To the Editor:
My psychophysiologist friend Manny Donchin’s critique (“fMRI: Not the only way to look at the human brain in action,” Observer, November 2006) of the Observer’s treatment of fMRI as the only psychophysiological measure worth its salt is well founded. However, as a psychophysiologist who has employed older and more low-tech peripheral measures like electrodermal activity to study psychological functions, I beg to differ with the implication of Manny’s letter that only central measures like ERP and fMRI can provide information about the “human brain in action.”
For at least 60 years, the phasic electrodermal response (referred to in those days at the “GSR”) was employed to study human classical conditioning. And although there is still dispute about whether human autonomic conditioning is simply a function of an awareness of the relation between the conditioned stimulus and the unconditioned stimulus, as far as I know no one disputes that the conditioning phenomenon itself is a psychological function or, in other words, “the brain in action.”
Ultimately, the utility of any psychophysiological measure (central or peripheral, old or new) is determined by its ability to differentiate among psychological functions. My recent experience with an even older and lower-tech electrodermal measure, tonic skin resistance level (SRL ), suggested that this relatively “primitive” measure can differentiate bidirectional effects of an acute smoking manipulation (single cigarette after 10 hours deprivation) on males and females (Furedy et al., (1999). Sexually dimorphic effect of an acute smoking manipulation on skin resistance but not on heart-rate during a cognitive verbal task. Integrative Physiological and Behavioral Science, 34, 207-214). The psychophysiological SRL (or its reciprocal, skin conductance level) measure also has been useful in identifying a failure in conceptual cognitive function (sensitivity to repetition and change in a series of stimuli) unique to male schizophrenics (http://www.psych.utoronto.ca/~furedy/Papers/sd/sfn01abs.doc). As the essential component of schizophrenia is loss of touch with some aspects of reality, the SRL measure’s ability to differentiate among psychological functions appears to be superior to both the ERP and the fMRI.
In the end, psychologists employ many dependent variables to study “the human brain in action,” and psychophysiologists can offer a unique contribution to this study because they employ dependent variables that are not under the subject’s conscious control. We should avoid quasi-territorial fights about the superiority of any particular psychophysiological measure that are based on ideological prejudices rather than evidence-based choices in the quest to understand the complex interactions that occur among social, psychological, and physiological functions that influence behavior.
University of Toronto