Volume 107, Issue 2, February 2000
Index of content:
- BIOACOUSTICS 
Anisotropy of ultrasonic propagation and scattering properties in fresh rat skeletal muscle in vitro107(2000); http://dx.doi.org/10.1121/1.428282View Description Hide Description
The anisotropy of frequency-dependent backscatter coefficient, attenuation, and speed of sound is assessed in fresh rat skeletal muscle within 5 h post-mortem. Excised rat semimembranosus and soleus muscles are measured in 37 °C Tyrode solution, with the muscle fibers at 90° and 45° orientations to the incident sound beam. Reflected and through transmission signals from either a 6- or 10-MHz focused transducer give frequency dependent information in the 4–14 MHz range. The attenuation coefficient in each muscle is consistently a factor of lower for propagation perpendicular to the fibers than at 45°, whereas speed of sound shows a much milder anisotropy, and is slightly faster for the 90° orientation. The largest anisotropy is seen in the backscatter coefficient, most notably in the semimembranosus where the magnitude at 90° is over an order of magnitude greater than at 45°, with the frequency dependence in both cases giving a power law between 1.5 and 2.0.
Spectral cues and perception of the vertical position of targets by the big brown bat, Eptesicus fuscus107(2000); http://dx.doi.org/10.1121/1.428283View Description Hide Description
Big brown bats (Eptesicus fuscus) were trained to discriminate between vertical angles subtended by paired beads suspended from fishing line. Bats were rewarded for choosing the smaller of the two angles presented. The difference between the angles was changed systematically using a transformed up–down procedure and the bats’ ability to detect the difference was measured at different vertical locations. When the beads were centered at +20° (above the horizon), at 0° (the horizon), and at −20° (below the horizon), vertical angle acuity (VAA) was maintained between 2.9° and 4.1°. At more extreme vertical positions both bats showed loss of acuity; when the beads were centered around −40°, VAA was 6.7° or 8.3° and at +40, VAA was worse than 21° (the largest difference tested). When the tragi of both ears were bent down and glued to the side of the face, bats showed severe loss of acuity for beads centered at −20° (VAA 18.3° and 20.1°), but maintained their angle acuity for beads centered at +20° (VAA 3.8° and 4.9°). The results are consistent with the spectral cues created by the filtering of the external ear.