Similarity-scaling studies of dot-pattern classification and recognition.

Classification performance in a dot-pattern, prototype-distortion paradigm (e.g., M. I. Posner and S. W. Keele, 1968) was modeled within a multidimensional scaling (MDS) framework. MDS solutions were derived for sets of dot patterns that were generated from prototypes. These MDS solutions were then used in conjunction with exemplar, prototype, and combined models to predict classification and recognition performance. Across 3 experiments, an MDS-based exemplar model accounted for the effects of several fundamental learning variables, including level of distortion of the patterns, category size, delay of transfer phase, and item frequency. Most important, the model quantitatively predicted classification probabilities for individual dot patterns in the sets, not simply general trends of performance. There was little evidence for the existence of a prototype-abstraction process that operated above and beyond pure exemplar-based generalization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Non-Fourier information in bandpass noise patterns

Random dot patterns and white-noise luminance textures are widely used in psychophysical experiments to study low-level visual processes. Because these noise patterns are broadband, bandpass filtered versions are employed to limit their frequency content. It is not recognized, however, that bandpass noise patterns have amplitude-modulation (AM) components. The AM signal is not present in the Fourier spectrum, nonetheless, it is a valid signal for second-order mechanisms. We characterize the properties of the AM signal in bandpass noise textures: the relevant periodicities of the AM signal are always much lower than the actual passband; the upper frequency limit of the AM signal increases with the linear bandwidth. We present psychophysical data to demonstrate the perceptual significance of the AM signal in bandpass noise. We provide a method for obtaining AM-free bandpass patterns, and compare psychophysical performance in experiments employing AM-present and AM-free bandpass noise patterns as stereoscopic stimuli. The results show that the AM component contributes to stereoscopic discrimination performance at large disparities. We suggest that the low-frequency AM signal is a possible confounding factor in experiments employing bandpass noise textures, and that linear filtering can isolate spatial scales effectively only for linear systems.     

Temporal characteristics of visual memory.

In order to infer the temporal relations among iconic, short-term, and long-term components of visual memory, random dot patterns were used as memory stimuli in six recognition memory experiments. Experiment 1 demonstrated that recognition was still above chance for intervals up to 12 s. In Experiments 2 and 3, an intervening masking stimulus was found to be effective only if presented within the first 500 ms of the interval. The remaining three experiments employed a two-target task, with the second target replacing the masking stimulus. Recognition performance with the second target was the same as that in a single-target task, whereas performance with the first target was almost at chance level. Increasing the interval between the targets resulted in a gradual improvement in the recognition of the first target. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Naive statics: Current misconceptions on equilibrium.

Studied common concepts regarding the equilibrium of objects in 3 experiments, using a total of 85 17–45 yr old Ss. Groups of Ss (including some experts in statics) were asked to solve problems like finding the resting position of objects suspended either by their center of gravity or at some point more or less removed from the center of gravity. Results show that, with few exceptions, Ss confused neutral equilibrium with the stable equilibrium that is assumed when the object is symmetrical with its vertical axis. This error is explained, together with the errors found in tasks in which objects were not suspended by their center of gravity, by the hypothesis that Ss conceive equilibrium as an equaling of the potential energy of gravity. The possibility that Ss' mistakes may be due to an impression of equilibrium connected to conditions of perfect symmetry is discussed, as is the hypothesis of the coexistence of naive and objective concepts in the human system of knowledge. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The location of noisy visual stimuli.

Examined the results of experiments where Ss were required to detect the misalignment of 2 abutting dot clusters on a monitor screen. Thresholds varied with the square root of dot density and did not appear to be affected by changing the sampling strategy used to generate the random dot clusters. Comparison of the Ss' performance with that expected of 3 information processing strategies suggested that Ss accomplished the task by locating the edges of the dot clusters rather than by extracting measures of global scope or of central position. The efficiency with which edge information was extracted was approximately 50% for low-density stimuli and declined exponentially with increasing dot density. (French abstract) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motion integration with dot patterns: effects of motion noise and structural information

