Our results showed that geometric cues to f/g disambiguate the accretion-deletion cues in our displays (
Figure 1), and biased the percept of 3-D rotation in proportion to their strength. These displays thus also provide a novel way of measuring f/g perception, since the percept of 3-D rotation tends to tracks the strength of the f/g geometric cue. Traditionally, f/g percepts have been measured simply by asking the subject which region they perceive as figural. Such direct explicit report tasks are, however, prone to individual biases, high-level interpretations, and extraperceptual factors (Struber & Stadler,
1999). Less prone to such factors was the visual short-term memory task proposed by Driver and Baylis (
1996), based on the assumption that figural regions have a stronger memory trace than ground regions. Typically, a subject would be presented with an f/g display and, subsequently, with a test display, containing one of the regions from the f/g display. A subject would then be found to be faster at recognizing the region in the test display if it were part of the figural than ground regions. Even though this task was used by many researchers as the gold standard, it has been remarked that the test display itself might be influencing the short-term memory effect (Hulleman & Humphreys,
2004). Hulleman and Humphreys (
2004) proposed yet another method based on visual search. In their displays, one region would be symmetric while others were not. If this symmetric region was also figural, subjects would more easily find it than when it was to be ground. However effective, this one symmetric region might confound the displays when another cue is to be measured. From a totally different tradition is the on-off method (Hoffman & Singh,
1997; Stevens & Brookes,
1988), which in the recent years has been applied to traditional alternating black-white regioned f/g stimuli (Peterson & Salvagio,
2008). Subjects are presented with a red dot on top of one of the regions and asked if it was on top of the figural region or not. The phenomenon in the current paper, as a methodology, overcomes many of the issues as present in the direct methods (explicit report, on-off method), because of the indirect nature of the question asked to subjects (“Which colored regions do you perceive as rotating?”). Such an indirect question was made possible by the perceptual coupling (Hochberg & Peterson,
1987) between the rotation percept and the f/g percept, present in our stimuli. Furthermore, the bistable nature of our stimulus makes it easy for the observer to report their observation. The usefulness of methods employing such stimuli has been pointed out before (e.g., Backus,
2009). Lastly, no second image need to be shown as a target (visual short-term memory method), nor does the geometry of the displays need to be changed (visual search method) that might influence our f/g perception.