Texture Contrast Research Articles

Geogenesis, pedogenesis, and multiple causality in the formation of texture-contrast soils

Coarse-over-fine vertical texture contrasts (VTC) are common in soils and weathering profiles in a variety of environmental settings, including many where inheritance or surficial processes alone cannot account for them. A multiple causality model is presented here which shows that texture contrasts can form in response to a combination of ubiquitous phenomena. There are six key elements: downward translocation by water, erosional winnowing, soil mixing by bioturbation, the tendency for surface clay additions to be mobilized while subsurface clays are more likely to remain in place, and biological facilitation of moisture flux. No element alone is sufficient to create a VTC, but not all are necessary in any given regolith. The model is illustrated by application to case studies in the Ouachita Mountains, Arkansas; ridgetops in eastern Kentucky; the lower coastal plain of North Carolina; and the upper coastal plain of east Texas. The implications for interpretation of soils, paleosols, and weathering profiles is that the presence of a textural contrast, by itself, does not connote any particular set of geogenic or pedogenic processs or controls. Texture contrasts may be geogenic, pedogenic, or both. Given the widespread occurrence of the mechanisms of the multiple causality model, vertical texture contrasts are inevitable.

The development of columnar peds in a texture contrast soil in the Pilliga State Forests, northwestern New South Wales

The development of columnar peds in a texture contrast soil in the Pilliga State Forests, northwestern New South Wales

Potential terrain controls on soil color, texture contrast and grain-size deposition for the original catena landscape in Uganda

Inspired by the catena concept, we returned to the landscape of origin for this idea in central Uganda and applied quantitative soil–landscape-modeling techniques to the study of soil formation. In particular, we employed Generalized Least Squares (GLS) regression to identify potential terrain (and other) controls on surface texture with the goal of explaining texture contrast formation for well-drained red soils, and fluvial deposition for yellow–gray lowland soils. Well-drained red soils and poorly drained yellow–gray soils were identified using a high-resolution spectroradiometer and soil redness was highly correlated with a measure of elevation above the valley floor. For the yellow–gray soils, sand content and sand grain size increased with greater slope gradient and in converging areas—evidence supporting fluvial control of surface soil composition. For red soils, texture contrast increased on lower backslopes, decreased over ferricrete-rich parent material, and had no significant association with either infiltration- or runoff-influenced locations. Surprisingly, texture contrast was also reduced or even inverted on fine scale convexities (<18 m in diameter). These findings were consistent with the following theoretical processes: (1) sand deposition on lower-backslopes, increasing texture contrast; (2) ferricrete weathering at the soil surface, reducing texture contrast; and (3) texture contrast inversion through termite turbation. A number of techniques proved useful in this study: (a) the use of GLS regression supported the interpretation of model coefficients in an explicitly spatial context; (b) thin-plate splines provided a flexible means of controlling the spatial scale of terrain index computation; and (c) the development of a new downslope-looking Elevation Above Stream (EASy) terrain index provided a powerful tool for the identification of poorly drained soils—a tool that could have applications in a variety of landscapes and environments. Overall, we found that the catena concept as a soil–terrain-modeling approach worked best on lower, less well-drained, depositional landscape components. For the well-drained portion of this landscape, there was little evidence to suggest that soil formation was controlled by hillslope hydrology as proposed by the catena concept. The catena concept interpreted in a broad sense challenges pedologists to explicitly link soil geographic patterns with specific soil forming processes and environmental controls—an approach that proved valuable in this study.

