bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Filter Combination in Human Pattern Vision: Channel Interactions Revealed by Adaptation
Authors: Meese Tim S , Georgeson Mark A
Published: January 2007

Above threshold, two superimposed sinusoidal gratings of the same spatial frequency (eg 1 cycle deg−1), of equal moderate contrast (eg C1 = C2 = 6%), and with orientations of ±45°, usually look like a compound structure containing vertical and horizontal edges (ie a blurred checkerboard). These feature orientations are very different from the dominant filter orientations in a wavelet-type (eg simple-cell) transform of the stimulus, and so present a serious challenge to conventional models of orientation coding based on labelled linear filters. Previous experiments on perceived structure in static plaids have led to the view that the outputs of tuned spatial filters are combined in a stimulus-dependent way, before features such as edges are extracted. Here an adaptation paradigm was used to investigate the cross-channel interactions that appear to underlie the spatial-filter-combination process. Reported are two aftereffects of selective adaptation: (i) adaptation to a 1 cycle deg−1 plaid whose component orientations are intermediate to those in a 1 cycle deg−1 test plaid ‘breaks’ perceptual combination of the components in the test plaid; (ii) adapting to a 3 cycles deg−1 plaid whose component orientations match those in a 1 cycle deg−1 test plaid facilitates perceptual combination of the components in the test plaid. The results are taken as evidence that spatial channels remote from those most responsive to a test plaid play a crucial role in determining whether the test plaid segments or coheres perceptually.
Temporal-Contrast Discrimination and its Neural Correlates
Authors: Chen Yue , Bedell Harold E , Frishman Laura J
Published: January 2007

Reported differences in neuronal contrast processing between the parallel magnocellular (M) and parvocellular (P) visual pathways invite the hypothesis that contrast discrimination in the human visual system is more sensitive at low contrasts and less sensitive at high contrasts, for stimuli modulated at high compared with low temporal frequencies. In the present study, an edgeless temporally modulated uniform field was selected as the stimulus for psychophysical contrast discrimination, and contrast-increment thresholds for pedestal contrasts ranging from 5.5% to 78.2% were determined with a temporal two-alternative forced-choice staircase procedure. The increment thresholds for five normal subjects were adequately fit by power functions with exponents that shifted continuously from about 0.5 (square-root-law behavior) to about 1.0 (Weber's-law behavior) as stimulus temporal frequency increased from 1 to 30 Hz. A neural simulation, with the use of published contrast-response functions of magnocellular and parvocellular neurons, adjusted with an estimate of response variance, produced two distinct ‘neural increment-threshold functions’ that were similar to the psychophysical results obtained at the highest and the lowest temporal frequencies, respectively. A shift from a relatively more noise-limited neural mechanism to one whose response is predominantly determined by gain is suggested to account for the change of the contrast-increment-threshold function with increasing temporal frequency.
Evidence of a Global Oblique Effect in Human Extrafoveal Vision
Authors: Pointer Jonathan S
Published: January 2007

Analysis of recently published human contrast-sensitivity data obtained along the cardinal and major oblique visual-field meridians of a single subject has demonstrated a consistently greater sensitivity at a given eccentricity to horizontally oriented as compared with obliquely oriented gratings. This difference was evident not only at foveal but also at several eccentric loci over a range of low to medium spatial frequencies. This observation is to be distinguished in extrafoveal fixation from the well-documented oblique effect, which describes the variation in sensitivity with orientation at a single visual-field locus. With periodic stimuli which were well localised in space and frequency, and had comparable spatial-summation properties, a spatial-frequency dependency of what could be termed the global oblique effect could be demonstrated along isoeccentric contours centred on the fovea (eccentricity 0 deg) out to an eccentricity of at least 40 deg.
Suppressive Effect of Multimodal Surface Representation on Ocular Smooth Pursuit of Invisible Hand
Authors: Watanabe Katsumi , Shimojo Shinsuke
Published: January 2007

A human observer can smoothly pursue her/his own voluntarily moved hand with the eyes in total darkness. The effects of a perceived stationary surface during ocular pursuit of the invisible hand were investigated. The task was to track the invisible hand smoothly with the eyes in a Ganzfeld (experiment 1), with a stationary visual surface in the light (experiment 2), or with a solid stationary surface in total darkness (experiment 3). It was found that smooth pursuit of the invisible hand occurred in the Ganzfeld as well as in total darkness, but was replaced by frequent saccades when a stationary surface was perceived through either the visual or the tactile sense. The results obtained with a Ganzfeld suggest that light alone does not prevent smooth pursuit of the invisible hand, and those obtained with a stationary surface suggest that perception of such a surface prevents smooth pursuit of the invisible hand and evokes saccades, regardless of the sense modality.
Independent Processing across Spatial Frequency in Moving Broadband Patterns
Authors: Eagle Richard A
Published: January 2007

