Disparity with respect to a local reference plane as a dominant cue for stereoscopic depth relief

Earlier studies showed that the disparity with respect to other visible points could not explain stereoacuity performance, nor could various spatial derivatives of disparity [Glennerster, A., McKee, S. P., & Birch, M. D. (2002). Evidence of surface-based processing of binocular disparity. Current Biology, 12:825-828; Petrov, Y., & Glennerster, A. (2004). The role of the local reference in stereoscopic detection of depth relief. Vision Research, 44:367-376.] Two possible cues remain: (i) local changes in disparity gradient or (ii) disparity with respect to an interpolated line drawn through the reference points. Here, we aimed to distinguish between these two cues. Subjects judged.. in a two AFC paradigm, whether a target dot was in front of a plane defined by three reference dots or, in other experiments, in front of a line defined by two reference dots. We tested different slants of the reference line or plane and different locations of the target relative to the reference points. For slanted reference lines or plane, stereoacuity changed little as the target position was varied. For judgments relative to a frontoparallel reference line, stereoacuity did vary with target position, but less than would be predicted by disparity gradient change. This provides evidence that disparity with respect to the reference plane is an important cue. We discuss the potential advantages of this measure in generating a representation of surface relief that is invariant to viewpoint transformations. (c) 2006 Elsevier Ltd. All rights reserved.

Receding and disparity cues aid relaxation of accommodation

Purpose. Accommodation can mask hyperopia and reduce the accuracy of non-cycloplegic refraction. It is, therefore, important to minimize accommodation to obtain a measure of hyperopia as accurate as possible. To characterize the parameters required to measure the maximally hyperopic error using photorefraction, we used different target types and distances to determine which target was most likely to maximally relax accommodation and thus more accurately detect hyperopia in an individual. Methods. A PlusoptiX SO4 infra-red photorefractor was mounted in a remote haploscope which presented the targets. All participants were tested with targets at four fixation distances between 0.3 and 2 m containing all combinations of blur, disparity, and proximity/looming cues. Thirty-eight infants (6 to 44 weeks) were studied longitudinally, and 104 children [4 to 15 years (mean 6.4)] and 85 adults, with a range of refractive errors and binocular vision status, were tested once. Cycloplegic refraction data were available for a sub-set of 59 participants spread across the age range. Results. The maximally hyperopic refraction (MHR) found at any time in the session was most frequently found when fixating the most distant targets and those containing disparity and dynamic proximity/looming cues. Presence or absence of blur was less significant, and targets in which only single cues to depth were present were also less likely to produce MHR. MHR correlated closely with cycloplegic refraction (r = 0.93, mean difference 0.07 D, p = n.s., 95% confidence interval +/-<0.25 D) after correction by a calibration factor. Conclusions. Maximum relaxation of accommodation occurred for binocular targets receding into the distance. Proximal and disparity cues aid relaxation of accommodation to a greater extent than blur, and thus non-cycloplegic refraction targets should incorporate these cues. This is especially important in screening contexts with a brief opportunity to test for significant hyperopia. MHR in our laboratory was found to be a reliable estimation of cycloplegic refraction. (Optom Vis Sci 2009;86:1276-1286)

Developmental changes in the balance of disparity, blur and looming/proximity cues to drive ocular alignment and focus

Accurate co-ordination of accommodation and convergence is necessary to view near objects and develop fine motor co-ordination. We used a remote haploscopic videorefraction paradigm to measure longitudinal changes in simultaneous ocular accommodation and vergence to targets at different depths, and to all combinations of blur, binocular disparity, and change-in-size (“proximity”) cues. Infants were followed longitudinally and compared to older children and young adults, with the prediction that sensitivity to different cues would change during development. Mean infant responses to the most naturalistic condition were similar to those of adults from 6-7 weeks (accommodation) and 8-9 weeks (vergence). Proximity cues influenced responses most in infants less than 14 weeks of age, but sensitivity declined thereafter. Between 12-28 weeks of age infants were equally responsive to all three cues, while in older children and adults manipulation of disparity resulted in the greatest changes in response. Despite rapid development of visual acuity (thus increasing availability of blur cues), responses to blur were stable throughout development. Our results suggest that during much of infancy, vergence and accommodation responses are not dependent on the development of specific depth cues, but make use of any cues available to drive appropriate changes in response.

