The Interval Between the CS and the UCS as a Determiner of Generalization Performance

Rats were trained in a conditioned taste aversion paradigm in order to determine whether a trace interval between the conditioned stimulus (CS) and the unconditioned stimulus (UCS) would result in the forgetting of stimulus attributes. Accordingly,subjects were conditioned with milk (CS), given either an immediate or a delayed injection of lithium chloride (UCS),and tested 48 h later with either milk or chocolate milk, a generalized flavor. The rats conditioned immediately following the presentation of the CS avoided milk more than chocolate milk, indicating discrimination between the two flavors. Those conditioned after a trace interval avoided both flavors equally, suggesting a loss of stimulus attributes of the original CS. Delay rats, however, still exhibited substantial learning when compared with controls not experiencing the UCS. These results allege a role for the forgetting of stimulus attributes during a trace interval in addition to following a complete learning episode.