Abstract
Two albino rats lever-pressed to avoid grid shock. Both subjects were trained with the simultaneous presentation of a 2500-cps tone and chamber light warning signal. Following stabilization of IRT patterns, one of the two stimulus components was deleted during one 6-hr. “probe” session. Later in the study the opposite stimulus component was deleted for a second 6-hr. “probe” session. Both subjects continued to place most avoidance responses in the presence of the tone-light combination or either component alone. Avoidance responding during a 6-hr. session with no warning signal showed a clear temporal discrimination. A subsequent 6-hr. “probe” session incorporated chamber vibration in substitution for the tone-light combination and resulted in efficient discriminated avoidance responding even though this stimulus modality had not been used during training sessions.