Steven Roodenrys

Chronic Effects of Brahmi (Bacopa monnieri) on Human Memory

A study is reported on the effects of Brahmi (Bacopa monniera) on human memory. Seventy-six adults aged between 40 and 65 years took part in a double-blind randomized, placebo control study in which various memory functions were tested and levels of anxiety measured. There were three testing sessions: one prior to the trial, one after three months on the trial, and one six weeks after the completion of the trial. The results show a significant effect of the Brahmi on a test for the retention of new information. Follow-up tests showed that the rate of learning was unaffected, suggesting that Brahmi decreases the rate of forgetting of newly acquired information. Tasks assessing attention, verbal and visual short-term memory and the retrieval of pre-experimental knowledge were unaffected. Questionnaire measures of everyday memory function and anxiety levels were also unaffected.

Sublexical or lexical effects on serial recall of nonwords

S. E. Gathercole, C. R. Frankish, S. J. Pickering, and S. Peaker (1999) reported 2 experiments in which they manipulated phonotactic properties of nonword stimuli and observed the effects on serial recall. Their results show superior recall for items consisting of more frequent phoneme pairs (biphone frequency). Biphone frequency was counted as the number of 3 phoneme words in which the phoneme pair occurs. In the first experiment of the current article, the authors made the same manipulation while controlling for the number of lexical neighbors and found no effect of biphone frequency. In the second experiment, the authors manipulated neighborhood size while controlling biphone frequency and found a significant effect of neighborhood size. The authors argued that serial recall of nonwords is influenced by lexical rather than sublexical knowledge.

Word-frequency and phonological-neighborhood effects on verbal short-term memory

Immediate memory span and maximal articulation rate were assessed for word sets differing in frequency, word-neighborhood size, and average word-neighborhood frequency. Memory span was greater for high- than low-frequency words, greater for words from large than small phonological neighborhoods, and greater for words from high- than low-frequency phonological neighborhoods. Maximal articulation rate was also facilitated by word frequency, phonological-neighborhood size, and neighborhood frequency. In a final study all 3 lexical variables were found to influence the recall outcome for individual words. These effects of phonological-word neighborhood on memory performance suggest that phonological information in long-term memory plays an active role in recall in short-term-memory tasks, and they present a challenge to current theories of short-term memory.

Serial recall and nonword repetition in reading disabled children

This study examined the performance on verbalshort-term memory tasks of specifically readingdisabled children relative to reading-age matched andchronological-age matched control groups. Memory spanfor words, highly wordlike nonwords and less wordlikenonwords, speech rates for these items, and nonwordrepetition were examined. The reading disabled groupperformed equivalently to the reading-age controls onall tasks, and worse than the chronological-agecontrols. An effect of the wordlikeness of thenonwords was found in all tasks. Differences inspeech rate accounted for the effect of wordlikenessin memory span but not for the difference betweenwords and nonwords, or for the difference betweengroups. The stimulus effects did not vary between thegroups suggesting that reading disabled children arenot impaired on the process which gives rise to theseeffects, however they are impaired on the taskoverall, even after speech rate differences are takeninto account. These results are consistent with thenotion that there is a long-term memory contributionto memory span which is related to reading ability.

Working memory function in attention deficit hyperactivity disordered and reading disabled children

The aim of the current study was to examine the nature of executive processing in working memory as a core deficit in attention deficit hyperactivity disorder (ADHD) as distinct from deficits associated with reading disability (RD). This involved examination of the working memory processes of the phonological loop and central executive (Baddeley, 1986) as a potential means of differentiating ADHD from RD. The participants were 16 ADHD/RD, 16 RD and 16 normal control children, matched for sex, age and IQ, who performed tasks tapping phonological loop function, a combination of phonological loop and central executive functioning, and tasks relying on central executive functioning. Analysis revealed that as the involvement of the central executive in tasks increased, ADHD/RD children performed worse than the other groups. This was on measures of controlled information processing, modifying and accommodating new input and supervisory capacity. These findings reflect the potential utility of the central executive in working memory in understanding the nature of executive processing deficits in ADHD. They also support the efficacy of these tasks in discriminating ADHD from RD.

Executive processing and attention deficit hyperactivity disorder: an application of the supervisory attentional system.

Children with attention deficit hyperactivity disorder (ADHD) display many behaviors consistent with an underlying deficit in executive processes. This study examines Norman and Shallices (1986) supervisory attentional system (SAS) as an approximation of executive functioning thought to be impaired in ADHD. Fifteen ADHD children were compared to a clinical control sample of learning disabled (LD) children and control children matched for age, gender, and IQ on a series of tasks designed to tap the functions of the SAS. The tasks assessed either the inhibition of a strongly triggered response (Star Counting Test, Hayling Sentence Completion Test, and the Random Generation Test) or impulsive responding in the absence of strong trigger-schema contingencies (Brixton Spatial Anticipation Test). Analyses revealed that the ADHD group was significantly impaired, in comparison to the LD and control groups, on tasks requiring the inhibition of a strongly triggered response. Further support for the fractionation of the SAS is provided by the differential performance of the groups on these tasks.