To better understand how local motion detectors merge their responses so as to permit the global determination of objects' movements in the visual field, direction discrimination of performance was measured using a flexible class of moving dots--two sets of dots translating sinusoidally 90 deg out of phase along orthogonal axes. When dots' velocities are combined, a global motion along a circular trajectory emerges, clockwise or counter-clockwise depending on the sign of the phase lag. However, the results of the present experiments indicate that dot patterns are segregated into distinct, but interacting, streams when each dot motion can be accurately determined. In contrast, perceptual coherence of the global motion occurs when each local motion signal is "blurred" by a "motion noise". Direction discrimination performance then increases regularly with both noise amplitude and noise frequency, i.e., noise speed. Performance also increases when relative motion between dots is added. Testing different dot configurations indicates that performance is better for spatial arrangements that display structural properties (a square shape), as compared to overlapping random distributions. Interestingly, when the delay between stimulus onset and motion onset increases up to 300 msec, performance improves when dot patterns convey come form of structural organization but not when the dots are distributed at random. Relations of these results to existing models of motion integration are considered.     

Spatial localization in left and right visual fields.

Presented a series of single dots tachistoscopically in either the left or the right visual field, Ss task being to locate the dot on a spatial map depicting all of the lot locations presented. 7 experiments were carried out with 232 right-handed male and female undergraduates. For men, localization of the dot was more accurate in the left than in the right visual field, under all testing conditions. Women showed the left-field superiority under some testing conditions; under others they showed no difference between fields. There was no sex difference in over-all accuracy of performance, and simple detection of a dot was not more accurate in 1 field than another for either sex. Results are discussed in terms of a probable "spatial coordinate" system in the right hemisphere of the brain. (French summary) (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In vitro hydrolysis of gliadin and casein peptides: secondary defect in coeliac disease shown by organ culture

The authors examined whether there is any correlation between the regression speed of cardiac beta (V3)-myosin heavy-chain (MHC) isozyme and duration of overload. The results showed that in the right ventricle of a 1-week overloaded group, the loaded ventricular MHC isozyme V3 (29 center dot 0 +/- 5 center dot 0%, P < 0 center dot 05) returned to the control level within 1 week after relief of overload (20 center dot 4 +/- 4 center dot 2%, P = NS), whereas in a 3 week overloaded group (32 center dot 8 +/- 5 center dot 3%, P < 0 center dot 05) it took 10 weeks (36 center dot 6 +/- 8 center dot 6%, P = NS). The left ventricle showed the same tendency as the right ventricle. In sham-operated rats, however, the changes in MHC isozyme V3 in the left ventricle were greater than those in the right ventricle. These results suggest that regression speed of the cardiac MHC isoform, changed by pressure overload, is accompanied by the duration of overload. Furthermore, the right and left ventricles may have different responsiveness to MHC isoform transitions in heart stresses.     

On the surprising salience of curvature in grouping by proximity.

The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the dot lattices used to study grouping by proximity, except that only one of the potential organizations is rectilinear; the others are curvilinear. The authors used the method of M. Kubovy and J. Wagemans (1995) to study grouping by proximity in DSGs. They found that in the competition between the most likely organizations, one rectilinear and the other curvilinear, the latter is more salient. This phenomenon cannot be explained by contemporary accounts of grouping by proximity or contour integration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of agency on movement interference during observation of a moving dot stimulus.

Human movement performance is subject to interference if the performer simultaneously observes an incongruent action. It has been proposed that this phenomenon is due to motor contagion during simultaneous movement performance-observation, with coactivation of shared action performance and action observation circuitry in the premotor cortex. The present experiments compared the interference effect during observation of a moving person with observation of moving dot stimuli: The dot display followed either a biologically plausible or implausible velocity profile. Interference effects due to dot observation were present for both biological and nonbiological velocity profiles when the participants were informed that they were observing prerecorded human movement and were absent when the dot motion was described as computer generated. These results suggest that the observer's belief regarding the origin of the dot motion (human-computer generated) modulates the processing of the dot movement stimuli on their later integration within the motor system, such that the belief regarding their biological origin is a more important determinant of interference effects than the stimulus kinematics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Movement disorders in the context of P.K. Anokhin's theory of functional systems

