The beat goes on: Rhythmic modulation of cortical potentials by imagined tapping.

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180° out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Variability of the southwest Indian Ocean

The variability in the southwest Indian Ocean is connected to the basin-scale and global-scale ocean circulation. Two bands of enhanced variability stretch across the Southern Indian Ocean east of Madagascar around 12 degrees S and 25 degrees S, respectively. They mark the preferred routes along which anomalies, generated by varying forcing over the central basin, near the eastern boundary or in the equatorial region, propagate westward as baroclinic Rossby waves. Sea-surface height anomalies pass along the northern tip of Madagascar and are observed by satellite altimetry to propagate into the central Mozambique Channel. There, eddies are subsequently formed that propagate southward into the Agulhas retroflection region. The anomalies along the southern band trigger the formation of large dipolar vortex pairs in the separation region of the East Madagascar Current at the southern tip of the island. South of Africa these eddies and dipoles trigger the shedding of Agulhas Rings that feed the Atlantic meridional overturning circulation with warm, salty, Indian Ocean water. Interannual variability of the forcing over the Indian Ocean, such as that associated with the Indian Ocean Dipole/El Nino climate modes, propagates along these pathways and leads to associated modulations of the eddy transports into the South Atlantic.     

Operation compatibility: A neglected contribution to dual-task costs.

Traditionally, dual-task interference has been attributed to the consequences of task load exceeding capacity limitations. However, the current study demonstrates that in addition to task load, the mutual compatibility of the concurrent processes modulates whether 2 tasks can be performed in parallel. In 2 psychological refractory period experiments, task load and process compatibility were independently varied. In Experiment 1, participants performed 2 mental rotation tasks. Task load (rotation angle) and between-task compatibility in rotation direction were varied. Results suggest more considerable parallel execution of compatible than of incompatible operations, arguing for the need to attribute dual-task interference not only to structural but also to functional capacity limitations. Experiment 2 tested whether functional capacity limitations to dual-task performance can be caused only by demanding processes or whether they are also induced by relatively automatic processes. Results indicate that an irrelevant circular movement of Stimulus 2 interfered more with mental rotation of Stimulus 1 if the rotation directions were opposite than if they were equal. In conclusion, compatibility of concurrent processes constitutes an indispensable element in explaining dual-task performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibitory inefficiency and failures of intention activation: Age-related decline in the control of saccadic eye movements.

Young and older adults' control of saccadic eye movements was compared using an antisaccade task, which requires the inhibition of a reflexive saccade toward a peripheral onset cue followed by an intentional saccade in the opposite direction. In 2 experiments, an age-related decline was found in the suppression of reflexive eye movements, as indicated by an increased proportion of saccades toward the cue, and a longer time needed to initiate correct antisaccades. The results from Experiment 2 suggested that older adults' slower antisaccades may be explained partly in terms of increased failures to maintain the cue-action representation at a sufficient activation level. The results suggest that the notion of selective preservation with age of the ability to inhibit spatial responses does not apply to the active inhibition of prepotent spatial responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating consciousness from inhibitory control: Evidence for unconsciously triggered response inhibition in the stop-signal task.

Theories about the functional relevance of consciousness commonly posit that higher order cognitive control functions, such as response inhibition, require consciousness. To test this assertion, the authors designed a masked stop-signal paradigm to examine whether response inhibition could be triggered and initiated by masked stop signals, which inform participants to stop an action they have begun. In 2 experiments, masked stop signals were observed to occasionally result in full response inhibition as well as to yield a slow down in the speed of responses that were not inhibited. The magnitude of this subliminally triggered response time slowing effect correlated with the efficiency measure (stop signal reaction time) of response inhibition across participants. Thus, response inhibition can be triggered unconsciously—more so in individuals who are good inhibitors and under conditions that are associated with efficient response inhibition. These results indicate that in contradiction to common theorizing, inhibitory control processes can operate outside awareness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delta Plots in the Study of Individual Differences: New Tools Reveal Response Inhibition Deficits in AD/HD That Are Eliminated by Methylphenidate Treatment.

