[Abstract Title]. - Society for Neuroscience

262. Visually-Guided Reaching II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 262.13/CC27
Topic: D.05.d. Visually guided reaching
Title: Postural instability modulates the gain of involuntary manual response elicited by visual
motion during reaching movement
Authors: *K. KADOTA 1 , H. GOMI 1,2 ;
1 Shimojo Implicit Brain Function Project, ERATO-JST, Kanagawa, Japan; 2 NTT
Communication Sci. Labs., Kanagawa, Japan
Abstract: We have reported about the manual following response (MFR), which is a reflexive
manual response during arm reaching evoked by a sudden visual background motion. From
functional view point, this response may contribute to adjust the arm trajectory affected by
postural motion and disturbances because the response direction is a parallel with visual motion.
If this is true, it would be expected that a gain of the MFR will be modulated according to the
state of posture and its stability. To clarify this hypothesis, we compared the MFR amplitude
when participants performed reaching under different postural stabilities.
First, to clarify the postural effect on the MFR gain, we compared the MFR amplitude with
participants in a standing or a sitting positions. The participants sat or stood in front of a large
screen (62 x 46 cm) with their eyes 50cm away from the screen surface, where a visual stimulus
was projected. The stimulus consisted of a sinusoidal grating pattern having a horizontal gray bar
and a small white target-marker placed at the center of gray bar. The participants were asked to
reach for the target. In two third of the trials, the grating pattern started to move horizontally
either leftward or rightward at constant velocities, which was initiated 60 ms after the handmovement
start. In the results, the MFR amplitude was greater when reaching was performed in
the standing than in the sitting position. In addition, this tendency varied according to the
velocity of the visual motion. In the next experiment, we examined the effect of postural stability
on the MFR gain. Like the first experiment, participants required performing reaching for the
visual target projected on the screen, but they were standing on a stable or an unstable (motordriven)
platform. In the unstable platform condition, the participant required to maintain their
posture during reaching because of an induced platform instability at every five trial-interval. In
contrast, there was no postural disturbance in the stable platform condition. In the unstable
condition, the participants generated greater MFR than that in the stable condition. Thus, the
postural instability could enhance the MFR amplitude.
These results would support the idea that the MFR gain is modulated according to the postural
stability states. Therefore, it is reasonable to assume that the MFR could contribute an online
correction of hand trajectory deviation caused by postural disturbance during reaching.
Disclosures: K. Kadota , None; H. Gomi, None.