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This study compared the conditioning of averaged evoked potentials in 11 psychotic and 11 normal children (57 experiments). Evoked potentials, like the blocking of alpha rhythm, can be conditioned by coupling a short sound of low intensity with an intense light flash. In normal children, the amplitude of the potential evoked by sound at the occipital region is small and quite variable. Its amplitude increases and its variability diminishes after coupling of sound and light. Also its form may resemble the potential evoked by light, especially in its rhythmic after‐effects. In psychotic children auditory evoked responses are variable and small and remain so during the coupling of sound and light. Instead, these patients respond to the sound with a late slow wave, which is strong and generalized. It is particularly prominent during conditioning and resembles the slow waves which follow the visual evoked potentials in these autistic children. This slow wave can be experimentally reproduced in normal Ss by Psilocybine. It also resembles in certain ways the slow waves provoked by movement or its anticipation in normal Ss but it appears here during sensorial conditioning which requires no movement. We suspect that this slow wave may reflect a diffuse motor component in the perceptual and associative processes of these autistic children.