Disparity-driven vs blur-driven models of accommodation and convergence in binocular vision and intermittent strabismus

Background. Current models of concomitant, intermittent strabismus, heterophoria, convergence and accommodation anomalies are either theoretically complex or incomplete. We propose an alternative and more practical way to conceptualize clinical patterns. Methods. In each of three hypothetical scenarios (normal; high AC/A and low CA/C ratios; low AC/A and high CA/C ratios) there can be a disparity-biased or blur-biased “style”, despite identical ratios. We calculated a disparity bias index (DBI) to reflect these biases. We suggest how clinical patterns fit these scenarios and provide early objective data from small illustrative clinical groups. Results. Normal adults and children showed disparity bias (adult DBI 0.43 (95%CI 0.50-0.36), child DBI 0.20 (95%CI 0.31-0.07) (p=0.001). Accommodative esotropes showed less disparity-bias (DBI 0.03). In the high AC/A and low CA/C scenario, early presbyopes had mean DBI of 0.17 (95%CI 0.28-0.06), compared to DBI of -0.31 in convergence excess esotropes. In the low AC/A and high CA/C scenario near exotropes had mean DBI of 0.27, while we predict that non-strabismic, non-amblyopic hyperopes with good vision without spectacles will show lower DBIs. Disparity bias ranged between 1.25 and -1.67. Conclusions. Establishing disparity or blur bias, together with knowing whether convergence to target demand exceeds accommodation or vice versa explains clinical patterns more effectively than AC/A and CA/C ratios alone. Excessive bias or inflexibility in near-cue use increases risk of clinical problems. We suggest clinicians look carefully at details of accommodation and convergence changes induced by lenses, dissociation and prisms and use these to plan treatment in relation to the model.

Disparity-defined objects moving in depth do not elicit three-dimensional shape constancy

Observers generally fail to recover three-dimensional shape accurately from binocular disparity. Typically, depth is overestimated at near distances and underestimated at far distances [Johnston, E. B. (1991). Systematic distortions of shape from stereopsis. Vision Research, 31, 1351–1360]. A simple prediction from this is that disparity-defined objects should appear to expand in depth when moving towards the observer, and compress in depth when moving away. However, additional information is provided when an object moves from which 3D Euclidean shape can be recovered, be this through the addition of structure from motion information [Richards, W. (1985). Structure from stereo and motion. Journal of the Optical Society of America A, 2, 343–349], or the use of non-generic strategies [Todd, J. T., & Norman, J. F. (2003). The visual perception of 3-D shape from multiple cues: Are observers capable of perceiving metric structure? Perception and Psychophysics, 65, 31–47]. Here, we investigated shape constancy for objects moving in depth. We found that to be perceived as constant in shape, objects needed to contract in depth when moving toward the observer, and expand in depth when moving away, countering the effects of incorrect distance scaling (Johnston, 1991). This is a striking example of the failure of shape con- stancy, but one that is predicted if observers neither accurately estimate object distance in order to recover Euclidean shape, nor are able to base their responses on a simpler processing strategy.

Latitude and longitude vertical disparities

The literature on vertical disparity is complicated by the fact that several different definitions of the term “vertical disparity” are in common use, often without a clear statement about which is intended or a widespread appreciation of the properties of the different definitions. Here, we examine two definitions of retinal vertical disparity: elevation-latitude and elevation-longitude disparities. Near the fixation point, these definitions become equivalent, but in general, they have quite different dependences on object distance and binocular eye posture, which have not previously been spelt out. We present analytical approximations for each type of vertical disparity, valid for more general conditions than previous derivations in the literature: we do not restrict ourselves to objects near the fixation point or near the plane of regard, and we allow for non-zero torsion, cyclovergence, and vertical misalignments of the eyes. We use these expressions to derive estimates of the latitude and longitude vertical disparities expected at each point in the visual field, averaged over all natural viewing. Finally, we present analytical expressions showing how binocular eye position—gaze direction, convergence, torsion, cyclovergence, and vertical misalignment—can be derived from the vertical disparity field and its derivatives at the fovea.

