Step 2: Calibrating voice amplitudes
The pilot sample of our study consisted of 19 participants. The following are their threshold data (Table 2):
Threshold data of a pilot sample
To calibrate the amplitudes of the voices for the VHT, we set the mean threshold for -5900 and SD for 150 which are approximately to the obtained values. We then used a range of voice amplitudes for the practice and the main VHT. The voice intensities in the main VHT ranged from three SDs above to two SDs below the mean threshold. Thus the intensities were −5450, −5600, −5750, −5900, −6050, and −6200 as Figure 1 indicates.
Voice amplitudes (i.e. volume) of the sound files in the main VHT E-Studio file
The voice amplitudes in the practice VHT include those of the main phase and also louder ones: −1000, −1500, −2000, −2500, −3000, −3500, −4000, −4500, −4700, −4900, −5000, −5200, −5450, −5600, −5750, −5900, −6050, and −6200 as Figure 2 indicates.
Voice amplitudes (i.e. volume) of the sound files in the practice VHT E-Studio file
Note. A range of amplitudes are used to ensure that participants are presented with below threshold to suprathreshold voice intensities so that the task remains sufficiently ambiguous to facilitate top-down perceptual processes and thus false alarm responses. Majority of the voices in the practice test are quite loud. This is to obtain the actual reaction time of participants to clearly audible voices. The range of sound amplitudes used in the task, however, can be changed depending on the objectives of a study.