The effect of psychotomimetics on therapist--patient matching of speech "rhythms".

This study examined the effects of lysergic acid (LSD) and dextroamphetamine (DA) on therapist--patient matching of speech rhythms (mean phrase period) in psychotherapy. LSD, DA, and placebo (PL) were administered repeatedly over a 1 1/2-year period to seven patients in a randomized double-blind design. The second, fourth, and sixth encounters with LSD, DA, and PL were analyzed. These therapy dialogues were processed by an on--off detector of speech which computed probabilities of vocalizing when already talking (T), when listening (L), and when pausing (P) for therapist and patient, respectively. The mean phrase period for the therapist and the patient was calculated from the vocalization probabilities (T, P). The results show that both LSD and DA significantly enhance therapist-patient matching of mean phrase period in the earliest (second) session, an effect that disappears for both drugs, but later for DA (sixth session) than for LSD (fourth session). At no time was this effect observed in PL sessions, nor was the matching a simple function of a therapist--patient convergence of the components (T, P) of the mean phrase period.