Biomedical subjects

John E Fisk

Publications and source records attributed to John E Fisk.

16 recordsLinked to original sources

PubMed2006

The effects of concurrent cannabis use among ecstasy users: neuroprotective or neurotoxic?

The research evidence regarding the potential effects of ecstasy suggests that it may be neurotoxic and that its use is associated with cognitive impairment. In recent years evidence has emerged suggesting that cannabinoids, the active ingredients in cannabis, can be neuroprotective under certain conditions. Given that many ecstasy users also consume cannabis at the same time, the possibility emerges that these individuals might be less susceptible to ecstasy-related impairment. The present paper reanalyses the data from a number of previous studies, contrasting the performance of those individuals who generally consume cannabis and ecstasy at the same time with those who generally consume ecstasy on its own. The two ecstasy-using groups are compared with non-ecstasy users on a range of measures including processing speed, random letter generation, verbal and visuo-spatial working memory span, reasoning and associative learning. The two ecstasy user groups did not differ significantly from each other on any of the measures. Both user groups were significantly worse than non-ecstasy users on measures of associative learning, verbal and visuo-spatial working memory and reasoning. The results suggest that consuming cannabis at the same time as ecstasy does not reduce the likelihood of cognitive impairment.

Age Factors↗

PubMed2006

Reasoning about complex probabilistic concepts in childhood.

The competencies of children, particularly their understanding of the more complex probabilistic concepts, have not been thoroughly investigated. In the present study participants were required to choose the more likely of two events, a single event, and a joint event (conjunctive or disjunctive). It was predicted that the operation of the representativeness heuristic would result in erroneous judgements when children compared an unlikely component event with a likely-unlikely conjunction (the conjunction fallacy) and when a likely component event was compared to a likely-unlikely disjunction. The results supported the first prediction with both older children aged between 9 and 10 years and younger children aged between 4 and 5 committing the conjunction fallacy. However, the second prediction was not confirmed. It is proposed that the basis of representativeness judgements may differ between the conjunctive and disjunctive cases with absolute frequency information possibly playing a differential role.

Child↗

PubMed2005

The differential effects of ecstasy/polydrug use on executive components: shifting, inhibition, updating and access to semantic memory.

RATIONALE/OBJECTIVES: Recent theoretical models suggest that the central executive may not be a unified structure. The present study explored the nature of central executive deficits in ecstasy users. METHODS: In study 1, 27 ecstasy users and 34 non-users were assessed using tasks to tap memory updating (computation span; letter updating) and access to long-term memory (a semantic fluency test and the Chicago Word Fluency Test). In study 2, 51 ecstasy users and 42 non-users completed tasks that assess mental set switching (number/letter and plus/minus) and inhibition (random letter generation). RESULTS: MANOVA revealed that ecstasy users performed worse on both tasks used to assess memory updating and on tasks to assess access to long-term memory (C- and S-letter fluency). However, notwithstanding the significant ecstasy group-related effects, indices of cocaine and cannabis use were also significantly correlated with most of the executive measures. Unexpectedly, in study 2, ecstasy users performed significantly better on the inhibition task, producing more letters than non-users. No group differences were observed on the switching tasks. Correlations between indices of ecstasy use and number of letters produced were significant. CONCLUSIONS: The present study provides further support for ecstasy/polydrug-related deficits in memory updating and in access to long-term memory. The surplus evident on the inhibition task should be treated with some caution, as this was limited to a single measure and has not been supported by our previous work.

Adult↗

PubMed2005

Reasoning deficits in ecstasy (MDMA) polydrug users.

