An Automated System for Sound Localization Testing in Hearing-Impaired Listeners

In this study, we aim to develop a fully automated system to measure sound localization ability in patients with hearing impairment. Although some systems include a certain level of automation, many sound localization tests still rely on examiner supervision and manual workflows. This protocol provides an end-to-end automated framework.

To begin, set up a soundproof booth with internal dimensions of approximately 3, 800 by 2, 200 by 2, 100 millimeters to provide a controlled free field listening environment, and install a semicircular loudspeaker rack with a radius of 3000 millimeters inside the booth. Mount seven loudspeakers on the rack at 30 degree intervals, spanning from minus 90 degrees to plus 90 degrees azimuth. Position all loudspeakers at the same height of approximately 1050 millimeters corresponding to head level when seated.

Place each loudspeaker at an equal distance from the participant's head. Connect the loudspeakers to a multi-channel audio interface using balanced shielded XLR audio cables. Control stimulus presentation and data acquisition using a windows-based personal computer running custom developed software.

For calibration, present a broadband noise stimulus that is root means square matched to the test stimuli from each loudspeaker. Place a class one precision sound level meter equipped with a free field microphone on a tripod at head level of approximately 1050 millimeters at the participant position. Measure the equivalent continuous sound level defined a Z weighted time averaged sound pressure level from each loudspeaker.

Adjust the output levels so that the measured equivalent continuous sound level is approximately 60 decibel sound pressure level across all loudspeakers. Prepare a height adjustable chair equipped with a headrest to stabilize the participant's head position during stimulus presentation. Ensure the headrest provides tactile feedback to help maintain a consistent forward facing head orientation during stimulus presentation.

Now seat the participant on the custom made chair so that the head aligns with the frontal loudspeaker at zero degrees azimuth corresponding to the central position of the semicircular array. Adjust the headrest to fit firmly against the occipital protuberance and instruct the participant to maintain contact with the headrest throughout the test. Place a touch pad directly in front of the participant and provide instructions on its use to record responses.

Enter the participant identification code and trial number into the graphical user interface. Select the hearing device status by choosing cochlear implant, hearing aid or no hearing aid, and start the familiarization sequence by selecting the familiarization button followed by start. Instruct the participant to maintain gaze toward the central loudspeaker throughout the sequence.

Present auditory stimuli automatically and sequentially from each loudspeaker during the familiarization sequence. Select the pre-test button on the graphical user interface to activate the pre-test mode. Instruct the participant to face the frontal loudspeaker and maintain a forward head orientation.

Direct the participant to press the start button on the touch pad when ready. Upon pressing the start button, present the first test sound from one of the loudspeakers. After the sound presentation, switch the touch pad display to a loud speaker map and record the participant's selection of the perceived sound source location.

Provide immediate feedback after each response. Display a confirmation message for correct responses before allowing progression to the next trial. Highlight the correct loudspeaker location on the map for incorrect responses, and replay the sound three times from that loudspeaker.

After the third trial, the pre-test is automatically terminated. After completion of the pre-test, select the main test button on the graphical user interface to start the main test sequence. Instruct the participant to press the start button on the touch pad to trigger presentation of a sound from one of the loudspeakers.

After the sound presentation, switch the touch-pad display to a loudspeaker map and record the participant's selection of the perceived sound location. Following each response, the next button is displayed on the screen. Advance automatically through the predefined number of trials and repeat the trial sequence until the main test is completed.

Let the system automatically terminate the session at the end and generate a CSV log file. Record each trial in the log file including the stimulus presented, the direction of the sound source and the participant's response. Verify the calculated localization performance metrics, including root means square error, mean absolute error and response bias in the results sheet.

A total of 34 participants were enrolled in this study with 20 adults having normal hearing and 14 adults with single-sided deafness. A representative participant with normal hearing exhibited accurate localization overall with responses aligned along the diagonal and one error at minus 90 degrees. The representative participant with right side deafness exhibited low overall localization accuracy with responses bias toward the intact left side across azimuth.

Using the ICF-based classification approach, most participants with single-sided deafness were categorized as exhibiting moderate to severe impairment. With one case of complete impairment and one case of no impairment. In contrast, the normal hearing group was mostly classified as having no impairment, except for one participant who showed mild impairment.

This protocol allows researchers to measure sound localization performance using a standardized and automated testing system. Maintaining a consistent head position during stimulus presentation is critical for obtaining accurate sound localization measurements. Future studies can apply this protocol to compare special hearing outcomes across listener groups and clinical interventions.