US alone trials presented during acquisition do not disrupt classical eyeblink conditioning: Empirical and computational findings

Studies of partial reinforcement in eyeblink conditioning have typically shown slower learning of a CS-US association when paired CS-US trials are interleaved with CS-alone trials. However, recent work has shown that CS-US learning is not slowed by interleaved US-alone trials. This discrepancy is surprising since both partial reinforcement protocols reduce the total number of paired CS-US trials. Previously, Kimble et al. (1955) reported that inserting a block of US-alone trials during CS-US training did not disrupt eyeblink acquisition. Here, we sought to replicate and extend these findings by comparing interleaved vs. blocked US-alone trials during CS-US paired training. Ninety-seven undergraduates volunteered for this experiment for research credit. Participants received 60 acquisition trials, consisting of either 100% CS-US paired trials, 50% US-alone trials intermixed with CS-US paired trials, or a block of 20 US-alone trials inserted between blocks of 20 CS-US trials. We also utilized a previously published computational model of hippocampal and cerebellar learning to test the effects of these US-alone protocols. Both empirical and computational results supported the finding that US-alone trials, either intermixed or inserted as a block of trials, do not disrupt acquisition of conditioned eyeblinks. Possible neural substrates of these US-alone effects are discussed.