Models for preattentive texture discrimination: Fourier analysis and local feature processing in a unified framework

Spatial frequency analysis and local feature analysis may be considered to be examples of a class of models for texture discrimination. In this theoretical framework, texture discrimination relies on differences in the distribution of responses generated in linear receptive fields placed randomly on the texture. If the set of receptive fields is taken to be a collection of gratings, spatial-frequency analysis is recovered. If the set of receptive-fields is taken to be a collection of local feature templates, a corresponding local-feature model is recovered. In order to test such models, it is necessary to construct distinct texture pairs that elicit similar distributions of responses for all of the postulated receptive field profiles: the model prediction is that such textures are not discriminable. A method is provided for construction of such textures which test generic models within this framework. This framework includes not only strict Fourier analysis, but also models which postulate a collection of arbitrarily-shaped local feature detectors, and models which postulate both Fourier analysis and local feature detection.     

A neural network model for texture discrimination

A model of texture discrimination in visual cortex was built using a feedforward network with lateral interactions among relatively realistic spiking neural elements. The elements have various membrane currents, equilibrium potentials and time constants, with action potentials and synapses. The model is derived from the modified programs of MacGregor (1987). Gabor-like filters are applied to overlapping regions in the original image; the neural network with lateral excitatory and inhibitory interactions then compares and adjusts the Gabor amplitudes in order to produce the actual texture discrimination. Finally, a combination layer selects and groups various representations in the output of the network to form the final transformed image material. We show that both texture segmentation and detection of texture boundaries can be represented in the firing activity of such a network for a wide variety of synthetic to natural images. Performance details depend most strongly on the global balance of strengths of the excitatory and inhibitory lateral interconnections. The spatial distribution of lateral connective strengths has relatively little effect. Detailed temporal firing activities of single elements in the lateral connected network were examined under various stimulus conditions. Results show (as in area 17 of cortex) that a single element's response to image features local to its receptive field can be altered by changes in the global context.     

Electrophysiological investigation of the texture discrimination mechanisms

In electrophysiological and psychophysical experiments, we investigated mechanisms of the visual system underlying local and global texture processing. Textures included rectangular matrixes composed of Gabor patches (sine wave grating windowed by a Gaussian envelope). Orientation of each grating varied from 0 to 165 degrees with the step of 15 degrees. Matrixes differed by the amount of Gabor patches with vertical or horizontal orientation. The observers' task was to discriminate the dominant orientation. The advantage of such stimuli involved a possibility to calculate global statistics of the textures, which we considered as the difference between whole amount of vertical and horizontal orientations in the stimulus irrespective of their location. The local statistics was calculated as relative amount of spatially organized nearby gratings (i. e. collinear contours). The subjects' accuracy was low in discriminating less organized textures and gradually improved with the amount of vertically of horizontally oriented Gabor patches, while the reaction time decreased. Visual evoked potentials (VEPs) recorded from occipital lobes revealed different dependencies of their components' magnitude on the amount of equally oriented gratings. Amplitude of the late positive component P3 with latency 400 ms directly depended on the texture discriminability, and N2 wave with latency 180 ms had an S-like dependence. Opposite to that, the magnitude of P2 wave with latency 260 ms was maximal in response to less organized textures and gradually decreased with the amount of equally oriented gratings. The dependencies received were compared with the textures' statistics. Data analysis allowed us to suppose that, in the conditions of our experimental paradigm, two mechanisms were involved in discrimination of the textures--the local and the global processing. We believe that by recording VEPs one can separately investigate activity of these two processes.     

Visual discrimination of textures with identical third-order statistics

We found a new class of two-dimensional random textures with identical third-order statistics that can be effortlessly discriminated. Discrimination is based on local granularity differences between these iso-trigon texture pairs. This is the more surprising since it is commonly assumed that texture granularity (grain) is determined by the power spectrum which, in turn, can be obtained from the second-order statistics. Because textures with identical third-order statistics must have identical second-order statistics (i.e., identical power spectra), visible texture granularity is not controlled by power spectra, and not even by third-order statistics.     

