Although there is a great deal of knowledge regarding the phylo- and ontogenetic plasticity of the neocortex, the precise nature of environmental impact on the newborn human brain is still one of the most controversial issues of neuroscience. The leading model–system of experience-dependent brain development is binocular vision, also called stereopsis. Here, we show that extra postnatal visual experience in preterm human neonates leads to a change in the developmental timing of binocular vision. The onset age of binocular function, as measured by the visual evoked response to dynamic random dot correlograms (DRDC-VEP), appears to be at around the same time after birth in preterm (4.07 mo) and full-term (3.78 mo) infants. To assess the integrity of the visual pathway in the studied infants, we also measured the latency of the visual-evoked response to pattern reversal stimuli (PR-VEP). PR-VEP latency is not affected by premature birth, demonstrating that the maturation of the visual pathway follows a preprogrammed developmental course. Despite the immaturity of the visual pathway, clearly demonstrated by the PR-VEP latencies, our DRCD-VEP data show that the visual cortex is remarkably ready to accept environmental stimulation right after birth. This early plasticity makes full use of the available extra stimulation time in preterm human infants and results in an early onset of cortical binocularity. According to our data, the developmental processes preceding the onset of binocular function are not preprogrammed, and the mechanisms turning on stereopsis are extremely experience-dependent in humans.

Dynamic random dot correlograms (DRDCs) are binocular stimuli that evoke a percept and a visual evoked potential (VEP) only in case of a mature and functional binocular system. DRDC-VEP is a method extensively used to study cortical binocularity in human infants and nonverbal children. Although the DRDC-VEP was invented 3 decades ago, neither the fundamental parameters, including contrast, of the stimulation nor the cerebral processing mechanisms have been clarified. The objective of the present study was to investigate the variability and detectability of adults' VEPs to DRDC under different stimulus contrast conditions. DRDCs were presented on the red and green channels of a computer monitor and were viewed with red-green goggles. The steady state DRDC-VEPs were recorded in healthy adult volunteers, and response reliability was assessed by the T(circ)(2) statistic. DRDC-VEP amplitude was independent of contrast, while VEP phases showed a weak correlation with contrast. Contrast invariance of DRDC-VEP amplitude suggests a very high contrast gain and dominant magnocellular input to the binocular correlation processing system.

Dichoptic therapy is a promising method for improving vision in pediatric and adult patients with amblyopia. However, a systematic understanding about changes in specific visual functions and substantial variation of effect among patients is lacking. Utilizing a novel stereoscopic augmented-reality based training program, 24 pediatric and 18 adult patients were trained for 20 h along a three-month time course with a one-month post-training follow-up for pediatric patients. Changes in stereopsis, distance and near visual acuity, and contrast sensitivity for amblyopic and fellow eyes were measured, and interocular differences were analyzed. To reveal what contributes to successful dichoptic therapy, ANCOVA models were used to analyze progress, considering clinical baseline parameters as covariates that are potential requirements for amblyopic recovery. Significant and lasting improvements have been achieved in stereoacuity, interocular near visual acuity, and interocular contrast sensitivity. Importantly, astigmatism, fixation instability, and lack of stereopsis were major limiting factors for visual acuity, stereoacuity, and contrast sensitivity recovery, respectively. The results demonstrate the feasibility of treatment-efficacy prediction in certain aspects of dichoptic amblyopia therapy. Furthermore, our findings may aid in developing personalized therapeutic protocols, capable of considering individual clinical status, to help clinicians in tailoring therapy to patient profiles for better outcome.

Although dynamic random-dot correlogram evoked visual potentials (DRDC-VEPs) are a three-decade-old method to detect the cortical binocularity in humans and animals, our knowledge of the influence of fundamental stimulus parameters and the underlying cerebral processing mechanisms has remained limited. The purpose of this study was to evaluate the effect of luminance on DRDC-VEPs in adults. The variability and detectability of DRDC-VEPs were investigated under different stimulus luminance conditions with neutral density filters. Our results have demonstrated that DRDC-VEPs can be evoked in a wide luminance range, and the response amplitude was practically independent of luminance between 4.75 cd m(-2) and 0.015 cd m(-2), while DRDC-VEP latencies showed a strong linear correlation with log luminance. There is, however, a limit (0.06 cd m(-2)) below which DRDC-VEPs are not reliably recordable. Luminance reduction-induced delays in DRDC-VEP latencies cannot be explained simply by retinal mechanisms, since their regression slope does not follow the course of electroretinogram and cortical evoked potential latencies. Luminance independence of DRDC-VEP amplitude suggests that binocular correlation-processing cortical neurons receive input predominantly from the magnocellular visual pathway.

Although development of binocularity is an extremely experience-dependent process, our data suggest that DRDC-VEP phase and P1 latency mature independently from visual experience. We propose that both the phase shift and decreasing P1 latency are indicators of myelination and increasingly faster signal transmission in the developing visual system.