Intelligibility of laryngectomees' substitute speech: automatic speech recognition and subjective rating

Substitute speech after laryngectomy is characterized by restricted aero-acoustic properties in comparison with laryngeal speech and has therefore lower intelligibility. Until now, an objective means to determine and quantify the intelligibility has not existed, although the intelligibility can serve as a global outcome parameter of voice restoration after laryngectomy. An automatic speech recognition system was applied on recordings of a standard text read by 18 German male laryngectomees with tracheoesophageal substitute speech. The system was trained with normal laryngeal speakers and not adapted to severely disturbed voices. Substitute speech was compared to laryngeal speech of a control group. Subjective evaluation of intelligibility was performed by a panel of five experts and compared to automatic speech evaluation. Substitute speech showed lower syllables/s and lower word accuracy than laryngeal speech. Automatic speech recognition for substitute speech yielded word accuracy between 10.0 and 50% (28.7+/-12.1%) with sufficient discrimination. It complied with experts' subjective evaluations of intelligibility. The multi-rater kappa of the experts alone did not differ from the multi-rater kappa of experts and the recognizer. Automatic speech recognition serves as a good means to objectify and quantify global speech outcome of laryngectomees. For clinical use, the speech recognition system will be adapted to disturbed voices and can also be applied in other languages.