The authors' own findings and the data available in the literature as to movement diseases (MD) in animals and man were reviewed in the context of P. K. Anokhin's theory of functional systems. The functional system of the human body's gravity center is detailed. There is evidence for that disintegration processes underlying MD first occur in the mnestic sphere since due to genetic and/or ontogenetic causes, memory has no preserved no motor programme required to achieve the end net efficiency of performance of this functional system,--to maintain the definite position of the gravity center of the body and its related vegetative status upon stress-induced vestibular exposures. Based on the above concepts of the pathogenesis of MD, its preventive measures have been proposed and tested, which include drug (nootropic agents) and non-drug (a special complex of physical exercises for children aged 2 to 7 years, which will form permanent motor programs in memory in definite periods of their ontogenesis) measures.     

Discrimination of letters and random dot patterns by pigeons and humans.

Conducted 2 exploratory experiments to compare pigeon and human perception of visual stimuli. In a 3-choice discrimination task, 3 white Carneaux pigeons learned to distinguish each letter of the alphabet from all the other letters and each of 16 random dot patterns from all the others, and Ss' discrimination errors were used to generate a matrix of interletter and interpattern similarities. Human estimates of letter similarity were obtained from previous literature, and 6 human adults rated the similarity of the dot patterns. Performances of the humans and of 6 pigeons were described and compared through correlation, multidimensional scaling, and cluster analysis, and fits of the data by simple-feature and template models were computed and compared. The correlation between pigeon and human similarity matrices was .68 for letters and .72 for dot patterns. The other analyses revealed broadly similar patterns of results from the 2 species but suggested that, relative to human data, the best fits to the pigeon data required fewer dimensions, fewer features, and fuzzier templates. There was some indication that pigeon discriminations depended on relatively simple features, and several of these were tentatively identified. It is suggested that the different methods employed could have influenced these apparent differences between pigeons and humans, but, overall, findings suggest considerable cross-task and cross-species generality in the processing of these simple forms. (47 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perceptual units in the acquisition of visual categories.

A series of experiments provided evidence that the representational structure of categories comprising dot patterns is based on pattern parts and pattern configuration rather than on pattern elements. Similarity judgments and postacquisition classification data could not be explained in terms of element-level perceptual units, even for categories of dot patterns with 7 of their 8 dots in the exact same relative location. The importance of higher order perceptual units was indicated by evidence that long-term retention of information specific to previously learned category exemplars, which is typical of natural objects, can also be obtained for artificial dot patterns, providing their structure reflects perceptual characteristics identified in Tversky and Hemenway's (1984) study of natural objects: Members of the same category had to be perceptually distinctive at the pattern configuration level and perceptually similar at the level of pattern parts. The level of within-category similarity for a set of categories (relative to between-categories similarity) did not predict whether item-specific information would be retained; long-term retention appears to require both within-category similarity and dissimilarity, but at different levels of perceptual structure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Elevated serum neopterin level: its relation to endotoxaemia and sepsis in patients with major burns

The present study was conducted to determine the relationship between levels of neopterin and endotoxin in the circulation, and whether the neopterin level was related to the development of severe sepsis after extensive burns. This prospective study included 35 patients with burn size greater than 30% (30-98%), and 22 healthy volunteers who served as a comparison group. Neopterin levels increased in most patients on day 3 post-burn, but they were not significantly correlated with the extent of the burn surface (P > 0 center dot 05). A high serum neopterin level was found in patients with sepsis (n = 15), and a marked elevation persisted throughout the observation period. The difference between septic and non-septic patients (n = 20) became significant on 14 and 28 days post-burn. Although the presence of early endotoxaemia did not influence the alterations in serum neopterin, patients with endotoxaemia had much higher neopterin values than those who showed no endotoxaemia from the second week onward (P < 0 center dot 05-0 center dot 01). In addition, circulating endotoxin and neopterin levels were positively correlated in patients who developed endotoxaemia on day 14 (r = 0 center dot 368, P < 0 center dot 05) and day 21 (r = 0 center dot 439, P < 0 center dot 01) after major burns. These results suggest that thermal injury can lead to an elevation of serum neopterin independent of the burn surface area. The initial increase in the neopterin level may be a part of the acute-phase response to tissue injury itself, whereas the endotoxin release in the circulation may be responsible for the continuous induction of neopterin during the late stage. In addition, the presence of a constant high neopterin level is associated with a critical event in the development of severe burn sepsis.     

