Anomalous phase relations in threshold-level responses from gerbil auditory nerve fibers

Phase-locked responses at near-threshold levels obtained from single units in the auditory nerve of gerbils show that the relation between phase lag and linear frequency often contains an unexpected microstructure. In frequency regions below 1 kHz that are also an octave or more below CF, phase curves often have multiple straight-line segments, rapid slope changes, or other major inflections. These detailed features of the phase curves are not accounted for by any identified artifact. For example, the anomalous features cannot be removed simply by lowering the stimulus level; they remain down to levels where phase locking first occurs. Phase curves for single units with the same CF recorded from different animals can have similar microstructures, suggesting that the form of the phase curves may reflect some joint effect of stimulus frequency and CF or longitudinal position.