We propose to develop an advanced noise reduction and audio stimulus presentation system for use during studies of hearing employing functional Magnetic Resonance Imaging (fMRI). fMRI is being used extensively to produce images of brain activity while a subject actively performs a task or receives sensory stimulation. The process of acquiring fMRI brain images in response to auditory stimulation is especially difficult because the noise generated by fMRI equipment is extremely intense, with levels up to 130 dB SPL, and so interferes significantly with the intended acoustic stimuli. In addition, FMRI apparatus employs an intense magnetic field that excludes the use of many materials commonly used in audio devices so that it is impossible to use conventional earphones for sound presentation. In addition, commercially available systems, while designed to present acoustic stimuli adequately, provide only modest attenuation of ambient noise. ? ? The goal of the proposed system is to provide maximum possible attenuation of ambient sound while providing audio signals of research quality. The methods to be used to achieve these goals include the combination of three attenuation techniques: (1) a circumaural muff, (2) insert earplugs, and (3) active noise reduction (ANR) within the muff. ANR is an effective complement to an earplug and a muff because it provides highest attenuation at low frequencies, while plugs and muffs attenuate better at higher frequencies. A small electrostatic transducer coupled to a sound channel in the earplug will deliver stimuli. Another, larger electrostatic transducer in the muff will be used in conjunction with a small microphone and circuitry to form an ANR system. In Phase I a complete prototype system will be constructed for assessment of feasibility, attenuation, audio quality, and compatibility with the fMRI magnetic field. Device attenuation will be measured using subject threshold shifts. The system will be refined and further developed into a manufacturable prototype in Phase II. ? ?
