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Fisk JE, Murphy PN, Montgomery C, Wareing M.
“Comment on Halpern et. al (2011)”.
Addiction. 2011 Jul 03;106(7):1268-9.
The study by Halpern and co-workers  published recently in this journal reports findings in which ecstasy users with modest use of other drugs did not exhibit deficits on the majority of measures that were administered. This paper may be criticized on a number of grounds, but our focus here will be on two main areas: the nature of the sample and the choice of measures that were administered.
First, as the authors acknowledge, the sample is not representative of typical ecstasy/polydrug users. While the stated rationale for this choice has its merits, clearly it limits the generalizability of any inferences that might be drawn. More specifically, relatively heavy users of ecstasy are not well represented in Halpern et al.'s sample. Furthermore, the absence of an ecstasy-related deficit on many of the measures does not give ecstasy a clean bill of health (as the authors acknowledge), as the restriction on the use of other drugs reduces the possibility of detecting cocktail effects in which ecstasy may interact with other drugs such as alcohol, producing both acute and more longer-lasting deficits .
The second criticism of Halpern et al.'s study involves the choice of measures that were used. First, as in many studies concerning illicit drug use the tests administered were not informed by current theoretical perspectives in cognitive psychology. Many of the measures that are commonly used were developed for use with clinical groups and often lack the sensitivity to detect the subtle deficits present in recreational drug users. Furthermore, it is not surprising that many of the measures administered by Halpern et al. failed to reveal ecstasy-related deficits because these measures have failed to do so in the past. For example, four of five studies utilizing the Trail-Making Test Part B (TMT-B) revealed no statistically significant differences (the remaining one yielding ambiguous results) . Furthermore, a recent review of the literature  has demonstrated that, in relation to the Wisconsin Card Sorting Test (WCST) and the Stroop test, the majority of studies have failed to reveal ecstasy-related deficits; and only half of those studies using the F, A and S letter variant of the verbal fluency paradigm reported statistically significant ecstasy-related deficits. It is worthy of note that a more demanding task, Chicago word fluency, has been found to be associated with ecstasy-related deficits. The same review  has also shown that the majority of studies using simple spatial span or Corsi block tapping also failed to reveal ecstasy-related deficits.
Utilizing recent perspectives from cognitive psychology, in a number of studies [5,6] we have demonstrated that ecstasy/polydrug users are selectively impaired in executive pre-frontal tasks which require the updating of the contents of the working memory system. Other executive component processes which require the switching of attention (e.g. as assessed by the TMT-B and the WCST) or the inhibition of pre-potent responses (the Stroop) appear to be spared. Thus, in closing, we would argue that Halpern et al.'s results were not entirely unexpected. However, the implications of their findings are perhaps rather limited.
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