Comparison of two multichannel tactile devices as supplements to speechreading in a postlingually deafened adult

The purpose of this study was to conduct a single-subject comparison of the effectiveness of two multichannel vibrotactile devices that encode different classes of speech information. One device, the Portapitch, is designed to convey fundamental frequency (F0) and its variation over time. The other, the TACTAID 7, is designed to convey the first two formant frequencies (F1 and F2) and their variation over time.

The subject, a postlingually deafened adult, underwent an intensive 17-wk training and testing protocol with the Portapitch and then completed a similar 17-wk protocol with the TACTAID 7. Performance measures were obtained on phonetic-contrast perception by speechreading alone, tactile device alone, and speechreading plus tactile device, and on open-set word and sentence recognition by speechreading alone and speechreading plus tactile device.

On phonetic-contrast testing, the subject demonstrated some ability to perceive voicing, stress, and intonation contrasts using the Portapitch, but gave little evidence of phonetic-contrast perception with the TACTAID 7. On open-set word recognition testing, no significant improvements were seen with either device. On open-set sentence recognition testing, the subject showed a significant 9 percentage point enhancement effect using the Portapitch; the mean 5 percentage point enhancement effect provided by the TACTAID 7 was not statistically significant.

A small advantage was seen in favor of the tactile display of F0 relative to the tactile display of formant frequency information on both phonetic-contrast testing and open-set sentence recognition. The difference, however, was of questionable significance and could have been confounded with an order effect. Nevertheless, the subject's preference was for the tactile formant frequency display.