Supplementary material from "Dazzle camouflage: Benefits and problems revealed"

During WWI, ships were painted in high contrast 'dazzle' patterns believed to distort, amongst other things, submariners' perceptions of direction when aiming their torpedoes, but was this strategy effective? Here we investigated the effects of different camouflage patterns, including versions used in the war, on the perceived direction of travel for a 3D computer model of the RMS Mauretania. Our results showed that texture gradients ‘twisted’ the perceived direction of the ship, the effect being ~10° for a regular pattern of circles. We also found a second, larger effect, 'hysteresis', that biased perceived target directions to parallel the horizon for directions of travel within approximately +/-30° of 90° (left-right). Hysteresis persisted outside this central plateau, causing perceived directions to be offset from veridical. The twist and hysteresis effects combined linearly and were constructive (enhancing protection) or destructive (diminishing protection) depending on the directions of (i) travel and (ii) the 'twisting' texture gradients. However, the strength of hysteresis reduced as a function of experience. Our simulated torpedo attacks suggest that systematic perceptual distortion of direction by dazzle might have been effective only where submariners had low hysteresis and ships were fast enough to benefit from the perceptual error imposed by twist.