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Seven subjects participated in experiment 1, and eight subjects participated in
experiment 2. In both experiment, Vibrotactile somatosensory stimuli were delivered by
five piezoelectric benders. In experiment 1, the five benders were attached to the left
palm, the right palm, the sole of the left foot, the sole of the right foot, and the right hip
(Fig. 1A). In experiment 2, the benders were attached to the thumb (DI), the third
(middle) finger (D3), and the fifth (pinky) finger (D5) of the right hand (adjacent fingers
were not stimulated because of mechanical constraints introduced by the benders); the
right foot; and the right hip (Fig. IB). A similar rapid event-related design was used for
both experiments (Fig. IC). Each 5-minute scan series contained 150 two-second trials
(corresponding to the MRI repetition time, TR, of 2 sec) with 10 hip target trials, 40
fixation baseline trials with no somatosensory stimulus, and 25 of each of the other four
benders. Trial ordering was counter-balanced so that each trial type was equally likely to
be preceded by any Other trial type, and experimental power was maximized by jittering
(randomizing) the interval between two trials of the same type (Dale 1999). Six scan
series were collected from each subject. There was no task during hand or foot
stimulation, other than to maintain visual fixation on central crosshairs. During hip
stimulation trials, subjects were required to make an eye movement to a visually
presented target. This ensured that subjects remained alert and attentive throughout
the experiment. Because hip trials were analyzed separately (and not used for the
classification analysis) any brain activity related to the eye movement responses could
not contribute to classification performance.