Skewed symmetry: A nonaccidental property used to perceive visual forms.

Mathematically, skewed symmetry is a nonaccidental property because it can be interpreted as bilateral symmetry in depth viewed from a nonorthogonal angle. To find out whether this is a useful property in the perception of visual forms, 4 experiments were designed in which the Ss had to determine whether 2 symmetric or random patterns were the same regardless of possible affine transformations between them. The results provided mixed evidence: Although there was always a large symmetry advantage, skewed symmetry was only perceived as bilateral symmetry in depth for dot patterns with higher order types of symmetry (Exp 1), when the dots were connected to form closed polygons (Exp 2 and 4), or when they were surrounded by a frame to enhance their planarity (Exp 3). In other cases, Ss relied on local groupings on the basis of proximity or curvilinearity, which are qualitatively affine invariant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Through a narrow window: Sample size and the perception of correlation.

A theoretical analysis (Y. Kareev, 1995b) of the sampling distribution of correlations led to the surprising conclusion that the use of small samples has a potential advantage for the early detection of a correlation. This is so because the distribution is highly skewed, and the smaller the sample size, the more the distribution is skewed. This article describes 2 experiments that were designed as empirical tests of this conclusion. In Experiment 1 (N?=?112), the authors compared the predictions of participants differing in their working-memory capacity (hence in the size of the samples they were likely to consider). In Experiment 2 (N?=?144), the authors compared the predictions of participants who viewed samples of different sizes, whose size was determined by the authors. The results fully supported Y. Kareev's conclusion: In both experiments, participants with lower capacity (or smaller samples) indeed perceived the correlation as more extreme and were more accurate in their predictions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Skew reduces test-retest reliability.

Demonstrates that skew will reduce the test-retest reliability of otherwise normal data and that the greater the skew is, the greater will be the decrease in reliability. In the first section, equations are derived for the test-retest reliability of lognormal data, a skewed distribution that can be returned to normality by the log transformation. The second analytic treatment derives equations for reliability with power transformations (xa) that will produce skew in originally normal data. Finally, analysis of test-retest correlations of actual skewed measures confirmed that if skew was minimized by transformation toward symmetry, then the reliabilities increased; the increase in reliability was related to the extent of skew. Researchers are cautioned to consider transforming data that are skewed to obtain greater symmetry and, thus, improve the test-retest reliability of the resulting measure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manipulating symmetry in the coordination dynamics of human movement.

J. A. S. Kelso and J. J. Jeka (see record 1992-41720-001) demonstrated that symmetry is a useful conceptual tool to distinguish the coordination between components with similar vs different anatomical properties. The present experiments studied human arm–leg patterns to test whether their coordinative asymmetry was changed by manipulating the inertial properties of a single limb. The results showed that (1) consistent with model predictions, adding weight to the arm or the leg minimized or enhanced coordinative asymmetry, respectively and (2) the response to a perturbation slowed as movement frequency increased but in a fashion that reflected the underlying coordinative asymmetry. The observed coordinative effects suggest the influence of neural phase relationships and emphasize that symmetry plays an important role in understanding coordination in systems in which control cannot be traced unequivocally to a single end-effector or a neurophysiological substrate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Layout geometry in the selection of intrinsic frames of reference from multiple viewpoints.

Four experiments investigated the roles of layout geometry in the selection of intrinsic frames of reference in spatial memory. Participants learned the locations of objects in a room from 2 or 3 viewing perspectives. One view corresponded to the axis of bilateral symmetry of the layout, and the other view(s) was (were) nonorthogonal to the axis of bilateral symmetry. Judgments of relative direction using spatial memory were quicker for imagined headings parallel to the symmetric axis than for those parallel to the other viewing perspectives. This advantage disappeared when the symmetric axis was eliminated. Moreover, there was more consistency across participants in the selection of intrinsic axes when the layout contained an axis of bilateral symmetry than when it did not. These results indicate that the layout geometry affects the selection of intrinsic frames of reference supporting the intrinsic model of spatial memory proposed by W. Mou and T. P. McNamara (2002) and by A. L. Shelton and T. P. McNamara (2001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions between symmetry and elongation in determining reference frames for object perception.

