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@Article { 5515,
   title = {Imagined Self-Motion Differs from Perceived Self-Motion: Evidence from a Novel Continuous Pointing Method},
   journal = {PLoS One},
   year = {2009},
   month = {11},
   volume = {4},
   number = {11},
   pages = {1-11},
   abstract = {Background

The extent to which actual movements and imagined movements maintain a shared internal representation has been a matter of much scientific debate. Of the studies examining such questions, few have directly compared actual full-body movements to imagined movements through space. Here we used a novel continuous pointing method to a) provide a more detailed characterization of self-motion perception during actual walking and b) compare the pattern of responding during actual walking to that which occurs during imagined walking.
Methodology/Principal Findings

This continuous pointing method requires participants to view a target and continuously point towards it as they walk, or imagine walking past it along a straight, forward trajectory. By measuring changes in the pointing direction of the arm, we were able to determine participants' perceived/imagined location at each moment during the trajectory and, hence, perceived/imagined self-velocity during the entire movement. The specific pattern of pointing behaviour that was revealed during sighted walking was also observed during blind walking. Specifically, a peak in arm azimuth velocity was observed upon target passage and a strong correlation was observed between arm azimuth velocity and pointing elevation. Importantly, this characteristic pattern of pointing was not consistently observed during imagined self-motion.
Conclusions/Significance

Overall, the spatial updating processes that occur during actual self-motion were not evidenced during imagined movement. Because of the rich description of self-motion perception afforded by continuous pointing, this method is expected to have significant implications for several research areas, including those related to motor imagery and spatial cognition and to applied fields for which mental practice techniques are common (e.g. rehabilitation and athletics).},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.plosone.org/article/fetchObjectAttachment.action;jsessionid=7EC338C2BF98904DAB7CCEA3B5344BA6.ambra02?uri=info\%3Adoi\%2F10.1371\%2Fjournal.pone.0007793\&representation=PDF},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1371/journal.pone.0007793},
   EPUB = {e7793},
   author = {Campos, JL and Siegle, JH and Mohler, BJ and B{\"u}lthoff, HH and Loomis, JM}
}

@Article { 5516,
   title = {Measurement of instantaneous perceived self-motion using continuous pointing},
   journal = {Experimental Brain Research},
   year = {2009},
   month = {5},
   volume = {195},
   number = {3},
   pages = {429-444},
   abstract = {In order to optimally characterize full-body self-motion perception during passive translations, changes in perceived location, velocity, and acceleration must be quantified in real time and with high spatial resolution. Past methods have failed to effectively measure these critical variables. Here, we introduce continuous pointing as a novel method with several advantages over previous methods. Participants point continuously to the mentally updated location of a previously viewed target during passive, full-body movement. High-precision motion-capture data of arm angle provide a measure of a participant’s perceived location and, in turn, perceived velocity at every moment during a motion trajectory. In two experiments, linear movements were presented in the absence of vision by passively translating participants with a robotic wheelchair or an anthropomorphic robotic arm (MPI Motion Simulator). The movement profiles included constant-velocity trajectories, two successive movement intervals separated by a b
rief pause, and reversed-motion trajectories. Results indicate a steady decay in perceived velocity during constant-velocity travel and an attenuated response to mid-trial accelerations.},
   department = {Department B{\"u}lthoff},
   web_url = {http://springerlink.metapress.com/content/t0625668v1651t45/fulltext.pdf},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1007/s00221-009-1805-6},
   author = {Siegle, JH and Campos, JL and Mohler, BJ and Loomis, JM and B{\"u}lthoff, HH}
}

