Inhibition of delay a century later: A systematic review and Meta-analysis

Inhibition of delay has received relatively little attention compared with other Pavlovian phenomena, despite its early description by Pavlov. This review examined the conditions under which inhibition of delay develops and evaluated evidence for it both as a phenomenon, reflected in temporal discrimination of the conditioned stimulus, and as a mechanism involving inhibitory processes acting early in the stimulus. Inhibition of delay has been observed across many species and procedures, typically after extensive training and most often with aversive unconditioned stimuli. Although this diversity suggests broad generality, evidence from appetitive conditioning remains limited and inconsistent. A meta-analytic assessment indicates that temporal discrimination reliably emerges under inhibition-of-delay protocols, but substantial unexplained variability points to unidentified procedural moderators. Evidence for inhibitory processes includes gradual reductions in responding early in the conditioned stimulus, increases in response latency, and recovery of responding following disinhibition, retention intervals, or context changes. However, formal tests of conditioned inhibition have produced mixed findings, indicating that the inhibition involved differs from standard Pavlovian conditioned inhibition and may more closely resemble extinction-like processes. Overall, inhibition of delay appears to be a robust yet incompletely understood form of temporal inhibition that warrants further systematic investigation.