The aim of the experiments was to discover whether the visual system has independent access to motion information at different spatial scales when presented with a broadband stimulus. Subjects were required to discriminate between a pair of two-frame motion sequences, one containing a coherently displacing pattern and the other containing a pattern with high-frequency noise. The stimuli were either narrowband (1 octave) or broadband (6 octaves spanning 0.23–15.0 cycles deg−1) and their power spectra were either flat or followed a 1 /f2 function. For the broadband stimuli, noise was introduced cumulatively into increasingly lower frequencies. For the narrowband stimuli, noise was introduced into the same frequency band as the signal. All stimuli could be defined by the lowest noise frequency ( n1) they contained. For each stimulus, the largest spatial displacement across the two frames at which the task could be performed was measured ( dmax). For the narrowband stimuli, dmax increased as n1 was lowered. This was true over the entire frequency range for the 1 /f2 stimuli, though the task became impossible for the flat-spectrum stimuli at the lowest frequencies. This is attributed to the very low contrast of these latter stimuli. The dmax values for the broadband stimuli tended to shadow those of the narrowband stimuli with the equivalent values of n1 being around 25% lower. The data were modelled by spatiotemporally filtering the stimuli and considering the amount of directional power in the signal and noise sequences. The results suggest that there must be multiple spatial-frequency channels in operation, and that for broadband patterns the visual system has perceptual access to these individual channel outputs, utilising different filters depending on the task requirements.
Interactions of Spatial Frequency and Unequal Monocular Contrasts in Stereopsis
Authors: Cormack Lawrence K , Stevenson Scott B , Landers David D
Published: January 2007

Increasing the contrast of just one eye's image degrades stereothresholds; this phenomenon is referred to as the stereo contrast paradox. In experiment one, this paradox was found to be absent in dynamic random-element stereograms; thresholds were simply limited by the lower of the two eyes' contrasts. In experiment two, in which narrowband Gabor targets were used, the paradox was found to be strongest at relatively low spatial frequencies (1 cycle deg−1). As spatial frequency was increased, the paradox gradually disappeared. At relatively high spatial frequencies (5 cycles deg−1), thresholds were generally limited by the lower of the two eyes' contrasts, as was found for the dynamic noise targets. These results demonstrate the interactions of spatial frequency and contrast in binocular image combination and yield clues as to the different roles which high and low spatial frequencies may play in stereopsis.
Spatial Scale in Stereo and Shape from Shading: Image Input, Mechanisms, and Tasks
Authors: Mallot Hanspeter A
Published: January 2007

The problem of spatial scale in depth perception can be considered at three stages: image input, mechanisms, and depth descriptors specific for certain tasks. A review is presented of a number of earlier experiments supporting the distinction between a coarse, correlation-based mechanism and a feature-matching mechanism of stereopsis in terms of their respective inputs and outputs. In order to measure the influence of the correlation mechanism on the perception of three-dimensional shape, a shape-probe experiment was designed. For smooth intensity profiles with constant disparity, the results show that perceived shape is largely independent of overall disparity but does make use of shape from shading as well as the assumption that brighter parts are in front (proximity–luminance covariance).
Color from Motion: Dichoptic Activation and a Possible Role in Breaking Camouflage
Authors: Cicerone Carol M , Hoffman Donald D
Published: January 2007

‘Color from motion’ describes the perception of a spread of subjective color over achromatic regions seen as moving. The effect can be produced in a display of multiple frames shown in quick succession, each frame consisting of a fixed, random placement of colored dots on a high-luminance white background with color assignments of some dots, but not dot locations, changing from frame to frame. Evidence is presented that the perception of apparent motion and the spread of subjective color can be activated by binocular combination of disjoint signals to each eye. The dichoptic presentation of every odd-numbered frame of the full stimulus sequence presented to one eye and, out of phase, every even-numbered frame to the other eye produces a compelling perception of color from motion equal to that seen with the full sequence presented to each eye alone. This is consistent with the idea that color from motion is regulated in sites at or beyond the convergence of monocular pathways. When the background field in the stimulus display is of low luminance, an amodally complete object, fully colored and matching the dots defining the moving region in hue and saturation, is seen to move behind a partially occluding screen. Observers do not perceive such an object in still view. Hence, color from motion can be used by the visual system to produce amodal completion, which suggests that it may play a role in enhancing the visibility of camouflaged objects.
Paradoxical Rest
Authors: Gerbino Walter , Bruno Nicola
Published: January 2007

Paradoxical absence of motion in a rotating pattern is reported. The effect requires that the motion of the paradoxically stationary figure be underspecified by local motion signals, and that the paradoxically stationary figure be well segregated. This is consistent with proposals that figural segregation affects the integration of local motion signals.
The Effects of Visual Discomfort and Pattern Structure on Visual Search
Authors: Conlon Elizabeth , Lovegrove William , Hine Trevor , Chekaluk Eugene , Piatek Kerry , Hayes-Williams Kerry
Published: January 2007