Abilities in tactile discrimination of textures in adult rats exposed to enriched or impoverished environments

In previous studies, we have shown that housing in enriched environment for about 3 months after weaning improved the topographic organization and decreased the size of the receptive fields (RFs) located on the glabrous skin surfaces in the forepaw maps of the primary somatosensory cortex (SI) in rats [Exp. Brain Res. 121 (1998) 191]. In contrast, housing in impoverished environment induced a degradation of the SI forepaw representation, characterized by topographic disruptions, a reduction of the cutaneous forepaw area and an enlargement of the glabrous RFs [Exp. Brain Res. 129 (1999) 518]. Based on these two studies, we postulated that these representational alterations could underlie changes in haptic perception. Therefore, the present study was aimed at determining the influence of housing conditions on the rat’s abilities in tactile texture discrimination. After a 2-month exposure to enriched or impoverished environments, rats were trained to perform a discrimination task during locomotion on floorboards of different roughness. At the end of every daily behavioral session, rats were replaced in their respective housing environment. Rats had to discriminate homogeneous (low roughness) from heterogeneous floorboards (combination of two different roughness levels). To determine the maximum performance in texture discrimination, the roughness contrast of the heterogeneous texture was gradually reduced, so that homogeneous and heterogeneous floorboards became harder to differentiate. We found that the enriched rats learned the first steps of the behavioral task faster than the impoverished rats, whereas both groups exhibited similar performances in texture discrimination. An individual “predilection” for either homogeneous or heterogeneous floorboards, presumably reflecting a behavioral strategy, seemed to account for the absence of differences in haptic discrimination between groups. The sensory experience depending on the rewarded texture discrimination task seems to have a greater influence on individual texture discrimination abilities than the sensorimotor experience related to housing conditions.

Soil development on dolerite and its implications for landscape history in southeastern Tasmania

Soil genesis has been examined using field description, particle-size distributions, chemical properties, mineralogy and elemental distributions of five soil profiles developed on dolerite on Mt. Nelson and Tolmans Hill near Hobart in Tasmania. The soils form a sequence ranging from a Black Vertosol (P8) to four texture contrast soils, namely, a Eutrophic Brown Chromosol (P5), two Mottled-Subnatric Grey Sodosols (MN8 and P4), and a Mottled-Mesonatric Grey Sodosol (P7). The soil stratigraphic and pedological relationships of these soils have been investigated to help understand their distribution and improve understanding of soil formation history. The knowledge of the soil stratigraphy and weathering features aided in the determination of the broader landscape history. The field observations show the local dolerite has been subjected to both deep weathering and severe erosional periods. Pockets of deeply weathered dolerite occur adjacent to thin A/C soils or hard outcropping rock. Deeper colluvial soil materials occur on lower slopes. The presence of protruding dolerite columns now buried by transported clayey slope-wash materials indicates partial landscape stripping followed by reburial. The presence of buried stone-lines separating the upper profile from the clayey subsoils supports the idea of a second major erosional–depositional cycle. A pronounced variation between the A and B horizons particle-size distribution, mineralogy and elemental distribution supports the conclusion that the modern soils are composed of several sedimentary layers which cap a variable thickness of in situ weathered dolerite (termed “mealy material”) above fresh dolerite. Bedrock jointing, veins and rock fabric extend upward from the bedrock into the mealy material, but are truncated abruptly at the contact with the clayey subsoil. Soil-forming processes have operated to modify soil colours and mottling, soil structure and cation chemistry. These findings have important implications for landscape history, slope processes and the improved understanding of the distribution of dolerite-derived soils in Tasmania.

Modelling trends in woody vegetation structure in semi-arid Australia as determined from aerial photography

