No abstract

A method for generating a reinforcement schedule that closely approximates idealized VI schedules in which reinforcement assignments occur randomly in time (RI schedules) is described. Response rates of pigeons exposed for 20 sessions to this schedule appeared very similar to response rates characteristic of arithmetic series VIs. The distribution function describing these schedules was derived and its relations to other VI distributions, as well as to FI and random ratio (RR) were shown.

No abstract

The form of classically conditioned suppression of instrumental performance associated with a fixed duration pre-aversive stimulus (CS) was quantitatively analysed over 300 acquisition trials. The temporal discriminations characteristic of this CER procedure were found to vary in form according to the stage of training. When the pre-aversive stimulus was subsequently made variable from trial to trial and its termination unpredictable, no change in average suppression during the CS occurred although the temporal discrimination was lost. Increasing the intensity of the aversive stimulus (US) produced an increase in average conditioned suppression of about the same degree whether the aversive stimulus was preceded by a fixed or variable duration CS.