Unpleasant somatic and perceptual side effects can be induced when viewing striped repetitive patterns, such as a square wave or a page of text. This sensitivity is greater in participants with higher scores on a scale of visual discomfort. In three experiments the effect that this sensitivity has on performance efficiency in a reading-like visual search task was investigated. In experiments 1 and 2, the ‘global’ structure of the patterns was manipulated to produce a square-wave, a checkerboard, and a plaid pattern. It was found that the group that suffered severe visual discomfort took significantly longer than other groups to perform the task, with interference greatest with presentation of the square-wave-like pattern. This supports the prediction of greatest distraction of visual attention from the local target elements with presentation of the pattern structure inducing greatest visual discomfort. In experiment 3, the internal pattern components were manipulated and task difficulty reduced. A no-interference and two interference patterns, one with a global characteristic only and the second made up of distracting line elements, containing global and local components were used. The global pattern structure produced interference effects on the visual-search task. All groups performed with the same speed and accuracy on the task involving the no-interference pattern, a finding attributed to reduced task difficulty McConkie and Zola's model of visual attention was used to explain these results.
Reproduction of Object Shape is More Accurate without the Continued Availability of Visual Information
Authors: Amorim Michel-Ange , Loomis Jack M , Fukusima Sergio S
Published: January 2007

An unfamiliar configuration lying in depth and viewed from a distance is typically seen as foreshortened. The hypothesis motivating this research was that a change in an observer's viewpoint even when the configuration is no longer visible induces an imaginal updating of the internal representation and thus reduces the degree of foreshortening. In experiment 1, observers attempted to reproduce configurations defined by three small glowing balls on a table 2 m distant under conditions of darkness following ‘viewpoint change’ instructions. In one condition, observers reproduced the continuously visible configuration using three other glowing balls on a nearer table while imagining standing at the distant table. In the other condition, observers viewed the configuration, it was then removed, and they walked in darkness to the far table and reproduced the configuration. Even though the observers received no additional information about the stimulus configuration in walking to the table, they were more accurate (less foreshortening) than in the other condition. In experiment 2, observers reproduced distant configurations on a nearer table more accurately when doing so from memory than when doing so while viewing the distant stimulus configuration. In experiment 3, observers performed both the real and imagined perspective change after memorizing the remote configuration. The results of the three experiments indicate that the continued visual presence of the target configuration impedes imaginary perspective-change performance and that an actual change in viewpoint does not increase reproduction accuracy substantially over that obtained with an imagined change in viewpoint.
The Perception of Scale-Dependent and Scale-Independent Surface Structure from Binocular Disparity, Texture, and Shading
Authors: Tittle James S , Norman J Farley , Perotti Victor J , Phillips Flip
Published: January 2007

The integration of binocular disparity, shading, and texture was measured for two different aspects of three-dimensional structure: (1) shape index, which is a measure of scale-independent structure, and (2) curvedness, which is a measure of scale-dependent structure. Binocular disparity was found to contribute significantly more to judged shape index than it does to judged curvedness, and shading and texture were both found to contribute more to judged curvedness than to judged shape index. These results demonstrate that different cues do not contribute equally to different aspects of perceived surface structure. This finding suggests that, for the case of linear integration, multiple cues to three-dimensional structure do not combine on the basis of a single type of representation shared by all the ‘shape-from-X’ processes in the visual system.
The Influence of Feature-Based Information in the Age Processing of Unfamiliar Faces
Authors: George Patricia A , Hole Graham J
Published: January 2007

The influence of the internal features (eyes, nose, and mouth) in the age processing of unfamiliar faces was examined. Younger and older versions of the faces of six individuals (covering three different age ranges, from infancy to maturity) were used as donor stimuli. For each individual in turn, the effects on age estimates of placing older features in the younger face version (or vice versa) were investigated. Age estimates were heavily influenced by the age of the internal facial features. Experiment 2 replicated these effects with a larger number of faces within a narrower age range (after growth is complete and before major skin changes have occurred). Taken together, these two experiments show that the internal facial features may be influential in conveying age information to the perceiver. However, the mechanisms by which features exert their influence remain difficult to determine: although age estimates might be based on local information from the features themselves, an alternative possibility is that featural changes indirectly influence age estimates by altering the global three-dimensional shape of the head.
Young Infants' Perception of Illusory Contours in Dynamic Displays
Authors: Johnson Scott P , Aslin Richard N
Published: January 2007

Ninety-six 4-month-old infants were habituated to one of three computer-generated displays depicting two rod parts above and below an occluding box. In the first display, the surfaces and boundaries of the rod and box were specified by dense surface texture. Their depth segregation was specified by accretion and deletion of background texture and motion shear. In the second display, the unity of the rod parts and box, and their depth segregation, were specified only by illusory contours. In the third display, the boundaries of the rod and box were specified by illusory contours, perceptible only via spatiotemporal integration of accretion and deletion of sparse-background-texture elements. Infants appeared to perceive object unity, and segregate the rod and box surfaces, in all three displays, indicating use of illusory contours to perceive bounded surfaces in depth. The results suggest a cognitive contribution to perception of some illusory contours, abilities which seem to be present by at least 4 months of age.
Linear-Vection Chronometry along Spinal and Sagittal Axes in Erect Man
Authors: Giannopulu Irini , Lepecq Jean-Claude
Published: January 2007

