Influence of stimulus amplitude on unintended visuomotor entrainment Manuel Varlet a,b,⇑ , Charles A. Coey b , R.C. Schmidt c , Michael J. Richardson b a Movement to Health Laboratory, EuroMov, Montpellier-1 University, Montpellier, France b Perceptual-Motor Dynamics Laboratory, Department of Psychology, University of Cincinnati, Cincinnati, OH, USA c Department of Psychology, College of the Holy Cross, Worcester, MA, USA article info Article history: Available online 15 November 2011 PsycINFO classifications: 2330 2346 2260 3020 Keywords: Visuomotor coordination Eye movements Amplitude Period abstract Rhythmic limb movements have been shown to spontaneously coordinate with rhythmic environmental stimuli. Previous research has demonstrated how such entrainment depends on the difference between the movement periods of the limb and the stimulus, and on the degree to which the actor visually tracks the stimulus. Here we present an experiment that investigated how stimulus ampli- tude influences unintended visuomotor entrainment. Participants performed rhythmic forearm movements while visually tracking an oscillating stimulus. The amplitude and period of stimulus motion were manipulated. Larger stimulus amplitudes resulted in stronger entrainment irrespective of how participants visually tracked the movements of the stimulus. Visual tracking, however, did result in increased entrainment for large, but not small, stimu- lus amplitudes. Collectively, the results indicate that the movement amplitude of environmental stimuli plays a significant role in the emergence of unintended visuomotor entrainment. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Rhythmic human movements spontaneously coordinate with those of other individuals or environ- mental stimuli during visual interaction (e.g., Oullier, de Guzman, Jantzen, Lagarde, & Kelso, 2008; Schmidt & O’Brien, 1997; Schmidt, Richardson, Arsenault, & Galantucci, 2007; Varlet, Marin, Lagarde, 0167-9457/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.humov.2011.08.002 ⇑ Corresponding author at: Movement to Health Laboratory, EuroMov, Montpellier-1 University, 700 Avenue du Pic Saint Loup, 34090 Montpellier, France. Tel.: +33 467 415 767; fax: +33 467 415 704. E-mail address: manuel.varlet@gmail.com (M. Varlet). Human Movement Science 31 (2012) 541–552 Contents lists available at SciVerse ScienceDirect Human Movement Science journal homepage: www.elsevier.com/locate/humov