Purpose. Wallach's ratio rule (1948) suggests that the perceived lightness of a test disk embedded in a higher luminance surround is determined by the surround/disk (S/D) luminance ratio. Our goal was to test whether infantsÍ lightness perception follows WallachÍs ratio rule.
Methods. We developed a new hybrid technique combining familiarization-novelty paradigm (Fagan, 1974) and FPL (Teller, 1979) to measure infantsÍ novelty responses to a change in perceived lightness. In the familiarization phase of each trial, infants were exposed to two identical 9¡ disks embedded in a large surround (30 deg x 48 deg), with a S/D ratio of 6:1. In the test phase, the surround luminance was increased or decreased by a factor of 3. The infant was presented one disk that maintained the same luminance as the familiarization disks (but with a different S/D ratio) and another disk that maintained the original S/D ratio (but with a different luminance). It is expected that infants will prefer the disk that looks novel to them. Appropriate control conditions regarding intrinsic preferences were included.
Results. Infants stared consistently more at the luminance-matched disk than at the ratio-matched disk. This behavior indicates that the ratio-matched disk was seen as familiar, whereas the luminance-matched disk was seen as novel in the new surround.
Conclusions. At least to a first approximation, infant's lightness perception follows Wallach's ratio rule. Experiments with a more finely graded series of test disks are in progress.