Accounting of carbon stocks in woody vegetation for greenhouse purposes requires definition of medium term trends with accurate error assessment. Tree and shrub cover was sampled through time at randomly located sites over a large area of central Queensland, Australia using aerial photography from 1945 to 1999. Calibration models developed from field data for the same land types as those represented within the study area allowed for the extrapolation of overstorey and understorey cover, basal area and biomass values and these were modelled as trends over the latter half of the 20th century. These structural attributes have declined over the region because of land clearing with values for biomass changing from a mean of 58.0(±1.2) t/ha in 1953 to 41.1(±1.0) t/ha in 1991. The biomass of Acacia on clay and Eucalypt on texture contrast soils land types has declined most dramatically. Within uncleared vegetation there was an overall trend of increase from 56.1(±1.2) t/ha in 1951 to 67.6(±1.3) t/ha in 1995. The increase in structural attributes within uncleared vegetation was most pronounced for the Eucalypt on texture contrast soils and Eucalypt on clay land types. It was demonstrated that the sites sampled were representative of their land types and that spatial bias of the photography, undetected tree-killing, sampling error, inherent variability of structural attributes and measurement error should not have impacted greatly on bias or precision of trend estimates for well-sampled land types. Certainly the errors are not likely to be substantial for trends averaged over all land types and they provide an accurate assessment of the magnitude and direction of change. The technique presented here would appear to be a robust means of accounting for the above-ground woody component of woodlands and open forests and will also contribute to a broader understanding of savanna dynamics.

Objective landslide detection and surface morphology mapping using high-resolution airborne laser altimetry

A map of extant slope failures is the most basic element of any landslide assessment. Without an accurate inventory of slope instability, it is not possible to analyze the controls on the spatial and temporal patterns of mass movement or the environmental, human, or geomorphic consequences of slides. Landslide inventory maps are tedious to compile, difficult to make in vegetated terrain using conventional techniques, and tend to be subjective. In addition, most landslide inventories simply outline landslide boundaries and do not offer information about landslide mechanics as manifested by internal deformation features. In an alternative approach, we constructed accurate, high-resolution DEMs from airborne laser altimetry (LIDAR) data to characterize a large landslide complex and surrounding terrain near Christchurch, New Zealand. One-dimensional, circular (2-D) and spherical (3-D) statistics are used to map the local topographic roughness in the DEMs over a spatial scale of 1.5 to 10 m. The bedrock landslide is rougher than adjacent unfailed terrain and any of the statistics can be employed to automatically detect and map the overall slide complex. Furthermore, statistics that include a measure of the local variability of aspect successfully delineate four kinematic units within the gently sloping lower half of the slide. Features with a minimum size of surface folds that have a wavelength of about 11 to 12 m and amplitude of about 1 m are readily mapped. Two adjacent earthflows within the landslide complex are distinguished by a contrast in median roughness, and texture and continuity of roughness elements. The less active of the earthflows has a surface morphology that presumably has been smoothed by surface processes. The Laplacian operator also accurately maps the kinematic units and the folds and longitudinal levees within and at the margins of the units. Finally, two-dimensional power spectra analyses are used to quantify how roughness varies with length scale. These results indicate that no dominant length scale of roughness exists for smooth, unfailed terrain. In contrast, zones with different styles of landslide deformation exhibit distinctive spectral peaks that correspond to the scale of deformation features, such as the compression folds. The topographic-based analyses described here may be used to objectively delineate landslide features, generate mechanical inferences about landslide behavior, and evaluate relatively the recent activity of slides.

P‐20: Display Related Effects of Terrain‐Texture Density and Contrast on Perceived Air Speed in Simulated Flight

AbstractThe display‐dependent effects of both terrain texture density and contrast were assessed using a speed maintenance task in a high‐performance flight simulator. Density and contrast varied in opposite directions with simulated distance, and were found to have opposite effects on perceived speed. The functional range of the interaction between density and contrast was estimated.

Evaluation of ferrolysis in soil formation

SummaryThe concept of ferrolysis as defined in the 1970s by Brinkman and co‐workers is mentioned in the recent literature as a dominant process to explain clay disintegration, interlayering of clay minerals, and strong texture contrast of duplex soils, in which bleaching and mottling are predominant features. Ferrolysis is based on biochemical reduction of free iron(III) oxides to Fe2+ and re‐oxidation of Fe2+ during alternating reducing and oxidizing conditions in the soil. The acidity produced during the oxidation is assumed to release cations from silicates which results in the destruction of clay minerals. A detailed analysis of data from chemical analyses, laboratory experiments, and mineralogical and micromorphological investigations, which have been considered to sustain the ferrolysis theory, has been carried out. Some soils in Belgium and France, which have been considered to be formed mainly by ferrolysis, show strong textural contrast or albeluvic features. It has been shown that the development of these soils is due to clay translocation rather than to clay destruction by ferrolysis. Fine quartz and chlorite, assumed to be secondary minerals formed during ferrolysis, are more likely formed by disintegration of larger quartz and chlorite particles.

