Choice between delayed reinforcers in an adjusting-delay schedule: The effects of absolute reinforcer size and deprivation level

Choice between two reinforcers differing in magnitude and delay was investigated in rats using an adjusting-delay discrete-trials schedule in which the two reinforcers were associated with two levers (A and B). The delay to Reinforcer A (the smaller reinforcer) was always 2 sec, whereas the delay to Reinforcer B was varied in accordance with the distribution of choices in successive blocks of trials. In Experiment 1, the mean delay to the large reinforcer during the last 5 of 60 training sessions was greater when the rats were maintained at 80% than when they were maintained at 90% of their free-feeding body weights. In Experiment 2, the delay to the larger reinforcer was greater when the two reinforcers consisted of one and two 45-mg food pellets than when they consisted of three and six pellets. The results are consistent with a model of “self-control” which posits hyperbolic relations between reinforcer value and reinforcer magnitude, and between reinforcer value and delay of reinforcement.     

Assessing Growth in a Diagnostic Classification Model Framework

A common assessment research design is the single-group pre-test/post-test design in which examinees are administered an assessment before instruction and then another assessment after instruction. In this type of study, the primary objective is to measure growth in examinees, individually and collectively. In an item response theory (IRT) framework, longitudinal IRT models can be used to assess growth in examinee ability over time. In a diagnostic classification model (DCM) framework, assessing growth translates to measuring changes in attribute mastery status over time, thereby providing a categorical, criterion-referenced interpretation of growth. This study introduces the Transition Diagnostic Classification Model (TDCM), which combines latent transition analysis with the log-linear cognitive diagnosis model to provide methodology for analyzing growth in a general DCM framework. Simulation study results indicate that the proposed model is flexible, provides accurate and reliable classifications, and is quite robust to violations to measurement invariance over time. The TDCM is used to analyze pre-test/post-test data from a diagnostic mathematics assessment.     

The semantic Simon effect in Tourette's syndrome and obsessive-compulsive disorder

Core symptoms of Tourette's syndrome (TS) and obsessive-compulsive disorder (OCD) may be attributed to an impairment in inhibitory control. Neuropsychological studies have addressed inhibition in both disorders, but findings have been inconsistent. The aim of this study was to examine cognitive inhibition, using a semantic Simon effect paradigm, in patients with TS and OCD. Furthermore, to address comorbidity a group of TS+OCD patients was also examined. Results indicated that patients with TS and OCD were affected by the inhibitory components of the task. TS groups performed similarly to controls on simple and choice RT tasks, but were particularly compromised as increasingly complex inhibitory demands were imposed. OCD patients were slower and committed more errors than controls, especially in the more cognitively demanding conditions, and were particularly disadvantaged by incongruent stimulus-response compatibilities. Findings implicate possible fronto-striatal dysfunction, are consistent with previously reported inhibitory deficits in TS and OCD, and support the theory that comorbid TS+OCD is more closely linked to pure TS than OCD.     

The perception of emotion from body movement in point-light displays of interpersonal dialogue

We examined whether it is possible to identify the emotional content of behaviour from point-light displays where pairs of actors are engaged in interpersonal communication. These actors displayed a series of emotions, which included sadness, anger, joy, disgust, fear, and romantic love. In experiment 1, subjects viewed brief clips of these point-light displays presented the right way up and upside down. In experiment 2, the importance of the interaction between the two figures in the recognition of emotion was examined. Subjects were shown upright versions of (i) the original pairs (dyads), (ii) a single actor (monad), and (iii) a dyad comprising a single actor and his/her mirror image (reflected dyad). In each experiment, the subjects rated the emotional content of the displays by moving a slider along a horizontal scale. All of the emotions received a rating for every clip. In experiment 1, when the displays were upright, the correct emotions were identified in each case except disgust; but, when the displays were inverted, performance was significantly diminished for some emotions. In experiment 2, the recognition of love and joy was impaired by the absence of the acting partner, and the recognition of sadness, joy, and fear was impaired in the non-veridical (mirror image) displays. These findings both support and extend previous research by showing that biological motion is sufficient for the perception of emotion, although inversion affects performance. Moreover, emotion perception from biological motion can be affected by the veridical or non-veridical social context within the displays.     

The effects of a pre-movement delay on the kinematics of prehension in middle childhood

The present study examined the effects of a pre-movement delay on the kinematics of prehension in middle childhood. Twenty-five children between the ages of 5 and 11 years made visually open-loop reaches to two different sized objects at two different distances along the midline. Reaches took place either (i) immediately, or (ii) 2 s after the occlusion of the stimulus. In all age groups, reaches following the pre-movement delay were characterised by longer movement durations, lower peak velocities, larger peak grip apertures and longer time spent in the final slow phase of the movement. This pattern of results suggests that the representations that control the transport and grasp component are affected similarly by delay, and is consistent with the results previously reported for adults. Such representations therefore appear to develop before the age of 5.     

Age and responding-hand related changes in performance of neurologically normal subjects on the line-bisection and chimeric-faces tasks

This study investigated age and responding-hand (left, right, and bimanual) related changes in visuospatial attention. Two tasks were completed by 107 neurologically normal right-handed subjects ranging in age from 5 to 70 years and distributed across four age groups. Task-specific differences between groups were apparent. In the line-bisection task, the younger and older groups displayed symmetrical neglect while the young and middle groups displayed pseudoneglect. In the chimeric-faces task the leftward bias was less pronounced in the older group and more susceptible to responding-hand effects in the middle and older groups. Whilst results, especially those of the bimanual method, provided strong support for an activation model, they imposed an age limitation on its appropriateness as an explanation for performance on the chimeric-faces task. Results are discussed as reflecting changes in the corpus callosum and right hemisphere.     

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