The Effect of a Notch Filter in Sound Preprocessing of Active Middle Ear Implants on Speech Perception

The effect of two different notch filters in sound pre-processing of active middle ear implant (AMEI) on speech perception was studied.

Speech perception was tested in 20 adults with AMEI using the Oldenburg sentence test (OLSA) in quiet at a fixed presentation level of 65 dB HL. Three conditions were tested: notch filter option not active, acoustic notch filter activated at a center frequency of 4 kHz and acoustic notch filter activated at a center frequency of 6 kHz.

Hearing thresholds were significantly affected by the notch filters at the particular center frequencies. The drop in hearing thresholds at 4 and 6 kHz was about 15 dB HL (median value). Pair comparisons between condition "notch filter option not activated" and "notch filter activated" reached significance for both center frequencies, i.e. p < 0.01. In contrast, no significant differences were seen between the word recognition scores of the OLSA speech test obtained for each of the three conditions.

Speech perception in quiet was not affected while a notch filter at 4 or 6 kHz was activated in sound pre-processing in patients with an AMEI. However, according to subjective feedback from the patients, the listening effort was increased as soon as one of the notch filters was activated.