Urgency is a non-monotonic function of pulse rate

Why are natural sounds detected faster than pips?

Simple reaction times (RTs) were used to measure differences in processing time between natural animal sounds and artificial sounds. When the artificial stimuli were sequences of short tone pulses, the animal sounds were detected faster than the artificial sounds. The animal sounds were then compared with acoustically modified versions (white noise modulated by the temporal envelope of the animal sounds). No differences in RTs were observed between the animal sounds and their modified counterparts. These results show that the fast detection observed for natural sounds, in the present task, could be explained by their acoustic properties.