The nonparametric Behrens‐Fisher problem with dependent replicates

Purely nonparametric methods are developed for general two-sample problems in which each experimental unit may have an individual number of possibly correlated replicates. In particular, equality of the variances, or higher moments, of the distributions of the data is not assumed, even under the null hypothesis of no treatment effect. Thus, a solution for the so-called nonparametric Behrens-Fisher problem is proposed for such models. The methods are valid for metric, count, ordered categorical, and even dichotomous data in a unified way. Point estimators of the treatment effects as well as their asymptotic distributions will be studied in detail. For small sample sizes, the distributions of the proposed test statistics are approximated using Satterthwaite-Welch-type t-approximations. Extensive simulation studies show favorable performance of the new methods, in particular, in small sample size situations. A real data set illustrates the application of the proposed methods

The effects of immediate vision on implicit hand maps

Perceiving the external spatial location of the limbs using position sense requires that immediate proprioceptive afferent signals be combined with a stored body model specifying the size and shape of the body. Longo and Haggard (Proc Natl Acad Sci USA 107:11727–11732, 2010) developed a method to isolate and measure this body model in the case of the hand in which participants judge the perceived location in external space of several landmarks on their occluded hand. The spatial layout of judgments of different landmarks is used to construct implicit hand maps, which can then be compared with actual hand shape. Studies using this paradigm have revealed that the body model of the hand is massively distorted, in a highly stereotyped way across individuals, with large underestimation of finger length and overestimation of hand width. Previous studies using this paradigm have allowed participants to see the locations of their judgments on the occluding board. Several previous studies have demonstrated that immediate vision, even when wholly non-informative, can alter processing of somatosensory signals and alter the reference frame in which they are localised. The present study therefore investigated whether immediate vision contributes to the distortions of implicit hand maps described previously. Participants judged the external spatial location of the tips and knuckles of their occluded left hand either while being able to see where they were pointing (as in previous studies) or while blindfolded. The characteristic distortions of implicit hand maps reported previously were clearly apparent in both conditions, demonstrating that the distortions are not an artefact of immediate vision. However, there were significant differences in the magnitude of distortions in the two conditions, suggesting that vision may modulate representations of body size and shape, even when entirely non-informative

Effects of organic additives on the formation of solids from hypersaline geothermal brine

Studies are underway to identify compounds that will, at cost-effective concentrations, inhibit scale and solids formation when added to the brine at the high-temperature (approximately 200{sup 0}C) front end of the plant. The study reported here constitutes a preliminary, bench-test screening of 49 substances, the most promising of which will be examined later in on-line pilot plant studies. A variety of substances were tested, including both simple and polymeric alcohols, ethers, aldehydes, carboxylic acids, amines, amides, cellulose derivatives, and classes of materials such as detergents, surfactants, and coupling agents. An inorganic phosphate, KH{sub 2}PO{sub 4}, and a chelating agent EDTA, also were tested. In the present work the additives were mixed with hypersaline brine that had been acidified to pH 4.0 +- 0.3 and flashed to 1 atm, approximately 100{sup 0}C, in the LLL Geothermal Field Test Apparatus near Niland, California. The rate of disappearance of dissolved silica from the treated brine was compared with the rate for untreated brine as a measure of the effectiveness of the additive. (JGB

Visual detail about the body modulates tactile localisation biases

The localisation of tactile stimuli requires the integration of visual and somatosensory inputs within an internal representation of the body surface, and is prone to consistent bias. Joints may play a role in segmenting such internal body representations, and may therefore influence tactile localisation biases, although the nature of this influence remains unclear. Here, we investigate the relationship between conceptual knowledge of joint locations and tactile localisation biases on the hand. In one task, participants localised tactile stimuli applied to the dorsum of their hand. A distal localisation bias was observed in all participants, consistent with previous results. We also manipulated the availability of visual information during this task, to determine whether the absence of this information could account for the distal bias observed here and by Mancini and colleagues (2011). The observed distal bias increased in magnitude when visual information was restricted, without a corresponding decrease in precision. In a separate task, the same participants indicated, from memory, knuckle locations on a silhouette image of their hand. Analogous distal biases were also seen in the knuckle localisation task. The accuracy of conceptual joint knowledge was not correlated with tactile localisation bias magnitude, although a similarity in observed bias direction suggests that both tasks may rely on a common, higher-order body representation. These results also suggest that distortions of conceptual body representation may be more common in healthy individuals than previously thought

