) (p < 0.001) and to dome-shaped tumors (0.07 i 0.03%) (p < 0.0001). CONCLUSIONS: The ultrasonographic pattern suggests vascular congestion in the heads of mushroom-shaped tumors,probably due to strangulated blood vessels in the tumor neck.

Adult↗
PubMed2006

A comparative study of shape representation in macaque visual areas v2 and v4.

We compared aspects of shape representation in extrastriate visual areas V2 and V4, which are both implicated in shape processing and belong to different hierarchical levels. We recorded responses of cells in awake, fixating monkeys to matched sets of contour and grating stimuli of low or intermediate complexity. These included simple stimuli (bars and sinusoids) and more complex stimuli (angles, intersections, arcs, and non-Cartesian gratings), all scaled to receptive field size. The responses of cells within each area were substantially modulated by each shape characteristic tested, with substantial overlap between areas by many response measures. Our analyses revealed many clear and reliable differences between areas in terms of the effectiveness of, and response modulation by, various shape characteristics. Grating stimuli were on average more effective than contour stimuli in V2 and V4, but the difference was more pronounced in V4. As a population, V4 showed greater response modulation by some shape characteristics (including simple shape characteristics) and V2 showed greater response modulation by many others (including complex shape characteristics). Recordings from area V1 demonstrated complex shape selectivity in some cells and relatively modest population differences in comparison with V2. Altogether, the representation of 2-dimensional shape characteristics revealed by this analysis varies substantially among the 3 areas. But surprisingly, the differences revealed by our analyses, individually or collectively, do not parallel the stepwise organization of the anatomical hierarchy. Commonalities of visual shape representation across hierarchical levels may reflect the replication of neural circuits used in generating complex shape representations at multiple spatial scales.

Animals↗
PubMed2003

Crown-down tip design and shaping.

The shaping affects of three types of stainless-steel files that differ only in tip shape were studied using curved canals in acrylic blocks. Ninety curved canals were divided by degree of curvature into three equal groups of 30. The canals in each group were shaped using a crown-down technique and files possessing one of the three different tip shapes. The tip shapes were biconical tip (Flex-R), conical tip (Mor-Flex), and pyramidal tip (Flex-O). The canals were photographed before and after shaping and the finished shape analyzed. The incidences of transportation, ledging, and instrument damage were recorded during instrumentation. National Institutes of Health image software was used to measure the longitudinal cross-sectional areas and cross-sectional diameters at specified canal depths. Statistical analysis showed a significant difference in the preparations between the three tip shapes. Biconical tip files (Flex-R) produced the least transportation and no ledges. Pyramidal tip files (Flex-O) produced the most transportation, ledges, and damaged files. Only pyramidal-shaped tips developed ledges and experienced file separation. The participants reported less difficulty shaping with a biconical-tipped file and the greatest technical difficulty with a pyramidal-shaped tip. This study suggests that during crown-down rotational instrumentation, biconical file tips maintain the original canal curvature better and more frequently than do conical and pyramidal file tips.

Analysis of Variance↗
PubMedDate not supplied

Impaired capacity of cerebellar patients to perceive and learn two-dimensional shapes based on kinesthetic cues.

This study addresses the issue of the role of the cerebellum in the processing of sensory information by determining the capability of cerebellar patients to acquire and use kinesthetic cues received via the active or passive tracing of an irregular shape while blindfolded. Patients with cerebellar lesions and age-matched healthy controls were tested on four tasks: (1) learning to discriminate a reference shape from three others through the repeated tracing of the reference template; (2) reproducing the reference shape from memory by drawing blindfolded; (3) performing the same task with vision; and (4) visually recognizing the reference shape. The cues used to acquire and then to recognize the reference shape were generated under four conditions: (1) "active kinesthesia," in which cues were acquired by the blindfolded subject while actively tracing a reference template; (2) "passive kinesthesia," in which the tracing was performed while the hand was guided passively through the template; (3) "sequential vision," in which the shape was visualized by the serial exposure of small segments of its outline; and (4) "full vision," in which the entire shape was visualized. The sequential vision condition was employed to emulate the sequential way in which kinesthetic information is acquired while tracing the reference shape. The results demonstrate a substantial impairment of cerebellar patients in their capability to perceive two-dimensional irregular shapes based only on kinesthetic cues. There also is evidence that this deficit in part relates to a reduced capacity to integrate temporal sequences of sensory cues into a complete image useful for shape discrimination tasks or for reproducing the shape through drawing. Consequently, the cerebellum has an important role in this type of sensory information processing even when it is not directly associated with the execution of movements.

Adult↗
PubMed1983

Regulation of Cell Shape in Euglena gracilis: I. Involvement of the Biological Clock, Respiration, Photosynthesis, and Cytoskeleton.