Many theories of object recognition posit that objects are encoded with respect to a perceptual frame of reference. Such theories assume that factors such as symmetry and elongation are critical for the assignment of an object's primary axis, and consequently for the extraction of an object's reference frame. The present experiments directly examined the relative roles played by symmetry and elongation in the determination of an object's primary axis, and the extent to which symmetry and elongation interact with one another. A total of 55 Ss (aged 15–27 yrs) participated in the experiments. The authors found that observers use both symmetry and elongation in extracting an object's primary axis, that the extent to which each cue dominates depends on its relative salience, and that symmetry and elongation are processed interactively, rather than in encapsulated modules. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odour coding is bilaterally symmetrical in the antennal lobes of honeybees (Apis mellifera)

The primary olfactory neuropil, the antennal lobe (AL) in insects, is organized in glomeruli. Glomerular activity patterns are believed to represent the across-fibre pattern of the olfactory code. These patterns depend on an organized innervation from the afferent receptor cells, and interconnections of local interneurons. It is unclear how the complex organization of the AL is achieved ontogenetically. In this study, we measured the functional activity patterns elicited by stimulation with odours in the right and the left AL of the same honeybee (Apis mellifera) using optical imaging of the calcium-sensitive dye calcium green. We show here that these patterns are bilaterally symmetrical (n=25 bees). This symmetry holds true for all odours tested, irrespective of their role as pheromones or as environmental odours, or whether they were pure substances or complex blends (n=13 odours). Therefore, we exclude that activity dependent mechanisms local to one AL determine the functional glomerular activity. This identity is genetically predetermined. Alternatively, if activity dependent processes are involved, bilateral connections would have to shape symmetry, or, temporal constraints could lead to identical patterns on both sides due to their common history of odour exposure.     

Curvilinear transformations of the dependent variable.

D. W. Levine and W. P. Dunlap (see record 1982-27158-001) concluded that tests on skewed data lack power. The present author contends that this conclusion is incorrect. What they have rediscovered is that curvilinear transformations change population means and population variances, as well as the form (skewness and kurtosis) of the population. Thus, such transformations change the noncentrality parameter, φ. When the null hypothesis is false, the power entries in the rows of their Table 1 are influenced by all of these characteristics. To attribute this change to skewness alone is incorrect. Many distinctions are pertinent to the choice of whether to use such transformations: informal data analysis vs formal inference on experiments based on strong theory, the size of the error term relative to the size of the treatment effects, considerations of interactions, simplicity of results, and statistical assumptions. Skewness is the least important of these factors. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of body rotation on children's left–right confusion: A challenge to bilateral symmetry theory.

The hypothesis that left–right confusion in children is determined by correspondence to the bilateral symmetry of the nervous system was tested by presenting left–right and up–down discrimination-learning problems to 80 preschoolers (mean age?=?4.25 yrs) who viewed these stimuli from either an upright or 90°-rotated body position. The data clearly contradict predictions based on the anatomical model. Regardless of body position, left–right confusion was primarily determined by the left–right relationship of the stimulus to environmental coordinates rather than by its relationship to the bilateral symmetry of the body. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of the original Ontario Child Health Study scales

This article presents evaluative information on the use of the original Ontario Child Health Study scales to serve as original-level measures of conduct disorder, hyperactivity and emotional disorder among children in the general (non clinic) population. Problem checklist assessments were obtained from parents and teachers of children aged six to 16 and youth aged 12 to 16 drawn from a general population (n = 1,751); and a mental health clinic sample (n = 1,027) in the same industrialized, urban setting. The results showed that the original OCHS scales possess adequate psychometric properties to be used as original-level measures of disorder. Correlations between individual items and their hypothesized scales were very strong, indicating convergent validity, while correlations between the same items and other (non hypothesized) scales were lower, indicating discriminant validity. Item analyses indicated that individual scale items possess both convergent and discriminant validity. Although the scales were skewed to the positive end of the continuum, they demonstrated good internal consistency (all estimates > or = 0.74) and test-retest (all estimates > or = 0.65) reliability. Finally, three different validity analyses confirmed hypotheses about how the original OCHS scales should perform if they provide useful measures of disorder.     

