Blodgett's (1919) "Ship camouflage" 105 years on: A misperception of dazzle perception revealed and redressed

During WWI, dazzle camouflage involved painting allied shipping with bold geometric patterns to disrupt the perceptions of enemy submariners. The first experiment to provide quantitative results on this (Blodgett, 1919; MIT Libraries, MA) used scale models and mechanical simulation, and reported enormous perceptual errors for their perceived direction of travel (up to ∼60°), possibly due to a "twist" effect from forced perspective. However, Blodgett's work did not meet modern standards and the organisation of his report complicates evaluation. Here, we produce (i) reformatted and (ii) heavily edited versions of the original report to improve readability, and (iii) provide a critical reappraisal of the work including (iv) a detailed reanalysis of Blodgett's data and (v) a new control experiment on edited images of the original stimuli. After addressing problems with Blodgett's analysis and control experiment, we found results indicating a twist of only about 7°, but a much larger "hysteresis" effect (∼19-23°) where perceived direction was drawn to the horizon regardless of dazzle. This effect combined both constructively and destructively with "twist", depending on the direction of the target ship. These reappraised findings resolve an apparent conflict with the second quantitative experiment on dazzle ships conducted over a century later using computer displays online (Lovell et al., 2024; Royal Society Open Science). We conclude that Blodgett's approach and data remain of interest today, but his conclusions substantially overestimated the effectiveness of dazzle camouflage in biasing the perceived directions of ships. However, other potential benefits of dazzle, including perceptual variance, await systematic investigation.