1-Back reinforcement matching and mismatching by pigeons: Implicit or explicit learning?

In human learning a distinction has been made between implicit and explicit learning. Implicit learning is thought involve automatic processes of the kind involved in Pavlovian conditioning, while explicit learning is thought to involve conscious hypothesis testing and rule formation, in which the ability to report the rule used to learn the task is taken as evidence. Because non-verbal animals cannot provide such evidence, several indirect methods have been proposed. One of these methods is faster learning by humans of certain explicitly learned tasks than implicitly learned tasks, but pigeons do not show a similar difference. Another method involves the 1-back-reinforcement conditional discrimination (if A choose X, if B choose Y) in which feedback following the conditional response is delayed until the next trial. It has been argued that implicit learning cannot occur over the delay between the conditional response and the reinforcer on the next trial, yet, it has been found that monkeys can learn this 1-back reinforcement task. We have argued that such learning can occur implicitly. We have found that pigeons, a species not thought to learn explicitly, can show significant learning of both 1-back reinforcement matching and 1-back reinforcement mismatching, two versions of the 1-back-reinforcement conditional discrimination. We propose that the evidence for explicit learning by non-verbal animals suffers from alternative simpler accounts because the rationale for explicit learning is based on assumptions that likely are not correct.