Effect of frequency difference on sensitivity of beats perception

Two vibrations with slightly different frequencies induce the beats phenomenon. In tactile perception, when two pins of different frequencies stimulate the fingertips, an individual perceives a beats caused by a summation stimulus of the two vibrations. The present study demonstrates experimentally that humans can perceive another vibration based on the beats phenomenon when two tactile stimuli with slightly different frequencies are stimulated on the finger pad with a small contactor in different locations at the same time. Moreover, we examined the amplitude of the detection threshold to be able to perceive beats phenomenon on the index finger with 5 carrier frequency (63.1, 100, 158.5, 251.2, and 398.1 Hz) and 4 beats frequency (2.5, 3.98, 6.31, and 10 Hz) when two stimuli 1 mm distance apart are vibrated at a slightly different frequency. From the experiments, it is concluded that the amplitude threshold to be able to perceive beats decreases as the standard frequency increases under 398 Hz. Furthermore, from comparing the absolute detection threshold and beats detection threshold, as the carrier frequency increases, the required amplitude at two pins for the detection of beats decreases compared to absolute vibration

Myosin Light-Chain Kinase Is Necessary for Membrane Homeostasis in Cochlear Inner Hair Cells

The structural homeostasis of the cochlear hair cell membrane is critical for all aspects of sensory transduction, but the regulation of its maintenance is not well understood. In this report, we analyzed the cochlear hair cells of mice with specific deletion of myosin light chain kinase (MLCK) in inner hair cells. MLCK-deficient mice showed impaired hearing, with a 5- to 14-dB rise in the auditory brainstem response (ABR) thresholds to clicks and tones of different frequencies and a significant decrease in the amplitude of the ABR waves. The mutant inner hair cells produced several ball-like structures around the hair bundles in vivo, indicating impaired membrane stability. Inner hair cells isolated from the knockout mice consistently displayed less resistance to hypoosmotic solution and less membrane F-actin. Myosin light-chain phosphorylation was also reduced in the mutated inner hair cells. Our results suggest that MLCK is necessary for maintaining the membrane stability of inner hair cells

Empirical and biophysical estimations of human cochlea’s psychophysical tuning curve sharpness

Despite the advances in cochlear research, the estimation of auditory nerve fiber frequency tuning of human cochlea is mostly based on psychophysical measurements. Although efforts had been made to estimate human frequency tuning sharpness from various physiological measurements which are less species dependent such as the compound action potential and stimulus-frequency otoacoustic emission delay, conclusions on the relative frequency tuning sharpness compared with that of other mammals vary. We simulated the biophysical human cochlea’s tuning curve based on physiological measurements of human cochlea and compared the human frequency tuning sharpness with results from empirical methods as well as experimental data of other mammalian cochleae. The compound action potential are more accurate at frequencies below 3 kHz while the stimulus frequency-otoacoustic emission delay are more accurate at frequencies above 1 kHz regions. The results from mechanical cochlear models, with support from conclusions of the other two empirical methodologies, suggest that the human frequency tuning sharpness at frequencies below 1 kHz is similar to common laboratory mammals but is exceptionally sharp at higher frequencies