RATIONALE/OBJECTIVES: Previous research has shown that ecstasy users are impaired in thinking and reasoning. The present study sought to explore the possibility that syllogistic reasoning errors in ecstasy users were due to an inability to construct a model of the premises due to working memory limitations. METHODS: Twenty-nine ecstasy users and 25 nonecstasy user controls completed abstract syllogistic reasoning problems varying in difficulty. Pairs of premises were provided, and participants were required to generate conclusions that followed necessarily from them. RESULTS: On the easier problems, both groups performed at well above chance although nonusers achieved significantly more correct responses. Consistent with existing research, on the more difficult problems, errors by nonusers were characterised by incorrect conclusions suggesting that while nonusers have the working memory capacity to construct a single model of the premises, this is not an exhaustive representation and usually results in an erroneous conclusion. On the other hand, for all problem types, ecstasy users, rather than produce incorrect responses, were more likely to fail to generate a conclusion. CONCLUSIONS: The present results are consistent with the possibility that ecstasy users with their reduced working memory capacity may experience difficulty in constructing even a single model of the premises. While this might be attributable to the effects of 3,4-methlylenedioxymethamphetamine neurotoxicity, many of the ecstasy users in the present study were polydrug users. Thus, the possibility that other drugs including cannabis and cocaine might contribute to the present results cannot be excluded.

Adult↗

PubMed2005

The nature of ecstasy-group related deficits in associative learning.

RATIONALE/OBJECTIVES: Research has revealed associative learning deficits among users of ecstasy; the present study explored the component processes underlying these deficits. METHODS: Thirty-five ecstasy users and 62 non-ecstasy users completed a computer-based, verbal paired-associates learning task. Participants attempted to learn eight sequentially presented word pairs. After all eight had been presented, the first member of each pair was displayed and participants attempted to recall the second. Eight trials were administered. Correct responses on each trial, forgetting at various levels of learning, perseveration errors and the rate at which the associations were learned (trials to completion) were all recorded. RESULTS: MANOVA revealed that ecstasy users performed worse overall and subsequent ANOVAs showed that users performed significantly worse on virtually all measures. Regression analysis revealed that over half of the ecstasy-group related variance in trials to completion was attributable to group differences in initial learning and forgetting. In relation to forgetting, it appears that cannabis use may be an important determinant. In relation to rate of learning (trials to completion) and initial learning, both ecstasy and cannabis may be implicated. CONCLUSIONS: There appears to be abundant evidence of associative learning deficits among ecstasy users. However, it appears that a range of illicit drugs including cannabis and ecstasy may contribute to these deficits.

Adult↗

PubMed2005

Visuo-spatial working memory deficits in current and former users of MDMA ('ecstasy').

Verbal working memory and executive deficits have been observed in ecstasy users. The present study sought to establish whether these also extended to visuo-spatial working memory. Thirty-six current ecstasy users, 12 former users (abstinent for at least 6 months) and 31 individuals that had never used ecstasy were tested on a maintenance plus type visuo-spatial working memory task. The task required participants to recall a sequence of specially marked cells in a four-by-four matrix display while at the same time performing a concurrent visual judgement task. Both the current and former user groups registered impairments relative to nonusers. These remained significant following statistical controls for a range of potentially confounding variables including the use of various other drugs during the 3 months prior to testing. Users were unimpaired on a simple spatial span measure suggesting that the deficits observed reflected the executive aspects of the spatial working memory task. Also consistent with executive involvement, statistical controls for measures of verbal working memory performance (computation span) removed half of the ecstasy-related variance in spatial working memory. The possibility that the pattern of results obtained might reflect some general impairment in information processing efficiency is discussed.

Adult↗

PubMed2005

Syllogistic reasoning performance in MDMA (Ecstasy) users.

Previous research has demonstrated working memory and executive deficits in recreational users of MDMA (3,4-methylenedioxymethamphetamine; Ecstasy). In turn, both of these constructs have been implicated in syllogistic reasoning performance. Twenty-two MDMA users (mean age = 21.36) and 26 MDMA nonuser controls (mean age = 21.31) were tested on syllogisms of varying difficulty and on measures of working memory and executive functioning. MDMA users were significantly impaired in aspects of syllogistic reasoning, and the effect remained significant after the authors controlled for the use of other drugs. However, the MDMA-related variance was reduced to below statistical significance following control for group differences in working memory span. The results are consistent with the possibility that MDMA-related deficits in aspects of executive functioning result in impaired reasoning performance among MDMA users.

Adolescent↗

PubMed2005

Reasoning about conjunctive probabilistic concepts in childhood.

While adults are known to exhibit biases when making conjunctive probability judgments, little is known about childhood competencies in this area. Participants (aged between four and five years, eight and ten years, and a group of young adults) attempted to select the more likely of two events, a single event, and a conjunctive event containing, as one of its components, the single event. The problems were such that the objective probabilities of the component events were potentially available. Children in both age groups were generally successful when the single event was likely. However, when it was unlikely, a majority of children rejected it, choosing the conjunctive event instead, thereby committing the conjunction fallacy. A substantial minority of adults also committed the fallacy under equivalent conditions. It is concluded that under certain conditions children are capable of normative conjunctive judgments but that the mechanisms underpinning this capacity remain to be fully understood.

Adult↗

PubMed2004

Visuospatial memory impairments in users of MDMA ('ecstasy').

RATIONALE: Previous studies have presented conflicting findings regarding visuospatial span deficits in MDMA ('ecstasy') users, possibly attributable to a lack of distinction between simple visuospatial span and visuospatial working memory span. Both draw upon central executive processing, while the latter also involves concurrent goal-orientated visuospatial processing. OBJECTIVES: This study compared visuospatial working memory span for MDMA users and controls. An additional concurrent task also loading on the central executive tested for inter-group differences related to central executive workload. METHOD: MDMA user group (25 current users, 10 previous users and 18 non-users) was between-participants, and dual task condition (concurrent alphabetic generation, random letter generation, and no dual task) was within-participants. The visuospatial working memory task required participants to serially recall a spatial sequence while simultaneously completing a visual judgement task, and was completed on its own and under dual task conditions. RESULTS: Overall, non-users performed significantly better than both MDMA user groups. However, contrary to expectation, the performance decrement among users was no worse with concurrent random generation than under control conditions. Analyses controlling for background variables and the use of other drugs in the previous 3 months showed that the main effect of MDMA remained significant following control for intelligence, alcohol, amphetamines and cocaine, among other potential confounds. Unclear results were found following control for cannabis use. CONCLUSIONS: The MDMA users experienced deficits in visuospatial working memory span. The lack of interaction between dual task condition and user group may be due to inter-group differences in central executive utilisation under different task conditions.

Adult↗

PubMed2004

Verbal working memory deficits in current and previous users of MDMA.

Previous research suggests that MDMA users are impaired in various aspects of cognitive functioning, however, it remains unclear whether they might experience deficits in established measures of verbal working memory functioning. In the present study current and previous MDMA users were compared with non-users on verbal working memory measures including reading and computation span. Both user groups were found to be impaired on the computation span measure while current users also exhibited impairment in reading span. The MDMA-related deficit on the computation span measure remained significant following the introduction of statistical controls for the potentially confounding effects of cannabis and other drugs. The results are discussed in the context of recent research on executive processes. It is suggested that MDMA may produce differential effects on specific components within a fractionated executive system.

Adult↗

PubMed2004

Dyslexic students have more everyday cognitive lapses.

There is a dearth of information about the everyday performance difficulties of adult dyslexic people. This study investigates the empirical support for anecdotal reports of increased vulnerability to distraction in dyslexia, using the self-report Cognitive Failures Questionnaire (CFQ). Two groups of university students, a dyslexic group and a non-dyslexic control group, were asked to complete the CFQ. The dyslexic group reported a higher frequency of everyday lapses in cognition, scoring significantly higher on a number of CFQ items. Representative problems include distractibility, over-focusing (so that relevant peripheral information is missed), and word-finding difficulties. A similar measure administered to close friends of dyslexic people, the CFQ-for-others, yielded results consistent with those of the CFQ, with major findings being that their friends considered them to be more disorganised, more distractible, and more absent-minded than normal. The results indicate clearly the continuing effects of dyslexia on cognition in adulthood and demonstrate that dyslexic impairments are not limited to "artificial" laboratory tasks or even literacy tasks but, instead, pervade everyday life.

Adult↗

PubMed2004

Age-related impairment in executive functioning: updating, inhibition, shifting, and access.

