Publication Date

2015-05-22

Availability

Open access

Embargo Period

2015-05-22

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biomedical Engineering (Engineering)

Date of Defense

2015-05-13

First Committee Member

Ozcan Ozdamar

Second Committee Member

Jorge Bohorquez

Third Committee Member

Suhrud Rajguru

Fourth Committee Member

Christopher Bennett

Fifth Committee Member

Rafael Delgado

Abstract

When two pure-tone (2T) stimuli with slightly different frequencies are presented independently to each ear, an auditory illusion, called binaural beats (BB), is perceived as a faint pulsation over a single tone. The frequency of the perceived tone is equal to the mean frequency of 2T and the pulsation has a rate equal to the difference of the two. The interaction of the 2T stimuli, inside the auditory cortex, can be recorded in the form of auditory steady state responses (ASSR) using conventional electroencephalography (EEG) or magnetoencephalography (MEG). The recorded ASSR usually have small amplitudes and require additional signal processing to separate them from the surrounding cortical activity. The transient auditory evoked potentials (AEPs) may provide more information about the physiology behind the generation of the BBs. Currently most methods can only generate transient AEPs to binaural phase disparities in random noise, or use amplitude modulating (AM) tones to trigger a binaural frequency difference (BFD). For this dissertation, a method was developed which uses two frequency modulating (FM) sounds to generate an instantaneous BFD which only lasts for the duration of a single or unitary beat. One major advantage of this method is that it separates the beating rate from the BFD allowing for independent control of the beat occurrences. This dissertation provides an in depth description of the stimulus generation and acquisition methodology used to evoke transient AEPs to unitary BBs. Several studies were designed to characterize the behavior of the AEPs to some of the key stimulus parameters design and to obtain an optimal set of parameter values that can be used to generate robust transient AEPs. The result was a method that can be used to generate unitary BBs that have equivalent characteristics to the BBs generated using the 2T method. Furthermore the studies showed that the method is capable of generating BBs that evoke repeatable and robust transient AEPs with large amplitudes and late latencies.

Keywords

Binaural Beats; Transient Auditory Evoked Potentials; Frequency Modulation

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