Differences between naïve and expert observers’ vergence and accommodative responses to a range of targets

Purpose: Vergence and accommodation studies often use adult participants with experience of vision science. Reports of infant and clinical responses are generally more variable and of lower gain, with the implication that differences lie in immaturity or sub-optimal clinical characteristics but expert/naïve differences are rarely considered or quantified. Methods: Sixteen undergraduates, naïve to vision science, were individually matched by age, visual acuity, refractive error, heterophoria, stereoacuity and near point of accommodation to second- and third-year orthoptics and optometry undergraduates (‘experts’). Accommodation and vergence responses were assessed to targets moving between 33 cm, 50 cm, 1 m and 2 m using a haploscopic device incorporating a PlusoptiX SO4 autorefractor. Disparity, blur and looming cues were separately available or minimised in all combinations. Instruction set was minimal. Results: In all cases, vergence and accommodation response slopes (gain) were steeper and closer to 1.0 in the expert group (p = 0.001), with the largest expert/naïve differences for both vergence and accommodation being for near targets (p = 0.012). For vergence, the differences between expert and naïve response slopes increased with increasingly open-loop targets (linear trend p = 0.025). Although we predicted that proximal cues would drive additional response in the experts, the proximity-only cue was the only condition that showed no statistical effect of experience. Conclusions: Expert observers provide more accurate responses to near target demand than closely matched naïve observers. We suggest that attention, practice, voluntary and proprioceptive effects may enhance responses in experienced participants when compared to a more typical general population. Differences between adult reports and the developmental and clinical literature may partially reflect expert/naïve effects, as well as developmental change. If developmental and clinical studies are to be compared to adult normative data, uninstructed naïve adult data should be used.

Requirements for building information modeling based lean production management systems for construction

Smooth flow of production in construction is hampered by disparity between individual trade teams' goals and the goals of stable production flow for the project as a whole. This is exacerbated by the difficulty of visualizing the flow of work in a construction project. While the addresses some of the issues in Building information modeling provides a powerful platform for visualizing work flow in control systems that also enable pull flow and deeper collaboration between teams on and off site. The requirements for implementation of a BIM-enabled pull flow construction management software system based on the Last Planner System™, called ‘KanBIM’, have been specified, and a set of functional mock-ups of the proposed system has been implemented and evaluated in a series of three focus group workshops. The requirements cover the areas of maintenance of work flow stability, enabling negotiation and commitment between teams, lean production planning with sophisticated pull flow control, and effective communication and visualization of flow. The evaluation results show that the system holds the potential to improve work flow and reduce waste by providing both process and product visualization at the work face.

Differential effects of thyroid hormone manipulation and ß adrenoceptor agonist administration on uncoupling protein mRNA abundance in adipose tissue and thermoregulation in neonatal pigs

We have shown that there is significant disparity in the expression of uncoupling proteins (UCP) 2 and 3 between modern-commercial and ancient-Meishan porcine genotypes, commercial pigs also have higher plasma triiodothyronine (T(3)) in on the first day of life. T(3) and the sympathetic nervous system are both known to regulate UCPs in rodents and humans; their role in regulating these proteins in the pig is unknown. This study examined whether thyroid hormone manipulation or administration of a selective beta3 adrenoceptor agonist (ZD) influenced plasma hormones, colonic temperature and UCP expression in adipose tissue of two breeds of pig. To mimic the differences observed in thyroid hormone status, piglets from Meishan and commercial litters were randomly assigned to control (1 ml/kg water), T(3) (10 mg/kg) (Meishan only), methimazole (a commonly used antithyroid drug) (50 mg/kg) (commercial only) or ZD (10 mg/kg) oral administration for the first 4 days of postnatal life. Adipose tissue UCP2/3 mRNA abundance was measured on day 4 using PCR. T(3) administration raised plasma T(3) concentrations and increased colonic temperature on day 4. UCP3 mRNA abundance was higher in Meishan, than commercial piglets (p = 0.042) and was downregulated following T(3) administration (p = 0.014). Irrespective of genotype, ZD increased UCP2 mRNA abundance (Meishan p = 0.05, commercial p = 0.03). Expression of neither UCP2 nor 3 was related to colonic temperature, regardless of treatment. In conclusion, we have demonstrated a dissociation between thyroid hormones and the sympathetic nervous system in the regulation of UCPs in porcine adipose tissue. We have also suggested that expression of adipose tissue UCP2 and 3 are not related to body temperature in piglets.

