Date of Degree

2-2022

Document Type

Dissertation

Degree Name

Ph.D.

Program

Psychology

Advisor

Diana Reiss

Committee Members

James Gordon

Martin Chodorow

Marcelo Magnasco

Subject Categories

Cognition and Perception | Comparative Psychology

Keywords

Lateralization, viewing side bias, bottlenose dolphin, social processing, video stimuli

Abstract

Cetacean field studies have reported consistent population-level side biases for foraging behaviors and this right side feeding bias is arguably the strongest in any species next to handedness in humans. Notably, experimental studies with cetaceans, particularly dolphins, have struggled to find laterality in other behaviors, and some have reported patterns that are inconsistent with those typically found in vertebrates. Side biases related to social processing have been reported in a few observational studies of wild delphinids but have not been successfully evaluated in a controlled experimental context. This dissertation investigated viewing side biases of bottlenose dolphins in two contexts: when viewing familiar conspecifics in adjacent pools (Study 1), and when viewing video footage of the same conspecifics when presented in a controlled video study (Study 2) to evaluate how dolphins perceive and respond to social and non-social categories of video stimuli. Study 2 had two parts, first full-size videos with more varied movement were presented (Study 2A), then reduced-size videos with limited, centralized movement were presented (Study 2B).

In Study 1, viewing (10 days, 11 hr/day) by two male bottlenose dolphins were evaluated for duration and eye use (left or right) when looking through the holes in the gates between adjacent pools that contained familiar conspecifics at the National Aquarium in Baltimore, MD. Overall, Study 1 provided evidence for viewing side biases and how those biases were related to concurrently occurring events and acoustic signals. The patterns found for feed (right eye/left hemisphere), monitoring conspecifics (left eye/right hemisphere), and higher arousal (left eye/right hemisphere) were consistent with the typical pattern of hemispheric processing found in vertebrates. Additionally, this is the first study with delphinids to find evidence of modulation of viewing by arousal. Future laterality studies with delphinids should evaluate multiple and potentially influential variables, including those related to arousal.

In Study 2, the behavioral and acoustic responses of the same two dolphins were evaluated during viewing social and non-social videos rear-projected onto a large (8 ft X 4 ft) display screen affixed to an underwater window. In Study 2A, eighteen novel 30-second videos (6 social, 6 feed, 6 control) were presented four times each, over the course of 6 sessions. For both dolphins, the results indicate more time spent viewing, more broad-burst pulse signals detected, and less echolocation signals detected during social videos than during feed and control videos. These findings demonstrate a high motivation to view, an ability to discriminate and respond with different acoustic signals for social versus the other video categories, which provides support for the future use of videos to investigate perception and cognition with delphinids. The broad burst-pulse response detected during social videos may be evidence of a social response, but this cannot be determined from this study alone and needs to be replicated in future studies. Both dolphins positioned themselves primarily head-on, using binocular vision, and tracked the on-screen movement with their rostrums. Due to the lack of sustained lateral viewing independent of the movement of the stimuli on the screen, side biases when viewing videos could not be evaluated. However, we assessed side biases when the dolphins swam past the screen (swim-bys). The results indicate that both dolphins initially had a left side bias, and then switched to a right side bias during experimental sessions, which may be related to the left hemispheres’ involvement in approach behaviors and processing of stimuli that are deemed non-threatening. In Study 2B, 12 novel videos were presented 4 times each over 4 sessions.

Due to the lack of approaches to the screen only one dolphin’s data could be analyzed and there were no significant differences between the video categories for that dolphin. But again, viewing was very close to the screen and primarily binocular. The use of video stimuli for laterality studies may not be feasible without requiring dolphins to station at a specific distance from the screen. The viewing position adopted by the dolphins may be related to multiple factors including: a preference to view with the temporal area of best vision, depth perception cues, or simultaneous processing with both hemispheres.

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