Design and evaluation of a personal digital assistant-based research platform for cochlear implants

Abstract

This paper discusses the design, development, features, and clinical evaluation of a personal digital assistant (PDA)-based platform for cochlear implant research. This highly versatile and portable research platform allows researchers to design and perform complex experiments with cochlear implants manufactured by Cochlear Corporation with great ease and flexibility. The research platform includes a portable processor for implementing and evaluating novel speech processing algorithms, a stimulator unit which can be used for electrical stimulation and neurophysiologic studies with animals, and a recording unit for collecting electroencephalogram/evoked potentials from human subjects. The design of the platform for real time and offline stimulation modes is discussed for electric-only and electric plus acoustic stimulation followed by results from an acute study with implant users for speech intelligibility in quiet and noisy conditions. The results are comparable with users' clinical processor and very promising for undertaking chronic studies.

Fig. 1

Functional diagram of the SDIO board.

Fig. 2

(a) PDA-based processor with PDA, BTE, RF coil, and SDIO interface board (plugged in the SDIO port) and (b) SDIO board connected via an extender flat flex cable.

Fig. 3

(a) Portable SDIO-BiSTM main board and (b) SDIO BiSTM daughter board.

Fig. 4

Generic signal flow of sound processing using PDA-based processor in real-time and offline modes.

Fig. 5

Signal Flow in the PDA-based speech processor in real-time mode. The acoustic signal is picked up by the microphone (A), sent (via the headset cable) to the SDIO interface board (D), which is then sent to the PDA (B). The PDA processes the signal and generates a set (one for each channel of stimulation) of amplitude electrode pairs (C). The stimulus data are sent to the SDIO interface board (D), which is then coded for transmission to the cochlear implant as RF bursts (E). For bimodal (EAS) stimulation, the acoustic signal is processed through an audio processing routine simultaneously with electric processing. The processed audio buffer is sent to the transducer (F) which presents the acoustic signal to the ear via the insert ear-tips. Both electric and acoustic stimuli are synchronized in time and provided to the user without any delay. A sample of interactive user interface is shown on the PDA screen in the figure above.

Fig. 6

Software organization on the PDA and FPGA logic.

Fig. 7

High-level diagram for offline-mode setup.

Fig. 8

Device connectivity and data exchange in an offline mode.

Fig. 9

Percentage correct mean speech intelligibility of nine subjects as a function of SNR and processor type. Error bars represent SEM.

Fig. 10

Mean audiogram of five bimodal subjects for the hearing-aid ear. Error bars represent SEM.

Fig. 11

Percentage correct mean speech intelligibility for EAS condition of five bimodal subjects as a function of SNR and processor type. Error bars represent SEM.

Fig. 12

Estimated marginal mean intelligibility scores for acoustic alone (A_alone), electric alone (E_alone), and EAS for the three processor types. Error bars represent SEM.