The retina of the newborn human infant

Infant color vision: the effect of test field size on Rayleigh discriminations

The capacity of 1- and 3-month-old infants to discriminate 589 nm and 650 nm test fields from a 589 nm surround was tested using the forced-choice preferential looking (FPL) technique. The size of the test field ranged from 1 to 8 degrees. Test field size strongly influenced the infants' performance. One-month-olds discriminated 8 and 4 degrees (but not 2 degrees) 650 nm fields from the 589 nm surround; 3-month-olds discriminated 4 and 2 degrees (but not 1 degree) 650 nm fields from the 589 nm surround. The dependence of performance on field size suggests that infants' discrimination failures with small fields are due to immaturities of spatial processing or postreceptoral chromatic mechanisms, rather than to any absence or anomaly of receptor types. In addition, adult subjects rated the hue, brightness, and salience of the test stimuli at 0, 26, 52, and 78 degrees eccentricity. The analogy often made between infant vision and adult peripheral vision is discussed in relation to these data.

Characteristics of saccades in human infants

Infants (14-151 days) and adults were shown two-dimensional geometric forms or stimuli from a set of highly textured patterns. Their eye movements were recorded by an infrared corneal reflection eye movement recorder as they freely scanned the stimuli. For both infants and adults, linear relationships were found between the peak velocities of fast eye movements and their amplitudes (main sequences). Infants viewing texture stimuli had main sequences with slopes comparable to those of adults. Infants viewing simple geometric forms made slower saccades. They also showed more eye movement oscillations which analyses showed were probably back-to-back saccades. Both the slower saccades and saccadic oscillations were attributed to factors related to the attentional value of the stimuli.

Spatial summation in dark-adapted human infants

Behavioral measures of spatial summation in 4- and 11-week old human infants were obtained using the forced-choice preferential looking technique. Infants exhibit complete spatial summation over large areas (4 weeks: 8.9 degrees; 11 weeks: 5.5 degrees), much larger than those of adults tested in the same apparatus (2.6 degrees). Thus, infants' summation areas are larger than adults' by factors of 12 at 4 weeks and 4 at 11 weeks. It is argued that at most, one-half of this difference between the infant and adult data may be due to optical factors (e.g. defocus and small eye size). The remainder probably reflects differences in the neural organization of the immature and mature visual systems.

Development of vernier acuity in infants

The development of vernier acuity in human infants aged 2-9 months was assessed by a preferential looking procedure using a vernier-motion display. The displacement of vernier offsets gives the impression of motion only when the vernier offsets are detected. Grating acuity of the same group of infants was also measured by a preferential looking procedure. Vernier acuity was found to be superior to grating acuity only after 3 months of age. This superiority of vernier acuity was compared with the superiority of stereoscopic acuity to grating acuity. The two classes of hyperacuity proved to be almost equivalent in terms of their developmental time-courses. A common physiological basis for the development of hyperacuities is suggested.

Development of retinal and cortical responses to pattern reversal in infants: a selective review

Infant contrast sensitivity and visual acuity evaluated by recording steady-state visual evoked potentials (VEP) in response to sinusoidal gratings improve considerably during the first 6 months of life. Qualitatively similar findings are obtained in kittens 3-12 weeks old. In infants, the improvement in VEP acuity with age parallels the increase in retinal acuity estimated from electroretinographic (ERG) steady-state responses to sinusoidal gratings. Spatial frequency selective mechanisms with bandwidth substantially narrower than the overall contrast sensitivity function seem to be present in the visual system of very young infants. These findings are compared with data reported in the literature about the development of the cat and monkey visual system.

Development of fixation and pursuit eye movements in human infants

Visual fixation and pursuit abilities of human infants were tested during their first year of life. Eye as well as head position was measured. Results show that the fixation of visual targets is accomplished by a head rotation accompanied by a series of small eye saccades. The number of these saccades increases with target eccentricity but progressively decreases with age. Pursuit of a moving visual target is performed by a smooth eye and head movement only if the target velocity is low. The maximum speed of pursuit progressively increases with age. The results are compatible with the relatively late development of the fovea.

