Synthesized Speech Rate and Pitch Effects on Intelligibility of Warning Messages for Pilots

Abstract

In civilian and military operations, a future threat warning system with a voice display could warn pilots of other traffic, obstacles in the flight path, and/or terrain during low altitude helicopter flights. The present study was conducted to learn whether speech rate and voice pitch of “phoneme” synthesized speech affects pilots' accuracy and response time to typical threat warning messages. Helicopter pilots engaged in an attention-demanding “flying” task and listened for voice threat warnings presented in a background of simulated helicopter cockpit noise. Performance was measured by flying task performance, threat warning intelligibility, and response time to threat warnings. Pilot ratings were elicited for the different voice pitches and speech rates. Significant effects were obtained only for response time to messages and for pilot ratings, both as a function of speech rate. For the few cases when pilots forgot to respond to a voice message, they remembered 90% of the messages accurately when queried for their response 8 to 10 s later.