A voluntary motor response that is prepared in advance of a stimulus may be triggered by any sensory input. This study investigated the combination of visual and kinesthetic inputs in triggering voluntary torque responses. When a visual stimulus was presented alone, subjects produced a fast and accurate increase in elbow flexion torque. When a kinesthetic stimulus was presented instead of the visual stimulus, subjects produced a similar response with a reduced response latency. When a visual stimulus was presented in combination with a kinesthetic stimulus, subjects initiated their responses after either a visual or a kinesthetic response latency, depending on the relative timing of the two stimuli. An analysis of response amplitude suggested that when visual and kinesthetic stimuli were combined, both stimuli triggered a response. The results are more consistent with a simple behavioral model of addition of visual and kinesthetic responses (which predicts that the response to combined stimuli should be the sum of individual responses) than with a model of exclusion of one response (which predicts that the response to combined stimuli should be identical to either the visual or the kinesthetic response). Because addition of visually and kinesthetically triggered responses produced a response with an erroneously large amplitude, it is suggested that visual and kinesthetic inputs are not always efficiently integrated.
Bibliographical noteFunding Information:
The authors wish to thank Lesley Klumpp, Valerie Rae McClain, and ]ames R. Wilson for help with the literature search and data analysis. Research in this laboratory is supported by United States Public Health Service Grant AN37017, National Research Service Award NS07661, and a grant from The Medical Research Foundation of Oregon, Inc. Correspondence should be addressed to Dr. M. Flanders, Neurological Sciences Institute, Good Samaritan Hospital & Medical Center, 1120 N. W. 20th Avenue, Portland, Oregon 97209.
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