Ultrastructural diurnal changes of the retinal photoreceptors in the embryo of a viviparous teleost (Poecilia reticulata P.)

All diurnal changes studied - ellipsosome excepted - start at midgestation, following differentiation of photoreceptors and pigment-epithelium cells. These are: (1) shedding of the tips of the light-sensitive photoreceptor outer segments and subsequent phagocytosis by the pigment-epithelium; (2) retinomotor movements of pigment-epithelium processes, rods and cones; (3) changes of cone square-mosaics into row-mosaics at night. Newly-differentiated photoreceptors in the embryo are, therefore, already vulnerable to disruption of cyclical systems. Several inherited human retinal diseases, such as Retinitis pigmentosa, are thought not to affect differentiation of photoreceptors but their cyclical renewal pathways. The retina of the guppy-embryo is, therefore, a valuable model for such studies.

Developmental changes in the human visual system as reflected by the latency of the pattern reversal VEP

Pattern reversal visually evoked potentials (VEPs) were recorded from 439 infants and young children ranging in age from 1 month to 5 years in response to large and small checks. Qualitative analysis of the VEP wave form showed that the first major positive component, P1, is consistently present at all ages, while the frequency of occurrence of later positive components is more variable. The proportion of infants showing late positive components increases with age; by 1 year, the frequency of occurrence of late components for large checks is more adult-like than for small checks. The latency of P1 was analyzed quantitatively. Results showed that P1 latency decreases rapidly during the first year of life for both large and small checks and that the time course of the latency change differs as a function of check size. VEPs to large checks attain adult-like P1 latency values by about 1 year of age, while the P1 latency of VEPs to small checks has still not reached adult levels by 5 years of age. Data from 12 infants tested longitudinally between 1 and 7 months of age using both checkerboards and square wave gratings show no difference in P1 latency between checkerboards and gratings comprised of large (30-240 min) pattern elements, but for patterns with small (7.5 and 15 min) elements, P1 latency to checks is significantly longer than P1 latency to stripes. These results are explained on the basis of the difference in the fundamental spatial frequency between checks and stripes.

The effects of screen size and eccentricity on acuity estimates in infants using preferential looking

The study examined whether screen size (10 degrees vs 19 degrees dia.) and separation (3 degrees vs 10 degrees eccentricity of inner edges) affect the estimates of acuity obtained with 1-3 month infants tested by forced-choice preferential looking. One and 2-month infants (but not 3-month olds) showed higher acuity estimates with the larger screens. Screen separation did not significantly affect acuity estimates for any of the age groups. Possible factors underlying these results are discussed.

The development of light adaptation in human infants

Increment threshold functions were measured from -4.0 to 1.2 log cd/m2 in 7-12-week-old infants using a behavioral forced-choice paradigm. The slopes of the infant functions were considerably shallower than the slopes of adult functions over the same luminance range. The value of the infant slope increased rapidly between 7 and 12 weeks postnatally. A number of explanations for this developmental shift are considered. It is concluded that changes with age in either spatial summation or intensity-response function gain could cause the increase in slope.

Visual acuity in the young infant is highest in a small retinal area

Visual potentials (VEP) evoked by alternating gratings were recorded daily in one infant between 10 and 13 weeks of age and at 20 weeks of age. The VEP amplitude was measured for a stimulus field of increasing area at low and high spatial frequencies. At low spatial frequencies the VEP amplitude increases with increasing stimulus area, while at high spatial frequencies (near visual acuity) the VEP amplitude remains constant for stimulus field sizes beyond 2 deg. These findings parallel those obtained in the adult, and indicate that visual acuity of the infant is not uniform across the retina but is highest in a small region, as in the adult.