Masters Thesis

Assessing Tactile Sensitivity Using a Psychophysical Staircase Procedure in the Bottlenose Dolphin, Tursiops truncatus

Little research has been conducted on the somatosensory system of odontocete cetaceans and it remains uncertain how important the sense of touch is to their perception of the environment. In this study, tactile sensitivity to high-frequency displacement of the skin was quantified in two adult bottlenose dolphins (Tursiops truncatus) using a haptic device (tactor). The magnitude of skin displacement was controlled by varying the voltage to the tactor, which presented a sinusoidal stimulus at a rate of 250 Hz for a period of one second. Tactile sensitivity thresholds were determined using an adaptive staircase procedure in which dolphins reported tactile perception of the stimulus by producing a whistle. Displacement thresholds ranged from 3.0 to 39.9 μm with the greatest sensitivity found along the rostrum and around the melon and blowhole of the dolphin. Sensitivity decreased caudally along the body of the dolphin with the tip of the tail fluke being the least sensitive location tested (i.e. no threshold could be obtained at the fluke). The results support hypotheses that the hairless follicles located on the dolphin’s rostrum are important to a dolphin’s ability to perceive the environment. The reduction in tactile sensitivity of the appendages is consistent with the role of these body parts in stabilization and locomotion, but which have become less important for use in exploration or sensing of the environment.

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