Visual feedback modulates inherent bias in a visuomotor center-out pointing task

SOLANO, AGUSTIN; GIMENEZ, IGNACIO; DELLA MAGGIORE, VALERIA

Buenos Aires

Congreso; 2nd Latin American Brain Mapping Network Meeting; 2017

Latin American Brain Mapping Network Meeting (LABMAN)

Visuomotor adaptation is a type of motor learning in which subjects learn to adjust their motor output to counter a distortion of visual feedback. Experimentally it is studied during reaching or pointing movements by rotating a cursor that represents the position of the hand. Recently, it has been observed that reaching movements during the baseline training period, i.e., before the perturbation is applied, present an inherent bias in the magnitude of the final error. In other words, movements do not hit the target precisely but show a systematic bias that varies with movement direction. It has been suggested that this bias may result from several factors such as the biomechanics of the effector, a discrepancy between vision and proprioception and/or the inability to estimate the initial position of the hand. In our lab, this bias has also been observed in undisturbed movements when using a joystick to perform pointing movements. Here, we measured this bias and studied how it is modulated by visual feedback. A group of right-handed subjects performed center-out movements during a baseline period using a joystick operated with their thumb and index to control a cursor displayed on a computer screen. To quantify the intrinsic bias, subjects performed a block of 384 movements to 24 targets displayed concentrically without visual feedback of the cursor. To evaluate how this intrinsic bias was modulated by visual feedback, subjects performed a second block of the same duration while seeing the cursor´s trajectory and the movement end point. We found that the magnitude of the natural bias depends on the direction of the target and the existence of visual feedback. After providing feedback there is a decrease in the magnitude of the bias for some directions, suggesting the presence of adaptation learning. Other directions, however, show no difference in the level of bias with and without feedback. Finally, we found that the pattern of the bias across all directions is similar to the one observed in reaching experiments suggesting that the bias may not reflect biomechanical differences associated with the effector but may be intrinsic to the movement direction. Our results suggest that visuomotor studies should take into consideration this bias for future studies to factor additional adaptation for some but not all targets. We are currently working together with reaching laboratories to determine the source of this bias.