Generating an F0 Contour
Following the process of converting the audio waveform into F0 contours, the contours are segmented into individual trials with each pitch-shift stimulus.
Averaging Voice F0 Contours
Following the process of converting the audio waveform into F0 contours and segmenting them into individual trials with each pitch-shift stimulus, the average of the group of individual contours is calculated (middle graph below).
Examples of average responses to upward (top) and downward (bottom) pitch-shift stimulus. In both cases, the response is in the opposite direction to the stimulus and are called “Compensating Responses”. Also shown in this figure are control trials in which no pitch-shift stimulus was presented.
Example of a compensating response (above) and a following response (below). Following responses are fewer in number; these change in the same direction as the stimulus.
EEG Signals from Multiple Electrodes
Another technique we use is to record brain electrical signals during the pitch-shift paradigm in an effort to understand the neural mechanisms underlying these processes. An electrode cap consisting of 32 or 64 EEG electrodes is placed on the subject’s head. During the testing as the subject is vocalizing and hearing his/her voice pitch shifted, electrodes pick up tiny electrical signals from the brain. Recordings from the electrodes are synchronized with the pitch-shift stimulus. After the recording session is completed, the electrical potentials from each electrode are averaged over the course of all the pitch-shifts, resulting in an Event Related Potential (ERP).
Examples of Event Related Potentials (ERPs):
Brain Event-Related Potentials from EEG Electrodes
Below are averages of ERPs recorded from musicians with perfect pitch, relative pitch and non-musicians during a pitch-shift study. The larger amplitude of the P200 ERP in perfect pitch musicians may reflect neural mechanisms that endow them with unique musical abilities.