The role of the output phonological buffer in the control of speech timing: a single case study.

A patient with a selective impairment of speech output, associating phonemic paraphasias and pervasive preverbal pauses, it is described. Experimental data are discussed in relation to current models of speech production. On clinical evaluation, the pattern of paraphasias was strongly suggestive of a functional lesion affecting the output phonological buffer. This hypothesis received substantial support from a study of word and non-word repetition, as well as from a study of picture naming latencies, with various imposed delays between stimulus presentation and vocal response. In order to determine the origin of the preverbal pauses, the patient was also submitted to other timed motor tasks implicity probing higher levels of word production (gender decision and phonemic matching). We suggest that the pauses probably resulted from the conjunction of several mechanisms, including a general slowing apparent in all timed motor tasks, as well as a more specific time lag in speech initiation originating from the output buffer or from the articulator itself.