92
of ten were detected. The auditory stimulus, which was a pure 500 Hz sine-wave tone,
was delivered via two computer speakers that were approximately 30 cm to the left and
right of a centrally located fixation light emitting diode (LED). The tone was 200 ms in
duration, 59 dB in intensity, and produced the percept of a central sound.
Participants fixated the central LED, which signaled the start of each trial with a
200 ms flash. Three hundred ms after fixation offset, one of four conditions was
delivered: auditory stimulus alone, somatosensory stimulus alone, auditory stimulus
with somatosensory stimulus, or no stimuli. Participants performed a two-alternative
force choice (2-AFC) task; they verbally reported on each trial whether or not they felt
the somatosensory stimulus and were instructed to ignore the auditory stimulus. Once
the verbal response of the participant was entered into the computer by the
experimenter, the next trial commenced after 500 ms. A total of 160 trials (40 trials for
each condition) was completed by each participant.
ResultsandDiscussion
An ANOVA was conducted on the behavioral responses, with auditory stimulus
(present vs. absent) and somatosensory stimulus (present vs. absent) as the two within-
Subject factors and the proportion of trials that resulted in a somatosensory percept as
the dependent variable. There was a highly significant main effect of the
somatosensory stimulus on detection (F1,ιg = 96.32, p < .001), demonstrating that the
electrical current successfully produced a somatosensory percept. The main effect of
the auditory stimulus was not significant {Flιg = 2.25, p = .15), indicating that sound