Abstract

When an unresolvable grating of high retinal contrast is presented intermittently by modulating its contrast at constant average luminance, observers experience uniform field flicker. For long-wavelength cones, this contrast-modulation flicker can be seen for fringe periods almost as small as the diameter of a cone, implying no substantial neural spatial integration prior to the compressive or sensitivity-regulating nonlinearity responsible. We now report that the short-wavelength cone system, despite its greater spatial integration than the other cone systems, can generate contrast-modulation flicker for spatial frequencies as high as 50 cpd, a value comparable to that of the other cone systems in the same retinal area. Spatial resolution at the nonlinear site is in all cases apparently limited by the size of the cones. Likewise, little temporal filtering (in the range up to 15 Hz) precedes the S cone nonlinearity: evidently the reduced sensitivity for rapid flicker seen by S cones is due to postreceptoral limitations.

© 1992 Optical Society of America