Fake Tilt-Shift Miniaturisation Causes Negative D-Prime for Detecting Reality

Tilt-shift lens technology can produce photographs of distant objects with very narrow depths of field. For scenes with appropriately placed foreground and background, fake tilt shift (FTS) effects can be achieved by applying blur gradients to the upper and lower parts of a conventional photograph. Either way, the treatment causes real scenes to look like small-scale models. This happens because the blur depth-cue implies that the object is close, and therefore small to be within view. Previous attempts to study this used subjective measures of perceived distance, which are complicated by cognitive strategy. We improved on this by devising a 2AFC performance task where participants viewed pairs of achromatic railway scenes for 5 seconds. The target scene was real; the other was a detailed 1:76 scale model. There were six treatments of the real photographs: null, total blur, FTS blur, inverse FTS blur, orthogonally oriented FTS blur, and FTS blur with no gradient (ie, a strip of focus through a blurred image). Each of the six real photographs was given each of the treatments and compared to each of the six model photographs. Each of the 36 participants performed 6 trials in random order. For the null treatment, observers detected reality reliably, whereas for FTS blur with and without gradients the model world was mistaken for reality. Participants were at chance for the other treatments. We conclude that the key factor for achieving FTS miniaturization is the correct alignment of the treatment with the subject, not the inclusion of a blur gradient