The present study investigates the onset latencies for linear vection along both the spinal and the sagittal axis in erect human adults. For each axis, both directions have been investigated (upward vs downward, forward vs backward). The vection-onset latency is thought to be shortened by the decrease of the conflict between visual and vestibular afferents. Since this sensory conflict can be presumed to be more important in the horizontal sagittal axis than in the vertical spinal one, the vection-onset latencies have been hypothesised to be longer in the former case than in the latter. Additionally, since the magnitude of this sensory conflict can be presumed to be the same between the two opposite directions within each axis, the vection-onset latencies have been expected not to vary between directions within each axis. The results confirm both these hypotheses.
The Dynamic Specification of Surfaces and Boundaries
Authors: Cunningham Douglas W , Shipley Thomas F , Kellman Philip J
Published: January 2007

Sequential changes in small separated texture elements can produce perception of a moving form with continuous boundaries. This process of spatiotemporal boundary formation may exist to provide a robust means of detecting moving objects that occlude more distant textured surfaces. Whereas most research on spatiotemporal boundary formation has been focused on boundary and shape perception, two experiments are reported here on the perception of surface qualities in spatiotemporal boundary formation. In experiment 1 a free-report procedure was used to investigate whether surface perception can be determined by dynamic information alone, apart from static spatial differences. Results showed that dynamic information was sufficient to determine the appearance of a surface. This dynamic information may play an important role in other aspects of perception. In experiment 2, it was shown that dynamically specifying an extended, opaque surface facilitated edge perception. Implications for the relation of boundary and surface perception and for theories of perceptual transparency are discussed.
Test of a Convergence Model for Color Transparency Perception
Authors: Chen Vincent J , D'Zmura Michael
Published: January 2007

Models of color transparency suggest that a region in which colors of surfaces converge in color space will appear transparent. The convergence is described by a transparency parameter a and a target of convergence. To test such models psychophysically, observers were presented a display with four colored areas. The colors of three of the areas were chosen in advance by the experimenter. The task of the observer was to choose the color of the fourth area to make a central region appear transparent. Settings for the fourth color were collected for a total of twenty-four color combinations chosen from three planes in color space. Observers' settings agreed well with the model, which predicts that choices for the fourth color lie along a line segment in color space that is parameterized by a. The results suggest further that color discriminability and color opponency also influence transparency judgment.
Rigid Objects That Appear to Bend
Authors: Griffiths A Fuzz , Zaidi Qasim
Published: January 2007

Simple rigid objects are presented that appear to bend when viewed from certain angles. These illusions illustrate that perspective information is used by the stereo system, that projective distortions can override rigidity constraints in motion perception, and that touch only corrects the illusion for a local region.
Hens Use Occlusion to Judge Depth in a Two-Dimensional Picture
Authors: Forkman Björn
Published: January 2007

Hens ( Gallus gallus domesticus) were taught to peck at a touch screen. On the screen was a grid on which a square and a circle were depicted. The square and the circle were given different positions at random for each trial, but were never overlapping. The hens were rewarded for pecking at the symbol that was higher up on the grid/screen, ie at the one that to a human observer was seen as being further away. Every tenth trial was a probe trial in which the animals were presented with either the circle overlapping the square or vice versa. The hens were never rewarded during the probe trials. As mentioned, the hens had learned to peck at the symbol that appeared to be further away during the nonprobe trials. During the probe trials the hens pecked at the symbol that was occluded, ie in the absence of any other cues they used occlusion to determine which of the two symbols was further away. The results suggest that not only can nonhuman animals use image height as a cue but that they can generalise this to situations in which occlusion is the only depth cue present.
Single Units and Visual Cortical Organization
Authors: Lennie Peter
Published: January 2007

The visual system has a parallel and hierarchical organization, evident at every stage from the retina onwards. Although the general benefits of parallel and hierarchical organization in the visual system are easily understood, it has not been easy to discern the function of the visual cortical modules. I explore the view that striate cortex segregates information about different attributes of the image, and dispatches it for analysis to different extrastriate areas. I argue that visual cortex does not undertake multiple relatively independent analyses of the image from which it assembles a unified representation that can be interrogated about the what and where of the world. Instead, occipital cortex is organized so that perceptually relevant information can be recovered at every level in the hierarchy, that information used in making decisions at one level is not passed on to the next level, and, with one rather special exception (area MT), through all stages of analysis all dimensions of the image remain intimately coupled in a retinotopic map. I then offer some explicit suggestions about the analyses undertaken by visual areas in occipital cortex, and conclude by examining some objections to the proposals.
Facial Aging, Attractiveness, and Distinctiveness
Authors: Deffenbacher Kenneth A , Vetter Thomas , Johanson John , O'Toole Alice J
Published: January 2007

