Feature synergy depends on feature contrast and objecthood.

Pairs of texture figures, defined by contrast in spatial frequency, orientation or both cues (redundant texture definition) had to be detected within a homogeneous Gabor field. In line with expectation we find better detection performance for arrangements with higher feature contrast along the border where the figures abut. Redundantly defined figures show synergy, a significant performance increase compared to the prediction of independent processing of orientation and spatial frequency cues. As found in previous studies [Spatial Vision 16 (2003) 459; Vision Research (submitted for publication)] this performance advantage is negatively correlated with visibility. In particular, figures with high border feature contrast are easily detectable but show weak synergy whereas figures with low border feature contrast are barely detectable but remarkably benefit from redundant texture definition. Closer analysis reveals that the form of the figures is also crucial: As long as they maintain a clear two dimensional shape the synergy effect is only marginally affected by variation figure size and border length. But when they degrade to one dimensional Gabor element arrays, synergy almost completely vanishes. The results imply that both factors, low visibility and objecthood, are critical for feature synergy. We conclude that facilitation across feature domains serves to segregate figure from ground when the signal from a single domain is too weak to enable object detection and vanishes under conditions of stable object vision.