Figure 4.

Unit circle histogram plots of phase of 100 Hz (left, blue) and 700 Hz (right, red) responses from FFRs recorded in the guinea pig inferior colliculus to two ‘a’s that start 180 degrees out of phase. The 100 Hz fundamental frequency is extracted from the envelope, which is phase invariant, while the 700 Hz first formant is extracted from the temporal fine structure, which varies with the phase of the stimulus. The 100 Hz responses maintain a consistent phase angle regardless of the stimulus polarity while the 700 Hz responses flip their phase angle by ~180 degrees, similar to the phase shift between the two ‘a’ stimuli. The average phase angle for each frequency and polarity are indicated by the black arrows, whose length indicates the consistency of that phase angle across trials (individual vectors).