Influence of porcine genotype on the abundance of thyroid hormones and leptin in sow milk and its impact on growth, metabolism and expression of key adipose tissue genes in offspring

Neonatal mortality is greater in commercial porcine genotypes, compared with the ancient Meishan breed that rapidly lay down adipose tissue; this may be related to hormones, such as triiodothyronine (T3) or leptin. Leptin is present in maternal milk; however, the extent to which this supply provides the neonate with leptin is unknown, but may play a role in growth and development. We investigated whether thyroid hormones and leptin concentrations in maternal milk differed between genotypes; and whether this influenced piglet concentrations or expression of genes involved in adipose tissue regulation. Eight Meishan and six commercial sows were entered into the study and milk samples from the day of parturition to day 4 postpartum was taken daily. The median birth weight piglet in each litter had a daily venous blood sample taken and was euthanised on day 4. Gene expressions of IGF-I, IGF-binding protein 3 (IGFBP-3), peroxisome proliferators activated receptor (PPAR) and glucocorticoid receptor (GR) were measured in adipose tissue using real-time PCR. T3 was increased in Meishan milk, but not in piglet plasma. Milk thyroxine was similar between breeds but commercial piglet levels were significantly higher. Leptin was higher in commercial sow milk throughout the study. Milk leptin was strongly correlated to plasma leptin during the first postnatal days and also to organ and body weight in Meishan piglets that also had significantly higher expression of GR, but not IGF-I, IGFBP-3 or PPAR. In conclusion, we have found a significant disparity in the provision of thyroid hormones in Meishan and commercial sow’s milk. These changes are not always translated to plasma concentrations of hormone in the piglet. Leptin appears to have a stronger role in growth and development in the Meishan genotype compared with commercial; along with the increased GR expression, this may also represent a potential mechanism behind the rapid accumulation of adipose tissue in Meishan piglets.

Physical properties of Hydropsyche siltalai (Trichoptera) net silk

Most suspension-feeding trichopterans spin a fine-silk capture net that is used to remove suspended matter from the water. The efficiency of these nets has previously been studied by considering the geometry of the web structure but the material from which the nets is constructed has received little attention. We report measurements of the tensile strength and extensibility of net silk from Hydropsyche siltalai. These measurements place caddisfly silk as one of the weakest natural silks so far reported, with a mean tensile strength of 221 +/- 22 megaNewtons (MN)/m(2). We also show that H. siltalai silk can more than double in length before catastrophic breakage, and that the silk is at least 2 orders of magnitude stronger than the maximum force estimated to act upon it in situ. Possible reasons for this disparity include constraints of evolutionary history and safety margins to prevent net failure or performance reduction.

Dilettantes, discipline and discourse: requirements management for construction

Requirements management (RM), as practised in the aerospace and defence sectors, attracts interest from construction researchers in response to longstanding problems of project definition. Doubts are expressed whether RM offers a new discipline for construction practitioners or whether it repeats previous exhortations to adopt a more disciplined way of working. Whilst systems engineering has an established track record of addressing complex technical problems, its extension to socially complex problems has been challenged. The dominant storyline of RM is one of procedural rationality and RM is commonly presented as a means of controlling dilettante behaviour. Interviews with RM practitioners suggest a considerable gulf between the dominant storyline in the literature and how practitioners operate in practice. The paper challenges construction researchers interested in RM to reflect more upon the theoretical debates that underpin current equivalent practices in construction and the disparity between espoused and enacted practice.