Recovery of surface pose from texture orientation statistics under perspective projection

In a seminal paper, Witkin (1981) derived a model of surface slant and tilt recovery based on the statistics of the orientations of texture elements (texels) on a planar surface. This model made use of basic mathematical properties of probability distributions to formulate a posterior distribution on slant and tilt given a set of image orientations under orthographic projection. One problem with the Witkin model was that it produced a posterior distribution with multiple maxima, reflecting the inherent ambiguity in scene reconstruction under orthographic projection. In the present article, we extend Witkin’s method to incorporate the effects of perspective projection. An identical approach is used to that of Witkin; however, the model now reflects the effects of perspective projection on texel orientation. Performance of the new model is compared against that of Witkin’s model in a basic surface pose recovery task using both a maximum a posteriori (MAP) decision rule and a rule based on the expected value of the posterior distribution. The resultant posterior of the new model is shown to have only one maximum and thereby the ambiguity in scene interpretation is resolved. Furthermore, the model performs better than Witkin’s model using both MAP and expected value decision rules. The results are discussed in the context of human slant estimation.     

A cluster analysis based on graph theory

Summary A clustering method is presented that groups sample plots (stands or other units) together, based on their proximity in a multidimensional test space in which the axes represent the attributes (species) of the individuals (sample plots, etc.). The resulting dendrogram is used to make subjective judgements on the type and distinctiveness of the groupings. The method is demonstrated on the vegetation data from 43 sample plots in mixed white spruce stands in Saskatchewan. The results were related to the levels of 31 habitat variables. Significant differences among the groups were shown to exist for basal area, height growth, and root penetration of white spruce and for field capacity and pH of the soil. When possible the nomenclature of Fernald (1950) is followed for the Pteridophyta and Spermatophyta; elsewhere Rydberg's (1954) nomenclature is followed. The nomenclature of Grout (1928–1940) is used for the Musci, with the exception ofCalliergonella schreberi, which is replaced byPleurozium schreberi (Willd) Mitt.     

Contribution to the theory of discrimination learning

In the first two sections, which deal, respectively, with simple and double (or successive) discrimination, a comparison is made between the theory presented and certain experiments on time discrimination. Section III sets forth a possible theoretical approach to multiple choice discrimination.     

Mechanism for food texture preference based on grittiness

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A tentative typology of European scrub and forest communities based on vegetation texture and structure

Utilitarian and fundamental, floristic and structural classifications of forest and scrub communities are compared. Their advantages and disadvantages and their interrelations are discussed. The necessity of a structural classification as complementary to a floristic classification is emphasized. It seems difficult, if not impossible, to combine the two. The existing structural classifications are reviewed. They are not very detailed and often mixed with a habitat classification. A new, detailed and purely structural system for woods and scrub in Europe is proposed in the form of an identification key. The main criteria used are — in order of diminishing importance —: (1) architecture of the dominant layer, (2) photoperiodicity (evergreen vs. deciduous) of that layer, (3) leaf size and leaf form of that layer, (4) presence/absence of thorns/spines, (5) presence of a second tree layer, shrub layer, dwarf shrub layer, herb layer and/or moss layer, (6) deciduousness of these layers, (7) main growth forms, (8) leaf size and leaf consistency, (9) leaf inclination and (10) height of these layers.In all 27 scrub types and 45 wood types are described. They have been named after a combination of two more or less characteristic and dominant genera. The system is open and hierarchical. Broader units have also been described.Comm. No. 388 of the Biological Station Wijster, Department of Silviculture and Forest Ecology, Agricultural University, Wageningen     

