Emotional States Alter Force Control During a Feedback Occluded Motor Task Stephen A. Coombes, Kelly M. Gamble, James H. Cauraugh, and Christopher M. Janelle University of Florida, Gainesville The aim of the current experiment was to determine the extent to which pleasant and unpleasant emotional states altered the ability of men and women to control force production on a feedback occluded motor task that was not direction specific. Participants produced a precision pinch grip with visual feedback. After 5 s, feedback was occluded and replaced with a pleasant, unpleasant, or neutral image. The amplitude, variability, and structure of force production were calculated. As expected, the removal of visual feedback led to progressive force decay. More important, relative to neutral conditions, pleasant and unpleasant emotional states led to greater force production, resulting in attenuated force decay. The variability and structure of force production were not altered by affective state. In addition, men and women performed similarly across all conditions for all measures. We conclude that when sustained force production is not directed toward or away from the body, pleasant and unpleasant emotional states similarly excite the motor system. Neurobiological mechanisms are proposed to account for these findings. Implications and future research directions are discussed. Keywords: emotion, force, variability, error, gender Tasks requiring sustained isometric contractions have frequently been used in the motor control literature as a vehicle to better understand the impact of multiple factors on the functioning hu- man motor system. Within force control protocols, participants are typically required to generate and sustain a predetermined level of force, usually a percentage of their maximum voluntary contrac- tion (MVC), allowing the impact of environmental factors on the functioning motor system to be indexed in real time. Substantial work has documented the rate of decay in force production as differing levels of force are maintained. For exam- ple, Vaillancourt and Russell (2002) required participants to sus- tain a target force level at a predetermined percentage of MVC (5%, 15%, 25%, 35%, 45%, 55%, 65%, and 75%) for 20s. For the initial 8s of each trial, subjects viewed real time visual feedback, but in a portion of the trials, visual feedback was removed for the remaining 12s. Subjects were instructed to maintain the target force level as accurately as possible during the entire trial. Find- ings corroborated previous evidence in that force production (at all MVC levels) began to decay approximately 0.5 to 1.5s following the removal of visual feedback (Vaillancourt, Slifkin, & Newell, 2001), leading the authors to posit that the 0.5 to 1.5s time period represented a limit on the temporal capacity that accurate visuo- motor information can be retained in short-term memory. The pattern of force decay progressed exponentially during the remain- der of the no feedback trials and there was greater force decay over time as target force level increased. More important, variability (as indexed by standard deviation) within the decaying force trace remained stable within each trial. Variability in precision pinch grip force production is influenced by a number of factors. Specifically, variability is attenuated when (a) using three as compared to two digits to generate low force output (Sosnoff, Jordan, & Newell, 2005), (b) when visual feed- back is presented with greater visual gain (Sosnoff, Valantine, & Newell, 2006), (c) when force levels are relatively low (Vaillan- court & Russell, 2002), and (d) when visual feedback is presented more frequently (Sosnoff & Newell, 2005; Vaillancourt, Mayka, & Corcos, 2006). The precision pinch grip task has been particularly useful in advancing our understanding of how stress, age, and gender impact force control. For example, Noteboom and col- leagues (Noteboom, Fleshner, & Enoka, 2001) demonstrated that experiencing unpleasant arousal (manipulated by threat of shock) results in increased variability of a sustained pinch grip task (target force = 4N;  10% MVC), a pattern that was more profound in individuals who self-reported moderate as compared to low trait anxiety (Noteboom, Barnholt, & Enoka, 2001). Christou and colleagues (Christou, 2005; Christou, Jakobi, Crit- chlow, Fleshner, & Enoka, 2004) later clarified these initial find- ings in two papers that used a similar threat of shock protocol to demonstrate that variability is exacerbated when unpleasant arousal is manipulated simultaneously with the occlusion of visual feedback. More important, they suggested that the enhanced force fluctuations caused by the stressor (evidenced by increases in standard deviation, coefficient of variation, and information trans- mission) were due to an increase in low-frequency output of the spinal motor neurons. That is, greater variability was associated with increased power within the 1 to 2 Hz frequency range of the power spectrum. Thus, the precision pinch grip task has been tremendously helpful in developing our understanding of the functioning motor Stephen A. Coombes, Kelly M. Gamble, James H. Cauraugh, and Christopher M. Janelle, Department of Applied Physiology and Kinesiol- ogy, University of Florida. Correspondence concerning this article should be addressed to Stephen A. Coombes, University of Florida, Department of Applied Physiology and Kinesiology, P.O. Box 118205, 100 FLG, Gainesville, FL 32611. E-mail: scoombes@ufl.edu Emotion Copyright 2008 by the American Psychological Association 2008, Vol. 8, No. 1, 104 –113 1528-3542/08/$12.00 DOI: 10.1037/1528-3542.8.1.104 104