Perception of the symmetrical patterning of human gait by infants.

Two experiments tested 3- and 5-month-old infants' sensitivity to properties of point-light displays of human gait. In Experiment 1, infants were tested for discrimination of point-light displays of a walker and a runner, which, although they differed in many ways, were equivalent with regard to the phasing of limb movements. Results revealed that 3-month-old, but not 5-month-old, infants discriminated these displays. In Experiment 2, the symmetrical phase-patterning of the runner display was perturbed by advancing two of its limbs by 25% of the gait cycle. Both 3- and 5-month-old infants discriminated the walker display from this new phase-shifted runner display. These findings suggest that 3-month-old infants respond to the absolute and relative motions within a single limb, whereas 5-month-old infants respond primarily to the relations between limbs and, in particular, to the bilateral symmetry between the limbs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of symmetry in infancy.

Symmetrical visual patterns, particularly vertically symmetrical ones, are preferred and processed faster than asymmetrical patterns by adults. Results of 3 experiments with 61 4- and 12-mo-olds show that (a) 4-mo-old infants showed no preference for symmetry, but they processed vertically symmetrical patterns more efficiently than horizontally symmetrical or asymmetrical ones; and (b) by 12 mo, infants preferred vertical symmetry to horizontal symmetry and asymmetry. Thus, preference for symmetry seems to develop late, whereas recognition of vertical symmetry is innate, matures very quickly, or is learned very early. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facial asymmetry and attractiveness judgement in developmental perspective.

This study examined the role of facial symmetry in the judgment of physical attractiveness. Four experiments investigated people's preference for either somewhat asymmetrical portraits or their symmetrical chimeric composites when presented simultaneously. Experiment 1 found a higher selection rate for symmetrical faces with neutral expression for portraits of old people, and Experiment 2 indicated this may be because symmetry serves as cue for youth in old age. In Experiments 3 and 4 participants examined portraits with emotional expressions. Experiment 3 found a higher selection rate for asymmetrical faces, and Experiment 4 indicated this may be because observers perceived them as more genuine and natural. This study suggests that the low degree of facial asymmetry found in normal people does not affect attractiveness ratings (except for old age), probably because observers are not tuned to perceive it. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Atropine fails to block the overconsumption of sugar solutions by hypothalamic hyperphagic rats.

Adult female Sprague-Dawley rats given bilateral parasagittal knife cuts in the medial hypothalamus (VMH group) were hyperphagic and became obese on a chow diet, compared with sham-operated controls. VMH Ss also overconsumed, relative to controls, sucrose and glucose solutions during 30-min/day tests. Pretreating VMH and control Ss with atropine methyl nitrate (1.0, 5.0, or 10.0 mg/kg) reduced their intake of the sugar solutions in 3 of 5 experiments, and in all experiments it suppressed their 24-hr chow intake. However, VMH Ss continued to drink more of the sugar solutions than the controls after all atropine treatments, and in 3 of 4 experiments their hyperphagia on the chow diet was not blocked by the atropine. Results do not support the hypothesis that vagally stimulated insulin release or other cholinergically mediated cephalic responses of digestion are essential for the expression of hypothalamic hyperphagia and finickiness. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A 3D deformable surface model for segmentation of objects from volumetric data in medical images

