 He noted that various non-human primates perform self-directed activities such as grooming and scratching in situations likely to involve anxiety and uncertainty, and that these behaviours are increased by anxiogenic (anxiety-producing) drugs and reduced by anxiolytic (anxiety-reducing) drugs.In humans, he noted that similar self-directed behaviour, together with aimless manipulation of objects (chewing pens, twisting rings), can be used as indicators of 'stressful stimuli and may reflect an emotional condition of negative affect'.The subsequent development of research on displacement activities was a direct consequence of Konrad Lorenz's works on instincts.