The alga Euglena gracilis Z. changes its shape two times per day when grown under the synchronizing effect of a daily light-dark cycle. At the beginning of the light period when photosynthetic capacity is low, the population of cells is largely spherical in shape. The mean cell length of the population increases to a maximum in the middle of the light period when photosynthetic capacity is greatest, and then decreases for the remainder of the 24-hour period. The population becomes spherical by the end of the 24-hour period when the cycle reinitiates. These changes are also observed under constant dim light conditions (up to 72 hours) and are therefore controlled by the biological clock and represent a circadian rhythm in cell shape. In constant dim light, the cell division rhythm is either arrested or slowed considerably, while the cell shape rhythm continues.The involvement of respiratory and photosynthetic pathways in the cell shape changes was investigated with energy pathway inhibitors. Antimycin A and NaN(3) both inhibited the round to long and long to round shape changes, indicating that the respiratory pathways are involved. DCMU and atrazine inhibited the round to long shape change but did not affect the long to round transition, indicating that light-induced electron flow is necessary only for the round to long shape change.The influence of the cell shape changes on the photosynthetic reactions was investigated by altering cell shape with the cytoskeletal inhibitors cytochalasin and colchicine. Both inhibitors blocked the round to long and long to round shape changes. Cytochalasin B was found to have minimal cytotoxic effects on the photosynthetic reactions, but colchicine significantly inhibited light-induced electron flow and the in vivo expression of the photosynthetic rhythm.

Journal Article↗
PubMed1993

Relationships between color, shape, and pattern selectivities of neurons in the inferior temporal cortex of the monkey.

1. To examine the way in which information from different visual submodalities is integrated in the inferior temporal (IT) cortex of the monkey, we studied the relationships between the color, shape, and pattern selectivities of individual neurons in IT cortex of two awake macque monkeys. Neurons were recorded while each animal performed a visual fixation task. For each neuron, we analyzed selectivity for the visual submodalities of color, contour shape, and textural pattern using preselected standard sets of visual stimuli, namely colored geometrical shapes with certain patterns. 2. About two thirds (62%) of single neurons whose activities were recorded from the anterior part of IT cortex, which included the ventral bank of the superior temporal sulcus, responded to one or more of the stimuli in the standard sets of stimuli used. An index (stimulus selectivity index) was calculated for each neuron to quantify how well a cell discriminated the preferred stimulus from the least preferred stimulus in each set of stimuli. The stimulus selectivity index, as well as the statistical significance of the variation in the responses to the stimuli within a given set, was used to classify a cell as selective or not selective in a given submodality. Of the neurons whose responses were analyzed quantitatively, 69% were selective for color, 68% were selective for shape, and 82% were selective for pattern. 3. Of the neurons that were tested with respect to the selectivity for color and for shape, 45% were selective both for color and shape, 50% were selective for either color or shape, and only 5% were not selective for color or shape. These frequencies were not significantly different from those predicted from the occurrence of the selective and nonselective neurons in each submodality if the independence of the selectivities for color and shape is assumed. We also found that the color preference of individual neurons does not depend on the shape of the stimulus. These results indicate that there was no overt interaction between the selectivities for color and shape in these IT neurons. 4. Of the neurons that were compared with respect to the selectivity for color and for pattern, 58% were selective both for color and pattern, 38% were selective for either color or pattern, and only 4% were not selective for color or pattern. There was no correlation between the degree of color selectivity and the degree of pattern selectivity of individual neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Evidence for the use of scene-based frames of reference in two-dimensional shape recognition.

A series of reaction time (RT) experiments are reported in which subjects had to match pairs of two-dimensional shapes. The shapes were either symmetrical or asymmetrical and were arranged into either symmetrical or asymmetrical displays. In the initial experiments the shapes straddled the vertical midline of the display. It was found that Same RTs to symmetrical displays were shorter than Same RTs to asymmetrical displays, and that Same RTs to symmetrical shapes were shorter than Same RTs to asymmetrical shapes. Moreover, display symmetry and shape symmetry produced an additive effect on responses. This pattern of results obtained when both shapes were presented simultaneously and when a delay was introduced between the presentation of one shape and the presentation of the other. However, display and shape symmetry interacted when the displays were rotated 90 deg within the plane so that the shapes straddled the horizontal meridian. The implications of these results are discussed in terms of both a transformational account of shape recognition and an account concerning the imposition and use of scene-based frames of reference.

Form Perception↗
PubMed1982

Thromboxane A2/prostaglandin H2 directly stimulates platelet shape change independent of secreted ADP.

The relative contribution of thromboxane (TX)A2/prostaglandin (PG)H2 and ADP to platelet shape change was determined using the specific TXA2/PGH2 antagonist, 13-azaprostanoic acid (13-APA) and the ADP antagonist, ATP. Shape change was induced in human platelet-rich plasma with doses of arachidonic acid (AA) or the PG endoperoxide analog U46619, which did not cause measurable ATP/ADP release. Pretreatment of platelet-rich plasma with 13-APA completely inhibited shape change to AA or U46619 but did not inhibit ADP-induced shape change. In contrast, ATP completely blocked shape change to ADP but not to AA or U46619. In addition, 13-APA and ATP also selectively reversed shape change. Thus, 13-APA added 1.5 min subsequent to AA or U46619 resulted in almost complete reversal of the shape change response. However, 13-APA did not reverse ADP-induced shape change. A similar selectivity was observed with ATP which reversed shape change to ADP but not to AA or U46619. These findings provide evidence that the interaction of TXA2/PGH2 with its receptor results in the direct stimulation of shape change independent of secreted ADP. Furthermore, maintenance of this shape change response appears to require continued occupation of the TXA2/PGH2 receptor.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