Columella footplate motion and the cochlear microphonic potential in the embryo and hatchling chicken
Standard PZE driver and probe configuration. Key components of the assembly include the piezo driver, the driver rod (aluminum), and probe (stainless steel). The probe was a hollow tube having a length of . Not to scale.
Schematic of the sealed calibration cylinder, : Length of the chamber , : Peak to peak piston displacement. The microphone (Mic) was inserted to form the major portion of one wall of the calibration chamber. The probe of the PZE diver was replaced by a cylindrical piston and the piston end was inserted into the calibration chamber to a position of length from the microphone. Peak-to-peak displacements were produced by the PZE driver. Displacement amplitude was calculated based upon pressure changes measured by the microphone in the cylinder chamber (cylinder , piston , cylinder , piston ).
Schematic diagram of coupling along the sound conduction path between the driver probe tip, columella footplate (FP), scala vestibuli (SV), scala media (SM), cochlear partition, recessus scala tympani (RST), and the round window (RW). OW=oval window. The probe tip was slipped over the columella stump and advanced until seated against the outer face of the footplate. Schematic represents the bony cochlear wall and membranous partitions showing the entrance of sound via the stapes footplate into the scala vestibuli. Pressure is developed in the scala vestibuli by the vibration of the footplate (footplate velocity, , footplate area, , volume velocity, ) causing sound to be conducted across the cochlear partition along the cochlear impedance path to the round window (RW). Not to scale.
PZE displacement of the PZE driver probe tip as a function of attenuation level and frequency (Hz). Displacement was measured using laser interferometry (filled circles) and pressure measurements (open triangles) in a calibration volume at re: . Pressure measurements were also made at , and . The dotted line represents the overall mean of interferometry measurements across frequencies of at attenuation. Indicates that the mean for was significantly higher than the mean value across frequencies. Interferometry values for are summarized in Table I.
Tip velocity [ (mm/s)] vs dB attenuation (dB re:50 ) as measured using a laser vibrometer. These are seven representative examples of 12 interferometry calibration sequences for stimulus levels between and attenuation. Measurements were made in steps. Regression lines were calculated for each of 12 frequencies. In the interest of clarity we show only the regression line for . All slopes were [log(velocity)/dB] and hence linear (equivalent to 1 decade/). Here we present seven of the twelve frequencies studied. The data for attenuation are values from Table I, and values calculated using calibration regression lines for the respective individual frequencies “Regress.” Here the Table I values may be contrasted with values at re: predicted by the regression line for each frequency (“Regress,” filled circles).
Representative recordings at three attenuation levels from one embryo (left) and hatchling (right). Calibration bars reflect scales for amplitude vertically, and time (ms) horizontally.
Hatchling (PH) cochlear microphonic amplitude (, ) plotted against displacement for a stimulus applied directly to the columella footplate. Curves for five hatchlings are shown. Horizontal axes show displacement , particle velocity (mm/s) and dB keSPL.
Representative cochlear microphonic amplitudes are plotted as a function of footplate displacement . Each curve represents results for one animal. amplitudes were recorded in response to direct footplate stimulation at four different frequencies. Left panel illustrates data for hatchings (PH). Right panel illustrates data for embryos (Emb). Dotted line represents a linear relation of .
Hatchling (PH) and embryo (Emb) cochlear microphonic response to direct footplate stimulation. amplitude is shown as a function of footplate particle velocity (mm/s) with displacement held constant. Two displacement levels are shown (Dotted lines ; solid lines or as shown). Frequency was increased in eight steps from 100 to in order to introduce the corresponding stepped increases in footplate velocity. The legend identifies each symbol and frequency given in Hz.
Transform ratio of plotted in dB re: as a function of frequency for hatchlings (top) and embryos (middle and bottom). Dotted line shows /octave slope.
Displacement , velocity (mm/sec) and dB keSPL values at re: . Mean and standard deviation (SD) values are based on results from all laser interferometry measurements.
Mean amplitude at re: (displacement ). amplitudes for embryos were significantly less than those for hatchlings .
Log-Log regression line of vs PZE displacement plot for hatchling chicken. Units: and across hatchlings (A) and embryos (B).
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