tested individually and initially asked to read the information sheet and complete the consent form, followed by the demographics questionnaire (age, gender, and native language). Following this, participants were provided with two different listening tasks and two different headphone conditions (presented in a counterbalanced order) along with a quiet baseline condition (half of the participants completed the baseline condition prior to the experiment while the other half completed this after the experiment). In the monosyllabic word test, participants were asked to listen to the recorded speech stimuli, which consisted of 50 phonetically balanced monosyllabic words (e.g., ace, end, his, jump, shoe, wood) with the carrier phrase ‘‘You will say ...’’. Participants were provided approximately 3 s to state the word they just heard. All words were recorded for analysis (words recorded on the Sony handheld digital recorder). This was repeated for both headphones conditions.
For the aviation phrase task, participants were asked to listen to the prerecorded aviation phrases, which consisted of 50 aviation ATC instructions. For example, ‘‘Tango Hotel Oscar – Climb to 7500, watch for traffic at 9 O’clock’’, or ‘‘Juliet Hotel Kilo – Traffic 2 O’clock, climb to 3000 feet report passing 1000’’. Items given in bold in these examples were removed and participants had to recall these items.
Between each phrase participants were given approximately ten seconds to complete the accompanying fill-in-the-blanks answer sheet (written). Each fill-in-the-blanks exercise contained the aviation phrase with between one and two random words missing. This was repeated in both headphones conditions. For both audio conditions (monosyllabic and aviation phrases), participants were allowed to set the desired volume level, consistent with what occurs presently within the aviation industry.
The audio (monosyllabic and aviation phrases) and listening (noise cancelling and non-noise cancelling) conditions were presented in a counterbalanced order, as per a Latin squares experimental design. During each listening task (except the quiet baseline condition) continuous aircraft noise was produced from the sound source. This was produced from the digital audio file recorded in the Cessna 172 during flight (recorded using NGARA sound acquisition system), as referred to above. The level at ear of the subject was adjusted to be comparable with the level measured during the flight. In cockpit noise for a Cessna 172 was chosen because this type of aircraft is widely used