Is size perception based on monocular distance cues computed automatically?

The study reported here examined whether size perception based on monocular distance cues is computed automatically. Participants were presented with a picture containing distance cues, which was superimposed with a pair of digits differing in numerical value. One digit was presented so as to be perceived as closer than the other. The digits were of similar physical size but differed in their perceptual size. The participants’ task was to decide which digit was numerically larger. It was found that the decision took longer and resulted in more errors when the perceptual size of the numerically larger digit was smaller than the perceptual size of the numerically smaller digit. These results show that perceived size affects performance in a task that does not require size or distance computation. Hence, for the first time, there is empirical support for the working assumption of the visual perception approach that size perception based on monocular distance cues is computed automatically.     

Purkinje cell activity in the cerebellar anterior lobe after rabbit eyeblink conditioning

The cerebellar anterior lobe may play a critical role in the execution and proper timing of learned responses. The current study was designed to monitor Purkinje cell activity in the rabbit cerebellar anterior lobe after eyeblink conditioning, and to assess whether Purkinje cells in recording locations may project to the interpositus nucleus. Rabbits were trained in an interstimulus interval discrimination procedure in which one tone signaled a 250-msec conditioned stimulus-unconditioned stimulus (CS-US) interval and a second tone signaled a 750-msec CS-US interval. All rabbits showed conditioned responses to each CS with mean onset and peak latencies that coincided with the CS-US interval. Many anterior lobe Purkinje cells showed significant learning-related activity after eyeblink conditioning to one or both of the CSs. More Purkinje cells responded with inhibition than with excitation to CS presentation. In addition, when the firing patterns of all conditioning-related Purkinje cells were pooled, it appeared that the population showed a pattern of excitation followed by inhibition during the CS-US interval. Using cholera toxin-conjugated horseradish peroxidase, Purkinje cells in recording areas were found to project to the interpositus nucleus. These data support previous studies that have suggested a role for the anterior cerebellar cortex in eyeblink conditioning as well as models of cerebellar-mediated CR timing that postulate that Purkinje cell activity inhibits conditioned response (CR) generation during the early portion of a trial by inhibiting the deep cerebellar nuclei and permits CR generation during the later portion of a trial through disinhibition of the cerebellar nuclei.     

What is the prevalence of adult ADHD? Results of a population screen of 966 adults

To provide a better estimate of the prevalence of ADHD in adulthood, the authors complete a telephone survey of 966 randomly selected adults. They compute two diagnoses from the survey data. Participants meeting Diagnostic and Statistical Manual of Mental Disorders (4th ed.) criteria for both childhood and adulthood are defined as narrow ADHD. Broad ADHD adds to that definition those meeting subthreshold criteria. Cronbach's alpha is .90 for the 18 DSM-IV symptoms in childhood and .88 when rated for current symptoms in adulthood. No one item unduly influences the reliability of the total score. The authors find similar results in separate analyses of hyperactive-impulsive and inattentive symptoms. They estimate prevalences of 2.9% for Narrow ADHD and 16.4% for Broad ADHD. Having ADHD is associated with lower levels of education and employment status. These findings suggest that adult ADHD is a common disorder associated with impaired functioning.     

Using data augmentation to obtain standard errors and conduct hypothesis tests in latent class and latent transition analysis

Latent class analysis (LCA) provides a means of identifying a mixture of subgroups in a population measured by multiple categorical indicators. Latent transition analysis (LTA) is a type of LCA that facilitates addressing research questions concerning stage-sequential change over time in longitudinal data. Both approaches have been used with increasing frequency in the social sciences. The objective of this article is to illustrate data augmentation (DA), a Markov chain Monte Carlo procedure that can be used to obtain parameter estimates and standard errors for LCA and LTA models. By use of DA it is possible to construct hypothesis tests concerning not only standard model parameters but also combinations of parameters, affording tremendous flexibility. DA is demonstrated with an example involving tests of ethnic differences, gender differences, and an Ethnicity x Gender interaction in the development of adolescent problem behavior.     

