Objective: This study assessed a single subject's ability to detect the difference limen (DLs) for his self-generated intraoral air pressure while his oral and nasal cavities were experimentally coupled.
Method: The subject, a 46-year-old man, uses a speech bulb prosthesis to cover an unrepaired cleft of his hard and soft palates. The subject's oral and nasal cavities were experimentally coupled by drilling different size holes through the speech-bulb component of the prosthesis to approximate conditions of velopharyngeal insufficiency. There were four hole-size conditions (10, 15, 20, and 30 mm(2)), a no-prosthesis condition, and pre- and postbaseline conditions with the prosthesis intact. The subject blew into a tube connected to a pressure transducer and was presented with a series of paired pressure loads. The first pressure load of each pair was the referent (1, 3, or 5 cm H(2)O), and the second was a preselected comparator load of a different amount. The subject blew into the tube with sufficient force to center the voltage meter's needle at the zero mark. The subject then reported whether the second pressure load required more, less, or equal breath pressure, compared with the referent pressure load of that pair.
Results: Size of the hole coupling the oral/nasal cavities did not significantly affect the subject's difference limen.
Conclusion: Experimental coupling of the oral/nasal cavities did not affect this subject's ability to detect differences in his self-generated intraoral air pressure.