A standard facial caricature algorithm has been applied to a three-dimensional (3-D) representation of human heads, those of Caucasian male and female young adults. Observers viewed unfamiliar faces at four levels of caricature—anticaricature, veridical, moderate caricature, and extreme caricature—and made ratings of attractiveness and distinctiveness (experiment 1) or learned to identify them (experiment 2). There were linear increases in perceived distinctiveness and linear decreases in perceived attractiveness as the degree of facial caricature (Euclidean distance from the average face in 3-D-grounded face space) increased. Observers learned to identify faces presented at either level of positive caricature more efficiently than they did with either uncaricatured or anticaricatured faces. Using the same faces, 3-D representation, and caricature levels, O'Toole, Vetter, Volz, and Salter (1997, Perception 26 719–732) had shown a linear increase in judgments of face age as a function of degree of caricature. Here it is concluded that older-appearing faces are less attractive, but more distinctive and memorable than younger-appearing faces, those closer to the average face.
Early Demonstrations of Subjective Contours, Amodal Completion, and Depth from Half-Occlusions: “Stereoscopic Experiments with Silhouettes” by Adolf von Szily (1921)
Authors: Ehrenstein Walter H , Gillam Barbara J
Published: January 2007

If all-black figures are used, certain monocular appendages to binocular shapes are seen in depth, either nearer (when in a medial position) or further (when in a lateral position) than the binocular shape itself. These appendages also link to form subjective contours in front of the binocular shape or amodal completions behind it. These and other discoveries by von Szily, made before 1921, anticipate a number of modern findings.
The Position of Moving Objects
Authors: Lappe Markus , Krekelberg Bart
Published: January 2007

Moving objects occupy a range of positions during the period of integration of the visual system. Nevertheless, a unique position is usually observed. We investigate how the trajectory of a stimulus influences the position at which the object is seen. It has been shown before that moving objects are perceived ahead of static objects shown at the same place and time. We show here that this perceived position difference builds up over the first 500 ms of a visible trajectory. Discontinuities in the visual input reduce this buildup when the presentation frequency of a stimulus with a duration of 42 ms falls below 16 Hz. We interpret this relative mislocalisation in terms of a spatiotemporal-filtering model. This model fits well with the data, given two assumptions. First, the position signal persists even though the objects are no longer visible and, second, the perceived distance is a 500 ms average of the difference of these position signals.
Does Visual Perspective Matter in Imitation?
Authors: Sambrook Thomas D
Published: January 2007

Theories purporting to explain the cognitive processes underlying imitation and its taxonomic distribution have proliferated in recent years but a common assumption is that imitators must adopt a model's mental or visual perspective. Data on thirty-six adult subjects were used to test the hypothesis that imitative learning of knots would suffer a decrement proportional to the disparity of visual perspectives on the task that the subject held between observation and performance. There was no significant effect of visual perspective on performance, nor was there a trend in the predicted direction. This was in spite of significant preferences on the part of subjects for minimising the angle of disparity, assessed both by their behaviour and introspective report. The cognitive basis for human imitation is discussed in the light of these findings.
Cone Contributions to Colour Constancy
Authors: Rinner Oliver , Gegenfurtner Karl R
Published: January 2007

Colour constancy refers to the stable perception of object colour under changing illumination conditions. This problem has been reformulated as relational colour constancy, or the ability of the observer to discriminate between material changes and changes in illumination. It has been suggested that local cone excitation ratios play a prominent role in achieving such constancy. Here we show that perceptual colour constancy measured by achromatic adjustments is to a large part complete after 25 ms. This speaks against a prominent role for receptor adaptation, which takes significantly longer. We also found no difference in colour constancy between colour changes that were compatible with a change of illuminant, and between colour changes where local cone ratios were uncorrelated between the two illuminants. Our results show that constant cone ratios are not necessary for colour constancy.
Revision: Is Visual Perception a Requisite for Visual Imagery?
Authors: Kaski Diego
Published: January 2007

Vision is the most highly developed sense in man and represents the doorway through which most of our knowledge of the external world arises. Visual imagery can be defined as the representation of perceptual information in the absence of visual input. Visual imagery has been shown to complement vision in this acquisition of knowledge—it is used in memory retrieval, problem solving, and the recognition of properties of objects. The processes underlying visual imagery have been assimilated to those of the visual system and are believed to share a neural substrate. However, results from studies in congenitally and cortically blind subjects have opposed this hypothesis. Here I review the currently available evidence.
Coolamon subterranean clover (Trifolium subterraneum L. var. subterraneum)
Authors: Nichols P. G. H. , Barbetti M. J. , Sandral G. A. , Dear B. S. , de Koning C. T. , Lloyd D. L. , Evans P. M. , Craig A. D. , Si P. , You M. P.
Published: January 2007

