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during the recording. Sampling occurred at 20 Hz. The
analog SC signal was then be digitized by the Multifunction
board, which physically resides in the backplane of the
Compaq computer. Software control was accomplished by
customized programs.
Corrugator and zygomatic EMG was recorded using 2-mm
Ag/AgCl electrodes placed unilaterally over the corrugator
and bilaterally over the zygomatic muscle regions after the
skin was cleansed with 70% EtOH. Zygomatic EMG was
collected bilaterally because motoneuron pathways which
innervate the lower face are largely contralateral (Rinn,
1S84). On the other hand, corrugator EMG was collected
ipsilaterally because motorneurons innervating the upper
face muscles are for the most part, bilateral (Rinn, 1984).
Additionally, to control for possible laterality effects,
the LH NCs had electrodes placed over their left brow and
the RH NCs had electrodes placed over their left. Muscle
regions were designated using the placement specified by
Tassinary, Cacioppo, & Geen (1989) Four Colbourn model
S75-01 High Gain Bioamplifiers with bandpass filters were
used to record the signals. Filter level was set at 90-1000
Hz and coupling at 10 Hz (Fridlund & Cacioppo, 1986) Data
was integrated with Colbourn model S76-01 Contour Following
Integrator with a time constant set at 500 milliseconds.
Sampling rate was 20 Hz.