Functional bandwidth of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

Abstract

The frequency band that an Atlantic bottlenose dolphin (Tursiops truncatus) used to perform an echolocation target discrimination task was determined using computer simulated phantom targets. The dolphin was trained to discriminate frequency filtered phantom targets from unfiltered ones in a go/no-go paradigm. The dolphin's performance indicated perception of echo alteration only when applied filters interfered with the frequency band between 29 and 42 kHz. The dolphin did not behaviorally convey perception of applied filters that affected frequencies outside this functional bandwidth, such as a low pass 43 kHz or a high pass 28 kHz filter. The upper limit of the functional bandwidth at 42 kHz corresponded with the dolphin's upper hearing limit of 45 kHz, as determined through auditory evoked potential measurements. The lower limit of the functional bandwidth corresponded to a drop in intensity below 30 kHz within the dolphin's echolocation clicks. The randomized presentation of different filters showed that the dolphin paid attention to the entire 29-42 kHz band for each trial, not just subsets. The absence of temporal cues between some of the targets the dolphin could discriminate indicated that in these cases the target discrimination cues were based solely on the frequency content.