Metacontrast masking and stimulus contrast polarity.

A recent report [Becker, M. W., & Anstis S. (2004). Metacontrast masking is specific to luminance polarity. Vision Research, 44, 2537-2543] of a failure to obtain metacontrast with target and mask stimuli of opposite contrast polarity is reexamined in an experiment that systematically varies not only stimulus contrast polarity but also target size and target-mask onset asynchrony (SOA). The results show that (a) although, as previously shown [Breitmeyer, B. G. (1978a). Metacontrast with black and white stimuli: Evidence of inhibition of on and off sustained activity by either on or off transient activity. Vision Research, 18, 1443-1448], metacontrast is weaker with stimuli of opposite contrast polarity, (b) substantial metacontrast can be obtained with targets and masks of opposite contrast polarity, especially (c) when the target is small. We conclude that Becker and Anstis's failure to obtain metacontrast with stimuli of opposite contrast polarity is due to their use of a single, relatively large, SOA value.