Forward Masking of Auditory Evoked Potentials in Dolphins in Monaural and Dichotic Sound Stimulation: Implications for the Precedence Effect and Biosonar

Non-invasive recordings were made of short-latency auditory evoked potentials (SLAEP) in the bottlenose dolphin Tursiops truncatus produced in response to paired pulse sound stimuli (conditioning and tes stimuli) delivered through transducers in contact with the acoustic window on the lower jaw. Two types of stimulation were used: monaural (both stimuli through one transducer) and dichotic (conditioning and test stimuli delivered through different transducers, one in contact with the right acoustic window and the other in contact with the left acoustic window). The conditioning and test stimuli had the same characteristics; theinterval between them varied over the range 0.15–10 msec. During monaural stimulation, suppression of the test response was the same over the range of intervals 0.15–0.5 msec; the response was recovered on further increases in the interval. In dichotic stimulation, the most marked suppression of the test response occurred at an interval of 0.5 msec, with recovery of responses at shorter and longer intervals. Complete recovery occurred when the interval was shortened to 0.15 msec and lengthened to 2 msec. The significance of these results for the precedence effect and for dolphin biosonar is discussed.