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Experiment 2
ExperimentaIParadigm
The Vibrotactile somatosensory stimulus in Experiment 2 was delivered by five
piezoelectric benders attached to the left and right hand and foot of the subject and the
right hip. Trial duration and TR were both 2 s (clustered acquisition was not used) and
there were five trial types, each containing stimulation of a single bender. The driving
voltage consisted of a 200 Hz sine wave modulated by a 4 Hz square wave envelope.
There was no task during hand or foot stimulation. Hip stimulation trials (catch trials)
required subjects to make an eye movement to a visual target (the word "TARGET") in
the upper right corner of the display screen, which was otherwise blank except for white
fixation crosshairs (the target and fixation crosshairs were always present, so there Were
no visual transients associated with changes in the display). fMRI data from the catch
trials were analyzed separately, so that oculomotor activations in catch trials would not
confound the somatosensory activations measured in hand and foot trials; only the
responses in hand and foot trials are reported here. In the rapid event-related design,
each 5-minute scan series contained 150 trials (corresponding to 150 TRs) with 25 of
each of the four types of hand and foot trials, 10 catch trials and 40 fixation baseline
trials. Subjects performed 4-6 runs. A report on somatosensory responses in area MST
using the data collected for Experiment 2 has been previously published (Beauchamp, et
al. 2007).