Coolamon is a mid-season to late-season flowering F4-derived crossbred subterranean clover of var. subterraneum, developed by the collaborating organisations of the National Annual Pasture Legume Improvement Program. It is a replacement for Junee and has been selected for release on the basis of its greater herbage production and persistence, and its resistance to both known races of clover scorch. Coolamon is recommended for sowing in Western Australia, New South Wales, Victoria, South Australia and Queensland. It is best suited to well-drained, moderately acidic soils in areas with a growing season of 6.5–8 months that extends into November. Coolamon is best suited to phase farming and permanent pasture systems. It can also be used in cropping rotations, but at least 2 years of pasture are required between crops. Coolamon has been granted Plant Breeders Rights in Australia.
Izmir subterranean clover (Trifolium subterraneum L. var. subterraneum)
Authors: Nichols P. G. H. , Sandral G. A. , Dear B. S. , de Koning C. T. , Lloyd D. L. , Evans P. M. , Craig A. D. , Nutt B. J. , Barbetti M. J. , Si P. , You M. P.
Published: January 2007

Izmir is a hardseeded, early flowering, subterranean clover of var. subterraneum (Katz. et Morley) Zohary and Heller collected from Turkey and developed by the collaborating organisations of the National Annual Pasture Legume Improvement Program. It is a more hardseeded replacement for Nungarin and best suited to well-drained, moderately acidic soils in areas with a growing season of less than 4.5 months. Izmir seed production and regeneration densities in 3-year pasture phases were similar to Nungarin in 21 trials across southern Australia, but markedly greater in years following a crop or no seed set. Over all measurements, Izmir produced 10% more winter herbage and 7% more spring herbage than Nungarin. Its greater hardseededness and good seed production, makes it better suited to cropping rotations than Nungarin. Softening of Izmir hard seeds occurs later in the summer–autumn period than Nungarin, giving it slightly greater protection from seed losses following false breaks to the season. Izmir is recommended for sowing in Western Australia, New South Wales, Victoria, South Australia and Queensland. Izmir has been granted Plant Breeders Rights in Australia.
Electrolyte supplementation of live export cattle to the Middle East
Authors: Beatty D. T. , Barnes A. , Taplin R. , McCarthy M. , Maloney S. K.
Published: January 2007

Eighty Bos taurus crossbred steers sourced from southern Western Australia were monitored to assess the efficacy of electrolyte supplementation on board a livestock vessel travelling to the Middle East during the northern hemisphere summer. Electrolytes (1.8 g/L NaHCO3 and 3.5 g/L KCl) were added to the drinking water of treatment steers (n = 39) allocated to three pens on the starboard side of the ship. Control steers (n = 40) were allocated to three pens on the port side of the ship. The combined area of the three treatment and three control pens was 61.1 and 63.6 m2 respectively, giving a stocking density of 1.57 and 1.55 m2 per steer, respectively. Steers were loaded in Fremantle, Western Australia and given 3 days to acclimatise to on-board conditions before being weighed (day 1), after which electrolyte supplementation began while the vessel docked at Port Headland, Western Australia. Feed and water were available ad libitum throughout the experiment. Steers were weighed again on day 18, before discharge in the Middle East. During electrolyte supplementation, wet bulb temperature ranged from 21.3 (day 2) to 31.8°C (day 18). Over the last 3 days of the experiment, wet bulb temperature ranged from 29.0 to 31.8°C with no diurnal variation or night-time cooling. No open-mouth panting was recorded in either group and although animals encountered periods of high heat and humidity (as indicated by increased respiratory rates), the steers were not considered clinically heat stressed during the experiment. After 18 days of electrolyte supplementation, treatment steers had a 2.9 ± 1.7% liveweight advantage compared with control steers (P < 0.001). Urine was collected on days 8 and 16 of the experiment and treatment steers maintained a higher urine pH compared with control steers on both days (day 8; 8.6 v. 8.2 and day 16; 8.2 v. 7.9; P < 0.01). Liveweight advantages and improved regulation of acid–base balance may provide welfare and economic benefits to the live export industry.
Unraveling the three-metal-ion catalytic mechanism of the DNA repair enzyme endonuclease IV
Authors: Ivanov Ivaylo , Tainer John A. , McCammon J. Andrew
Published: January 2007

Endonuclease IV belongs to a class of important apurinic/apyrimidinic endonucleases involved in DNA repair. Although a structure-based mechanistic hypothesis has been put forth for this enzyme, the detailed catalytic mechanism has remained unknown. Using thermodynamic integration in the context ofab initioquantum mechanics/molecular mechanics molecular dynamics, we examined certain aspects of the phosphodiester cleavage step in the mechanism. We found the reaction proceeded through a synchronous bimolecular (ANDN) mechanism with reaction free energy and barrier of −3.5 and 20.6 kcal/mol, in agreement with experimental estimates. In the course of the reaction the trinuclear active site of endonuclease IV underwent dramatic local conformational changes: shifts in the mode of coordination of both substrate and first-shell ligands. This qualitative finding supports the notion that structural rearrangements in the active sites of multinuclear enzymes are integral to biological function.
Chromosome-wide linkage disequilibrium as a consequence of meiotic drive
Authors: Dyer Kelly A. , Charlesworth Brian , Jaenike John
Published: January 2007

