By using a force-sensing isometric manipulandum, response force waveforms were recorded from rats performing a duration differentiation. For 2 rats exteroceptive cues were correlated with response force exceeding the force criterion and with attainment of the 1.60-sec. duration required for reinforcement. The other 3 rats received no exteroceptive support, the water reinforcer being delivered upon response termination. In the last phase of the experiment, reinforcement was contingent upon holding response force within a force “band” for a specified time. Relative frequency distributions of response duration indicated that differentiation of duration was more accurate in the presence of exteroceptive cues than in the absence of such stimuli. Spectral analysis of individual response waveforms indicated that rhythmic force oscillations (2 to 6 hz) predominated, despite the subjects' reliance on exteroceptive stimuli. Introduction of the joint force-band-duration contingency reduced but did not completely abolish the oscillations for both cued and uncued subjects. Over-all the results suggest that the rhythmic force variations observed here may be unselected or elicited components of the response rather than manifestations of a proprioceptive self-cueing process.
Counterconditioning of shock by a water reinforcer in rabbits
