Potential benefits and limitations of three types of directional processing in hearing aids

The purpose of this study was to evaluate hearing aid users' performance on four tasks across three types of directional processing implemented by the same pair of commercially available behind-the-ear hearing aids. The three types of directional processing were mild, moderate, and strong. The mild processing aimed at emulating the directionality of an unoccluded ear. The moderate processing was a traditional adaptive directional type. The strong directional processing was a cue-preserving bilateral beamformer. The four tasks included gross localization, sentence recognition, listening effort, and subjective preference.

Eighteen adults aged 48 to 83 years ((Equation is included in full-text article.)= 69.1, σ = 10.9) with sensorineural hearing loss participated in this study. Each participant was fitted bilaterally and the three types of directional processing were matched for frequency response but varied by directionality (mild, moderate, and strong). Performance was always evaluated in background noise, which surrounded the listener. Sentence recognition was evaluated in low and moderate reverberation, while gross localization, listening effort, and subjective ratings were evaluated only in moderate reverberation. Sentence recognition and gross localization were evaluated using auditory-only and auditory-visual stimuli (talker's face visible). The gross localization task included assessment of the ability to identify the origin of words, in addition to the ability to recall those words. Listening effort was evaluated using auditory-visual stimuli and a dual-task paradigm where the secondary task was a simple reaction time to a visual stimulus.

The results revealed similar gross localization abilities across moderate and strong directional processing when visual stimuli were present. Conversely, localization accuracy was significantly poorer with the strong directional processing than with moderate directional processing in auditory-only conditions, but only for signals presented at the greatest eccentricities (±60 degrees). Regardless of signal to noise ratio or degree of reverberation, the moderate and strong directional processing resulted in significantly better sentence recognition in noise than the mild directional processing. In addition, sentence recognition in moderate reverberation was significantly better with strong directional processing than with moderate directional processing (~ 4 to 12 rationalized arcsine units across conditions), regardless of signal to noise ratio. Although not statistically significant, the same trend was present in low reverberation. There were no significant differences in listening effort or subjective preference across directional processing.

The strong directional processing, which was a cue-preserving bilateral beamformer, provided additional sentence recognition benefit in realistic listening situations. Furthermore, despite reducing the interaural differences, the authors measured no significant negative consequences on listening effort or subjective preference, although it is unknown whether differences might be found using more sensitive measures. In addition, gross localization was disrupted at large eccentricities if visual cues were not present. While further study is needed, these results support consideration of this cue-preserving, bilateral beamformer technology for patients who experience difficulty with speech recognition in noise, which is not adequately addressed by conventional directional hearing aid processing.