Adaptation by natural selection proceeds most efficiently when alleles compete solely on the basis of their effects on the survival and reproduction of their carriers. A major condition for this is equal Mendelian segregation, but meiotic drive can short-circuit this process. The evolution of drive often involves multiple, interacting genetic components, together with enhancers and suppressors of drive. Chromosomal inversions that suppress crossing over are also frequently associated with drive systems. This study investigates the effects of these processes on patterns of molecular evolution in the flyDrosophila recens, which is polymorphic for a driving X chromosome (XD). Whereas standard wild-type chromosomes exhibit high levels of polymorphism at multiple loci, all of the XDchromosomes effectively carry a single multilocus haplotype that spans at least 130 cM. The XDis associated with a complex set of inversions that completely suppresses recombination between the standard wild-type chromosome and XDin heterozygous females, which maintain nonrandom associations among loci that presumably interact epistatically for the expression of drive. The long-term costs of foregoing recombination may be substantial; in combination with its low equilibrium frequency, this makes the XDchromosome susceptible to the accumulation of deleterious mutations. Consistent with this, XDchromosomes are apparently fixed for a recessive mutation that causes female sterility. Thus, the XDinD. recensappears to be in chromosome-wide linkage disequilibrium and in the early stages of mutational degradation.
Ligand configurational entropy and protein binding
Authors: Chang Chia-en A. , Chen Wei , Gilson Michael K.
Published: January 2007

The restriction of a small molecule's motion on binding to a protein causes a loss of configurational entropy, and thus a penalty in binding affinity. Some energy models used in computer-aided ligand design neglect this entropic penalty, whereas others account for it based on an expected drop in the number of accessible rotamers upon binding. However, the validity of the physical assumptions underlying the various approaches is largely unexamined. The present study addresses this issue by using Mining Minima calculations to analyze the association of amprenavir with HIV protease. The computed loss in ligand configurational entropy is large, contributing ∼25 kcal/mol (4.184 kJ/kcal) to Δ
G
°. Most of this loss results from narrower energy wells in the bound state, rather than a drop in the number of accessible rotamers. Coupling among rotation/translation and internal degrees of freedom complicates the decomposition of the entropy change into additive terms. The results highlight the potential to gain affinity by designing conformationally restricted ligands and have implications for the formulation of energy models for ligand scoring.
The specialized cytosolic J-protein, Jjj1, functions in 60S ribosomal subunit biogenesis
Authors: Meyer Alison E. , Hung Nai-Jung , Yang Peizhen , Johnson Arlen W. , Craig Elizabeth A.
Published: January 2007

J-proteins and Hsp70 chaperones function together in diverse cellular processes. We identified a cytosolic J-protein, Jjj1, of
Saccharomyces cerevisiae
that is associated with 60S ribosomal particles. Unlike Zuo1, a 60S subunit-associated J-protein that is a component of the chaperone machinery that binds nascent polypeptide chains upon their exit from the ribosome, Jjj1 plays a role in ribosome biogenesis. Cells lacking Jjj1 have phenotypes very similar to those lacking Rei1, a ribosome biogenesis factor associated with pre-60S ribosomal particles in the cytosol. Jjj1 stimulated the ATPase activity of the general cytosolic Hsp70 Ssa, but not Ssb, Zuo1's ribosome-associated Hsp70 partner. Overexpression of Jjj1, which is normally ≈40-fold less abundant than Zuo1, can partially rescue the phenotypes of cells lacking Zuo1 as well as cells lacking Ssb. Together, these results are consistent with the idea that Jjj1 normally functions with Ssa in a late, cytosolic step of the biogenesis of 60S ribosomal subunits. In addition, because of its ability to bind 60S subunits, we hypothesize that Jjj1, when overexpressed, is able to partially substitute for the Zuo1:Ssb chaperone machinery by recruiting Ssa to the ribosome, facilitating its interaction with nascent polypeptide chains.
Imaging synaptosomal calcium concentration microdomains and vesicle fusion by using total internal reflection fluorescent microscopy
Authors: Serulle Yafell , Sugimori Mutsuyuki , Llinás Rodolfo R.
Published: January 2007

Transmitter release at chemical synapses is triggered by high calcium concentration microprofiles at the presynaptic cytosol. Such microprofiles, generated by the opening of voltage-dependent calcium channels at the presynaptic plasma membrane, have been defined as calcium concentration microdomains. Using total internal reflection fluorescent microscopy in conjunction with calcium and vesicular release indicator dyes, we have directly visualized the close apposition of calcium concentration microdomains and synaptic release sites at single synaptic terminals from the CNS from rat cerebellar mossy fiber and squid optic lobe. These findings demonstrate the close apposition of calcium entry and release sites and the dynamics of such site locations over time. Kinetic analysis shows that vesicles can be released via two distinct mechanisms: full-fusion and kiss-and-run. Calcium triggers vesicular motion toward the membrane, and the speed of such movement is calcium concentration-dependent. Moreover, the immediately available vesicular pool represents molecularly trapped vesicles that can be located at a larger distance from the plasma membrane than the field illuminated by total internal reflection fluorescent microscopy.
‘Streptococcus milleri’ aortic valve endocarditis and hepatic abscess
Authors: Rashid Rashid M. , Salah Wajeeh , Parada Jorge P.
Published: January 2007

