How simultaneous is the perception of binocular depth and rivalry in plaid stimuli?

Psychophysical experiments have demonstrated that it is possible to perceive both binocular depth and rivalry in plaids (Buckthought and Wilson 2007, Vision Research47 2543-2556). In a recent study, we investigated the neural substrates for depth and rivalry processing with these plaid patterns, when either a depth or rivalry task was performed (Buckthought and Mendola 2011, Journal of Vision11 1-15). However, the extent to which perception of the two stimulus aspects was truly simultaneous remained somewhat unclear. In the present study, we introduced a new task in which subjects were instructed to perform both depth and rivalry tasks concurrently. Subjects were clearly able to perform both tasks at the same time, but with a modest, symmetric drop in performance when compared to either task carried out alone. Subjects were also able to raise performance levels for either task by performing it with a higher priority, with a decline in performance for the other task. The symmetric declines in performance are consistent with the interpretation that the two tasks are equally demanding of attention (Braun and Julesz 1998, Perception & Psychophysics60 1-23). The results demonstrate the impressive combination of binocular features that supports coincident depth and rivalry in surface perception, within the constraints of presumed orientation and spatial frequency channels.