Abstract
The purpose of this study was to assess S-cone discrimination in the presence of two adapting fields. The stimulus consisted of an equiluminant 12°–16° test annulus (13.0 cd/m2) surrounded by a circular inner and a rectangular outer adapting field. Discrimination was determined by a spatial 2AFC procedure for annulus s=S/(L+M) chromaticities between 0.6 and 1.6. In Experiment 1, the l=L/(L+M) chromaticities in all fields were fixed at 0.665. The s chromaticities of the adapting fields were 0.6, 1.0 or 1.6. When the adapting fields had equal s chromaticities, discrimination was best at adapting s=0.6 or 1.0 but was relatively stable at various test chromaticities for adapting s=1.6. When the adapting fields had different s chromaticities, discrimination functions were almost identical for the inner-outer adapting field pairs consisting of the same chromaticity combinations, with adapting s=0.6 or 1.0 playing a more dominating role in determining discrimination threshold. In Experiment 2, the two adapting fields had the same s chromaticities (0.6, 1.0 or 1.6) but one of the adapting fields had a different l, as 0.625 or 0.705, from the test and the other adapting field (l=0.665). The introduction of an l difference in one adapting field improved S-cone discrimination for the adapting s=0.6 or 1.0 only at high test s chromaticities. These results indicated that the two adapting fields jointly contribute to S-cone discrimination and two cardinal axes interact in a complex way.