As. Feng et al., DETECTION OF GAPS IN SINUSOIDS BY FROG AUDITORY-NERVE FIBERS - IMPORTANCE IN AM CODING, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 175(5), 1994, pp. 531-546
Physiological studies were carried out in the frog (Rana pipiens pipie
ns) eighth nerve to determine: (i) whether the modulation rate or the
silent gap was the salient feature that set the upper limit of time-lo
cking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detect
ion capacity of individual eighth nerve fibers. Time-locked responses
of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristi
c frequency) showed that the synchronization coefficient was a low-pas
s function of the modulation rate. In response to PAM stimuli having d
ifferent pulse durations, a fiber gave rise to nonoverlapping modulati
on transfer functions. The upper cut-off frequency of time locking was
higher when tone-pulses in PAM stimuli had shorter duration. The fact
that the cut-off frequency was different for the different PAM series
suggested that the AM rate was neither the sole, nor the main, determ
inant for the decay in time-locking at high AM rates. Gap detection ca
pacity was determined for 69 eighth nerve fibers by assessing fiber's
spiking activities to paired tone-pulses during an OFF-window and an O
N-window. It was found that the minimum detectable gap of eighth nerve
fibers ranged from 0.5 to 10 ms with an average of 1.23-2.16 ms depen
ding on the duration of paired tone pulses. For each fiber, the minimu
m detectable gap was longer when the duration of tone pulses comprisin
g the twin-pulse stimuli was more than four times longer. When the syn
chronization coefficient was plotted against the silent gap between to
nes pulses in the PAR?I stimuli, the gap response functions of a fiber
as derived from multiple PAM series were equivalent to gap response f
unctions deriving from twin-pulse series suggesting that it was the si
lent gap which primarily determined the upper limit of time-locking to
PAM stimuli.