Stimulus Type Effect on Phonological and Semantic errors (STEPS) occurs when a person, following brain damage, produces phonemic errors with non-number words (e.g., lale for tale), but produces semantic errors with number words (e.g., thirteen for forty-two). Despite the relative frequency of this phenomenon, it has received little scholarly attention thus far. To explain STEPS, the Building Blocks hypothesis has been proposed (Cohen, Verstichel, & Dehaene, 1997; Dotan & Friedmann, 2015): the phonological output buffer includes single phonemes as the units of speech production for words, whereas entire number words are the building blocks of multi-digit production. Impairment in the phonological output buffer results in the incorrect selection of these units, leading to phonemic errors when producing non-number words, but semantic errors when producing numbers. In the present study we consider two patients, one with a deficit in the phonological output buffer, and one with a deficit in the phonological input buffer but with a preserved phonological output buffer. Number word and non-number word repetition, naming, and reading abilities were assessed. As expected, STEPS was found in the patient with deficits in the phonological output buffer in the three tasks; more notably, evidence of STEPS was also found for the patient with deficits in the phonological input buffer in the repetition task. Since our results cannot be fully explained by the Building Blocks hypothesis in its present form, we discuss the suitability of this hypothesis for the current data, and consider alternative accounts of STEPS.
