(Color online) (A) DP-grams and (B, C) DPOAE L/P maps for a normal human measured at L 1, L 2 = 75, 75 dB SPL. DP-grams in A1 obtained with an IT near f dp (light gray line at top) or without an IT (black line) demonstrate the ability in humans to extract a residual with a steep phase gradient (dashed gray line in A3) consistent with a DPOAE reflection component from f dp (dashed gray line at bottom in A1). DP-grams in A2 show that an even larger residual (gray line at bottom) with shallow phase slope (light gray line in A3) indicative of a distortion component can be obtained with a 1/3-oct IT. Panel B shows DPOAE L/P maps with the IT near f dp. The IT removes some, but not all of the vertical phase banding (white arrows in B4) and extracts a small patchy residual (B5) with vertical phase banding (white arrows in B6). Panel C shows the effects of a 1/3-oct IT on DPOAE L/P maps. Here the IT removes essentially all the vertical phase banding (C4) and extracts a residual (C5) with both horizontal (black arrow in C6) and vertical phase bandings (white arrow in C6) suggesting that DPOAE components with both reflection- and distortion-like properties arise basal to the IT in humans. On this and subsequent figures, the black dashed horizontal lines on the level and phase plots demark the optimal f 2/f 1 ratio for acquiring commonly measured 2f 1−f 2 DP-grams. On all DPOAE L/P maps, data for the 2f 1−f 2 and 2f 2−f 1 DPOAEs are displayed above and below, respectively, the white dashed horizontal line at f 2/f 1 = 1.0 (not labeled). The thin white diagonal dashed lines through the phase plots (panels B and C−2, −4, −6) represent constant f 2 trajectories beginning at 15 kHz in the top right of each plot, and ending at 1 kHz in the lower left region that can be used as a reference for this and other DPOAE L/P maps. See text for complete details of this and following figures.
(Color online) (A) DP-grams and (B, C) DPOAE L/P maps for a rabbit illustrating the effects of an IT near f dp or a 1/3-oct IT. In the rabbit DP-gram analysis, both IT conditions were capable of extracting residuals but they were associated with shallow phase slopes (A3) consistent with a DPOAE distortion component. The DPOAE L/P maps with the IT near f dp (B) and with the 1/3-oct IT (C) supported and extended the DP-gram findings. Thus the near f dp IT had little effect on the DPOAE L/P maps, but did extract a small residual (white arrow in B5) with clear horizontal phase bands indicative of a distortion component (white arrow in B6). In the 1/3-oct IT situation, the IT removed essentially all the vertical phase banding obvious in the control (C2) L/P plot, and the DPOAEs were associated with very orderly horizontal phase bands (white arrows in C4). The residual was large (C5) and contained both horizontal (white arrow in C6) and vertical banding (black arrow in C6) consistent with the existence of both reflection- and distortion-like components at or above the 1/3-oct IT-frequency place.
(Color online) (A) DP-grams for a chinchilla and (B) corresponding DPOAE L/P maps illustrating the effects of an IT near f dp or (C) a 1/3-oct IT. In the DP-grams, regardless of the location of the IT, residuals exhibited shallow phase slopes (A3) except for a small segment associated with apical curvature observable in the DPOAE L/P maps of all species. The IT near the f dp extracted a larger residual (B5) than in the rabbit, with a mixture of phase patterns (B6), with some being clearly horizontal (white arrow in B6), and others being somewhat vertical (black arrows in B6) making it difficult to rule out the existence of reflection components in the chinchilla. In the 1/3-oct IT condition, the IT removed essentially all vertical phase banding (C4) leaving behind a phase map with very orderly horizontal-phase characteristics. The residual extracted by the 1/3-oct IT was very large (C5), and contained both horizontal and vertical bandings again consistent with the existence of both reflection- and distortion-like components at or above the 1/3-oct IT frequency place.
(Color online) (A) DP-grams and (B) DPOAE L/P maps for a rat showing the effects of an IT near f dp or (C) a 1/3-oct IT. The near f dp IT DP-gram analysis for the rat revealed a small high-frequency residual (dashed gray line in A1) with a shallow phase slope (dashed gray line in A3). A much larger residual was revealed by the 1/3-oct IT (A2) with similar phase characteristics (solid gray line in A3). In the rat the DPOAE L/P maps were characterized by a large low-frequency component (white arrows in B1) with very striking vertical phase banding (white arrows in B2) for both 2f 1−f 2 and 2f 2−f 1 DPOAEs. Regardless of the reflection-like phase properties of this component, the IT near f dp had essentially no effect on the level (B3) or phase (B4) of this or other regions of the maps for the IT condition in spite of prominent vertical phase banding in the other DPOAEs above this low-frequency region. The small residual that could be extracted (white arrow in B5) was dominated by horizontal phase bands (B6). In the 1/3-oct IT condition, the most remarkable feature was the ability of the IT to almost completely remove the low-frequency component for both the 2f 1−f 2 and 2f 2−f 1 DPOAEs (region of white arrows in C4) and all the associated vertical phase banding (region of white arrows in C3) observed for the control condition of C2 leaving the resulting phase map (C4) dominated by nearly perfect horizontal phase bands. Thus, a very large portion of the rat DPOAE space was apparently composed of DPOAEs arising basal to the 1/3-oct IT place on the BM.
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