M- and L-cones in early infancy: I. VEP responses to receptor-isolating stimuli at 4- and 8-weeks of age

Chromatic visual evoked potentials: A review of physiology, methods and clinical applications

Objective assessment of the visual system can be performed electrophysiologically using the visual evoked potential (VEP). In many clinical circumstances, this is performed using high contrast achromatic patterns or diffuse flash stimuli. These methods are clinically valuable but they may only assess a subset of possible physiological circuitries within the visual system, particularly those involved in achromatic (luminance) processing. The use of chromatic VEPs (cVEPs) in addition to standard VEPs can inform us of the function or dysfunction of chromatic pathways. The chromatic VEP has been well studied in human health and disease. Yet, to date our knowledge of their underlying mechanisms and applications remains limited. This likely reflects a heterogeneity in the methodology, analysis and conclusions of different works, which leads to ambiguity in their clinical use. This review sought to identify the primary methodologies employed for recording cVEPs. Furthermore cVEP maturation and application in understanding the function of the chromatic system under healthy and diseased conditions are reviewed. We first briefly describe the physiology of normal colour vision, before describing the methodologies and historical developments which have led to our understanding of cVEPs. We thereafter describe the expected maturation of the cVEP, followed by reviewing their application in several disorders: congenital colour vision deficiencies, retinal disease, glaucoma, optic nerve and neurological disorders, diabetes, amblyopia and dyslexia. We finalise the review with recommendations for testing and future directions.

Rhythmic visual stimulation as a window into early brain development: A systematic review

Rhythmic visual stimulation (RVS), the periodic presentation of visual stimuli to elicit a rhythmic brain response, is increasingly applied to reveal insights into early neurocognitive development. Our systematic review identified 69 studies applying RVS in 0- to 6-year-olds. RVS has long been used to study the development of the visual system and applications have more recently been expanded to uncover higher cognitive functions in the developing brain, including overt and covert attention, face and object perception, numeral cognition, and predictive processing. These insights are owed to the unique benefits of RVS, such as the targeted frequency and stimulus-specific neural responses, as well as a remarkable signal-to-noise ratio. Yet, neural mechanisms underlying the RVS response are still poorly understood. We discuss critical challenges and avenues for future research, and the unique potentials the method holds. With this review, we provide a resource for researchers interested in the breadth of developmental RVS research and hope to inspire the future use of this cutting-edge method in developmental cognitive neuroscience.

Decoding of EEG signals reveals non-uniformities in the neural geometry of colour

The idea of colour opponency maintains that colour vision arises through the comparison of two chromatic mechanisms, red versus green and yellow versus blue. The four unique hues, red, green, blue, and yellow, are assumed to appear at the null points of these the two chromatic systems. Here we hypothesise that, if unique hues represent a tractable cortical state, they should elicit more robust activity compared to other, non-unique hues. We use a spatiotemporal decoding approach to report that electroencephalographic (EEG) responses carry robust information about the tested isoluminant unique hues within a 100-350 ms window from stimulus onset. Decoding is possible in both passive and active viewing tasks, but is compromised when concurrent high luminance contrast is added to the colour signals. For large hue-differences, the efficiency of hue decoding can be predicted by mutual distance in a nominally uniform perceptual colour space. However, for small perceptual neighbourhoods around unique hues, the encoding space shows pivotal non-uniformities which suggest that anisotropies in neurometric hue-spaces may reflect perceptual unique hues.

An eye tracking investigation of developmental change in bottom-up attention orienting to faces in cluttered natural scenes

This study examined the contribution of visual salience to bottom-up attention orienting to faces in cluttered natural scenes across development. We eye tracked participants 4 months to 24 years of age as they freely viewed 16 natural scenes, all of which had faces in them. In half, the face was also the winner-take-all salient area in the display as determined by the MATLAB SaliencyToolbox. In the other half, a random location was the winner-take-all salient area in the display and the face was visually non-salient. We found that proportion of attended faces, in the first second of scene viewing, improved after the first year. Visually salient faces attracted bottom-up attention orienting more than non-salient faces reliably and robustly only after infancy. Preliminary data indicate that this shift to use of visual salience to guide bottom-up attention orienting after infancy may be a function of stabilization of visual skills. Moreover, sociodemographic factors including number of siblings in the home and family income were agents of developmental change in orienting to faces in cluttered natural scenes in infancy.

Keep your eyes on development: the behavioral and neurophysiological development of visual mechanisms underlying form processing

Visual form perception is essential for correct interpretation of, and interaction with, our environment. Form perception depends on visual acuity and processing of specific form characteristics, such as luminance contrast, spatial frequency, color, orientation, depth, and even motion information. As other cognitive processes, form perception matures with age. This paper aims at providing a concise overview of our current understanding of the typical development, from birth to adulthood, of form-characteristic processing, as measured both behaviorally and neurophysiologically. Two main conclusions can be drawn. First, the current literature conveys that for most reviewed characteristics a developmental pattern is apparent. These trajectories are discussed in relation to the organization of the visual system. The second conclusion is that significant gaps in the literature exist for several age-ranges. To complete our understanding of the typical and, by consequence, atypical development of visual mechanisms underlying form processing, future research should uncover these missing segments.

Perception of Munker-White illusion in 4-8-month-old infants

There have been numerous studies of the Munker-White illusion, but few have focused on the perceptual development of it in human infants. Therefore, this study explores the perceptual development of the Munker-White illusion in infants. In this study, we created two kinds of Munker-White illusion patterns that had different subjective saturation, and investigated infants' preference for these two kinds of patterns. Previous studies have shown that infants had a preference for high colorimetric saturation stimuli. Therefore, if infants could perceive the Munker-White illusion, we postulated that they would show a preference for stimuli that have high subjective saturation. In experiment 1, 4-8-month-old infants showed a preference for the stimuli that had a higher subjective saturation. In experiment 2, we confirmed that the preference shown in experiment 1 was not dependent on the difference of the 'color area ratio' that existed in the stimuli of experiment 1. Our results suggest that 4-8-month-old infants can perceive Munker-White illusion.

