Pigeons (nine groups of seven) were given one acquisition session of 20 trials. The following day their responding was extinguished, and after a 30-min rest period they were tested for residual response strength. The groups differed with respect to (1) whether a distinctive stimulus was presented during acquisition on the first trial, the 15th trial, or not at all, (2) whether or not responses to the distinctive stimulus were reinforced, and (3) whether a distinctive stimulus, a standard stimulus, or a completely novel stimulus was presented on the test trial. Results supported the position that a stimulus associated with the onset of an acquisition session, but not with the extinction session, evokes greater response strength on a spontaneous recovery test trial than do other stimuli in the acquisition session. This holds true even if responses to this stimulus are never reinforced. In addition, it was found that, unlike a previous study that invoked five daily acquisition sessions, pigeons did not demonstrate increased responding to a novel stimulus.