Human Factors Evaluation of Vocoders for Air Traffic Control ... - FAA

helicopter background noise, which could confuse the participants and create bias. All messages
were, therefore, realistically comparable with those used in the field.
2.2.6 Test Length and Distribution
The research team decided that 90 minutes was a maximum time that could be asked of volunteer
participants. Preliminary investigations indicated that each participant could not complete all
test conditions with replications and remain under the time limit. To avoid this difficulty, the
researchers split the Subjective Ratings Test and the Message Completion Test at the sex of
speaker condition whereby each participant evaluated voice messages from a single sex of
speaker for both tests. Completed tests from two participants evaluated all test conditions.
Table 4 presents a summary of the test distribution.
The first two messages of the Subjective Ratings Test and Message Completion Test were
practice for the participants. The average total time remained below the target limit including a
10-minute break and planned instructions, and rarely exceeded 80 minutes.
Test
Total Test
Conditions
Table 4. Test Distribution
Conditions
Evaluated per
Test Participant
Subjective
Ratings 24 12
Message
Completion 24 12
Number of
Messages
3 per test
condition + 2
Practice
3 per test
condition + 2
practice
Test Time per
Message
Approximate
Test Time
60 seconds 38 minutes
30 seconds 19 minutes
Vocoder
Preference 8 8 1 60 seconds 8 minutes
Total 1 hour, 5
minutes
2.3 Data Acquisition
2.3.1 Participants
The test participants consisted of 207 current air traffic controllers. The test participants were
from Air Route Traffic Control Center (ARTCC), Air Traffic Control Tower (ATCT), and
Terminal Radar Control (TRACON) environments. Strict adherence to all federal, union, and
ethical guidelines on the use of human participants was upheld.
2.3.2 Experiment Staff
The personnel involved in the design and execution of this study included the Project Manager,
who is a Human Factors Professional, two Human Factors Specialists, one Human Factors
Engineer, a Supervisory Air Traffic Control Specialist (SATCS), and an Air Traffic Control
Specialist (ATCS). The SATCS served as the Subject Matter Expert (SME) and created all
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