Can US sensitization account for the electrodermal variant of the Perruchet effect?

Can US sensitization account for the electrodermal variant of the Perruchet effect? Amy McAndrew ( am375@exeter.ac.uk ) a a Gabrielle Weidemann b Ian P.L. McLaren a School of Psychology, College of Life and Environmental Sciences, University of Exeter, UK. b School of Social Sciences and Psychology, University of Western Sydney, Australia Abstract During experiments employing Perruchet's (1985) paradigm there are runs of reinforced (CS-US) trials and non-reinforced (CS-noUS) trials. Conditioned responding (CR) is measured, for example, using eyeblink responses (Perruchet, 1985), reaction times (Perruchet, Cleeremans, & Destrebeceqz, 2006), or changes in skin conductance (SCR; McAndrew, Jones, McLaren, & McLaren, 2012), as well as an online measure of expectancy for the unconditioned stimulus (US). A double dissociation between CR and conscious expectancy of the US is typically found, whereby expectancy of the US decreases while the CR increases across runs of successively reinforced trials. A gambler’s fallacy explanation can be offered for the expectancy data, whereas an associative explanation can be used to explain variations in the CR (consistent with the dual processing theory of McLaren, Green, & Mackintosh, 1994). However, skeptics of this effect have proposed nonassociative explanations of the CR data seen in these experiments. They note that every CS-US pairing is confounded by the presence of the US. Therefore, it is possible that US sensitization, the phenomenon whereby repeated US presentations leads to stronger unconditioned responding to the US, could produce the increasing CR pattern with successive reinforcements (Weidemann, Tangen, Lovibond, & Mitchell, 2009). Two experiments are presented investigating whether US sensitization can explain the recently published electrodermal version of the Perruchet effect. Keywords: Perruchet effect; US sensitization; Dual processing systems Introduction The Perruchet effect (Perruchet, 1985, Perruchet, Cleeremans, & Destrebeceqz, 2006) is often cited as one of the most convincing pieces of evidence of a dissociation between explicit, conscious, propositional processes and implicit, automatic, associative processes (e.g. Mitchell, De Houwer, & Lovibond, 2009). McAndrew, Jones, McLaren and McLaren (2012) ran an electrodermal variation of the classic Perruchet experiment in which participants saw a visual conditioned stimulus (CS), a brown cylinder, which was partially reinforced by an electric shock (the unconditioned stimulus, US). The participants made online expectancy ratings on every trial as to whether they thought the US was going to occur. Changes in their autonomic skin conductance response (SCR) were also measured as an index of conditioned responding (CR). We found that the SCR increased over successive reinforcements, while expectancy of the US decreased across the same sequence of trials. This mirrored the original findings of Perruchet and colleagues in both the eyeblink (Perruchet, 1985) and reaction time (RT; Perruchet, Cleeremans, & Destrebeceqz, 2006) variants of this paradigm. The gambler’s fallacy heuristic (Burns & Corpus, 2004), an explicit, propositional phenomenon, explained the expectancy data, implying that as participants experienced successive runs of reinforced (CS-US) trials, they were less likely to rate the subsequent trial as being paired with a US. Conversely, when participants experienced runs of successively non-reinforced (CS-noUS) trials they rated it as increasingly likely they would experience a US. However, this explanation did not apply to the SCR data, but an associative account did (e.g. McLaren, Forrest and McLaren, 2012). SCR increased over successive reinforcements, meaning that the CR was strongest when the participants had experienced a run of CS-US trials. In associative terms, during this type of Pavlovian conditioning, the link between the representation of the CS and the representation of the US was strengthened by the successively reinforced trials, producing a larger CR. However, after a run of CS-noUS trials, the link between the representations of the CS and the US was weakened by extinction, causing smaller changes in SCR and therefore a weaker CR. Hence, these results are consistent with a dual processing systems account of learning, with an explicit propositional system generating the expectancy data and an associative system the changes in SCR. The Perruchet effect is one of the most compelling examples of dual processing systems due to the simultaneous measurement of CR and expectancy. Previous research demonstrating dissociations between these two variables has often involved subliminal presentations of the CS (e.g. Balderston, & Helmstetter, 2010), but this research is often criticized about whether the presented stimuli are truly subliminal (e.g. Mitchel, De Houwer, & Lovibond, 2009). Alternatively, researchers have attempted to use post- conditioning questionnaires to assess contingency awareness, however it has been argued this type of measure could be subject to interference or forgetting influencing the reliability and validity of the awareness measure (Lovibond, & Shanks, 2002). The Perruchet paradigm however, overcomes these problems and is a more convincing demonstration of a double dissociation. However, the dual processing system account of the Perruchet effect depends critically on the assumption that the linear trend in CRs is the result of associative learning. Alternately the pattern of CRs could be accounted for by US sensitization; this effect refers to the increase in unconditioned responding (UR) seen when there is repeated exposure to a US (Weidemann, Tangen, Lovibond, & Mitchell, 2009). In the Perruchet experiments, every CS-US pairing unavoidably involves presentation of the US. Therefore, it may not be the pairing of the two stimuli (CS and US) strengthening or weakening the associative link between the stimuli that is causing fluctuations in the SCR.