Hearing and seeing are largely thought to be two seperate senses. Dolphins however also use sound to see, a technique known as echolocation (see illustration below) where an individual dolphin sends out an acoustic signal (clicks etc.) and whatever it hits, or bounces off of sends back to the dolphin where it can then “see” what it is. New evidence from the study of two dolphin brains – acquired from animals who stranded over a decade ago – shows that this process is even more complex than was originally thought.
In most mammalian species there is one area in the brain associated with hearing and one with vision. in dolphins however, by using a new technique called diffusion tensor imaging (DTI), researchers have found that the processing of sound takes place in more than just one area as the auditory nerve connects to not only the temporal lobe – the area of the brain in most mammalian species where hearing is processed – but also to another area in the brain known as the primary visual region.
This has led the authors to hypothesise that unlike the human brain for example, dolphins hear sound in more than just one place, likely because they use it for more than just hearing. Sound is the most important sense that dolphins have and they use it for not only exploring their environment but for communication, navigation and foraging.
Lead author Gregory Berns, a neuroscientist at Emory University, is excited by the similarities they found between the brain of dolphins and bats, also known to be experts at the use of echolocation, because although bats and dolphins are completely unrelated this research shows that they may have evolved similar mechanisms for using sound not just to hear, but to also create mental images. Berns considers that for the first time, we may be on the road to beginning to “really understand how the dolphins (and other animals) mind works and how they create perceptual experiences from their environment”.