A theory of hippocampal memory based on theta phase precession

 The neural dynamics of the hippocampal network for memory encoding of novel temporal sequences is proposed based on the theta rhythm modulated firing of place cells called theta phase precession. It is hypothesized that theta phase precession is generated at the entorhinal cortex by phase locking between local field theta oscillation and neural oscillators and that the hippocampal closed network with feedforward and backward projections employ theta phase precession to create selectivity in the associative connections needed for temporal sequence storage. Our analyses and computer experiments reveal that the phase precession generated by phase locking instantaneously endows stable phase relations among neural activities in the successively changing neural population. It is concluded that theta phase precession provides biologically plausible dynamics for the memory encoding of novel temporal sequences as episodic events. Received: 18 December 2002 / Accepted: 18 March 2003 / Published online: 20 May 2003 Correspondence to: Y. Yamaguchi (e-mail: yokoy@brain.riken.go.jp, Fax: +81-48-4676938) Acknowledgements. The author would like to express acknowledgement to Drs. McNaughton and Skaggs for their discussion and comment and to Dr. Amari for his continuous encouragement. Further thanks are given to Mr. Haga and Dr. Wu for their discussion and cooperation.     

Allocation and discrimination based on human odontometric data

This study contrasts the confidence with which individuals may be grouped and then re-allocated on the basis of odontometric data. These data are derived from the mesiodistal and buccolingual diameters of 202 Lengua Indians of Paraguay (100 males, 102 females), 125 Caucasoid schoolchildren (59 male, 66 female), and 206 Negroes (106 male, 100 female). Multivariate intergroup discrimination is effected by means of canonical and stepwise discriminant analysis, whilst allocation is evaluated by means of posterior and typicality probabilities. Bias is reduced by means of a jackknifing procedure. High levels of discriminatory confidence (each Wilk's Lambda, P less than 0.01) are matched by high percentage correct classification (Caucasoid, 67.4-75.0%; Negro, 71.0-77.3%; Amerindian, 65.2-78.1%). However, these results are not matched by allocatory procedures: only 21.7% of caucasoids, 21.4% of Negroes, and 28.8% of Amerindians could be re-allocated with probabilities in excess of 80%. It is concluded that while multivariate discriminant techniques may be usefully employed in the separation of different populations, individuals may not be assigned with the same degree of confidence, even with an a priori knowledge of their group membership.     

Sound texture perception via statistics of the auditory periphery: evidence from sound synthesis

Rainstorms, insect swarms, and galloping horses produce "sound textures"--the collective result of many similar acoustic events. Sound textures are distinguished by temporal homogeneity, suggesting they could be recognized with time-averaged statistics. To test this hypothesis, we processed real-world textures with an auditory model containing filters tuned for sound frequencies and their modulations, and measured statistics of the resulting decomposition. We then assessed the realism and recognizability of novel sounds synthesized to have matching statistics. Statistics of individual frequency channels, capturing spectral power and sparsity, generally failed to produce compelling synthetic textures; however, combining them with correlations between channels produced identifiable and natural-sounding textures. Synthesis quality declined if statistics were computed from biologically implausible auditory models. The results suggest that sound texture perception is mediated by relatively simple statistics of early auditory representations, presumably computed by downstream neural populations. The synthesis methodology offers a powerful tool for their further investigation.     

A robust method for diagnosis of morphological arrhythmias based on Hermitian model of higher-order statistics

Background  

Electrocardiography (ECG) signal is a primary criterion for medical practitioners to diagnose heart diseases. The development of a reliable, accurate, non-invasive and robust method for arrhythmia detection could assists cardiologists in the study of patients with heart diseases. This paper provides a method for morphological heart arrhythmia detection which might have different shapes in one category and also different morphologies in relation to the patients. The distinctive property of this method in addition to accuracy is the robustness of that, in presence of Gaussian noise, time and amplitude shift.     

Toward a theory of variability discrimination: finding differences

We sketch the outlines of a theory of variability discrimination that aggregates localized differences to mediate variability discrimination. This Finding Differences Model was compared to a Positional Entropy Model across four different data sets. Although the two models provide strong and similar fits across three of the data sets, only the Finding Differences Model is applicable to investigations involving multidimensional variability. Furthermore, the Finding Differences Model is based on an activation map that has been shown to have utility for visual search tasks, thus establishing its generality across task domains.