Issues in the development of multichannel tactile devices for hearing- impaired children and adults

We have discussed the influence of a number of individual factors in the successful use of tactile devices. Tactile devices, such as the Tickle Talker, have been primarily developed to provide additional speech information to be used in combination with speechreading, and in some cases aided residual hearing, addressing the particular individual's speech perception and communication needs. Evaluations have shown that enhancement of speech feature discrimination with the device may occur immediately on fitting, but effective integration of tactually encoded speech feature cues into combined-modality speech perception requires a minimum of 6 months habilitation. Tactile-alone perception of words and sentences has not been a priority addressed through either development of speech encoding strategies or training programs. In contrast, cochlear implants have been shown to provide significant speech information to those patients who received little or no benefit from the hearing aids. Increasingly, the documented ability of implantees to perceive open-set words and sentences in the implant-alone condition has been taken as evidence of device benefit, with the degree of supplementation of other sensory modalities such as lipreading of secondary import. The application of this evaluation philosophy to tactile devices would suggest that they provide very limited benefit only to hearing-impaired children or adults. The importance of this issue is illustrated in Figure 7, which shows speech perception results on PBK words for three congenitally deaf adolescents, each of whom were initially fitted with the Tickle Talker, and were subsequently implanted with the Nucleus multichannel cochlear implant (Sarant et al., 1995). If we compared the devices solely on the basis of benefits in supplementing lipreading and aided residual hearing, the results show comparable benefits for two of the three children (CI-L versus T-HA-L). Given that hearing-impaired children in everyday communication would use all available speech input (i.e., the combined modality condition), it might be argued that the results suggest that children would do equally well with either of the two devices. However, all three children showed some understanding of speech through their cochlear implant alone (CI), as compared with only one child showing very limited understanding of open-set speech using Tickle Talker plus hearing aids (T-HA) or hearing aids alone (HA). This device-alone perception in the case of cochlear implants provides a distinct communication advantage, because it allows conversation without the need for visual regard, and opens the possibility of telephone conversation. Each of these three children were experienced users of the Tickle Talker, and each was obtaining significant speech perception benefits from use of the tactile device. Yet in all three cases, the children and parents decided to proceed with cochlear implantation, despite the risks involved in cochlear implantation surgery. While this suggests that tactile devices may play a role in the preimplant habilitation and evaluation program in cochlear implant clinics, it also suggests that the perceived benefits available from cochlear implants were judged by these families to be superior to that offered by the Tickle Talker. Informal conversations with the families suggested that a significant premium was placed on the perceived speech perception benefits available from cochlear implants, based on observed benefits for other implanted children. In addition, further considerations were the cosmetic issues, reliability, and case of use of the different devices, and the fact that the cochlear implant was a commercial device in contrast to the 'research' Tickle Talker. The relative sophistication of cosmetic/engineering design for cochlear implants is dependent on the capital R and D investment of companies developing commercial cochlear implant systems for use in medical/clinic practice. Again, in contrast, only one U.S. company is a major commercial manufacturer of tactile devices, while most research organizations developing multiple channel tactile devices have focused limited resources primarily on speech perception benefits. To achieve more widespread use, tactile devices must address cosmetic issues, be robustly designed, reliable, and easy to use. An additional issue in motivating the decision to proceed with a cochlear implant instead of a tactile device may be the funding of devices. At present, cochlear implant systems in Australia are fully funded by public hospital services or private health insurance.