The Journal of Neuroscience, September 15, 1998, 18(18):7566-7580
Cognitive Channels Computing Action Distance and Direction
Raghuram B.
Bhat1 and
Jerome N.
Sanes1, 2
1 Department of Neuroscience, Division of Biology and
Medicine, Brown University, Providence, Rhode Island 02912, and
2 Scientific Institute Santa Lucia, Rome, 00179 Italy
Visually guided, goal-directed reaching requires encoding action
distance and direction from attributes of visual landmarks. We
identified a cognitive mechanism that seemingly performs visual motor
extension before action initiation and replicated and extended previous
results that identified a mechanism for visual motor mental rotation.
We find that humans systematically delay action onset while newly
planning increasingly distant arm movements beyond a visual landmark,
consistent with an internal representation for visual motor extension.
Onset times also changed systematically during concurrent mental
rotation and visual motor extension computations required to process
new directions and distances. Visual motor extension associated with
reaching slowed when participants needed to plan action direction
within the same time frame, whereas mental rotation efficiency was
unaffected by concurrent needs to prepare action distance. In contrast
to parallel direction and distance computations needed for direct
aiming to a visual target, the planning of new directions and distances
likely occurs at distinct times. When considered with previous
findings, the current results suggest the existence of an intermediate
component of motor preparation that engages a covert mechanism of
cognitive motor planning.
Key words:
voluntary movement; direction processing; distance
processing; reaching; mental calculations; movement planning
Copyright © 1998 Society for Neuroscience 0270-6474/98/18187566-15$05.00/0