The spatial speech test of real-world listening for assessing binaural hearing

The spatial speech test was developed to simultaneously assess the ability of listeners to identify speech and determine the relative location of target sound in the presence of noise (Bizley et al., 2015).

Listeners hear two sequentially presented words from adjacent speakers with a 30o separation and they identify the word and the relative direction of the 2nd word presentation relative to the 1st. The task is performed in the presence of multiple independent noise sources at an individually determined signal-to-noise ratio.

While this test provided a sensitive assessment of spatial hearing in normal hearing listeners, when bilateral hearing aid users were tested in the same task they were unable to perform the relative-localization aspect despite doing well on a standard clinical localization task measuring the ability to point to a speech source in silence.

Therefore, we sought to adapt the spatial speech test further to make it easier for hearing impaired listeners. To achieve this we maintained the dual-task element of the design, but restricted the noise sources to left or right space. We tested normal hearing listeners (n=11) and bilateral cochlear implant users from 8-80 years of age (n=10). In a subset of listeners we additionally assessed performance with each implant in turn.

The findings showed that the spatial location of the words had a significant effect on relative localization performance for both normal hearing and cochlear implanted listeners. For those tested in the unilateral cochlear implant condition it showed that relative localization performance was not above chance but in the bilateral cochlear implant condition listeners performed significantly better.

For the normal hearing listeners’ performance on the word identification aspect of the test was moderated by spatial separation of the words from the noise sources, this was not the case for the bilateral CI users.

Bilateral cochlear implant users were able to perform above chance in both speech perception and relative localization judgements in the presence of noise, although they did not demonstrate spatial release from masking. The test is sufficiently sensitive to detect binaural hearing abilities and demonstrated benefit from the second side implant for relative localization judgements.

References
Bizley JK, Elliott N, Wood KC, Vickers DA. (2015) Simultaneous Assessment of Speech Identification and Spatial Discrimination: A Potential Testing Approach for Bilateral Cochlear Implant Users? Trends Hear. 2015; 19 1-11.