Auditory evoked potential testing in Southern Hemisphere seals

Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leopard seal. Three frequencies from 1 to 4 kHz were tested at sound levels from 68 to 122 dB peak equivalent sound pressure level (peSPL). Results illustrate brainstem activity within the 1-4 kHz range, with better hearing sensitivity at 4 kHz. As is seen in human ABR, only wave V is reliably identified at the lower stimulus intensities. Wave V is present down to levels of 82 dB peSPL in the right ear and 92 dB peSPL in the left ear at 4 kHz. Further investigations testing a wider frequency range on seals of various sex and age classes are required to conclusively report on the hearing range and sensitivity in this species.

A single male Australian sea lion (Neophoca cinerea) was tested for its auditory sensitivity to in air sound. Short, broadband clicks were presented via headphones while the animal was immobilized during medical treatment. Click-evoked auditory brainstem responses (ABRs) were recorded in the animal after acoustic stimulation at decreasing sound pressure levels. A single wave was clearly and repeatedly identified in the neuronal responses and analyzed. Click-evoked brainstem activity was detectable in the presence of ambient and electrical noise at presentation levels down to 81 dB re 20 µPa peak equivalent sound pressure level for in air stimuli. As has been previously demonstrated for other pinniped species, this method is applicable for Australian sea lions and will be useful for auditory studies of individuals in captivity and in the field.