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Sound Localization Test Methods: Azimuth and ILD Localization

Sound localization is a crucial aspect of auditory perception, allowing us to identify the position of sound sources in our environment. Various tests have been developed to assess this ability, with two prominent methods being azimuth localization and interaural level difference (ILD) localization. Audiqueen software offers tools for conducting both of these tests.

Sound Localization

Sound Localization in humans

Azimuth Localization

The azimuth localization test is a typical method that utilizes multiple loudspeakers to assess a listener's ability to identify the horizontal angle (azimuth) of a sound source. This test requires an ASIO audio device, such as the SoundC hardware, to accurately present stimuli through the speakers.

Stimuli

Several default stimuli are available for the azimuth localization test, including:

  • A 1/3 octave narrow-band noise with a 4 kHz center frequency
  • Speech-Shaped Noise
  • LPF noise: low pass filtered noise with a cut-off frequency of 400 Hz
  • HPF noise: high pass filtered noise with a cut-off frequency of 3000 Hz

After selecting a stimulus, it is presented randomly through one of the configured speakers. Each stimulus has a duration of 3 seconds and is presented five times. Intensity roving within a range of ± 2.5 dB is applied randomly.

Apparatus

Supported apparatus for Localization tests are: Amplifier & Speakers and SoundC (currently up to 24 speakers).

Procedure

  1. Select A§E Azimuth Localization in the ribbon and click on New Measurement
  2. Select SoundC from the drop-down list
  3. In the Training mode, click on one of the speakers to send the stimulus to that speaker.
  4. In the Test mode, Audiqueen plays a stimulus and the listener should point to the speaker he/she feels the sound is coming from. Click on this speaker icon to enter the response.

Results

After the last presentation, Audiqueen plots an XY graph showing the median responses as a function of the real sources.

It also calculates the RMS value as a measure of the error compared to the normal line. The RMS is calculated as the root mean square for all speakers of (the median response - the normal response)

Where RS = the median response for Speaker S
N = the number of speakers
norm = the normal value for Speaker S

Azimuth Localization Test Procedure

ILD Localization

The A§E ILD localization test assesses localization acuity based on high-frequency interaural level differences. It only requires 2 loudspeakers. It is particularly useful for evaluating cochlear implant recipients, as it examines the central integration of binaural input by presenting a narrow-band noise centered at 4000 Hz through two loudspeakers with different intensities.

Procedure

  1. See this page to set up your hardware correctly (very important!).
  2. Select A§E ILD Localization in the ribbon and click on New Measurement
  3. Select the machine from the drop-down list
  4. Use the controls to select binaural as the test ear and the conduction and the presentation level
  5. In the Training mode, you can click on one of the speakers to present sound coming from that direction.
  6. In the Test mode, Audiqueen presents the stimulus with different ILDs (randomly), to simulate different sound sources and the patient should point to one of the (sham) speakers that he/she thinks is the real source.

Results

After the last presentation, Audiqueen calculates 2 values: (1) the variance of the responses, as an indication of the reliability of the patient's responses; and (2) the RMS value as a measure of the error compared to the normal line.

The variance is calculated as the average of the absolute value of every (score - the corresponding median score)

The RMS is calculated as the root mean square for all ILDs of (the median response - the normal response)

Where RILD = the median response at a given ILD
N = the number of ILD values
norm = the normal value for each ILD value

ILD Localization Test: Rationale and Procedure

Summary of Localization Tests

Here's a summary table highlighting the key differences and characteristics of the Azimuth and ILD localization tests:

Feature Azimuth Localization ILD Localization
Number of Speakers Multiple (up to 24 with SoundC) 2
Primary Focus Horizontal angle (azimuth) of sound source Interaural Level Differences
Stimulus Example Narrow-band noise, speech-shaped noise, LPF/HPF noise Narrow-band noise at 4000 Hz
Key Use Case General sound localization assessment Evaluation of cochlear implant recipients