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Experiment Author: Adapted from STEP and used with permission of Brian MacWhinney
This experiment compares the reaction time to respond to stimuli with the same hand as the eye that saw the stimulus and the reaction time to respond to stimuli with the opposite hand.
In this experiment, participants test their reaction time to visual stimuli with their right hand and left hand. A fixation point appears with a delay that ranges from 500 to 1500 milliseconds, followed by an "X" that appears on the left or right side of the fixation point. Participants press the spacebar as soon as the "X" appears.
Poffenberger, A.T., Jr. (1912). Reaction time to retinal stimulation with special reference to the time lost in conduction through nerve centers. Archives of Psychology, 23, 1-73.
Cited Experiment Abstract
Poffenberger (1912) first proposed that one could use reaction time (RT) to measure the time needed for neural signals to cross the corpus callosum, the large “nerve” connecting the two cerebral hemispheres. His reasoning was as follows. If you flash a light to the left (say) of the center of vision and ask a subject to press a key as soon as he or she sees the flash, then RT should be longer if the subject responds with the right hand. Because the right hemisphere receives the visual signal, a response with the left hand (controlled by the right hemisphere) is an “uncrossed” response. But if the response is by the right hand, the information about the signal must be transferred (via the corpus callosum) to the left hemisphere, in order for the right hand to respond. Poffenberger argued that the extra time needed for crossed responses is an estimate of the extra time required because neural signals must cross the corpus callosum.
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