Texture fading correlates with stimulus salience

Perceptual fading of texture targets on similarly textured backgrounds was studied in relation to stimulus salience using texture patterns defined by orientation contrast, shape contrast, and order contrast. In two independent experiments, perceptual salience of the targets was determined. In the first, the textural contrast of the stimuli was varied and their salience quantified using magnitude estimation; in the second, reaction time was measured for the same stimulus patterns. In a third experiment, stimulus fading time was determined. Whereas magnitude estimates and fading time increased, reaction time decreased with increasing textural contrast strength, the shape of the curves depending on the kind of texture pattern used. When fading time was plotted against target salience, the slopes of the regression lines for shape and order contrast were similar, while the slope for orientation contrast was steeper, indicating longer fading times at equal stimulus salience. A control experiment using short oriented bars instead of gratings revealed that this difference may be attributed to the abutting contour between the target and its surround. With this contour removed, the fading time was largely the same for all three kinds of texture patterns. In the absence of a border (no cancellation), the unconnected target areas appeared to change gradually in orientation, shape, and spatial arrangement, thereby assuming the properties of the background (substitution).

Inefficient visual search for second-order motion.

Visual search rate was used to assess attentional resources required for detection of opposing motions defined either by luminance or by modulations of texture contrast, flicker, or size. Though luminance-based targets were detected quickly, search through second-order motion was slow. Control experiments ruled out stimuli visibility, complexity, eccentricity sensitivity, and attributes of the carrier as possible accounts. Results suggest separate processing of the two types of stimuli: Luminance-based motion is detected by spatiotemporal filters, whereas second-order motion is likely processed by a capacity-limited, later stage. Rate-reducing effects of increased contrast and speed mirrored previous research suggesting that effortful feature tracking may be the mechanism.

Texture contrast aftereffects are monocular; texture density aftereffects are binocular

Two experiments examined interocular transfer for simple and dynamic aftereffects of density and contrast. Simple aftereffects of texture contrast were shown to be primarily monocular. Texture density aftereffects were shown to be primarily binocular. Similarly, dynamic aftereffects to repeated changes in contrast were found to be completely monocular; those to repeated changes in density were found to be entirely binocular. Since contrast and density aftereffects differ in their sensitivity to eye-of-origin, they likely depend on different neural loci, and are not manifestations of the same underlying adaptation. Consistent with this conclusion, it is proposed that, whereas contrast normalization (and perhaps contrast aftereffects) may be localized to simple cells in V1, density coding and normalization require computations only available in complex cells and beyond.

Visual aftereffects of sequential perception: dynamic adaptation to changes in texture density and contrast

Two new aftereffects are described in which the comparison of successively presented textures can be affected by prior exposure (adaptation) to biased sequences. A dynamic aftereffect of texture density can be produced using changes in non-Fourier texture density (using balanced-dot textures). An analogous dynamic aftereffect is demonstrated for texture contrast. These two effects are dissociated experimentally by the near absence of cross-adaptation. Evidence is also presented that the density effect is not one of texture motion (e.g. expansion/contraction of texture).

Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia

SummaryMineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl2) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO3– concentrations.The soil contained more mineral N in autumn (64–133 kg N ha−1 to 120 cm) than in spring (51–96 kg N ha−1), with NO3– comprising 70–77%. No NO3– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l−1 as NO3– initially but &lt; 1 mg N l−1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l−1 during winter. Losses of NO3– were small in surface runoff (0–2 kg N ha−1 year−1). In 1995, 9–19 kg N ha−1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha−1 in 1995 and 4–10 kg N ha−1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha−1 year−1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha−1 year−1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha−1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.

