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SEVERAL investigators1-3have recognized that intermittent visual stimulation such as occurs when the eyes scan a picture is associated in man with the appearance of discrete electric discharges, lambda waves, in the parietal and occipital areas of the scalp. A previous communication4reported the findings of similar waves in the monkey, dog, cat, and rabbit. Others working with monkeys,5,6dogs,7and cats8also noted the occurrence of discharges in the occipital region, which they likewise considered to be the equivalent of lambda waves in the human. The studies to be reported represent an extension of those previously reported findings.4Not only were conventional scalp, extradural, and depth recordings made but computer summation techniques also were employed; in particular a Computer of Average Transients (CAT) was triggered by eye-movement potentials, and the succeeding brain activity was summed.9Thus, it was possible to sum

THE PRESENT study was part of a series of investigations into the human electroencephalographic response to visual patterns and "pattern sensitivity" at this laboratory 1,2 ; in particular, the investigations are concerned with λ-waves, 3 which occur as a response to scanning of patterned visual fields in the electroencephalograms of normal human subjects and which also have been found in many varieties of animals. 4 Remond and associates 5 first investigated λ-waves, using a computer-averaging technique. They called the response obtained the "lambda complex." In the parieto-occipital region, it consisted of four main components. The first was negative (N 1 ), followed by a positive wave (P 1 ), and then by a negative (N 2 ) and a positive deflection (P 2 ). In the present investigation, briefly reported 6 previously, a slightly different technique, using the Computer of Average Transients (CAT), was employed. The method was based on the observation 7,8 that each

SINCE 1947, when Dawson 1 described a method which made it possible to record somatosensory evoked cortical potentials from the human scalp by means of a computeraveraging technique, there has been considerable interest in the broader applications of these methods. Recent studies by Bickford and associates 2 have focused attention on the occurrence of evoked motor responses in association with the more classical potentials of cortical origin. Widespread myogenic responses, below movement threshold, to sound and to photic stimulation have been described and have been named the "sonomotor response" and the "photomotor response," respectively. The contaminating effect that these potentials can have on evoked responses recorded from the scalp and the difficulties of their separation have already been stressed. This report describes the myogenic potentials resulting from median nerve stimulation and illustrates how these responses also may contaminate scalp-recorded somatosensory evoked responses. 3 In addition, studies undertaken to