Electronic Letters to:
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eLetters: Electronic letters published:
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fMRI and sex offenders
- Don MacFarlane (18 March 2009)
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Psychopathic traits and studies of deception
- Aamir Ehjaz (27 May 2009)
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Author response to Dr Ehjaz
- Rachael Fullam, Professor Mairead Dolan (3 June 2009)
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Don MacFarlane, CAMHS Consultant Belfast Trust
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donmac{at}doctors.org.uk Don MacFarlane
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The National Offender Management Service in Great Britain has proposed a three year pilot of mandatory polygraphy to help in the management of sex offenders during the phase of post-discharge into the community (Grubin). Following the pilot, a parliamentary decision will be taken as to the future of polygraph testing for sex offenders on a national basis. fMRI is thought to have 50% better reliability than polygraphy in lie detection, so the next logical step would appear to be post-haste to proceed with a similar pilot in this offender population. Considerable ground has yet to be made up but it is encouraging to see a first step has been taken to extend research to a quasi-clinical population in the first instance. The choice of members of university rugby teams as a proxy for a subclinical psychopathic population might raise some eyebrows and requires some explanation (Fullam et.al.). On a more positive note, the way in which the paper explains personality traits possibly associated with lying appears to have face validity. With reference to paedophilia, one can readily see how the combination of Machiavellian egocentricity, social potency, impulsive non -conformity and blame externalisation might combine to make a sexual offender a very effective groomer of children. Unfortunately, the paper appears to show that the presence of such traits also limits the usefulness of fMRI in lie detection. The question therefore arises whether this finding might also apply to polygraphy, and so have serious implications for the national polygraphy trial. On a more constructive note, the authors point out that reduced activation of the orbitofrontal cortex and caudate nuclei may be telltale signs of greater stress immunity. As shown by Mohamed et.al. , reduced activation of the ventral amygdalar fugal pathway, stria terminalis and hypothalamus might also point to the same effect. On balance, do the authors believe their research puts the nail in the coffin of any possible usefulness fMRI might have in lie detection in a psychopathic population, or can the issues highlighted by their paper be compensated for by future modifications of technique? 1 Grubin, D. (2006), Polygraph Pilot Study: Final Report, National Probation Directorate - available at http://www.probation.homeoffice.gov.uk/files/pdf/Polygraph%20Pilot%20Report%20 -%20July%202006.pdf 2. Fullam, R.S., McKie, S. And Dolan, D.C. Psychopathic traits and deception: functional magnetic resonance imaging study BJPsych (2009), 194, 229-235.~ 3. Mohamed, F.B.,Faro, S.H.,Gordon, N.J. et.al. Brain Mapping of Truth Telling and Deception (2006). Radiology, 238(2), 679-683. |
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Aamir Ehjaz, Specialty Registrar (Forensic Psychiatry) East London NHS Foundation Trust, London, UK
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aamir{at}doctors.org.uk Aamir Ehjaz
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The authors state the aim of this study was “to investigate the relationship between neural responses during deception and psychopathic personality traits…”. One of my main concerns is that, what the authors referred to as “deception” was not actually deception. The study subjects were aware that the truth is known and they were being asked to ‘lie’ for the study. I do not believe this to be a good enough surrogate for deception. For the purpose of the study, the word ‘lie’ was defined as “the intentional giving of a false response and awareness that the response is false rather than a mistake”. I believe this definition to be inadequate. The definition does not take into account that not only the participants were ‘told’ to provide the untrue answers but the fact that the true answers were known by the assessors also needs to be highlighted. This situation is more comparable to a dramatic performance or acting rather than deception. A more appropriate definition of a lie would include the intent to deceive that is always present in a lie. These participants did not intend to deceive anyone with the ‘false’ answers so they can not be seen as lying. Furthermore the study adopts an approach that does not take into account the emotional and contextual elements involved in deception. The consequences of lying or not lying during the study were also incomparable to the real life. This reduces the ecological validity of the study and makes the findings difficult to generalise. The participants were also “required” to make a motor response in order to select their answer. This adds further complexity to the analysis of the study results and further dents the ecological validity. One of the main findings of the study was that “mean response times (seconds) were significantly slower during the lie condition”. Although the stated P-value (0.024) shows a statistically significant difference, the actual difference of one tenth of a second (the difference between 2.66 and 2.56 seconds) only equates to about 4% delay. In clinical terms this does not appear to be significant. The fMRI does provide exciting opportunities for research but the overall the utility of this study appears to be very limited; further research of a higher quality is required in this fascinating but complex field. To overcome some of the problems with the methodology, the researchers would actually have to deceive the participants regarding the aims of such a study. The British Psychological Society provides extensive guidance regarding the use of deception in research (1). Reference: 1. http://www.bps.org.uk/the-society/code-of-conduct/ethical- principles-for-conducting-research-with-human-participants.cfm |
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Rachael Fullam, Post Doctoral Research Officer/Adjunct Lecturer Centre for Forensic Behavioural Science, Foresnicare and Monash University, Professor Mairead Dolan
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rachael.fullam{at}forensicare.vic.gov.au Rachael Fullam, et al.
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Dr Ehjaz appears to have misinterpreted the purpose of our study and his comments suggest a lack of awareness of the extensive literature examining the utility of fMRI for the detection of deception(1-4). The primary goal of the study was to examine the influence of psychopathic personality traits on neural responses exhibited during deception. As such, we used a direct replication of a previously published simple deception paradigm developed by Spence et al(5) and our definition of deception was lifted directly from Spences work in this area. We have clearly acknowledged in the paper that the work presented needs to be replicated with more sophisticated paradigms, including those with an emotional component. The issues surrounding deception paradigm design are adequately covered in the existing literature. Dr Ehjaz states that the main findings of the paper were the reported reaction time differences between the lie and truth conditions. This is not correct. The key findings of the study lie in the modulation of deception related BOLD responses by personality traits. The RT data is reported as a direct replication of Spence et als(5) finding and indicates increased cognitive load associated with the production of a lie at the same time as withholding a truthful response. In neural terms, a mean RT difference of 1/10 of a second is really rather significant. 1. Simpson JR. Functional MRI lie detection: too good to be true? J Am Acad Psychiatry Law 2008;36(4):491-8. 2. Bles M, Haynes JD. Detecting concealed information using brain- imaging technology. Neurocase 2008; 14(1):82-92. 3. Sip KE, Roepstorff A, McGregor W, Frith CD. Detecting deception: the scope and limits. Trends Cogn Sci. 2008;12(2):48-53. 4. Spence SA. Playing Devils advocate: The case against fMRI lie detection. Legal and Criminological Psychology 2008; 13: 11-25 5. Spence SA, Farrow TD, Herford AE, Wilkinson ID, Zheng Y Woodruff PWR. Behavioural and functional anatomical correlates of deception in humans. Neuroreport 2001; 12: 2849-53. |
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