The first-spike latency of neurones at any level of the auditory pathw
ay decreases with stimulus amplitude. As stimuli are generally shaped
with rise functions to avoid spectral splatter, a common interpretatio
n of the latency decrease is that the amplitude of the signal reaches
the neurone's firing threshold earlier during the rise time. We demons
trate here, for auditory cortex neurones and by varying the amplitude
and rise time of tonal stimuli, that this threshold model is inadequat
e to account for the observed latency changes, particularly when adapt
ive processes are taken into account. The data raise the possibility t
hat latency may be a function of other properties associated with a si
gnal's onset, such as rate change of peak pressure.