Emotional arousal does not affect delay eyeblink conditioning

Arousal can modulate information processing, including associative learning. However, there are conflicting results as to whether arousal affects eyeblink conditioning in humans. One potential problem with previous studies is that they have not taken into account factors that are known to affect conditioning. One such factor is the strength of the unconditioned response (UR). Despite evidence that greater UR leads to greater conditioned responses (CR), prior studies have not examined the role of the UR in CR performance. Prior studies have also usually classified subjects into low and high arousal groups based on a priori categorization without reliance on objective measures of arousal. The present study was designed to examine the impact of arousal on delay eyeblink conditioning. Changes in arousal levels were obtained by having participants view pictures selected for their a priori emotional and arousal values as being pleasant/arousing, unpleasant/arousing, or neutral/not arousing. Each subject viewed pictures of only one category. The spontaneous fluctuation of the skin conductance was taken as an index of physiological arousal. Subjects were divided into low and high arousal groups according to a median-split. Results showed that the rate of CR was positively related to the amplitude of the UR, but was not affected by emotional pictures or by physiological arousal. It is argued that changes in CR during arousal could be due to differences in unconditioned eyeblink strength rather than to changes in associative processes. (C) 2003 Elsevier B.V. All rights reserved.