Visual laterality in dolphins: importance of the familiarity of stimuli

Abstract

BackgroundMany studies of cerebral asymmetries in different species lead, on the one hand, to a better understanding of the functions of each cerebral hemisphere and, on the other hand, to develop an evolutionary history of hemispheric laterality. Our animal model is particularly interesting because of its original evolutionary path, i.e. return to aquatic life after a terrestrial phase. The rare reports concerning visual laterality of marine mammals investigated mainly discrimination processes. As dolphins are migrant species they are confronted to a changing environment. Being able to categorize new versus familiar objects would allow dolphins a rapid adaptation to novel environments. Visual laterality could be a prerequisite to this adaptability. To date, no study, to our knowledge, has analyzed the environmental factors that could influence their visual laterality.ResultsWe investigated visual laterality expressed spontaneously at the water surface by a group of five common bottlenose dolphins (Tursiops truncatus) in response to various stimuli. The stimuli presented ranged from very familiar objects (known and manipulated previously) to familiar objects (known but never manipulated) to unfamiliar objects (unknown, never seen previously). At the group level, dolphins used their left eye to observe very familiar objects and their right eye to observe unfamiliar objects. However, eyes are used indifferently to observe familiar objects with intermediate valence.ConclusionOur results suggest different visual cerebral processes based either on the global shape of well-known objects or on local details of unknown objects. Moreover, the manipulation of an object appears necessary for these dolphins to construct a global representation of an object enabling its immediate categorization for subsequent use. Our experimental results pointed out some cognitive capacities of dolphins which might be crucial for their wild life given their fission-fusion social system and migratory behaviour.

The Neocortex of Indian River Dolphins (Genus <b><i>Platanista</i></b>): Comparative, Qualitative and Quantitative Analysis

“…Indian river dolphins are adapted to a more or less stable but turbid riverine environment where the auditory system is the only reliable source of information for spatial orientation. In contrast, the bottlenose dolphin and other delphinids live in open-ocean habitats [Rice, 1990] that require a high degree of locomotor activity, diving capacity, and visual orientation [Blois-Heulin et al, 2012]. In combination with a versatile acoustic communication [Dubrovsky, 2004], these adaptations may be seen as preconditions for high encephalization in marine species and, even more remarkably, in combination with high cortical neuron densities.…”

Perspectives: The Looking Time Experimental Paradigm in Studies of Animal Visual Perception and Cognition

“…), and exhibit visual laterality with respect to object familiarity (captive bottlenose dolphins, T. truncatus : Blois‐Heulin et al. ; wild striped dolphins, Stenella coeruleoalba : Siniscalchi et al. ).…”

A Crucial Role of Attention in Lateralisation of Sound Processing?

“…The authors concluded that the RH processes high arousal independently of valence, although one alternative possibility is that anticipation of positive event may correspond to a quite ambiguous situation [68]. Following Baciadonna et al [67], one hypothesis therefore would be that lateralised processes concern intensity and not valence of the stimuli, two aspects of emotions separated in the circumplex model of Lang et al [69]. This would be in contrast to the valence theory [70] that predicts a clear impact of valence on the lateralisation of stimulus processing (see also [71,72]).…”