Miyake, Friedman, Emerson, Witzki, Howerter and Wager (2000) have argued that the central executive is fractionated consisting of at least three separable component processes: updating, shifting, and inhibition. The Wisconsin Card Sort Test, random letter generation, Brooks spatial sequences, reading and computation span, word fluency, and a measure of dual task performance were administered to 95 individuals aged between 20 and 81, average age 41.89. The executive measures were factor analyzed, using the oblique rotation method, yielding four factors. The factor structure obtained was broadly consistent with Miyake et al's. However, an additional factor, the only one not to show a significant performance decline with age, was also obtained and was believed to reflect the efficiency of access to long-term memory.

Adult↗

PubMed2004

Evidence for executive deficits among users of MDMA (Ecstasy).

Random letter generation and computation span are tasks known to load on executive, prefrontal resources. Previous research suggests that Ecstasy users are impaired on random letter generation. The current study, employing a larger sample (44 current Ecstasy users, and 59 non-Ecstasy users), together with more effective statistical controls for other drug use, failed to replicate previous findings. Ecstasy users were unimpaired on all measures of random generation performance. A significant difference was obtained on the computation span measure, with Ecstasy users scoring significantly lower than non-Ecstasy users. This difference remained statistically significant following control for various indicators of the use of other drugs including cannabis. The results are discussed in terms of the potential effects that Ecstasy might have on different component executive processes.

Adult↗

PubMed2003

The role of the executive system in visuo-spatial memory functioning.

Participants were presented with a spatial sequence in which between 4 and 10 cells were highlighted. On each trial list length was unknown to the participant who was required to serially recall the last four cells. Processing of longer lists is assumed to call upon the executive system, which is thought to be involved in updating the contents of the short-term visuo-spatial store. Study 1 revealed that loading the executive system with concurrent random letter generation impaired performance on the spatial task especially recall of the early serial positions. However, contrary to expectation the degree of impairment was no greater on the longer lists, where it had been assumed that updating would be occurring. Study 2 confirmed this finding and demonstrated that relative to sequences of known length, under conditions of uncertainty when the list length was unknown, spatial recall was impaired even on short sequences. The present results support the growing consensus, which is suggestive of closer links between visuo-spatial and executive processes. However, it remains unclear whether or not updating is actually occurring on the longer sequences, and if it is, what specific executive processes are involved.

Adolescent↗

PubMed2002

Syllogistic reasoning and cognitive ageing.

Gilinsky and Judd (1994) demonstrated that age-related impairment in syllogistic reasoning was in part due to reduced working-memory capacity. A total of 30 older (average age 66 years) and 34 younger persons (average age 24 years) were tested on syllogisms of various types as well as on other measures. Syllogistic reasoning was significantly correlated with education, processing speed, word span, and word fluency. Correlations with visuo-spatial processing and random letter generation were just short of significance. Syllogistic reasoning performance declined with age, although the deficit was no longer statistically significant following control for age-related differences in information-processing speed. On the other hand the inclusion of word fluency as an additional covariate boosted the apparent age effect, returning it to statistical significance. Thus it is possible that cognitive processes outside of working memory might underpin at least part of the apparent age deficit. This possibility is evaluated in the light of neuropsychological evidence implicating the prefrontal cortex in both the processing of syllogisms and more generally in cognitive ageing.

Adult↗

PubMed2002

Judgments under uncertainty: representativeness or potential surprise?

Tversky and Kahneman's (1983) account of conjunctive probability judgment in terms of the representativeness heuristic is questioned. Instead, potential surprise (Shackle, 1969) is proposed as an important mechanism underlying subjective probability judgment. Study 1 reveals that, consistent with Shackle's theory, probabilities assigned to conjunctions are predominantly determined by the magnitude of the smaller component event probability. Also consistent with Shackle, Study 2 shows that for disjunctions, this role is performed by the larger component. Study 3 again contrasts the relative roles played by the component events in determining the value assigned to the conjunction. The results of the study are consistent with two reasoning processes: one analytically based, in which due account is taken of both component events, the other heuristic in nature and consistent with Shackle's theory of potential surprise. The implications of these results for a range of different types of judgment, e.g. with regard to person perception, stereotyping, categorization, and typicality, are evaluated.

Adult↗