Unlike the ABR of humans in whom the fifth peak is the most prominent of the ABR ( Burkard, 2007), the most prominent peak in most animals is the first peak (few milliseconds latency), assumed to be the compound action potential of the auditory nerve. These responses are in the microvolt range when measured with dermal or subdermal electrodes, and thus the signal to noise ratio (SNR) affects the measured thresholds. Usually, the short-latency response (latency <30 ms), termed the auditory brainstem response (ABR), is used to measure thresholds and generate audiograms. The response represents the summated activity of the auditory pathway in response to sound stimulation. The method has been used on a variety of animals, both vertebrates and invertebrates ( Brandt et al., 2018 Brittan-Powell et al., 2002 Christensen et al., 2015a Corwin et al., 1982 Ladich and Fay, 2013) and amphibians are no exception ( Goutte et al., 2017 Schrode et al., 2014 Womack et al., 2017). Measurement of auditory evoked responses is widely used as a relatively non-invasive method to assess hearing sensitivity. The ltABR method is not a good choice for studying hearing thresholds above 1000 Hz because of the bias introduced by spike rate saturation in the nerve fibers and their inability to phase lock. The tABR method showed a similar audiogram when using relatively long-duration tone bursts (25 ms). In conclusion, the mABR method gave the most sensitive audiograms. Comparisons between subjectively (visual inspection by researchers) and objectively (thresholds defined by signal-to-noise ratio) defined audiograms showed very little variation. We showed that the frequency specificity of tone bursts becomes poorly defined with shorter duration at low frequencies. We found similar results below 1000 Hz, but when stimulating with long-duration tones, the sensitivity decreased more rapidly above this frequency. We measured sensitivity in a range from 100 to 3500 Hz, and the resulting audiograms show two sensitivity peaks at 400–600 Hz and 1500–1600 Hz (both sensitive down to 30 dB re. We used three different methods in the same individual frogs: stimulating with brief tone bursts (tABR), long-duration tones (ltABR) and masked ABR (mABR), where transients are masked by a long-duration sinusoid, and the sensitivity is assessed by the difference between unmasked and masked ABR. However, the experimental methods differ greatly in respect to stimulation, which may result in different audiograms. ABR measurements are relatively non-invasive, easy to reproduce, and allow the assessment of sensitivity when psychophysical data are difficult to obtain. Hearing sensitivity has been extensively investigated, often by measuring the auditory brainstem response (ABR).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |