Massed versus Distributed Practice in Learned Improvement of Speech Intelligibility

16. Abstract Student pilots or new air traffic controllers have two ways to learn to understand the noisy and distorted communications common to aircraft operations: they may learn as they are working on other aspects of the activity, or they may learn by devoting a continuous period of time to speech--intelligibility improvement. Work completed at this laboratory indicates that two listening sessions of less than 1 hour each can accomplish the improvement and, under some circumstances, a single session will do. The current experiments are intended to reveal some of the microstructure of this learning process. For the first experiment, subjects were divided into five groups: One was permitted 2 minutes of listening practice; another, 4· ' another, 8· ' another, 16; and the other, 32, Retests 2 weeks later showed intelligibility improvement as a function of the number of minutes of previous experience up to 16; the 2and 4-minute subjects appeared to be no different from subjects with no previous experience on this task, 8-minute subjects were somewhat better, and 32-minute subjects were indistinguishable from ones with a full hour of experience, Subjects for the second experiment were similarly divided except that each one returned to the laboratory three times a week until every listener had heard 32 minutes of distorted speech. The five groups are nearly indistinguishable from each other, which suggests that the nervous system stores even small amounts of information gained from practice with distorted speech to use later for comparisons and improvements,