Type A Clostridium botulinum, the causative agent of the food poisoning botulism disease, secretes botulinum neurotoxins along with seven neurotoxin associated proteins (NAPs). The function of NAPs has been shown to protect the neurotoxin from acidity, heat, and proteolytic attack in the environmental and gastrointestinal tract during the toxicogenesis of the botulism disease. One of the NAPs, purified from type A botulinum neurotoxin complex, showed hemagglutination activity. A direct interaction has been demonstrated between purified NAP, a 33-kDa hemagglutinin or Hn-33, and the neurotoxin by using Sephadex G-200 column chromatography. Furthermore, Hn-33 has complete resistance against proteolytic attack at pH 2.0 as well as at normal physiological pH. We have investigated digestion of the neurotoxin in the presence and absence of Hn-33. The neurotoxin alone has been found to be more susceptible to the enzymatic digestion than neurotoxin with Hn-33. The presence of Hn-33 changes the proteolytic fragmentation pattern of the neurotoxin. It seems that Hn-33 protects the neurotoxin from proteolysis either by structural modification of the neurotoxin or by blocking the protease accessible sites of the neurotoxin.     

Bilateral symmetry of biomechanical properties in rat femora

In many studies, bone healing and remodeling have been examined in various animal models using one femur as a control for the contralateral femur based on the assumption that they are bilaterally symmetrical. Symmetry studies have been limited mainly to geometrical properties. The purpose of this study was to determine whether or not there is symmetry in the mechanical properties of rat femora. Two strain gauges were attached to the anterior surface parallel to the long axis of explanted femora of retired female breeder and 120-day-old male Sprague Dawley rats. Femora were mechanically tested in cantilever bending and the strain values were recorded. Moments of inertia, cortical areas, and moduli of elasticity were determined from strains and cross-sectional properties. Female femora showed a bilateral strain difference of less than 2.2% and an elastic modulus difference of less than 8.7%. Males had less than 2.0% and 7.9% differences for strain and elastic moduli, respectively. Statistical analysis showed no significant difference between left and right femoral strain values for the females, but modulus differences were significant different at the p = 0.05 level. There was no significant difference in strain and modulus values for the males, indicating mechanical and geometrical symmetry of their femora.     

Transformations for within-subject designs: A Monte Carlo investigation.

Explored the use of transformations to improve power in within-S designs in which multiple observations are collected for each S in each condition, such as reaction time (RT) and psychophysiological experiments. Often, the multiple measures within a treatment are simply averaged to yield a single number, but other transformations have been proposed. Monte Carlo simulations were used to investigate the influence of those transformations on the probabilities of Type I and Type II errors. With normally distributed data, Z and range correction transformations led to substantial increases in power over simple averages. With highly skewed distributions, the optimal transformation depended on several variables, but Z and range correction performed well across conditions. Correction for outliers was useful in increasing power, and trimming was more effective than eliminating all points beyond a criterion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple comparison procedures for trimmed means.

Stepwise multiple comparison procedures (MCPs) based on least squares and trimmed estimators were compared for their rates of Type I error and their ability to detect true pairwise group differences. The MCPs were compared in unbalanced one-way completely randomized designs when normality and homogeneity of variance assumptions were violated. Results indicated that MCPs based on trimmed means and Winsorized variances controlled rates of Type I error, whereas MCPs based on least squares estimators typically could not, particularly when the data were highly skewed. However, MCPs based on least squares estimators were substantially more powerful than their counterparts based on trimmed means and Winsorized variances when the data were only moderately skewed, a finding which qualifies recommendations on the use of trimmed estimators offered in the literature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The detection of bilateral symmetry: Effects of surrounding frames.

Examined whether the detection of bilateral symmetry in the fronto-parallel plane is influenced by surrounding frames. The study was conducted with 12 Ss. When obliquely or vertically oriented rectangular frames were presented simultaneously surrounding the dot patterns, the frames influenced symmetry detection. Vertical symmetry detection was slower in the tilted frame than it was in the vertical frame, and tilted symmetry was detected faster in the tilted frame than it was in the vertical. When there was a time delay between frame and pattern onset, there was no measurable frame effect. Symmetry detection was slowed when not in line with the long axis of the frame, whereas symmetry detection was not affected when the frame axis was aligned with the symmetry axis. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)