Transient VEP and psychophysical chromatic contrast thresholds in children and adults

It has been found that humans are able to distinguish colours without luminance cues by about 2-4 months of age and that sensitivity to colour difference develops during childhood, reaching a peak around adolescence. This prolonged period of maturation is reflected by improvements in psychophysical threshold measures and by the VEP characteristics of morphology, latency and amplitude. An intra-individual comparison of VEP and psychophysical responses to isoluminant colour stimuli has not been made in children, however, and this was the aim of the present study. VEPs were recorded from 49 subjects, children (age range: 4.8-12.6 years) and adults (age range: 25.7-33.2 years). Psychophysical and VEP thresholds were both measured in 40 of those subjects. Nominally isoluminant chromatic (L-M) sinewave gratings were presented in onset-offset mode and identical stimuli were used for psychophysical and VEP recordings to allow comparison. In agreement with previous reports, morphology of the transient VEP in response to this stimulus differed considerably between children and adults. There was a significant difference between psychophysical and VEP thresholds in children, but not in adults. Our findings support and expand on previous work on maturation of the L-M chromatic pathway and indicate a larger discrepancy between VEP and psychophysical chromatic thresholds in children than in adults.

Visão de cores no primeiro ano de vida

Procedimentos comportamentais que permitem inferir capacidades sensoriais ou perceptuais em bebês e crianças baseiam-se, na sua maior parte, na descoberta seminal feita no fim da década de 1950 pelo psicólogo Robert Fantz. Desde o nascimento, há uma preferência do bebê por dirigir o olhar para estímulos complexos a fixá-lo em cenas monótonas. Baseado no novo conhecimento, o grupo liderado por Davida Teller na Universidade de Washington desenvolveu uma metodologia de avaliação psicofísica da visão em bebês, o que possibilitou grande avanço no estudo do desenvolvimento e da maturação de várias funções visuais básicas, como acuidade visual, visão de cores, visão de contrastes, estereopsia e visão de movimento. A presente revisão examina essa literatura, mostrando como é avaliada a visão em bebês e o que se conhece até o momento sobre a capacidade dos recém-nascidos de ver cores.

FPL and sweep VEP to tritan stimuli in young human infants

Young infants can distinguish red from green without brightness cues which shows that neural pathways processing color information (the 'red-green' color-opponent pathway) are functional early in life. There is some doubt over whether the 'blue-yellow' pathway is functional in young infants. Here, we show that infants behave like tritanopic adults until 2-3 months post-term age. By 3-4 months, infants distinguish tritan stimuli, and therefore, the 'blue-yellow' pathway must be functional by that age. Our sweep visual evoked potentials to identical stimuli, however, are not significantly above noise levels, in disagreement with the behavioral responses. We discuss several possible explanations for the discrepancy.

Rod-cone-interactions in deuteranopic observers: models and dynamics

We studied the interactions between rods and L-cones in deuteranopic human observers by stimulating the photoreceptors independently. Thresholds were determined using a PEST procedure for different ratios of rod to L-cone modulation without modulating the S-cones. Modulation frequency was either 2 or 10 Hz and the retinal illuminance ranged from 4.7 to 470 td (10.9-1090 scot td). We measured at 2, 7.5 and 20 degrees retinal eccentricity. The threshold data could be described by a model based on a vector addition of responses originating in the rods and the L-cones. The relative strength of rod signals relative to the L-cone signals increased with increasing retinal eccentricity and decreasing retinal illuminance. At 20 degrees eccentricity, rod and cone signals were of about equal magnitude at retinal illuminances as high as 470 td. Temporal frequency did not have a large effect on the ratio of rod to L-cone signal strength.

M- and L-cones in early infancy: III. Comparison of genotypic and phenotypic markers of color vision in infants and adults

Genetic analyses were performed on five male children (approximately 3 years), two suspect color-normals and three suspects for congenital color vision deficiencies. These classifications were based on visually-evoked potential (VEP) responses to M- and L-cone-isolating stimuli obtained in a previous study when each subject was either 4- or 8-weeks old. The present analyses were performed in a blind study to characterize the genotypes of these subjects. Four male adults with various color vision phenotypes were also tested as a control. DNA was isolated using a non-invasive technique followed by polymerase chain reaction (PCR) amplification and restriction enzyme analysis to examine the genomic DNA of each subject. The genetic analyses confirmed the VEP identification of two color defective infants, and were consistent with the diagnosis of two other infants as color normal. A third infant was predicted by VEP analysis to have a protan defect, but he did not have a gene array typically found in protan observers.

M- and L-cones in early infancy: II. Action spectra at 8 weeks of age

Field sensitivities were measured under conditions of M- and L-cone isolation for seven infants (8-12 weeks-old) and two adults, using silent-substitution and the visually evoked potential (VEP). The efficacy of the receptor-isolation conditions were first verified by measuring psychophysical and VEP-derived action spectra from two color-normal adults under conditions of M- and L-cone isolation. M- and L-cone action spectra obtained from the two methods were found to be similar to the Smith and Pokorny M- and L-cone fundamentals, respectively. The VEP-derived action spectra obtained from infants and adults were well fit by the Smith and Pokorny M- and L-cone fundamentals. These data, in conjunction with our previous study, confirm that M- and L-cones are operating by 8 weeks and possibly as early as 4 weeks of age.