Adaptation to motor-visual and motor-auditory temporal lags transfer across modalities

Previous research has shown that the timing of a sensor-motor event is recalibrated after a brief exposure to a delayed feedback of a voluntary action (Stetson et al. 2006). Here, we examined whether it is the sensory or motor event that is shifted in time. We compared lag adaption for action-feedback in visuo-motor pairs and audio-motor pairs using an adaptation-test paradigm. Participants were exposed to a constant lag (50 or 150 ms) between their voluntary action (finger tap) and its sensory feedback (flash or tone pip) during an adaptation period (~3 min). Immediately after that, they performed a temporal order judgment (TOJ) task about the tap-feedback test stimulus pairings. The modality of the feedback stimulus was either the same as the adapted one (within-modal) or different (cross-modal). The results showed that the point of subjective simultaneity (PSS) was uniformly shifted in the direction of the exposed lag within and across modalities (motor-visual, motor-auditory). This suggests that the TRE of sensor-motor events is mainly caused by a shift in the motor component

Haptic pop-out of movable stimuli

When, in visual and haptic search, a target is easily found among distractors, this is called a pop-out effect. The target feature is then believed to be salient, and the search is performed in a parallel way. We investigated this effect with movable stimuli in a haptic search task. The task was to find a movable ball among anchored distractors or the other way round. Results show that reaction times were independent of the number of distractors if the movable ball was the target but increased with the number of items if the anchored ball was the target. Analysis of hand movements revealed a parallel search strategy, shorter movement paths, a higher average movement speed, and a narrower direction distribution with the movable target, as compared with a more detailed search for an anchored target. Taken together, these results show that a movable object pops out between anchored objects and this indicates that movability is a salient object feature. Vibratory signals resulting from the movable ball were found to be a reasonable explanation regarding the sensation responsible for the pop-out of movability

Mechanism of Action of Cyclophilin A Explored by Metadynamics Simulations

Trans/cis prolyl isomerisation is involved in several biological processes, including the development of numerous diseases. In the HIV-1 capsid protein (CA), such a process takes place in the uncoating and recruitment of the virion and is catalyzed by cyclophilin A (CypA). Here, we use metadynamics simulations to investigate the isomerization of CA's model substrate HAGPIA in water and in its target protein CypA. Our results allow us to propose a novel mechanistic hypothesis, which is finally consistent with all of the available molecular biology data

Audiovisual time perception is spatially specific

Our sensory systems face a daily barrage of auditory and visual signals whose arrival times form a wide range of audiovisual asynchronies. These temporal relationships constitute an important metric for the nervous system when surmising which signals originate from common external events. Internal consistency is known to be aided by sensory adaptation: repeated exposure to consistent asynchrony brings perceived arrival times closer to simultaneity. However, given the diverse nature of our audiovisual environment, functionally useful adaptation would need to be constrained to signals that were generated together. In the current study, we investigate the role of two potential constraining factors: spatial and contextual correspondence. By employing an experimental design that allows independent control of both factors, we show that observers are able to simultaneously adapt to two opposing temporal relationships, provided they are segregated in space. No such recalibration was observed when spatial segregation was replaced by contextual stimulus features (in this case, pitch and spatial frequency). These effects provide support for dedicated asynchrony mechanisms that interact with spatially selective mechanisms early in visual and auditory sensory pathways

Irrelevant tactile stimulation biases visual exploration in external coordinates

Ossandón JP, König P, Heed T. Irrelevant tactile stimulation biases visual exploration in external coordinates. Scientific Reports. 2015;5(1): 10664