The authors highlight the utility of distribution-analytical techniques in the study of individual differences and clinical disorders. Cognitive deficits associated with attention-deficit/hyperactivity disorder (AD/HD) were examined by using delta-plot analyses of performance data (reaction time and accuracy) obtained through the use of a prototypical conflict task, the Eriksen flanker task. In 20 children with AD/HD (compared with matched control participants), overall performance measures indicated a marginal performance deficit. Delta-plot analyses indicated that performance deficits associated with AD/HD involve response inhibition but not automatic response activation. In a within-subjects titration study, the response inhibition deficit was eliminated by methylphenidate treatment, but these effects were highly dose specific. The beneficial effect of methylphenidate was clarified further after correcting for inter-individual variation in sensitivity to medicine dosage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is the age-complexity effect mediated by reductions in a general processing resource?

The rate of information processing, as revealed in measures of reaction time, slows with advancing age and this slowing is most evident as processing complexity increases. This phenomenon, known as the Age-Complexity effect, has been attributed to general changes in the speed of processing that affect all components of processing indiscriminantly, both within and across tasks in a particular processing domain. That the slowing is thought to be task- and process-independent has led to the additional inference that it reflects reductions in a general processing resource. On the basis of converging evidence identified in a review of both behavioral and chronopsychophysiological studies, we argue that the slowing induced by older age is not generalized, but rather is both task-dependent and process-specific and, as such, cannot be explained in terms of a diminished general processing resource. We close by speculating that elements of the age-induced slowing can be interpreted within the context of the cognitive-energetical model.     

Older age, traumatic brain injury, and cognitive slowing: Some convergent and divergent findings.

Reaction time (RT) meta-analyses of cognitive slowing indicate that all stages of processing slow equivalently and task independently among both older adults (J. Cerella & S. Hale, 1994) and adults who have suffered a traumatic brain injury (TBI; F. R. Ferraro, 1996). However, meta-analyses using both RT and P300 latency have revealed stage-specific and task-dependent changes among older individuals (T. R. Bashore, K. R. Ridderinkhof, & M. W. van der Molen, 1998). Presented in this article are a meta-analysis of the effect of TBI on processing speed, assessed using P300 latency and RT, and a qualitative review of the literature. They suggest that TBI induces differential slowing. Similarities in the effects of older age and TBI on processing speed are discussed and suggestions for future research on TBI-induced cognitive slowing are offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The risky business of dopamine agonists in Parkinson disease and impulse control disorders.

Risk-taking behavior is characterized by pursuit of reward in spite of potential negative consequences. Dopamine neurotransmission along the mesocorticolimbic pathway is a potential modulator of risk behavior. In patients with Parkinson's disease (PD), impulse control disorder (ICD) can result from dopaminergic medication use, particularly dopamine agonists (DAA). Behaviors associated with ICD include hypersexuality as well as compulsive gambling, shopping, and eating, and these behaviors are potentially linked to alterations to risk processing. Using the Balloon Analogue Risk Task, we assessed the role of agonist therapy on risk-taking behavior in PD patients with (n = 22) and without (n = 19) active ICD symptoms. Patients performed the task both “on” and “off” DAA. DAA increased risk-taking in PD patients with active ICD symptoms, but it did not affect risk behavior of PD controls. DAA dose was also important in explaining risk behavior. Both groups similarly reduced their risk-taking in high compared to low risk conditions and following the occurrence of a negative consequence, suggesting that ICD patients do not necessarily differ in their abilities to process and adjust to some aspects of negative consequences. Our findings suggest dopaminergic augmentation of risk-taking behavior as a potential contributing mechanism for the emergence of ICD in PD patients. (PsycINFO Database Record (c) 2011 APA, all rights reserved)