The wheel-turning performance of 140 hooded rats was studied both in a free-responding and in a discrete-trial avoidance situation. A 3 × 2 × 2 design, involving comparisons of three intertrial intervals (15, 30, and 60 sec.), two CS-UCS intervals (constant and variable), and two wheel-rotation criteria (90° and 360°), was employed in the free-responding condition. Differential avoidance was found to be a positive increasing function of the length of the intertrial interval, but it was not affected substantially by CS-UCS interval or by the rotation requirement. No group's performance exceeded 42% on any day. Performance with the discrete-trial technique improved significantly in the case of the 15 sec. ITI but not for the 60-sec. ITI. Problems involved in making meaningful comparisons of free-responding and discrete-trial procedures were discussed.
SOME EFFECTS OF INTERTRIAL-INTERVAL DURATION ON DISCRETE-TRIAL CHOICE