Perceptual use of nonaccidental properties.

Reviews the literature about the nonaccidental properties (NAPs) cotermination, straightness, and parallelism to trace their historical roots, to list the properties that function as NAPs, and to discuss the psychological evidence for their detection and use. Four experiments are reviewed, and four are fully described that were designed to test the perceptual use of skewed symmetry, which results from orthographic projection of planar bilateral or mirror symmetry. Despite the large symmetry advantage obtained in all experiments, skewed symmetry is only perceived as bilateral symmetry-in-depth in cases of closed polygons or dot patterns with higher-order types of symmetry. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bilaterally projecting neurons in the two visual pathways of chicks

The influence of stereoscopic vision on the perception of optic flow fields was investigated in experiments based on a recently described illusion. In this illusion, subjects perceive a shift of the center of an expanding optic flow field when it is transparently superimposed by a unidirectional motion pattern. This illusory shift can be explained by the visual system taking the presented flow pattern as a certain self-motion flow field. Here we examined the dependence of the illusory transformation on differences in depth between the two superimposed motion patterns. Presenting them with different relative binocular disparities, we found a strong variation in the magnitude of the illusory shift. Especially when translation was in front of expansion, a highly significant decrease of the illusory shift occurred, down to 25% of its magnitude at zero disparity. These findings confirm the assumption that the motion pattern is interpreted as a self-motion flow field. In a further experiment we presented monocular depth cues by changing dot size and dot density. This caused a reduction of the illusory shift which is distinctly smaller than under stereoscopic presentation. We conclude that the illusory optic flow transformation is modified by depth information, especially by binocular disparity. The findings are linked to the phenomenon of induced motion and are related to neurophysiology.     

Reversal of the Z- to B-conformation of poly(dA-dT) center dot poly(dA-dT) induced by netropsin and distamycin A

Poly(dA-dT) center dot poly(dA-dT) which adopts the Z-form at 5 M NaCl in presence of 95 mM Ni2+ions is reversed to the B-conformation by the nonintercalating drugs netropsin (Nt) and distamycin A (Dst). The drug-induced reversal from the Z-to B-form of poly(dA-dT) center dot poly(dA-dT) is evidenced by CD spectral changes at characteristic wavelengths around 295 nm and 248 nm. The drug-induced conformational transition is accompanied by a slow kinetic process. The results suggest the preference of these AT-specific drugs for the B-form and the inability of Nt and Dst to form a stable complex with the Z-form of poly(dA-dT) center dot poly(dA-dT).     

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)     

Subjective landmarks in perception and memory for spatial location.

Four experiments involving 125 undergraduates investigated the use of cognitive strategies for encoding spatial location in visual figures. Ss reproduced the position of a dot in a square figure that had distance markers placed along 2 sides. Ss' responses were biased toward imaginary points of intersection formed by the distance markers when Ss responded from memory (Exp 1) or while viewing the figures (Exp 2). Findings demonstrate that empty regions of a figure can serve as subjective landmarks for spatial localization. In Exp 3, dot relocation was similarly distorted toward physical cross marks placed at the intersections of distance markers. The attraction of dots to intersection points depended on the viewer employing a strategy of mentally projecting from distance markers to form imaginary intersections. In Exp 4, attraction toward intersection points was observed only when Ss employed the projection strategy. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of age on the learning of a nondeclarative category classification task

A category classification task was administered to participants in their twenties through their eighties. Participants studied a set of high distortions of a prototype dot pattern and were then asked to choose whether or not a new set of dot patterns (random patterns, high distortions, low distortions, and the prototype) belonged to the same category of dot patterns as studied. Participants were also administered a recognition test after studying a second set of dot patterns. There were no significant differences for age groups on the pattern recognition test. In 2 of the 3 analyses of the category classification task, there were no significant age effects. However, there was a small age effect in one analysis with the young making more accurate classifications on two aspects of the task. The results are consistent with the view that small age-related effects may exist for some tests of nondeclarative memory.