A laboratory school comparison of mixed amphetamine salts extended release (Adderall XR) and atomoxetine (Strattera) in school-aged children with attention deficit/hyperactivity disorder

Mixed amphetamine salts extended release (MAS XR; Adderall XR) and atomoxetine (Strattera) were compared in children 6 to 12 years old with attention deficit/hyperactivity disorder (ADHD) combined or hyperactive/impulsive type in a randomized, double-blind, multicenter, parallel-group, forced-dose-escalation laboratory school study. Primary efficacy measure was the SKAMP (Swanson, Kotkin, Agler, M-Flynn, and Pelham) behavioral rating scale. Changes in mean SKAMP deportment scores from baseline were significantly greater for MAS XR (n = 102) than for atomoxetine (n = 101) overall (-0.56 and -0.13, respectively; p < .0001) and at each week (p < .001). Adverse events were similar for both treatment groups. The extended time course of action and greater therapeutic efficacy of MAS XR suggests that it is more effective than atomoxetine in children with ADHD.     

Extinction-induced immobility in the water maze and its neurochemical concomitants in aged and adult rats: a possible model for depression?

Extinction of escape behavior in the water maze due to the removal of the platform, was hypothesized to induce a negative state, including the development of immobility, which is held to reflect a state of "despair" when measured in the forced swimming test. 27 aged and 8 adult animals (26 and 3 months old Wistar rats, respectively) were tested in the water maze during nine days with a platform hidden, followed by 7 days of extinction trials with the platform absent. As expected, both age groups developed immobility over the extinction trials, with the aged showing more than the adults. To examine whether the age difference in immobility was related to performance differences during acquisition, the aged were subdivided into superior, intermediate and inferior learners (n = 9 per group) on the basis of overall times to platform during acquisition, and compared with each other and the adults. Results showed that the aged inferior learners displayed the highest levels of immobility among the aged. Immobility scores were then correlated with post-mortem neurotransmitter contents in the hippocampus and ventral striatum. In the ventral striatum, levels of immobility were correlated with levels of acetylcholine, dopamine and the metabolite dihydroxyphenylacetic acid in the aged, and with norepinephrine in the adults. The data support the hypothesis that multiple extinction trials in the water maze result in immobility that may indicate "behavioral despair," and that striatal neurotransmitter systems correlate with the degree of its expression. The concept of extinction-induced despair is held to provide the promise of a conceptual and empirical model of human depression that is the consequence of loss of reinforcers.     

Potential noradrenergic targets for cognitive enhancement in schizophrenia

Substantial evidence suggests that alterations in noradrenergic function contribute to the cognitive impairments of schizophrenia. Activation of post-junctional alpha 2a-adrenergic receptors in the prefrontal cortex by the alpha 2a-selective agonist guanfacine has demonstrated some preliminary benefit in subjects with schizophrenia treated with atypical antipsychotics. alpha 1-adrenergic receptor activity may be less important in mediating the cognitive impairments of schizophrenia. beta-adrenergic receptors may serve as another potential target for cognitive remediation in schizophrenia. However, the potential increase in memory consolidation in schizophrenia patients produced by beta-adrenergic agonists may be outweighed by the impairment in cognitive flexibility and executive functioning produced by beta-adrenergic agonists. Finally, norepinephrine reuptake inhibitors, such as atomoxetine, hold promise as potential cognitive enhancers in schizophrenia because of their ability to indirectly but selectively increase extracellular dopamine concentrations in the prefrontal cortex.     

Attention and inhibition in bilingual children: evidence from the dimensional change card sort task

In a previous study, a bilingual advantage for preschool children in solving the dimensional change card sort task was attributed to superiority in inhibition of attention (Bialystok, 1999). However, the task includes difficult representational demands to encode and interpret the task stimuli, and bilinguals may also have profited from superior representational abilities. This possibility is examined in three studies. In Study 1, bilinguals outperformed monolinguals on versions of the problem containing moderate representational demands but not on a more demanding condition. Studies 2 and 3 demonstrated that bilingual children were more skilled than monolinguals when the target dimensions were perceptual features of the stimulus and that the two groups were equivalent when the target dimensions were semantic features. The conclusions are that bilinguals have better inhibitory control for ignoring perceptual information than monolinguals do but are not more skilled in representation, confirming the results of the original study. The results also identify the ability to ignore an obsolete display feature as the critical difficulty in solving this task.