What part of a vernier stimulus determines performance?

Vernier acuity was measured using a pair of long, abutting vertical sinusoidal luminance gratings. Performance was also measured for pairs of thin horizontal strips of grating whose vertical separation was varied in order to represent different parts of the original grating. At small strip separations, performance was equivalent to that for the long gratings only at high spatial frequencies. At moderate spatial frequencies, intermediate strip separations resulted in equivalent performance. This suggests that different parts of a vernier stimulus can mediate performance depending upon the underlying spatial frequency content. Implications for the effect of contrast upon different vernier configurations are examined.