Comparative effects of fatty acids on endothelial inflammatory gene expression

Background: Endothelial dysfunction may be related to adverse effects of some dietary fatty acids (FAs). Although in vitro studies have failed to show consistent findings, this may reflect the diverse experimental protocols employed and the limited range of FAs and end points studied. Aims: To investigate the effect of dietary FA type (saturated, monounsaturated, n-6 and n-3 polyunsaturated fatty acids), concentration, incubation time and cell stimulation state, on a broad spectrum of endothelial inflammatory gene expression. Methods: Using human umbilical vein endothelial cells, with and without stimulation (+/- 10 ng/ml TNF alpha), the effects of arachidonic (AA), docosahexaenoic (DHA), eicosapentaenoic (EPA), linoleic (LA), oleic (OA) and palmitic acids (PA) (10, 25 and 100 mu M), on the expression of genes encoding a number of inflammatory proteins and transcription factors were assessed by quantitative real time RT-PCR. Results: Individual FAs differentially affect endothelial inflammatory gene expression in a gene-specific manner. EPA, LA and OA significantly up-regulated MCP-1 gene expression compared to AA (p = 0.001, 0.013, 0.008, respectively) and DHA (p < 0.0005, = 0.004, 0.002, respectively). Furthermore, cell stimulation state and FA incubation time significantly influenced reported FA effects on gene expression. Conclusions: The comparative effects of saturated, monounsaturated, n-6 and n-3 polyunsaturated FAs on endothelial gene expression depend on the specific FA investigated, its length of incubation, cell stimulation state and the gene investigated. These findings may explain existing disparity in the literature. This work was funded by the EC, Framework Programme 6 via the LIPGENE project (FOOD-CT-2003-505944).

The psychological, neurochemical and functional neuroanatomical mediators of the effects of positive and negative mood on executive functions

In this review we evaluate the cognitive and neural effects of positive and negative mood on executive function. Mild manipulations of negative mood appear to have little effect on cognitive control processes, whereas positive mood impairs aspects of updating, planning and switching. These cognitive effects may be linked to neurochemistry: with positive mood effects mediated by dopamine while negative mood effects may be mediated by serotonin levels. Current evidence on the effects of mood on regional brain activity during executive functions, indicates that the prefrontal cortex is a recurrent site of integration between mood and cognition. We conclude that there is a disparity between the importance of this topic and awareness of how mood affects, executive functions in the brain. Most behavioural and neuroimaging studies of executive function in normal samples do not explore the potential role of variations in mood, yet the evidence we outline indicates that even mild fluctuations in mood can have a significant influence on neural activation and cognition. (c) 2006 Elsevier Ltd. All rights reserved.

Binocular coordination of the eyes during reading

Saccadic eye movements and fixations are the behavioral means by which we visually sample text during reading. Human oculomotor control is governed by a complex neurophysiological system involving the brain stem, superior colliculus, and several cortical areas [1, 2]. A very widely held belief among researchers investigating primate vision is that the oculomotor system serves to orient the visual axes of both eyes to fixate the same target point in space. It is argued that such precise positioning of the eyes is necessary to place images on corresponding retinal locations, such that on each fixation a single, nondiplopic, visual representation is perceived [3]. Vision works actively through a continual sampling process involving saccades and fixations [4]. Here we report that during normal reading, the eyes do not always fixate the same letter within a word. We also demonstrate that saccadic targeting is yoked and based on a unified cyclopean percept of a whole word since it is unaffected if different word parts are delivered exclusively to each eye via a dichoptic presentation technique. These two findings together suggest that the visual signal from each eye is fused at a very early stage in the visual pathway, even when the fixation disparity is greater than one character (0.29 deg), and that saccade metrics for each eye are computed on the basis of that fused signal.