A two-step detection system for defensive responses is differentially sensitive to polarization contrast in crabs

VERONICA PEREZ SCHUSTER; GABRIELA HERMITTE; JULIANA REVES SZEMERE; LUCCA SALOMON; MELANIE BASNAK; FEDERICO SEVLEVER; LUCAS D. LONGO; MERCEDES BENGOCHEA; MARTIN BERÓN DE ASTRADA

Bäckaskog Castle

Congreso; The Fourth International Conference on Invertebrate Vision; 2019

Lund University

The usage of polarized light to enhance object or motion detection, termed object-based polarization vision, has been recognized in a number of animals inhabiting intertidal and aquatic environments. However, the visual computations and neural mechanisms underlying such capabilities remain unknown. In the last couple of years we have been studying the polarization contrast sensitivity in the grapsid crab Neohelice granulata. We quantified the escape response and the changes in heart rate of animals evoked by a looming disk with an 82° polarization difference between the object and the background. More than 90% of the animals responded by freezing or escaping. We co-rotated the e-vector of light from object and background and found that the escape response varied periodically with a 90º period. Maximum responses were obtained for object and background e-vectors near the vertical and horizontal orientations. The cardiac response matched these results indicating that crab?s heart rate is a highly sensitive index of sensory perception. In line with theoretical models, our results provide experimental evidence that crabs perform a two-channel (vertical/horizontal) computation to achieve object-based polarization vision maximizing sensitivity in its natural environment (Basnak et al., 2018). To study how polarization contrast (PC) is combined with intensity contrast (IC) information we modified a 3D monitor to modulate differentially the intensity of vertical and horizontal polarized light. We confronted animals with edge motion stimuli translating laterally. The study included different IC and PC stimuli. This allowed us to identify two different phases of the crab?s cardiac response. The first phase might correspond with behavioral freezing while the second one with animal?s escape response. The former was elicited by light flashes, both polarization and low intensity contrast edge motion, and was steady along the repeated presentation of motion stimuli. Instead, the second phase of the response could only be elicited with high IC stimuli and, as is typical of the escape response, was largely reduced by repeated stimulation. The addition of polarization cues to an IC stimulus enhanced significantly the first but not the second phase of the response.