Learning to unlearn: The role of negative evidence in morphophonological learning

Abstract

Phonological forms often express many different morphological functions. Learning these functions is quite challenging. How do learners accomplish this? Linguistic studies often assume that learning involves co-occurrence of cues and outcomes –contiguity–, but research shows that mere contiguity cannot explain learning effects (Nixon, 2020, Ramscar et al., 2010). Error-driven learning theories (Rescorla and Wagner, 1972) instead assume learning to be contingency-based: Cues predict outcomes, and learning is viewed as a continuous process of adjusting predictions on the basis of errors. Cues compete with each other to predict outcomes. This cue competition drives learning. One effect of cue competition is unlearning – a cue losing its association to an outcome –, which has not yet yet been investigated empirically in morphophonological learning. This paper reports an artificial language learning experiment, as well as computational simulations, in which we investigated unlearning in morphophonology: We taught participants a morphophonological pattern, in which words forms contained two grammatical functions simultaneously. In a subsequent step they were shown word forms which contained only one of those functions. It turned out that the cue that was predictive of this single function in the second part of the experiment was less strongly associated with the other function – an effect that we explain as an effect of unlearning. Additionally, we also observed that the strength of unlearning depended on the salience of the cues.