Skin-Conductance, Alpha-Activity, and Vigilance

In the typical vigilance-situation, S is required to detect and to respond to slight and infrequent changes in stimulation over long periods of time. The usual finding has been that performance declines markedly after about a half-hour at the task.' Little attention has thus far been paid to the possibility of a relationship between performance in vigilance-tasks and electrophysiological measures of activation, such as skin-conductance and EEG alpha-activity. The present experiment was designed to investigate such a possibility. Method. The apparatus used to record skin-resistance was a Fels Dermohmeter, Model 22A. The zinc-zinc sulphate paste electrodes were attached to the soles of the feet by means of plastic clamps. Readings to the nearest 1000 0 were taken at the end of each minute and later translated into conductance-units. EEG-potentials were recorded from two chlorided silver-disk electrodes secured to the scalp by collodion and placed bilaterally over the occipital lobes about 1 in. above the occipital bulge. Two earlobe-electrodes were used for grounding, and no deflection in amplitude was observed on this channel. Conventional EEG-records were obtained by using a Grass Electroencephalograph, Model 111d. From the later stages of amplification of this instrument, the signal was fed into a band-pass electronic filter, rectified in an integrator preamplifier, Model 5U-IS, integrated in a unit-integrator, Model UI-I, and then further amplified and recorded with a polygraph recorder, Model 5. The characteristics of the filter were as follows: maximal relative transmission at 10 c.p.s., with 50% cut-off points, for sine-wave input at the electroencephalograph, at 7.3 and 12.9 c.p.s. The integrator, which provided mathematical integration (area under the curve), was reset each minute by an external timer. The 1-min. values were read to the nearest millimeter from the graphic record, and mean values later were computed for each 15-min. period. The vigilance-task involved the auditory presentation by tape-recording of a series of digits (1-9) in random order at the rate of 1 per sec. The signal to be detected consisted of a series of three successive odd digits, all of which were different. There were 36 such signals to be detected during the 90-min. session. In