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Texture segmentation was studied developmentally in kittens using a two-alternative forced choice jumping stand paradigm. None of 15 kittens tested solved a texture segmentation task based on orientation contrast prior to 83 days of age, despite their rapid acquisition age, despite their rapid acquisition of an analogous luminance-based image segmentation problem. However, three kittens showed rapid acquisition of the texture segmentation task when the textures were composed of non-oriented elements (dots and annuli), reaching criterion performance by 52-59 days of age. A control experiment demonstrated that kittens can discriminate between vertical and horizontal gratings comparable in line width to the oriented texture elements as early as 53 days of age. The surprisingly late appearance of orientation-based texture segmentation is considered in the context of current models of texture segmentation and is compared to recent reports of a similar finding in human infants [3,54].

Eye and brain growth were evaluated by measures of weight and surface dimensions at 11 ages spanning the period from birth to 150 days of age in the Mongolian gerbil (Meriones unguiculatus). Brain weight was found to increase very rapidly until day 18, followed by a more gradual increase to asymptote by 70 days of age. Eye growth follows overall body growth more closely than brain growth. Eye shape was found to change from ovoid to spherical over the first 70 days of life. The possible relationship between eye growth and retinal specialization is considered, and brain growth is compared across several rodent species.

The development of visual acuity for vertically oriented gratings was followed in gerbil pups from 34 days of age until adulthood using a jumping stand procedure. Acuity was found to improve gradually from an initial level of about 0.7 cycles/degree to asymptotic values of 1.2–1.6 cycles/degree by 70 days of age. Acuity did not vary as a function of viewing distance over the range tested (17.5 – 46 cm). Practice was found to play some role in the acuity changes seen but cannot alone explain the results. The contributions of other performance variables and of neural development are considered.

The segmentation of visual images on the basis of textural discontinuity was studied in cats using two behavioural paradigms. The first task (Experiment 1) required the animals to detect the presence of a target square of one texture embedded in a background of a second texture. The second task (Experiment 2) required the cats to discriminate between two forms (square and triangle) both of which were defined by texture-texture boundaries. Both detection and discrimination tasks were presented in a transfer paradigm in which the animals first learned a luminance-based form of the same problem. The results indicate that cats are able to segment a visual array on the basis of textural discontinuity in the absence of global luminance differences between figure and ground, and that they are able to use the contour information provided by texture-texture boundaries as a basis for form discrimination.

In order to evaluate the role played by chronological age or maturation in the decline of cortical plasticity during the critical period, kittens were given equal periods of monocular visual experience with each eye, separated by periods of dark-rearing. Experience with one eye was given at the same age in all animals (days 26-36), whereas the age at onset of reversal experience varied across animals. Monocular visual acuities were used as a behavioural index of sensitivity to reverse suturing. Our results demonstrate that sensitivity to reversal varies as a function of age alone when amount of visual experience is held constant. The size and direction of the interocular differences in visual acuity indicate that sensitivity declines steadily throughout the critical period. If reversal occurred on or before day 57, the initially deprived eye was able to gain superiority over the initially exposed eye. By 14 weeks of age the effects of reversal were negligible. The duration of dark-rearing within and beyond the critical period appeared to affect the absolute acuity levels attained but not the magnitude of interocular acuity differences.