@Poster { 5137,
   title = {High-precision capture of perceived velocity during passive translations},
   journal = {Journal of Vision},
   year = {2008},
   month = {6},
   volume = {8},
   number = {6},
   pages = {1043},
   abstract = {Although self-motion perception is believed to rely heavily on visual cues, the inertial system also provides valuable information about movement through space. How the brain integrates inertial signals to update position can be better understood through a detailed characterization of self-motion perception during passive transport. In this study, we employed an intuitive method for measuring the perception of self-motion in real-world coordinates. Participants were passively translated by a robotic wheelchair in the absence of visual and auditory cues. The traveled trajectories consisted of twelve straight paths, five to six meters in length, each with a unique velocity profile. As participants moved, they pointed continuously toward a stationary target viewed at the beginning of each trial. By using an optical tracking system to measure the position of a hand-held pointing device, we were able to calculate participants' perceived locations with a high degree of spatial and temporal precision. Differentiating perceived location yielded absolute instantaneous perceived velocity (in units of meters per second), a variable that, to the best of our knowledge, has not previously been measured. Results indicate that pointing behavior is updated as a function of changes in wheelchair velocity, and that this behavior reflects differences in starting position relative to the target. During periods of constant, nonzero velocity, the perceived velocity of all participants decreases systematically over the course of the trajectory. This suggests that the inertial signal is integrated in a leaky fashion, even during the relatively short paths used in this experiment. This methodology allows us to characterize such nonveridical aspects of self-motion perception with more precision than has been achieved in the past. The continuous-pointing paradigm used here can also be effectively adapted for use in other research domains, including spatial updating, vection, and visual-vestibular integration.},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/VSS\%20Poster\%20Final\%20Small_[0].pdf},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.journalofvision.org/8/6/1043/},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Naples, FL, USA},
   event_name = {8th Annual Meeting of the Vision Sciences Society (VSS 2008)},
   language = {en},
   DOI = {10.1167/8.6.1043},
   author = {Siegle, JH and Campos, JL and Mohler, BJ and Loomis, JM and B{\"u}lthoff, HH}
}

@Poster { 5462,
   title = {Imagined self-motion differs from perceived self-motion},
   journal = {Journal of Vision},
   year = {2008},
   month = {6},
   volume = {8},
   number = {6},
   pages = {1147},
   abstract = {Self-motion perception refers to the ability to perceive the speed and direction of movement through space. Past measures of self-motion perception have failed to directly assess the dynamic, instantaneous properties of perceived self-motion in real-world coordinates. Here we developed a novel continuous pointing method to measure perceived self-motion during translational movements. This experiment took place in a large, fully tracked, free-walking space. Participants viewed a target and then, with eyes closed, attempted to point continuously towards the target as they moved past it along a straight, forward trajectory. Pointing behaviour was tracked using a high-precision optical tracking system which monitored a hand-held pointing device. By using arm angle, we continuously measured participants' perceived location and, hence, perceived self-velocity during the entire trajectory. We compared the natural characteristics of continuous pointing in a control condition (sighted walking) with that during conditions in which particular sensory/motor cues were reduced, including: blind walking, passive transport, and imagined walking in the complete absence of physical movement. Results demonstrate that under all reduced cue conditions involving actual movement, perceived self-velocity and displacement were relatively accurate. Specifically, the pattern of pointing in the blind walking condition did not differ from that of the passive transport condition. This indicates that, for simple, linear trajectories with a raised-cosine velocity profile, inertial cues alone can be used to perceive self-motion. Perhaps most interestingly, the “signature” pattern of pointing observed during true self-motion (notably an increase in arm azimuth velocity upon target approach) was absent during imagined pointing. Consequently, continuous pointing reveals a characteristic arm trajectory that is unique to actual self-motion. This appears to be an automatic, obligatory process that is not reproduced during a purely cognitive representation of self-motion in the absence of movement. This method has direct implications for several research areas, including spatial cognition and navigation.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.journalofvision.org/8/6/1147/},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Naples, FL, USA},
   event_name = {8th Annual Meeting of the Vision Sciences Society (VSS 2008)},
   language = {en},
   DOI = {10.1167/8.6.1147},
   author = {Campos, JL and Siegle, J and Mohler, BJ and Loomis, JM and B{\"u}lthoff, HH}
}

@Poster { 5107,
   title = {High-precision capture of perceived self-motion with a continuous-pointing paradigm},
   year = {2008},
   month = {4},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/CyberWalk\%20Poster\%20Small_[0].pdf},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.cyberwalk-project.org/},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {T{\"u}bingen, Germany},
   event_name = {Cyberwalk Workshop 2008},
   language = {en},
   author = {Siegle, JH and Campos, JL and Mohler, BJ and Loomis, JM and B{\"u}lthoff, HH}
}

@Poster { 4767,
   title = {Distance perception in visual-to-tactile sensory substitution},
   year = {2007},
   month = {10},
   pages = {61},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/Sensory\%20substitution\%20poster_4767[0].pdf},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.esf.org/conferences/07226},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Sant Feliu de Guixols, Spain},
   event_name = {ESF-EMBO Symposium on Three Dimensional Sensory and Motor Space: Perceptual Consequences of Motor Action},
   language = {en},
   author = {Siegle, JH and Warren, WH}
}