GB1402508A - System for conveying sound information to the brain - Google Patents

Abstract

1402508 Hearing aids ZCM Ltd 27 March 1973 14719/73 Heading H4J [Also in Division A5] In a hearing system in which sound signals are converted into pulses whose width corresponds to the signal frequency and whose amplitude corresponds to the signal amplitude, the pulses are modulated on to a carrier which is also amplitude modulated by the original signal. Compared with the system disclosed in Specification 1,284,158, the additional modulation increases the modulation depth of the carrier from less than 5% to between 20 and 50% whereby an enhanced sensation of hearing particularly at high frequencies is obtained. The carrier frequency may be in the range 60 to 100 kHz or in the microwave range of 1000 MHz. In the latter case, the electrode system used for conveying signals to the user's body consists in a ring 78 connected to a coaxial cable outer 70 and spaced in insulating manner from a central disc 74 connected to the cable inner. The disc and possibly also the ring are covered in insulating material. The electrodes may be held against the user's neck with the aid of a strap (Figs. 3, 5, not shown). Alternatively the electrode structure may be held against the ear manually (Fig. 7, not shown), with headphones (Fig. 10, not shown) in which case stereophonic operation could be obtained, or with the assistance of a telephone handset (Figs. 8, 9, not shown). In order to maximize coupling of the aid to the ear, a highly-flexible fluid-filled bag may be interposed therebetween (Fig. 11, not shown). The outer portions of the ear may be folded over the ear channel prior to placement of the aid. Circuit comprises between two and ten trigger circuits 16-18 each having a different threshold. Their outputs are relatively delayed and then added and shaped in device 20 so as to produce an output whose pulse repetition rate corresponds to the amplitude of a sound impinging on microphone 10 and whose pulse width is related to the frequency of the sound. The input signal is also applied via control device 7 to the pulse signal so as to modulate it (waveform 24A) prior to modulation on to a high frequency carrier (waveform 28A). The output is taken from electrodes 30 which are connected to one side only of output transformer 29. It is suggested that the amplitude modulation causes a ripple of the basilas membrane of the cochlear duct such that the accompanying pulses may penetrate and cause nerve firing even in the absence of cochlear hairs or positive nerve action.