von Mises distributions are characterized by a circular mean and circular concentration (κ) parameter. The higher the value of κ, the tighter the distribution is around the mean. κ is analogous (but not equivalent) to the inverse of the standard deviation of a normal distribution. The value of κ was thus the most appropriate estimate of the
width of the spike phase distribution, and hence an appropriate estimate of the precision of spike times around the mean. To determine click here the significance of phase locking to a particular frequency we used Rayleigh’s Z test. The null hypothesis for this Z test is that the circular distribution is uniform at all phases. The p value for this test is approximated using the term e−Z such that a Z value of 3 and above indicates significant phase locking (Siapas et al., 2005). For cells that showed significant phase-locking, we also calculated mean phase and κ. We did not calculate κ for cells that were not significantly phase-locked because cells with a low number of spikes can exhibit an artificially large κ. This work was funded by NSF IOB-0522220 and DARPA N66001-10-C-2010 to R.D.B. and NIH T32-MH019118 and F32-MH084443 to S.C.F. “
“Human VE-822 hearing
is extraordinarily sensitive and discriminating. We can hear sounds down to the level of thermal fluctuations in the ear. Our ability to detect subtle differences in tones over a frequency span of three decades allows us to
distinguish human voices of nearly identical timbre. We additionally perceive sounds of vastly differing intensities, enabling us to discern the strumming of nylon strings on a classical guitar playing in concert with a full orchestra. It is remarkable that the ear can achieve such sensitivity despite the viscous damping that impedes the oscillation of structures within Adenosine the cochlea. Indeed, the frequency resolution of human hearing inferred from psychophysics is too great to be explained by passive resonance (Gold, 1948). Measurements of amplified, compressive vibrations within the cochlea (Rhode, 1971; Le Page and Johnstone, 1980) as well as the discovery that healthy ears produce sounds (Kemp, 1978)—so-called otoacoustic emissions—have established that the inner ear possesses an active amplification mechanism. The qualities of active hearing can be observed in the inner ear’s mechanical response to sound. A pure-tone stimulus elicits a traveling wave along the cochlear partition (von Békésy, 1960), a flexible complex of membranes that divides the spiral cochlea into three fluid-filled chambers. Increasing in amplitude as it propagates, the traveling wave peaks at a characteristic place for each specific frequency of stimulation, thereby delivering most of its energy to a select population of mechanosensory hair cells.