Does binocular disparity facilitate the detection of transparent motion?

Recent physiological studies have established that cortical cells that are tuned for the direction of motion may also exhibit tuning for binocular disparity. This tuning does not appear to provide any advantage in discriminating the direction of global motion in random-dot kinematograms. Here we investigated the possibility that this tuning may be important in the perception of transparent motion. Random-dot kinematograms were presented which contained coherent motion in a single direction or in two opposing directions. A greater proportion of signal dots was required for the detection of transparent motion than of motion in a single direction. This difference vanished when the two opposite directions of motion were presented with different disparities. These results suggest that the direction of global motion can be computed separately for surfaces which are clearly segregated in depth.     

Visual processing and dyslexia

Magnocellular-pathway deficits have been hypothesized to be responsible for the problems experienced by dyslexic individuals in reading. However, research has yet to provide a detailed account of the consequences of these deficits or to identify the behavioural link between them and reading disabilities. The aim of the present study was to determine the potential consequences of the magnocellular-pathway deficits for dyslexics in a comprehensive range of visual tasks. Dyslexics and nondyslexics were compared on their ability to (i) perform vernier-acuity and orientation-acuity tasks; (ii) perceive motion by using a range of measures common in the psychophysical literature (Dmin, Dmax, and global coherence); and (iii) perceive shapes presented in random-dot stereograms at a range of disparity pedestals, thereby dissociating stereopsis from vergence control. The results indicated no significant differences in performance between the dyslexic and nondyslexic subjects in terms of the visual-acuity measures. In general, dyslexics performed relatively poorly on measures of motion perception and stereopsis, although when considered individually some of the dyslexics performed better than some of the controls. The poor performance of the dyslexics in the stereo-gram tasks was attributable to a subgroup of dyslexics who also appeared to have severe difficulty with the motion-coherence task. These data are consistent with previous evidence that some dyslexics may have deficits within the magnocellular visual pathway.     

Hand-hemispace spatial compatibility,precueing, and stimulus-onset asynchrony

Summary The role of attention and the resolution of coding conflicts in hand-hemispace spatial-compatibility effects was examined in a precueing experiment in which visual and vibrotactile precues, with various stimulus-onset asynchronies (SOAs), were presented in blocked and random order. It was expected that precues at the shorter SOAs would fail to facilitate the shifting of attention, as they occur too close to the imperative stimulus to be informative. The task would therefore approximate one of choice reaction time (RT), resulting in a hand-hemispace spatial-compatibility effect. Conversely, the longer SOAs would provide the subject with sufficient time in which to shift attention fully, and would therefore result in a task more like that of simple reaction time (SRT). It was expected that the hand-hemispace spatial-compatibility effect would then be absent. As was expected, this effect was present at the shorter SOAs, and absent at the longer SOAs. In Experiments 2 and 3, provision of a visual precue further facilitated attentional deployment, as did blocking the presentation of various SOAs in Experiment 3. Vibrotactile and visual precues did not differ in their ability to direct attention, implying that these modalities orient attention and precue location in essentially similar ways. These findings are discussed within the context of the mechanisms thought to underlie the time course of spatial compatibility and the dissipation of a fading trace of interfering spatial codes.     

Behaviour of rats in multiple schedules of response-contingent and response-independent food presentation

During Phase I, three rats were exposed to two-component multiple schedules of response-independent food presentation. Low rates of lever-pressing were observed, and response rates in one component did not increase when food presentation was withheld in the other component. During Phase II, the same rats were exposed to two-component multiple schedules of response-contingent reinforcement. Much higher rates of lever-pressing were observed. Moreover, when reinforcement was withheld in one component, response rates in the other component increased (positive contrast), and when reinforcement was reinstated in the changed component, response rates in the other component declined (negative contrast). During Phase III, when food was again delivered independently of responding, the response rates declined again to low levels. These results indicate that the occurrence of non-instrumental lever-pressing is not a prerequisite for the occurrence of behavioural contrast in the rat, and thus cast doubt on the general applicability of the autoshaping theory of behavioural contrast     

Relationship between response rate and reinforcement frequency in variable-interval schedules: II. Effect of the volume of sucrose reinforcement

Three rats were exposed to variable-interval schedules specifying a range of different reinforcement frequencies, using three different volumes of .32 molar sucrose (.10, .05, and .02 milliliters) as the reinforcer. With each of the three volumes, the rates of responding of all three rats were increasing, negatively accelerated functions of reinforcement frequency, the data conforming closely to Herrnstein's equation. In each rat the value of the constant K_H, which expresses the reinforcement frequency needed to obtain the half-maximal response rate, increased with decreasing reinforcer volume, the values obtained with .02 milliliters being significantly greater than the values obtained with .10 milliliters. The values of the constant R_max, which expresses the theoretical maximum response rate, were not systematically related to reinforcer volume. The effect of reinforcer volume upon the relationship between response rate and reinforcement frequency is thus different from the effect of the concentration of sucrose reinforcement: In a previous experiment (Bradshaw, Szabadi, & Bevan, 1978) it was found that sucrose concentration influenced the values of both constants, R_max increasing and K_H decreasing with increasing sucrose concentration.     

Ageing effects on the attention demands of walking

Attention demands of walking were determined in six male and six female young adults (mean 26.3 yr) and 12 gender-matched healthy, active older adults (mean 71.1 yr) using a dual task procedure with a reaction time (RT) secondary task. In three conditions an auditory stimulus, a visual stimulus and both stimuli (auditory/visual) were presented. Relative to no-walking baselines, increased RT was found in all conditions revealing an attentional cost of normal walking. When participants traversed the laboratory walkway and also positioned one of their feet within a target area on the ground, attention demands were greater than in unconstrained walking. In the targeting task, RTs to the visual stimulus were longer than for the auditory stimulus due to the interference associated with viewing both the stimulus monitor and the foot-target. Older participants' RTs in the visual and auditory/visual conditions, but not in the auditory condition, were significantly longer than for the young group in both walking tasks but RTs for young and older adults were not different in no-walking baseline trials. Inspection of mean RT functions at time intervals following gait initiation (0-3000 ms from the first step) suggested a fluctuating attentional cost of walking with increased demands associated with contingencies requiring step length regulation. The findings have applied significance in demonstrating the possibility of increased falls and pedestrian accident risk in older individuals in dual task situations such as road crossing.     

Effects of approach velocity and foot-target characteristics on the visual regulation of step length.

Two questions emerge from the literature concerning the perceptual-motor processes underlying the visual regulation of step length. The first concerns the effects of velocity on the onset of visual control (VCO), when visual regulation of step length begins during goal-directed locomotion. The second concerns the effects of different obstacles such as a target or raised surface on step length regulation. In two separate experiments, participants (Experiment 1 & 2: n=12, 6 female, 6 male) walked, jogged, or sprinted towards an obstacle along a 10 m walkway, consisting of two marker-strips with alternating black and white 0.50 m markings. Each experiment consisted of three targeting or obstacle tasks with the requirement to both negotiate and continue moving (run-through) through the target. Five trials were conducted for each task and approach speed, with trials block randomised between the six participants of each gender. One 50 Hz video camera panned and filmed each trial from an elevated position, adjacent to the walkway. Video footage was digitized to deduce the gait characteristics. Results for the targeting tasks indicate a linear relationship between approach velocity and accuracy of final foot placement (r=0.89). When foot placement was highly constrained by the obstacle step length shortened during the entire approach. VCO was found to occur at an earlier tau-margin for lower approach velocities for both experiments, indicating that the optical variable 'tau' is affected by approach velocity. A three-phase kinematic profile was found for all tasks, except for the take-off board condition when sprinting. Further research is needed to determine whether this velocity affect on VCO is due to 'whole-body' approach velocity or whether it is a function of the differences between gait modes.     

Combining Item Response Theory and Diagnostic Classification Models: A Psychometric Model for Scaling Ability and Diagnosing Misconceptions

Traditional testing procedures typically utilize unidimensional item response theory (IRT) models to provide a single, continuous estimate of a student’s overall ability. Advances in psychometrics have focused on measuring multiple dimensions of ability to provide more detailed feedback for students, teachers, and other stakeholders. Diagnostic classification models (DCMs) provide multidimensional feedback by using categorical latent variables that represent distinct skills underlying a test that students may or may not have mastered. The Scaling Individuals and Classifying Misconceptions (SICM) model is presented as a combination of a unidimensional IRT model and a DCM where the categorical latent variables represent misconceptions instead of skills. In addition to an estimate of ability along a latent continuum, the SICM model provides multidimensional, diagnostic feedback in the form of statistical estimates of probabilities that students have certain misconceptions. Through an empirical data analysis, we show how this additional feedback can be used by stakeholders to tailor instruction for students’ needs. We also provide results from a simulation study that demonstrate that the SICM MCMC estimation algorithm yields reasonably accurate estimates under large-scale testing conditions.     

Hierarchical Diagnostic Classification Models: A Family of Models for Estimating and Testing Attribute Hierarchies

Although latent attributes that follow a hierarchical structure are anticipated in many areas of educational and psychological assessment, current psychometric models are limited in their capacity to objectively evaluate the presence of such attribute hierarchies. This paper introduces the Hierarchical Diagnostic Classification Model (HDCM), which adapts the Log-linear Cognitive Diagnosis Model to cases where attribute hierarchies are present. The utility of the HDCM is demonstrated through simulation and by an empirical example. Simulation study results show the HDCM is efficiently estimated and can accurately test for the presence of an attribute hierarchy statistically, a feature not possible when using more commonly used DCMs. Empirically, the HDCM is used to test for the presence of a suspected attribute hierarchy in a test of English grammar, confirming the data is more adequately represented by hierarchical attribute structure when compared to a crossed, or nonhierarchical structure.     

A systematic review of the literature on counselling and psychotherapy for the prevention of suicide: 2. Qualitative studies

Scope of review: The paper reports a meta‐synthesis of 13 qualitative studies of counselling and psychotherapy with people at risk of suicide. Publication time span: The studies considered were reported between 1997 and 2006. Publication origin: Seven studies were conducted in the UK, four in the USA, one in Canada, and one in Sweden. Findings: Themes in clients' and therapists' accounts of the process of counselling or psychotherapy were therapist qualities; therapy components; theoretical framework; and therapy techniques. Themes in their accounts of the effectiveness of counselling and psychotherapy were decrease in self‐destructive behaviour, and quality of life. Themes in clients' views of barriers to effective counselling or psychotherapy were therapist characteristics; therapy components; secrecy; and transferring to the real‐life situation. Secrecy was also identified as a barrier by therapists, as were responsibilities of the profession; training; and the nature of suicide and self‐harm. Facilitators of successful counselling and psychotherapy as identified by clients were responsibility; support; and teaching therapy skills to family members, the latter also being identified by therapists.