An analysis of chemical loads and forms in overland flow from dairy pasture in South Australia

AbstractTwo adjacent subcatchments on soils with very strong texture contrast between the A soil horizons (sandy loam texture) and B soil horizons (clay texture) in the Adelaide Hills, South Australia were instrumented to collect overland and subsurface flow from dairy pasture. Subcatchments were defined by exclusion drains in the upper reaches and stainless steel barriers at the lower boundary. Water samples were analysed for 20 different chemical fractions. Chemical loads were examined in order to determine relationships among simple empirical event and site characteristics, and between chemical fractions. All but five of the chemical fractions could be separated into one of two clear groups using a statistical technique based on the magnitude of simple correlation coefficients. The two groups consisted of either dissolved or particulate fractions. The clear separation into these groups is consistent with the majority of chemical fractions moving from pasture by one of only two processes. Simple empirical variables in a multiple regression explained a high proportion of variation in chemical loads in runoff water. These findings may have major implications in the modelling and prediction of chemical loads in runoff from agricultural catchments and the setting of environmental limits, in simplifying chemical loss predictions by adding a nutrient loss module to runoff volume predictions. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Variance of high contrast textures is sensed using negative half-wave rectification

A rectifying transformation is required to sense variations in texture contrast. Various theoretical and practical considerations have inclined researchers to suppose that this rectification is full-wave, rather than half-wave. In the studies reported here, observers are asked to judge which of two texture patches has higher texture variance. Textures are composed of small squares, with each square being painted with one of nine different luminances. Different texture variances are achieved by manipulating the histograms of the texture patches to be compared. When the nine luminances range linearly from 0 to 160 cd/m 2, the transformation mediating judgments of texture variance takes the form of a negative half-wave rectifier: texture variance judgments are determined exclusively by the frequencies of luminances below mean luminance in the textures being compared. However, when the nine luminances range linearly from 60 to 100 cd/m 2, two of three observers use a full-wave rectifying transformation in making texture variance judgments; the third observer continued to use a negative half-wave rectifier. The unexpectedly asymmetric roles played by low versus high luminances in texture variance judgments suggest that the off-center system may play a dominant role in human perception of texture contrast.

A lesion of cortical area V2 selectively impairs the perception of the direction of first-order visual motion.

Lesions of area MT/V5 in monkeys and its presumed homologue, the motion area, in humans impair motion perception, including the discrimination of the direction of global motion in random dot kinematograms. Here we report the results of similar tests on patient TF, who has a discrete and very small, unilateral infarct in the medial superior part of the right occipital cortex. Structural MRI, co-registered in software with a standardized human brain atlas, reveals that the lesion involves area V2. The patient was impaired in his retinotopically corresponding left lower quadrant on several motion tasks including discrimination in random dot kinematograms of direction, speed and motion-defined discontinuity. He was also impaired on tasks selectively involving first-order motion based on luminance contrast but not on second-order motion based on texture contrast. The results show that even though area MT/V5 is intact, motion perception is abnormal and, in particular, his perception of first-order motion is impaired.

Reliability and dimensionality of judgments of visually textured materials.

We extended perceptual studies of the Brodatz set of textured materials. In the experiments, texture perception for different texture sets, viewing distances, or lighting intensities was examined. Subjects compared one pair of textures at a time. The main task was to rapidly rate all of the texture pairs on a number scale for their overall dissimilarities first and then for their dissimilarities according to six specified attributes (e.g., texture contrast). The implied dimensionality of perceptual texture space was usually at least four, rather than three. All six attributes proved to be useful predictors of overall dissimilarity, especially coarseness and regularity. The novel attribute texture lightness, an assessment of mean surface reflectance, was important when viewing conditions were wide-ranging. We were impressed by the general validity of texture judgments across subject, texture set, and comfortable viewing distances or lighting intensities. The attributes are nonorthogonal directions in four-dimensional perceptual space and are probably not narrow linear axes. In a supplementary experiment, we studied a completely different task: identifying textures from a distance. The dimensionality for this more refined task is similar to that for rating judgments, so our findings may have general application.

