Effect of Delay of CS Termination and Similarity between CS and Safety Signal (FS) on the Extinction of Shuttlebox-Avoidance Responding

Abstract

Two groups of 48 rats were trained on an avoidance task with a 2000-Hz tone CS. A safety signal or feedback stimulus (FS) following a hurdle response was provided by either a 4000-Hz tone (FSI) or 8000-Hz tone (FS2) for two groups, respectively. During extinction FS1 and FS2 groups were divided into four subgroups receiving 0-, 2-, 5-, or 10-sec. delay of CS offset (and therefore FS onset), respectively. FS2 facilitated acquisition but not extinction of the avoidance response. Extinction was facilitated by greater delay of CS offset and greater similarity between CS and feedback stimulus, with the two variables exerting independent additive effects. Results support the proposition that the similarity of CS and feedback stimulus and the delay of reinforcement function independently in avoidance situations.