Handheld Tactile Sensory Substitution for the High-Frequency Hearing Impaired Jimmy Fong, Becky Jones, Jack Page, Ryan Thome, Matt Valaskey ABSTRACT Our research focuses on the development of a tactile sensory substitution device to provide missing high frequency sound information to persons with high frequency hearing loss (HFHL). Previous research has shown that high frequency consonants can be distinguished by their energy and frequency content. The sound signal of common words containing high frequency consonant sounds (California Consonant Test, CCT) was filtered into four separate frequency channels between 1.6 – 8 kHz. The sound present in each of the 4 channels was presented to the user via discrete vibrating motors, one placed at the tip of each of the 4 fingers. The vibrations give different patterns for different sounds, allowing the user to make a distinction between different high frequency sounds. This study will measure the subject’s ability to identify the location of the vibration, i.e. which finger is activated, the ability to learn the specific patterns, and the ability to use the vibrating pattern to increase word recognition ability. We employed a preliminary practice session to acclimate the subject with the tactile substitution device and then the CCT was administered both with and without the tactile substitution device. The testing consisted of playing a recorded word from the CCT from a single computer speaker while simultaneously presenting the word’s high frequency information via the four tactile stimulators and asking the subject to identify the played word from a closed set of four words. INTRODUCTION The number of hearing impaired Americans has more than doubled in the past 30 years with nearly 50 percent of Americans over the age of 65 affected [1]. It not only affects the elderly however, 1.4 million children under the age of 18 also have a hearing condition [2]. The most common type of hearing loss is sensorineural. About 90 percent of individuals who are hearing impaired have sensorineural hearing loss. This condition, also known as nerve deafness, consists of either damage to the inner ear or the nerves which transmit the messages from the ear to the brain. It is caused by disease, birth injury, or even aging. The most common form of sensorineural hearing loss is high frequency hearing loss. This is where an individual loses the ability to hear certain high frequency constants such as Sh, S, T, Th, P, or F sounds. Since these are some of the most common used consonants in the English language, high frequency hearing loss is truly detrimental to every day communication. High frequency hearing loss is not easily medically fixed because it is caused by damage to the nerve, so sound cannot simply be amplified to assist a person with communication. For example, hearing aids do not do an adequate job of fixing this problem because they only amplify the sound. This is why sensory substitution has been chosen as a method to replace the lost hearing at high frequencies. The goal of this project is to use sensory substitution, a technique for presenting environmental information missing in one sensory modality to another, to help replace this missing high frequency information. We proposed that a device that filters frequencies above 1,000 Hz into four bands and provided this information vibro-tactically to a subject would allowthem to be better able to discriminate between high frequency consonant sounds, thereby assisting in everyday communications. The device takes recorded sound, filters it into four different channels based on frequency, and then outputs all four channels to a sound card. The sound card outputs to a circuit that amplifies the sound and reduces the noise. The circuit then outputs to four vibrotactile transducers. The four transducers will then vibrate in response to high frequency sound inputs. Different fricative sounds will stimulate different vibrotactile transducers based on the frequency of the sound, allowing the user to associate a particular vibration with an unheard sound. Vibrotactile stimulation involves generating vibrations that activate mechanoreceptors in the skin. Vibrotactile transducers were chosen because of their ease of acquirement and implementation. Use of this device, to supplement for the loss of high frequency hearing, should aid the user in daily communications in regard to speech and hearing. There are a few existing devices which aim to use sensory substitution by substituting for hearing using vibro or electro stimulation, but these products are made specifically for people with complete hearing loss. For example, the Tickle Talker™ uses vibrotactile stimulation on the fingers of the user. Each finger receives stimulation from a different range of frequency and based on the pattern, strength, and duration of the vibration, the user can pick out a certain frequency range. Since this form of sensory substitution covers the whole spectrum of hearing, it is not sensible for a person with only high frequency hearing loss to use the device. They would have to sift through way too much information to get the signals they needed. With such a large learning curve, the user must spend hours with the device to learn minimal amounts of words. For example, after more than 40 hours of training, a certain user could only identify 70 words [3]. The high frequency user could adapt at a much faster rate to only a high frequency stimulator because they are only missing certain sounds, not the entire spectrum. Other similar devices include the Tacticon 1600 and the Tactaid VII. The Tacticon 1600 uses electro stimulation by putting electrodes on a belt around the user’s abdomen [4]. This device also covers the whole spectrum of hearing and has a steep learning curve. In similar ways, the Tactaid VII uses vibrations covering the entire range of human hearing [4]. The vibrators are attached to the user’s sternum, each corresponding to a certain frequency range. However, no device currently exists on the market that effectively assists people with high frequency hearing loss in their every day communications. MATERIALS AND METHODS Device Design The general function of the experimental device is to present the subject with a sample sound along with vibrational pulses that signify the presence of high frequency consonant sounds. The overall system consists of a laptop, a
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