Combining cues in contour orientation discrimination.

The perceived orientation of a Gabor-patch contour is determined, in part, by shifts in carrier phase between the patches [Popple, A. V. & Sagi, D., 2000. A Fraser illusion without local cues? Vision Research, 40, 873-878; Popple, A. V. & Levi, D. M., 2000a. A new illusion demonstrates long-range processing. Vision Research, 40, 2545-2549; Popple, A. V. & Levi, D. M., 2000b. Amblyopes see true alignment where normal observers see illusory tilt. Proceedings of the National Academy of Sciences of the United States of America, 97, 11667-11672]. Here we show that perceived orientation results from the combination of at least three stimulus cues: (1) patch orientation, (2) contour envelope orientation, and (3) between-patches orientation, which is a function of phase-shifts. In a series of three experiments, we investigated how these three cues were combined. The data are consistent with weighted cue combination.