Speech during sustained operations

Research was conducted to determine if alterations in the acoustical characteristics of voice occur over periods of sustained operations. Twelve male United States Air Force B-1B bomber aircrewmen participated in the study. The participants served in crews of four and performed three 36-hour experimental periods (missions) in a high-fidelity simulator. The missions were interspersed with 36-hour rest breaks. Data were lost from two members of the third team due to a communication malfunction. Speech, cognitive and subjective fatigue data were collected approximately every three hours for 11 trials per mission. Fundamental frequency and word duration were both found to vary significantly over trials (fundamental frequency F(10,90) = 2.63, p = 0.0076, word duration F(10,90) = 2.5, p = 0.0106). Speech duration results also showed a significant main effect of mission (F(2,18) = 6.91, p = 0.0082). The speech data follow the same trend as the data from the cognitive tests and subjective measures. A strong diurnal pattern is reflected in nearly all of the dependent measures. Overall, the results support the proposition that voice may be a valid indicator of a speaker's fatigue state.