Index of content:
Volume 103, Issue 2, February 1998
- BIOACOUSTICS 
The relationship of scattered subharmonic, 3.3-MHz fundamental and second harmonic signals to damage of monolayer cells by ultrasonically activated103(1998); http://dx.doi.org/10.1121/1.421250View Description Hide Description
Cultured Chinese hamster ovary cells attached to thin Mylar sheets were exposed to 3.3-MHz ultrasound in the presence of ultrasound contrast agent. The ultrasound beam was directed upward at the exposure chamber with the monolayer on the inside of the upper acoustic window. Cell membrane damage was detected by the firefly enzyme assay for released ATP and the subharmonic, fundamental, and second harmonic scattered signals were recorded. ATP release increased monotonically with increasing pressure amplitude above apparent thresholds of 0.28 MPa for 1-s continuous and 0.56 MPa for 100-s pulsed (10-μs pulses, 1-ms PRP) exposures with 5% The subharmonic signal and, to a lesser extent, the second harmonic signal both increased with the cell membrane damage, which suggests that these signals have predictive value for bioeffects. If the monolayer was positioned on the front window of the exposure chamber, cell membrane damage was greatly reduced, which confirms the protective influence of this configuration of monolayers reported in the literature. The effect decreased both at high (50%) or low (0.5%) concentrations of The strong nonlinear scattering of ultrasound by contrast agent gas bodies appears to provide useful indicators of gas body activity including cavitational bioeffects.
Control of vocal intensity in budgerigars (Melopsittacus undulatus): Differential reinforcement of vocal intensity and the Lombard effect103(1998); http://dx.doi.org/10.1121/1.421227View Description Hide Description
Call production in budgerigars was studied using operant conditioning. In several experiments, budgerigars were reinforced with food for producing calls that were above or below a criterion level of intensity. This differential reinforcement procedure was successful in controlling vocal intensity in both directions showing that the intensity with which budgerigars produce vocalizations is under voluntary control. In additional experiments, call intensity maintained by food reinforcement was measured both in the quiet and in the presence of various levels of broadband noise. Call intensity in budgerigars increased significantly in noise, paralleling the well-known Lombard effect in humans which is the reflexive increase in speech intensity during communication in noise. Call intensity was measured in broadband noise and in a notched noise (no energy between 1.5 and 4.5 kHz) with the same overall level. Results show that noise in the spectral region of contact calls is most effective in causing an increase in vocal intensity. In aggregate, these experiments show that budgerigars have voluntary control over the intensive aspect of their vocalizations, that they normally monitor their vocal output though external auditory feedback, and, like humans, they exhibit the Lombard effect.
103(1998); http://dx.doi.org/10.1121/1.421228View Description Hide Description
Using a go/no go response paradigm, a tucuxi (Sotalia fluviatilis guianensis) was trained to respond to pure-tone signals for an underwater hearing test. Auditory thresholds were obtained from 4 to 135 kHz. The audiogram curve shows that this Sotalia had an upper limit of hearing at 135 kHz; from 125 to 135 kHz sensitivity decreased by 475 dB/oct. This coincides with results from electrophysiological threshold measurements. The range of best hearing (defined as 10 dB from maximum sensitivity) was between 64 and 105 kHz. This range appears to be narrower and more restricted to higher frequencies in Sotalia fluviatilis guianensis than in other odontocete species that had been tested before. Peak frequencies of echolocation pulses reported from free-ranging Sotalia correspond with the range of most sensitive hearing of this test subject.