Q: Can you advise me as to how to treat prevocalic devoicing of stops?

This is what I have found works for me-

Voice

It’s all about “voice on” vs. “voice off” so begin by teaching the client about his voice.  Have him place his fingers on his neck to feel the vibration or lack thereof when he turns his voice on and when he turns it off.

Vowels

Use “Ah” and whispered “Ah” to teach him to turn his voice on and off at will.  Then use other voiced and whispered vowels.

Vowel Sequences

Teach him to produce a prolonged “Ah” and turn his voice on and off as he does so.

Continuants

Take this skill into consonant productions and start with [+Continuant] consonants.  I use the fricative cognate pairs: F-and-V, S-and-Z, Sh-and-Zh. These are easier to begin with because the sounds can be prolonged and the voicing feature can be understood more easily. Start by simply practicing each one in isolation.  Make sure the client is producing a strong voice on the voiced ones.

Fricative Sequences

Teach him to control voice-on and voice-off in continuous sequences of these fricatives.  Have him say F-V-F-V-F-V-F-V, and S-Z-S-Z-S-Z, and Sh-Zh-Sh-Zh-Sh-Zh.  Make sure he is exhaling continuously while he is turning his voice on and off. 

CV Sequences with Fricatives

Work on initial F, V, S, Z, Sh, and Zh in nonsense words and real words of simple CV construction––

• Fee, fah, foo
• Vee, vah, voo
• See, sah, soo
• Zee, zah, zoo
• Shee, shah, shoo
• Zhee, zhah, zhoo

Stops

Once the client can do it with the fricatives, then go to the stops.  The stops are harder for the child to do because they occur so quickly.  A stop can’t really be prolonged, so use an H.  For example, practice “Peee” as “P-H-eee.” The H will help him hear the transition from voice-off to voice-on.  Many clients can start right at this step.

Ear Training

Make sure you are training his ear to hear all of this as you go along.