CNBC Brain Bag
Title: A cross-modal reach redirection task in rhesus monkeys reveals faster processing for vibrotactile than visual stimuli
Presenter: Jason Godlove
Location: MI 3rd Floor Social Room
Additional Information: Please RSVP to Linda Moya (lhmoya@cmu.edu) by Friday, November 13, and indicate if you require a vegetarian meal.
Abstract: During natural behaviors, we must synthesize and react to  information across sensory modalities. For example,  if your arm brushes against an obstacle while reaching toward a visible object, you may redirect your reach. We designed a  novel behavioral paradigm to test whether animals can incorporate cross-modal sensory information to adjust a reaching  movement in progress. We found that monkeys reacted  faster to a vibrotactile stimulus than to a visual stimulus that instructed them to redirect the reach.

On each trial, two grey squares appeared, indicating the potential reach targets. When one square briefly flashed yellow,  the monkey reached toward it. In a subset of trials, at varying times during the movement, a second cue changed the reach  goal to the alternate target. This redirection stimulus could be either visual or vibrotactile. In visually-cued trials, the alternate  square flashed yellow. In tactilely-cued redirect trials, a small vibrating motor on the monkey’s left or right shoulder turned on briefly.

Monkeys could redirect their reaches in response to both visual and vibrotactile cues. Successful redirections were more likely  to occur when the redirect cue was presented earlier in the reach. We calculated a “redirection signal reaction time” (RSRT), measured  as the time between the redirection cue and the resulting change in reach direction. The RSRT was significantly shorter for vibrotactile  stimuli (188 ms) than for visual stimuli (221 ms) (t-test, p<0.05). This means the “point of no return”, beyond which a monkey cannot  correct its reach, depends on stimulus modality, and occurs later if the redirect cue is vibrotactile than if it is visual. These observations  argue that vibrotactile information can influence an ongoing movement more rapidly than can visual information.