Although well-recognized animal pathogens, group C streptococci are relatively rare causes of human infection. The phenotypically small-colony group C ‘Streptococcus milleri’ are typically associated with suppurative disease of soft tissue and organs, including liver abscesses, while bacteraemia and endocarditis are distinctly less common. Herein, a case of ‘S. milleri’ causing both endocarditis and liver abscess in the same patient is reported.
Characterization of the genetic background of Vibrio cholerae O1 biotype El Tor serotype Inaba strains isolated in Trivandrum, southern India
Authors: Mohapatra Saswat S. , Ramachandran Dhanya , Mantri Chinmay K. , Singh Durg V.
Published: January 2007

Isolates of Vibrio cholerae O1 biotype El Tor serotype Inaba associated with an outbreak of cholera in Trivandrum, southern India, were characterized. PCR testing revealed that all five isolates examined carried the TCP pathogenicity island, the CTX genetic element and the RTX toxin, and produced cholera toxin (CT). RFLP analysis revealed that these Inaba isolates possessed a single copy of the CTX element flanked by two tandemly arranged copies of the RS element upstream of the core region. The isolates were resistant to ampicillin, nalidixic acid, trimethoprim, sulfamethoxazole, streptomycin and the vibriostatic agent 2,4-diamino-6,7-diisopropylpteridine (O/129). Ribotyping of these Inaba isolates revealed a hybridization profile similar to a strain of serotype Ogawa prevalent in southern India.
Heme binding inhibits the fibrillization of amyloidogenic apomyoglobin and determines lack of aggregate cytotoxicity
Authors: Iannuzzi Clara , Vilasi Silvia , Portaccio Marianna , Irace Gaetano , Sirangelo Ivana
Published: January 2007

Myoglobin is an α‐helical globular protein containing two highly conserved tryptophanyl residues at positions 7 and 14 in the N‐terminal region. The double W/F replacement renders apomyoglobin highly susceptible to aggregation and amyloid‐like fibril formation under physiological conditions. In this work we analyze the early stage of W7FW14F apomyoglobin aggregation following the time dependence of the process by far‐UV CD, Fourier‐transform infrared (FTIR) spectroscopy, and heme‐binding properties. The results show that the aggregation of W7FW14F apomyoglobin starts from a native‐like globin state able to bind the prosthetic group with spectroscopic properties similar to those observed for wild‐type apoprotein. Nevertheless, it rapidly aggregates, forming amyloid fibrils. However, when the prosthetic group is added before the beginning of aggregation, amyloid fibrillization is inhibited, although the aggregation process is not prevented. Moreover, the apomyoglobin aggregates formed in these conditions are not cytotoxic differently from what is observed for all amyloidogenic proteins. These results open new insights into the relationship between the structure adopted by the protein into the aggregates and their ability to trigger the impairment of cell viability.
Symptoms of asthma and atopic disorders in preschool children: prevalence and risk factors
Authors: Wong G. W. K. , Leung T. F. , Ma Y. , Liu E. K. H. , Yung E. , Lai C. K. W.
Published: January 2007

Background
Published epidemiological data suggested that asthma and allergies may be increasing in preschool children. Identification of the risk factors is important for planning possible early intervention to prevent asthma. This study was designed to measure the prevalence of, and risk factors for, asthma and atopic disorders in preschool children from Hong Kong.

Methods
Children aged 2–6 years living in Hong Kong were recruited through the local nurseries and kindergartens for this study to ascertain the presence of symptoms of asthma and various possible risk factors. The parental questionnaire was developed based on the International Study of Asthma and Allergies in Childhood questionnaire.

Results
A total of 3089 children (1506 boys) from 14 nurseries and kindergartens participated in this study. The prevalence of wheeze ever and current wheeze were 16.7% and 9.3%. Two hundred and thirty‐four subjects were born in mainland China and migrated to Hong Kong subsequently. When compared with children born and raised in Hong Kong, children born in mainland China had significantly lower prevalence of current wheeze (3.4% vs. 9.6%, P<0.01). Two environmental factors in the first year of life were associated with wheezing attacks within the last 12 months. They were the use of foam pillow (Odds ratio: 1.45; 95% Confidence interval: 1.04–2.00) and the use of gas as cooking fuel (1.68; 1.03–2.75). Frequent use of paracetamol was also associated with wheezing attack in the past 12 months.

Conclusions
This study confirms the high prevalence of symptoms of atopic disorders in preschool children from Hong Kong. Early environmental exposure factors are important determinants of subsequent development of asthma symptoms in the preschool years. Further studies are needed to evaluate the possible pathogenetic role of the identified risk factors.