Mineralogia de solos com excesso de sódio no estado do Ceará

Foram estudados dois perfis de solos com problemas de sodicidade (Planossolo Solódico e Solonetz-Solodizado), no estado do Ceará, com o objetivo de conhecer a mineralogia das frações areia, silte e argila e os processos de alterações que ocorrem nos respectivos minerais. A areia e o silte grosso foram avaliados por microscopia de polarização e contraste de fase, enquanto o silte fino e a argila foram analisados por difração de raios-X. Utilizou-se, ainda, a microscopia eletrônica de varredura para obtenção de informações complementares sobre as transformações mineralógicas ocorridas nos horizontes dos dois perfis. Verificou-se que o Planossolo Solódico apresenta na fração argila quantidades mais ou menos equivalentes de caulinita e montmorilonita no horizonte 2Btn, o mesmo acontecendo com as proporções de caulinita e vermiculita no horizonte A. Nas outras frações, foram encontrados teores variáveis de quartzo, plagioclásios, hornblenda e biotita. Por sua vez, o Solonetz-Solodizado mostrou uma fração argila essencialmente caulinítica ao longo de todo o perfil e com quantidades variáveis de quartzo, feldspato e biotita nas outras frações. Em ambos os perfis, o enriquecimento de argila no Bt resultou essencialmente das alterações "In situ" dos minerais primários intemperizáveis contidos na rocha subjacente. A hipótese de alternância de processos de oxi-redução nos horizontes A e, ou, E, em razão da baixa permeabilidade do horizonte 2Btn, provocando um processo de ferrólise naqueles horizontes, é também uma alternativa de gênese que não pode ser descartada para explicar o alto contraste textural desses solos. O intemperismo da albita e de outros plagioclásios ricos em sódio, o clima semi-árido, e a drenagem impedida são os fatores condicionantes dos percentuais elevados de sódio, observados nos dois pedons. Também nos dois solos, os teores destoantes de quartzo, a geomorfologia da região e a presença de uma linha de pedras separando os horizontes A ou A + E do 2Btn revelam duplicidade de materiais originários.

Marenzio, Poland and the late polychoral sacred style

M ARENZIO's polychoral sacred music may be divided into two general types: one in which sonorities and the combining of textures play the dominant role; and another-more pointedly madrigalesque-in which characteristic rhythmic and melodic patterns serve to convey the textual meaning. The former type is more often associated with the presentation of full liturgical texts, such as the Magnificat, Te Deum and Mass, or hymns such as Ave maris stella and A solis ortus cardine; the latter tends to concentrate on a few verses (e.g. part of a psalm) that afford an opportunity to present a variety of pictorial images, as in the motets Exsurgat Deus, Deus venerunt gentes and Iniquos odio habui. The difference may be clarified by comparing a passage from a Magnificat with one from the motet Exsurgat Deus (see exx.1, 2). In ex.1 we observe an evenly flowing continuity, in which the vocal lines are uncomplicated and the texture reducible to simple chords. The two choirs divide a single text line and then join together to give emphasis to the word 'Abraham'. Text portrayal is achieved through a simple contrast of texture. Such a setting is perhaps more suited to larger numbers of performers and to the sounds of instruments to create interest. (Unfortunately we do not know how Marenzio used instruments.) In ex.2 the treatment is very different. The exhortation 'Exsurgat Deus' ('rise up, God') is transmitted through bold upward leaps, and the admonition 'dissipentur inimici' ('scatter [your] enemies') is depicted by short fragmented patterns. The focus is entirely on the individual lines and the images the singers invoke. This type of setting seems more