Postural displacements in response to emotional activation have recently been proposed as a direct and objective index of approach–avoidance behavior in humans. Here, we present the results of an experiment designed to assess spontaneous postural responses to discrete affective pictures, briefly presented in random order of valence. Our findings question the interpretation of phasic postural responses to emotional stimuli as approach–avoidance behavior. Further, we identify a robust dynamical pattern, characterized by specific features indicating that attentional processes may play a role in human postural responses to emotional stimuli.

Both the cue reactivity and startle reflex modulation paradigms have been used in addiction research to investigate the motivational mechanism of craving. However, while there is a growing body of literature that indicates the utility of 3D technology in addiction-relevant cue reactivity research, no study has been reported on its utility using the startle reflex modulation paradigm. The aim of the present study was to extend the 3D technology to research on tobacco craving using the startle reflex methodology. Participants were 32 university students who smoked more than 10 cigarettes daily. They participated in a psychophysiological testing to assess the modulation of the startle reflex induced by viewing pleasant, unpleasant, and tobacco-related 3D immersive environment stimuli (3D-IEs). Results confirmed that 3D-IEs were effective in inducing emotional states to modulate the startle response. Pleasant and unpleasant 3D-IEs modulated the startle response, as expected: The reflex was increased while viewing unpleasant stimuli and decreased while viewing pleasant ones. Tobacco-related 3D-IEs were similar to unpleasant stimuli in increasing the startle response. However, they were subjectively evaluated as positive, which suggests that the mechanism underlying craving coactivates both aversive and appetitive motivational tendencies.

Motivation to be abstinent is a relevant contextual factor accounting for variance in cue reactivity in individual smokers.

ARTICLE IN PRESS No. of Pages 12 c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e x x x( 2 0 1 2 ) xxx-xxx j o u r n a l h o m e p a g e : w w w . i n t l . e l s e v i e r h e a l t h . IntroductionIn experimental psychophysiology, human motor reactivity to sensory stimulation is usually indexed by surface electromyography (EMG), which requires the placement of several electrodes on the skin surface [1]. This limits the mobility of the subject and reduces the possible contexts in which motor responses can be recorded and evaluated. In * Corresponding author. addition, EMG captures only the activity of specific muscle groups, whereas certain motor reflexes to sensory stimuli, such as the startle reflex, involve a global motor response characterized by complex muscle contraction patterns at different body areas [2]. A detailed investigation of these global motor reactivity patterns, in relation to underlying physiological control mechanisms, could result in a more systematic mapping of psychophysiological processes under sensory stimulation.0169-2607/$ -see front matter

Erotic scenes and images of mutilated bodies are emotional stimuli that have repeatedly shown to evoke specific neurophysiological responses associated with enhanced attention and perceptual processing. Remarkably however, only a handful of studies have investigated human motor reactions to emotional activation as a direct index of physical approximation or withdrawal. Given the inconclusive results of these studies, the approach-avoidance distinction, one of the most salient concepts in human motivational research, remains a broadly exploited hypothesis that has never been empirically demonstrated. Here, we investigate postural responses elicited by discrete emotional stimuli in healthy young adults. We discover that both positive and negative affective pictures induce a significant posterior deviation from postural baseline equilibrium. Further, we find that neutral pictures also evoke posterior deviation, although with a less pronounced amplitude. Exploring the dynamical evolution of postural responses to emotional pictures at high temporal resolution, we uncover a characteristic profile that remains stable for stimuli from all three affective categories. In contrast, the postural response amplitude is modulated by the emotional content of the stimulus. Our observations do not support the interpretation of postural responses to affective picture-viewing as approach-avoidance behavior. Instead, our findings indicate the involvement of a previously unrecognized motor component of the physiological mechanism underlying human orienting responses.