title: Harbor seals (Phoca vitulina) can perceive optic flow under water.
abstract: Optic flow, the pattern of apparent motion elicited on the retina during movement, has been demonstrated to be widely used by animals living in the aerial habitat, whereas underwater optic flow has not been intensively studied so far. However optic flow would also provide aquatic animals with valuable information about their own movement relative to the environment; even under conditions in which vision is generally thought to be drastically impaired, e. g. in turbid waters. Here, we tested underwater optic flow perception for the first time in a semi-aquatic mammal, the harbor seal, by simulating a forward movement on a straight path through a cloud of dots on an underwater projection. The translatory motion pattern expanded radially out of a singular point along the direction of heading, the focus of expansion. We assessed the seal's accuracy in determining the simulated heading in a task, in which the seal had to judge whether a cross superimposed on the flow field was deviating from or congruent with the actual focus of expansion. The seal perceived optic flow and determined deviations from the simulated heading with a threshold of 0.6 deg of visual angle. Optic flow is thus a source of information seals, fish and most likely aquatic species in general may rely on for e. g. controlling locomotion and orientation under water. This leads to the notion that optic flow seems to be a tool universally used by any moving organism possessing eyes.
authors: University of Rostock, Institute for Biosciences, Sensory and Cognitive Ecology, Rostock, Germany.
authors: Nele
authors: N
authors: Gläser
authors: University of Bochum, General Zoology and Neurobiology, Bochum, Germany.
authors: Björn
authors: B
authors: Mauck
authors: University of Münster, Institute for Psychology, Münster, Germany.
authors: Farid I
authors: FI
authors: Kandil
authors: University of Münster, Institute for Psychology, Münster, Germany.
authors: Markus
authors: M
authors: Lappe
authors: University of Rostock, Institute for Biosciences, Sensory and Cognitive Ecology, Rostock, Germany.
authors: Guido
authors: G
authors: Dehnhardt
authors: University of Rostock, Institute for Biosciences, Sensory and Cognitive Ecology, Rostock, Germany.
authors: Frederike D
authors: FD
authors: Hanke
mesh_terms: D000818:Animals; D008297:Male; D057849:Optic Flow / Q000502:physiology*; D009949:Orientation; D046049:Phoca / Q000502:physiology*; D010775:Photic Stimulation; D013550:Swimming