Spectral sensitivity and chromatic discriminations in 3- and 7-week-old human infants.

The chromatic discrimination capabilities of 3- and 7-week-old infants were tested using 8 degrees, 417-, 448-, 486-, 540-, and 645-nm test fields embedded in a 547-nm surround and 486-nm test fields in a broadband red surround. In corroboration of earlier studies, few 3-week-old infants demonstrated chromatic discriminations, although their performance was somewhat better when one of the lights was long wavelength. Most 7-week-old infants could make chromatic discriminations, but they still demonstrated performance minima. The radiances of the test lights at the infants' performance minima were used to generate a spectral luminous efficiency curve. This curve agreed with both the adult heterochromatic brightness matches measured at 30 degrees of visual eccentricity in situ and the standard adult scotopic sensitivity curve V(lambda) over the short- and mid-wavelength range but deviated from both adult curves for the 645-nm test stimulus on a 547-nm surround. The results suggest that rod-initiated signals play a major role in infants' visual performance under the conditions tested.

Shifts in perception of size after adaptation to gratings.

After viewing a suitable grating of vertical stripes for 5 minutes, subjects overestimated the width of a rectangle by 6 percent. The shifts in perception of size occurred whether individual stripes in the grating were narrower than, equal to, or wider than the rectangle. Rectangle width was underestimated only if the grating stripes were extremely wide, with a spatial frequency lower than most of the effective amplitude spectrum of the rectangle. These findings (and complementary ones with horizontal gratings) suggest that the visual system codes size on the basis of spatial frequency components, rather than directly in terms of width.

Comparative judgment: tests of two theories using the Baldwin figure.

Two theories of comparative judgment were compared across four experiments on their ability to explain the Baldwin figure, a focal line whose apparent length is affected by square boxes at or near its endpoints. Left-box size, right-box size, line length, line-box distance, and other variables were varied in factorial designs to allow application of functional measurement methodology. The model from adaptation level theory did poorly in several respects. In particular, it had trouble with the pervasive lack of contrast. Further, it could not account for the fact that a box added contralaterally increased the illusion, whereas the same box added ipsilaterally decreased the illusion. The model from information integration theory did substantially better, though it too had trouble with some of the results. An alternative interpretation was suggested in which the Baldwin figure is viewed as a positive context or assimilation effect. This positive context formulation may generalize to other illusions, such as those produced by the Müller-Lyer and Ponzo figures.