Neurocognitive training for children with and without AD/HD

There is accumulating evidence that computerised cognitive training of inhibitory control and/or working memory can lead to behavioural improvement in children with AD/HD. Using a randomised waitlist control design, the present study examined the effects of combined working memory and inhibitory control training, with and without passive attention monitoring via EEG, for children with and without AD/HD. One hundred and twenty-eight children (60 children with AD/HD, 68 without AD/HD) were randomly allocated to one of three training conditions (waitlist; working memory and inhibitory control with attention monitoring; working memory and inhibitory control without attention monitoring) and completed with pre- and post-training assessments of overt behaviour (from 2 sources), trained and untrained cognitive task performance, and resting EEG activity. The two active training conditions completed 25 sessions of training at home over a 4- 5-week period. Results showed significant improvements in overt behaviour for children with AD/HD in both training conditions compared to the waitlist condition as rated by a parent and other adult. Post-training improvements in the areas of spatial working memory, ignoring distracting stimuli, and sustained attention were reported for children with AD/HD. Children without AD/HD showed behavioural improvements after training. The improvements for both groups were maintained over the 6-week period following training. The passive attention monitoring via EEG had a minor effect on training outcomes. Overall, the results suggest that combined WM/IC training can result in improved behavioural control for children with and without AD/HD.

The effects of stimulus set size and word frequency on verbal serial recall.

Two experiments are reported which examine immediate serial recall for high-and low-frequency words. The words in each list were either repeatedly drawn from the same small pool of candidates (in the closed set conditions) or each word only ever occurred once during the experiment (in the open set conditions). The results consistently show an effect of word frequency but the effect of set size was only apparent for low-frequency words. It is argued that both frequency and set size effects reflect processes concerning the “clean-up” of degraded short-term memory traces.

A pilot study of combined working memory and inhibition training for children with AD/HD

Building on recent favourable outcomes using working memory (WM) training, this study examined the behavioural and physiological effect of concurrent computer-based WM and inhibition training for children with attention-deficit hyperactivity disorder (AD/HD). Using a double-blind active-control design, 29 children with AD/HD completed a 5-week at-home training programme and pre- and post-training sessions which included the assessment of overt behaviour, resting EEG, as well as task performance, skin conductance level and event-related potentials (ERPs) during a Go/Nogo task. Results indicated that after training, children from the high-intensity training condition showed reduced frequency of inattention and hyperactivity symptoms. Although there were trends for improved Go/Nogo performance, increased arousal and specific training effects for the inhibition-related N2 ERP component, they failed to reach standard levels of statistical significance. Both the low- and high-intensity conditions showed resting EEG changes (increased delta, reduced alpha and theta activity) and improved early attention alerting to Go and Nogo stimuli, as indicated by the N1 ERP component, post-training. Despite limitations, this preliminary work indicates the potential for cognitive training that concurrently targets the interrelated processes of WM and inhibition to be used as a treatment for AD/HD.

Varying task difficulty in the Go/Nogo task: the effects of inhibitory control, arousal, and perceived effort on ERP components

Similar to other executive functions, inhibitory control is thought to be a dynamic process that can be influenced by variations in task difficulty. However, little is known about how different task parameters alter inhibitory performance and processing as a task becomes more difficult. The aim of this study was to investigate the influence of varying task difficulty, via manipulation of reaction time deadline (RTD), on measures of inhibitory control, perceived effort, and task-related arousal (indexed by skin conductance level). Sixty adults completed a visual Go/Nogo task (70% Go) after being randomly assigned to one of three task difficulty conditions: High, Medium and Low, with RTDs of 300, 500 or 1000 ms, respectively. Results revealed incremental increases in Go/Nogo errors and greater perceived effort with increasing difficulty. No condition differences were found for arousal, but the amplitude of the Nogo N2 increased and peaked earlier with increasing task difficulty. In contrast, the Nogo P3 effect was reduced in the High condition compared to the Low and Medium conditions. Finally, the amplitude of N1 and P2 showed differential effects, with Nogo N1 increasing with task difficulty, while the Nogo P2 decreased. This study provides valuable baseline behavioural and ERP data for appropriately manipulating difficulty (via RTD) in Go/Nogo tasks - highlighting the potential key role of not only the N2 and P3, but also the N1 and P2 components for task performance.