Beat-by-beat cardiac responses in normals and schizophrenics to events varying in conditional probability.

Anticipatory cardiac deceleration and poststimulus acceleration were studied in schizophrenic inpatients and controls during performance of a counting task. Reduced cardiac responding has been reported for schizophrenic patients for paradigms using relatively long intertrial intervals. During a relatively fast rate of stimulus presentation (3-s interstimulus interval), changes in cardiac interbeat interval were measured in 20 inpatient male chronic schizophrenics and 18 control volunteers. Subjects counted an infrequent tone which was always followed by at least one frequent tone. Control subjects showed significant anticipatory cardiac deceleration preceding the unpredictable tones, whereas patients did not show a differential cardiac deceleration. Control subjects showed poststimulus acceleration that was inversely proportional to the conditional probability of events, whereas patients exhibited greatly reduced poststimulus acceleration; patterns for both groups resembled findings previously observed for event-related potential and pupillary dilation data. Analysis of cardiac cycle time indicated significant variation in primary bradycardia associated with the delay between stimuli and immediately preceding R-waves in controls (replicating Lacey & Lacey, 1980), with only an immediate bradycardia at stimulus reception for patients regardless of cardiac cycle time. The data reinforce the notion that the manner in which information is used by schizophrenics, as reflected by cardiac responsivity, differs both quantitatively and qualitatively from that of controls.