Integrating SLAM with existing evidence: Comment on Walker and Hickok (2015).

Walker and Hickok (Psychonomic Bulletin & Review doi:10.3758/s13423-015-0903-7, 2015) used simulations to compare a novel proposal, the semantic-lexical-auditory-motor model (SLAM), to an existing account of speech production, the two-step interactive account (TSIA; Foygel & Dell, Journal of Memory and Language, 43:182-216, doi:10.1006/jmla.2000.2716, 2000). This commentary critically examines their assessment of SLAM. The cases in which SLAM outperforms TSIA largely reflect SLAM's ability to (poorly) approximate an existing theory of speech production incorporating two stages of phonological processing (the lexical + postlexical account). The fact that SLAM and TSIA can exhibit equivalent fits to the overall response distribution of a set of aphasic patients is unsurprising, since previous work has shown that overall response distributions do not reliably discriminate theoretical alternatives. Finally, SLAM inherits issues associated with TSIA's assumption of strong feedback between levels of representation. This suggests that SLAM does not represent an advance over existing theories of speech production.