Primacy effects induced by temporal or physical context shifts are attenuated by a preshift test trial

Abstract

When subjects are sequentially trained with a cue (A) paired separately with two outcomes (B and C) in different phases (i.e., A-B pairings followed by A-C pairings) testing in the training context after short retention intervals often reveals recency effects (i.e., stronger influence by A-C). In contrast, testing after long retention intervals or testing in a context different from that of training sometimes reveals primacy effects (A-B). Three experiments were conducted using rats in a Pavlovian conditioned bar-press suppression preparation to ascertain whether a nonreinforced test trial in the training context soon after training can attenuate this shift to primacy. Experiment 1 demonstrated that exposure to A shortly after both phases of training, but prior to a long retention interval, can attenuate shifts from recency to primacy otherwise observed with a long retention interval. Experiment 2 showed that exposure to A in the training context can also eliminate the shift from recency to primacy otherwise produced by shifting the physical context between training and test. Experiment 3 discredited a potential account of the results of Experiments 1 and 2. The effects observed in Experiment 1 and 2 are interpreted as early testing in the training context serving to initiate rehearsal of the A-C association due to the temporal proximity of A-C training.

Figure 1

Experiment 1: Mean suppression ratios in response to X after a long retention interval. Lower ratios indicate less bar-pressing and thus better conditioned responding to the fear-invoking stimulus. Therefore, higher scores are indicative of latent inhibition and extinction. Error brackets denote the standard error of the mean for each group. PE = preexposure. See Table 1 for procedural details.

Figure 2

Experiment 2: Mean suppression ratios in response to a test of X or Y on Day 14 or 15 after the initial test of Y on Day 13. Lower ratios indicate lower levels of bar-pressing and thus better conditioned responding to the fear-invoking stimulus. Therefore, higher scores are indicative of latent inhibition. Error brackets denote the standard error of the mean for each group. PE = preexposure. See Table 2 for procedural details.

Figure 3

Experiment 2: Mean suppression ratios in response to Y across two tests on Day 13 and Days 14 or 15. Lower ratios indicate less bar-pressing and thus better conditioned responding to the fear-invoking stimulus. Error brackets denote the standard error of the mean for each group. PE = preexposure. See Table 2 for procedural details.

Figure 4

Experiment 3: Mean suppression ratios in response to X on Day 15. Lower ratios indicate less bar-pressing and thus better conditioned responding to the fear-invoking stimulus. Therefore, lower scores are indicative of effective sensory preconditioning. Error brackets denote the standard error of the mean for each group. SPC = sensory preconditioning condition. UP = unpaired. See Table 3 for procedural details.