ORIGINAL RESEARCH ARTICLE published: 22 January 2013 doi: 10.3389/fpsyg.2012.00599 To lead and to lag – forward and backward recalibration of perceived visuo-motor simultaneity Marieke Rohde 1,2 * and Marc O. Ernst 1,2 1 Department of Cognitive Neurosciences, University of Bielefeld, Bielefeld, Germany 2 Cognitive InteractionTechnology Centre of Excellence, University of Bielefeld, Bielefeld, Germany Edited by: Marc J. Buehner, Cardiff University, UK Reviewed by: David M. Eagleman, Baylor College of Medicine, USA Jon S. Kennedy,The University of Birmingham, UK *Correspondence: Marieke Rohde, Department of Cognitive Neurosciences, University of Bielefeld, Universitaetsstr. 25, W3-246, 33615 Bielefeld, Germany. e-mail: marieke.rohde@ uni-bielefeld.de Studies on human recalibration of perceived visuo-motor simultaneity so far have been limited to the study of recalibration to movement-lead temporal discrepancies (visual lags). We studied adaptation to both vision-lead and movement-lead discrepancies, to test for differences between these conditions, as a leading visual stimulus violates the underlying cause-effect structure.To this end, we manipulated the temporal relationship between a motor action (button press) and a visual event (flashed disk) in a training phase. Participants were tested in a temporal order judgment task and perceived simultaneity (PSS) was com- pared before and after recalibration. A PHANToM©force-feedback device that tracks the finger position in real time was used to display a virtual button.We predicted the timing of full compression of the button from early movement onset in order to time visual stimuli even before the movement event of the full button press.The results show that recalibration of perceived visuo-motor simultaneity is evident in both directions and does not differ in magnitude between the conditions. The strength of recalibration decreases with percep- tual accuracy, suggesting the possibility that some participants recalibrate less because they detect the discrepancy. We conclude that the mechanisms of temporal recalibration work in both directions and that there is no evidence that they are asymmetrical around the point of actual simultaneity, despite the underlying asymmetry in the cause-effect relation. Keywords: time perception, visuo-motor integration, temporal recalibration, multisensory perception, simultaneity perception INTRODUCTION When determining the timing of multisensory events, our brains have to compensate for cross-sensory latencies that stem from physical sources (e.g., light travels faster than sound) as well as physiological sources (e.g., differences in sensory transduction or neural transmission times). A growing body of evidence shows that the mechanisms of latency compensation are plastic and that they can be recalibrated by exposing participants for some period of time to a systematic small temporal discrepancy between uni- modal events. Temporal recalibration of this kind has been shown, for instance, for the perception of audio-visual, audio-tactile, and visuo-tactile simultaneity (e.g., Fujisaki et al., 1994; Keetels and Vroomen, 2008; Di Luca et al., 2009). The perceived order of a voluntary movement event and an external sensory event seems to be no exception from this rule. Stetson et al. (2006) have shown that humans recalibrate to par- tially compensate for a 100 ms lag between a button press and a visual flash. Similar results were reported in experiments with rhythmic finger tapping, including studies of sensory-motor recal- ibration in other modality pairs (tactile-motor, auditory-motor) and where transfer across modalities was observed (Heron et al., 2009; Sugano et al., 2010; Keetels and Vroomen, 2012; Sugano and Vroomen, 2012). Heron et al. (2009) could show that visuo- motor temporal recalibration weakens with increasing temporal discrepancy. Arnold et al. (2012) have shown that this constraint of temporal proximity is relative to the time of button press, not to the time of movement planning or movement onset. Yet, these kinds of studies have so far been limited to scenarios where the movement event leads the temporal order 1 . It is not clear, how- ever, whether adaptation where an external sensory event precedes a voluntary movement is possible and, if it is, whether it follows the same rules as adaptation to movement-lead discrepancies. This is an interesting question because of the causal relationship that usually is accompanied with such sensory-motor events, i.e., a vol- untary button press may trigger a flash but not vice versa. Given this rationale, a possible hypothesis is that it is not possible or more difficult to adapt if a flash precedes the movement event because of a violation of the naturally occurring causal relationship. By con- trast, given that mechanisms of sensory-motor recalibration tend to operate symmetrically in space, a different hypothesis would be that recalibration should work symmetrically in time as well. Here we designed an experiment to empirically test these two alternative hypotheses. Evidence in the literature that supports the asymmetry hypoth- esis stems from several sources. For instance, differences in pro- cessing around the point of actual simultaneity have been found in audio-visual speech perception, where subjects tolerate much larger auditory lags than visual lags, leading to an asymmetric 1 A possible exception is a study by Kato et al. (2009) that presumably found evidence for vision-lead adaptation with very small temporal discrepancies (15 ms). To our knowledge, this research has not been published in article format. www.frontiersin.org January 2013 |Volume 3 | Article 599 | 1