The Effect of LPC Narrowband Processing and Bit Error Rate on Performance in a Sentence Verification Task

The comprehension of narrowband digital speech with bit errors was tested using a sentence verification task. The difficulty of the verification task was varied by using predicates that were either strongly or weakly related to the subjects (e.g., A toad has warts./A toad has eyes.). The test conditions included unprocessed speech and speech processed using a 2,400 bitdsec linear predictive coding (LPC) voice processing algorithm with random bit error rates of 0%, 2%, and 5%. In general, response accuracy decreased and reaction time (RT) increased with LPC processing and with increasing bit error rates. Weakly related true sentences and strongly related false sentences were more difficult than strongly related true sentences and weakly related false sentences, respectively. Interactions between sentence type and speech processing conditions are discussed. The longer time taken to react to degraded speech has implications for performance in military combat situa- tions where split-second decisions are required. The higher error rates with degraded sentences that contain little contextual information are particularly relevant to policy conversations that use a varied vocabulary.