Phonological similarity as an index of short-term memory precision

The concept of short-term memory (STM) precision has been defined as the resolution with which items are maintained in STM (Joseph et al., 2015). It has to be distinguished from STM capacity, which refers to the number of items that are recalled in a STM task. The latter notion is binary; a stimulus is either recalled or forgotten. On the other hand, the concept of STM precision suggests that items activated in STM may differ with respect to the resolution at which they are represented. The concept of STM precision has been studied in the visual STM domain but has received very little interest in the verbal STM domain. The present study assessed interindividual differences in the sensitivity to different degrees of phonological similarity between memory and probe items as a potential index of verbal STM precision. 60 young adults were presented auditory lists of 6 words. After a delay, a probe was presented, and the participants had to decide whether it had been in the list or not. Negative probes showed different degrees of phonological proximity with the target word in the memory list. Using Bayesian repeated measures ANOVA, we observed very strong evidence for an influence of phonological proximity on STM probe recognition performance: the more similar the negative probes to the target word, the higher the rate of false recognition. Critically, at an interindividual level, we observed significant variability in the sensitivity to the phonological proximity of distractors: some participants were very consistently misled by the distractors as a function of phonological proximity, while other participants showed very poor sensitivity to phonological proximity indicating that their memory representations had a low level of phonological resolution. This study suggests that memory-probe phonological similarity is an important variable for the development of measures of STM precision in the verbal domain.