Neural time and movement time in choice of whistle or pulse burst responses to different auditory stimuli by dolphins.

Echolocating dolphins emit trains of clicks and receive echoes from ocean targets. They often emit each successive ranging click about 20 ms after arrival of the target echo. In echolocation, decisions must be made about the target--fish or fowl, predator or food. In the first test of dolphin auditory decision speed, three bottlenose dolphins (Tursiops truncatus) chose whistle or pulse burst responses to different auditory stimuli randomly presented without warning in rapid succession under computer control. The animals were trained to hold pressure catheters in the nasal cavity so that pressure increases required for sound production could be used to split response time (RT) into neural time and movement time. Mean RT in the youngest and fastest dolphin ranged from 175 to 213 ms when responding to tones and from 213 to 275 ms responding to pulse trains. The fastest neural times and movement times were around 60 ms. The results suggest that echolocating dolphins tune to a rhythm so that succeeding pulses in a train are produced about 20 ms over target round-trip travel time. The dolphin nervous system has evolved for rapid processing of acoustic stimuli to accommodate for the more rapid sound speed in water compared to air.