Can Speech Perception Deficits Cause Phonological Impairments? Evidence From Short-Term Memory for Ambiguous Speech

Poor performance on phonological tasks is characteristic of neurodevelopmental language disorders (dyslexia and/or developmental language disorder). Perceptual deficit accounts attribute phonological dysfunction to lower-level deficits in speech-sound processing. However, a causal pathway from speech perception to phonological performance has not been established. We assessed this relationship in typical adults by experimentally disrupting speech-sound discrimination in a phonological short-term memory (pSTM) task. We used an automated audio-morphing method (Rogers & Davis, 2017) to create ambiguous intermediate syllables between 16 letter name-letter name ("B"-"P") and letter name-word ("B"-"we") pairs. High- and low-ambiguity syllables were used in a pSTM task in which participants (N = 36) recalled six- and eight-letter name sequences. Low-ambiguity sequences were better recalled than high-ambiguity sequences, for letter name-letter name but not letter name-word morphed syllables. A further experiment replicated this ambiguity cost (N = 26), but failed to show retroactive or prospective effects for mixed high- and low-ambiguity sequences, in contrast to pSTM findings for speech-in-noise (SiN; Guang et al., 2020; Rabbitt, 1968). These experiments show that ambiguous speech sounds impair pSTM, via a different mechanism to SiN recall. We further show that the effect of ambiguous speech on recall is context-specific, limited, and does not transfer to recall of nonconfusable items. This indicates that speech perception deficits are not a plausible cause of pSTM difficulties in language disorders.