ABSTRACT
Different parts of our brain do different things in response to sonic stimuli. Moreover, music is not detected by our ears alone; for example, music is also sensed through the skin of our entire body (Storr 1993) (Despins 1996). The response of our brain to external stimuli, including sound, can be measured by the activity of the neurones. The electrochemical behaviour of masses of neurones acting in small to very large groups in the brain produces a complex, multidimensional, pulsating electromagnetic field. Two methods are commonly used to measure this: PET (positron emission tomography) and EEG (electroencephalogram). Whilst PET measures the brain’s activity by scanning the flow of radioactive material previously injected into the subject’s bloodstream, EEG uses tiny electrodes (small metallic discs) pasted onto the surface of the skull by means of
electricity conducting gel. As the signals captured by the electrodes are in the order of just a few micro volts, an amplifier is used to increase their amplitudes several hundred times. Whilst PET gives a clear cross-sectional indication of the area of the brain where the bloodflow is more intense during the hearing process, EEG gives a voltage level vs. time graph of the electrical activity of the areas of the brain where the electrodes have been placed (Figure 5.1).
