Clinical experience with preferential looking acuity tests in infants and young children

Visual electrophysiology to achromatic and chromatic stimuli in premature and full term infants

We have previously reported on the development of black/white pattern reversal VEPs in premature babies of more than 30 weeks post-menstrual age (PMA). Unlike the flash VEP, the pattern reversal VEP shows a similar morphology to that of the full term infant and the major positive component (P1) decreased in latency with increasing PMA. The N1 and N2 components were more likely to be present with increasing maturity. In our present study we are examining the development of the transient chromatic pattern VEP. In order to produce a purely chromatic stimulus it is necessary to remove luminance cues. Based on forced choice preferential looking we developed a method of determining the isoluminant point for infants. Preference was tested for a flickering sinusoidal red and green grating over the uniform field. As sensitivity for chromatic flicker is much poorer than for luminance flicker, sensitivity is expected to be least when the residual luminance variation in the stimulus is at a minimum. The red/green luminance ratio at which this occurs represents the isoluminant point. From this method we found the subjective isoluminant point for infants of 2-3 months of age to be very close to the objective measure of isoluminance. Using this information, pattern reversal VEPs to 20 chromatic red/green and achromatic checks were studied and it would appear that pattern reversal VEPs cannot be obtained to isoluminant stimuli before 7 weeks chronological age.

Probability summation of acuity in the human infant

Raw data from two studies of monocular and binocular acuity development were used to determine whether a binocular acuity advantage as a function of age is predicted by probability summation and whether these predictions accurately describe the course of binocular acuity development. Two decision rules for the combination of the outputs of right eye and left eye "channels" were evaluated, the decision-threshold rule and the integration rule. Both decision rules predicted a binocular acuity advantage for infants and children aged 0-60 months. However, both rules failed to adequately describe the normal course of monocular and binocular acuity development. No binocular acuity advantage was found prior to 6 months of age while, after 6 months of age, binocular acuity was superior to monocular acuity by 0.12 log unit (0.4 octave). The absence of binocular acuity superiority prior to 6 months of age is consistent with suggestions by other authors that the immature human visual system combines information from the two eyes nonselectively.