Influence of Visual and Haptic Cues on Podokinetic After-Rotation

Abstract

Active countercircling on a rotating platform for 15 min causes individuals to involuntarily circle in the same direction when they step in place on firm ground. This is referred to as podokinetic after-rotation (PKAR). It is unclear how interjecting brief periods of visual or haptic inputs for a stable orientation reference affects PKAR. The authors studied this issue in 16 healthy individuals who participated in three sessions each. Following active countercircling, participants attempted to step in place for 30 min on firm ground. In two of three sessions, participants received full visual input or made fingertip contact with a stationary object for 30 s during 30 min of ongoing PKAR. All participants slowed or stopped rotating during the presence of visual or haptic inputs and resumed PKAR after removal of these inputs. Exponential functions fitted to angular trunk velocity versus time plots revealed no significant differences across conditions (p > .05). The preservation of PKAR after brief exposure to a visual or haptic reference is consistent with a slowly decaying velocity storage that is not reset or dumped after exposure to conflicting visual or haptic cues.

Podokinetic stimulation causes shifts in perception of straight ahead

“…In the present experiments, and in other published work on PKAR, the influence of vision is eliminated via use of a blindfold. If vision is permitted, it temporarily suppresses PKAR, but PKAR resumes unchanged when visual inputs are again removed (Falvo et al 2009). The vestibular system has its strongest influence in the first 1-2 minutes as subjects begin to turn during active stepping PKAR, but yaw plane related vestibular influences decline once a steady rate of turning is reached (Earhart et al 2004).…”

“…While the PKAR process likely involves a network of supraspinal structures, it is clear that a major contributor to PKAR must be an area where vestibular, somatosensory, and visual inputs as well as cerebellar inputs are received and integrated, as all are known to influence PKAR responses (Jürgens et al 1999, Hong et al 2007, Falvo et al 2009, Earhart et al 2004). This control center may regulate a global variable regarding spatial reference frame, with adaptations of this reference frame then influencing a multitude of networks in the spinal cord via descending pathways.…”

“…PKAR, like the leaning after-effect, is dependent upon the direction and speed of rotating treadmill stimulation and is only temporarily suppressed by brief periods of visual input (Weber et al 1998, Falvo et al 2009). The strong parallels between leaning after-effects and PKAR suggest that PKAR may also operate at the level of global, whole body variables regarding orientation in space, as has been proposed for leaning after-effects.…”

Stepping in Place While Voluntarily Turning Around Produces a Long-Lasting Posteffect Consisting in Inadvertent Turning While Stepping Eyes Closed

“…Based on visual checking of the data and on previously published analyses [21, 27–29], a function characterized by two time constants was chosen in order to describe the initial rise in the posteffect angular velocity, which is then followed by a slow decay over time. To this aim, the iterative conjugate gradient method of the Excel® Solver Utility was used, τ 1 and τ 2 being the time constants, C being the asymptotic value of the function, and A + B + C being the intercept with the ordinate.…”

“…Remarkably, such PKAR is not consciously perceived [14, 18]. Of note, a visual or haptic input given for few seconds during the PKAR period can reduce the PKAR velocity; when the new information is removed, the PKAR reappears [21]. …”