Previous research has documented that cetaceans can discriminate between humans, but the process used to categorize humans still remains unclear.  The goal of the present study was to replicate and extend previous work on the discrimination between familiar and unfamiliar humans by three species of cetaceans.  The current study manipulated the familiarity and activity level of humans presented to 12 belugas ( Delphinapterus leucas ) housed between two facilities, five bottlenose dolphins ( Tursiops truncatus ), and six Pacific white-sided dolphins ( Lagenorhynchus obliquidens ) during free-swim conditions.  Two measures of discrimination were coded from video recordings of each trial: lateralized visual processing and gaze duration.  No clear lateralization effects emerged at the species level, primarily due to extensive individual variability.  The results also indicated that activity level influenced gaze durations across species, and for some individuals, the interaction between human familiarity and activity level influenced gaze durations and eye preferences.  Unexpectedly, bottlenose dolphins had longer gaze durations for familiar humans whereas belugas and Pacific white-sided dolphins had longer gaze durations for unfamiliar humans.  All three groups displayed longer gaze durations for active humans as compared to neutral humans, and belugas and bottlenose dolphins had significantly longer gaze durations than Pacific white-sided dolphins.  These results indicate that the cetaceans can discriminate between unfamiliar and familiar humans and preferred active humans.  However, discrimination of humans via lateralized visual processing did not appear at the group level, but rather at the individual level which countered previous research.  This study is discussed within the contexts of attention and individual differences across animals of different species.

Lateralization of behaviors and information processing are common across species. Hypothesized to be crucial for more efficient responding to environmental stimuli, lateralization has been investigated for a number of topics. Cetaceans are proposed to be hemispheric specialists, given a small corpus callosum, complete decussation of the optic nerve, and the ability to respond to a different visual stimulus presented to each eye simultaneously. Research with cetaceans has shown strong biases in a number of behaviors, including swimming, foraging, social interactions, and responses to myriad visual stimuli. Given similar evolutionary pressures, different species of cetaceans should display similar lateralized preferences. Previous research with bottlenose dolphins in managed care and wild striped dolphins indicated a right eye preference when viewing unfamiliar objects. The purpose of the current study was to evaluate the eye preference of belugas, bottlenose dolphins, and Pacific white-sided dolphins (lags) in managed care when viewing familiar and unfamiliar objects. The results from 11 belugas, 5 bottlenose dolphins, and 5 lags indicated that consistent group level eye preferences were not present. The belugas preferred to view both types of objects with both eyes, with the majority of the belugas showing a left-eye preference when a monocular gaze was used. Bottlenose dolphins tended to view both objects with their right eye while lags used their left eye when viewing objects. These results may have been affected by viewing objects below water versus above water. The belugas and the Pacific white-sided dolphins were able to view the objects below water, which may have elicited more naturalistic visual examinations of the objects (i.e., greater ecological validity). Viewing objects within one’s habitat may facilitate the discrimination of an object rather than simply its detection, which is may be more likely when encountering stimuli above the surface of the water as the bottlenose dolphins had to do in the present and past research. Future research should compare if presentation of the stimulus above water versus below water affects the eye preference displayed.