Abstract: The difference in the phonological encoding in silent speech between persons who stutter (PWS) and persons who do not stutter (PNS) is one of the most convincing evidences of the abnormal phonological processing among PWS. Thus far, the most influential theory concerning the potential link between phonological encoding and stuttering is the Covert Repair Hypothesis (CRH), in which the primary symptoms of stuttering represent overt manifestations of covert corrections of speech plan errors that are caused by the delayed phonological encoding of speech sounds. The present study intended to investigate the role of phonological encoding in silent speech.
The participants were 12 PWS who were matched in gender, age, educational attainment, and handedness with 12 PNS. Each participant performed 3 parallel experiments: monitoring target phonemes (including Shengmu (initial consonants of Chinese syllables), Yunmu (simple or compound vowels of Chinese syllables), and Tones in Chinese phonetics) during concurrent silent picture naming. In addition, each participant performed 3 extra tasks to control the extraneous variables: an overt picture naming task, a task of monitoring target pure tones in aurally presented tonal sequences, and a simple motor task requiring finger button clicks in response to an auditory tone.
The results indicated that the response time of PWS was almost the same as that of the PNS in Shengmu monitoring, but was significantly slower in Yunmu and Tone monitoring than that of the PNS. No significant between-group differences emerged for response time during the picture naming, auditory monitoring, or simple motor tasks. The findings were interpreted to suggest a specific deficiency at the level of phonological monitoring, rather than a general monitoring, reaction time, or auditory monitoring deficit in PWS. Further, the findings supported the Covert Repair Hypothesis.
The following conclusions can be drawn. First, there was no lack of attention resources when the Chinese PWS monitored the target Shengmu, while the PWS were significantly slower than the PNS in monitoring the target Yunmu and Tone. Second, the Chinese PWS had a deficit in the Chinese phonological monitoring, and the deficit was probably caused by the delayed phonological encoding of the PWS

Key words: stuttering, phonological encoding, phoneme monitoring, Covert Repair Hypothesis