The Design Of Portable Auditory Steady State Responses System

Auditory Steady State Response (ASSR) is a kind of evoked potential picked fromhuman’s scalp electroencephalogram (EEG). In clinical, ASSR is useful for threeaspects. Firstly, ASSR can be used to do objective audiometry. Secondly, by measuringthe amplitude of ASSR, neurologic disorders can be evaluated. At last, ASSR can beused to judge the depth of anesthesia. However, all the three aspects above are stillunder researching. And just due to the necessity of a deeper understanding for ASSR, aconvenient and stable system for ASSR experiment is very important. As ASSR is veryweak compared to the background EEG, the experiment system should keep the stablestatus for a long time.In this article, a portable embedded ASSR experiment system is proposed. Not likethe traditional design that composed independent auditory stimuli generator withcommercial EEG amplifier, the system proposed in this article made the twocomponents together. And with a120*120*50mm~3’s volume, the system can outputauditory stimuli and pick up human’s EEG signal at the same time. The core processoris TI’s TMS320C5515digital signal processor (DSP). Two DSP chips were used tobuild the system, and one was used to control the stimuli generator and the other wasresponsible for the EEG amplifier. There were2input and output (IO) pins to simulatethe serial communication and to exchange information between the2processors.2pieces of SD cards were used to store the sounds for stimulating and EEG signal pickedup by the system. Two kinds of file formats were designed to store the data for auditorystimulation and to express the stimulation sequences. The software in this system wascompatible with those two file formats, and the software could analyze the stimulationsequences and play the stimuli according to the sequences.In order to test the capacity of the system,3kinds of experiments were done. Firstof all, the part of auditory stimuli generator was assessed. An oscillograph was used torecord the output waveform, observe the stimuli and measure the delay between thetrigger and the signal. And commercial EEG amplifier was used to do ASSRexperiments on6subjects. And the experiments’ results were in accordance withtraditional conclusions. Secondly, the EEG amplifier in this system was separatedly assessed. A function signal generator was used to output standard waveforms, and usingthose waveforms, the input impedances, noise levels, common mode rejection ratiowere measured. At last, a simple stimuli sequence was used to conduct ASSRexperiments on4subjects. And before the real ASSR experiments, extra experimentswere conducted to ensure that the responses in specific frequency were real ASSR butnot electromagnetic interference induced by the system.All in all, the system proposed in this article is portable, low power-consumption,and can afford long-time stable working. It can be used to conduct ASSR experimentsfor research.