When animals are faced with visual stimuli that indicate an imminent threat, they commonly produce a defensive response. Both figure contrast polarity and motion have long been found to be used by vertebrate and invertebrate species to recognize visual threats. The polarization of light has also been shown to contribute to contrast sensitivity in many aquatic and intertidal animals. However, whether polarization and luminance are processed jointly or in parallel visual channels remains unresolved. We developed a massed adaptation–recovery paradigm (29 trials of training, 5 trials of testing) in the crab Neohelice granulata with different looming stimuli. We switched luminance polarity (OFF↔ON), motion direction (Right↔Left) and angle of polarization (AoP) while holding intensity and degree of linear polarization fixed (Vertical↔Horizontal). By analyzing both the kinematics of the escape response and the proportion of trials that evoked escaping, we found that the response recovered after every switch. Particularly, the recovery after the polarization swap indicates that vertical and horizontal polarization signals adapt separately, rather than acting as a single polarization contrast channel. These results support a parallel-channel account in which polarization and luminance are at least partially independent for threat detection.