Human scotopic spatiotemporal sensitivity: a comparison of psychophysical and electrophysiological data

The aim of the study was to investigate spatiotemporal visual functions under scotopic and photopic conditions in order to acquire human psychophysical and electrophysiological data that are comparable with contrast sensitivities based on single-unit recordings in animal experiments. Static and dynamic contrast sensitivities (CSs) and steady-state visual evoked potentials (VEPs) were measured under photopic and scotopic conditions in healthy volunteers. The results from the CS experiment indicated that the inclusion of temporal modulation and the application of scotopic luminance levels uniformly resulted in a relatively increased sensitivity for low spatial frequencies. Similarly, analysis of the second harmonic component of the VEPs demonstrated a shift from band-pass to low-pass functions. These results suggest that, under scotopic conditions, human visuospatial processing is characteristically predominated by the functional activity of the magnocellular pathways.     

Incremental binocular amplitude of the pattern visual evoked potential during the first five months of life: electrophysiological evidence of the development of binocularity

The amplitude of the pattern visual evoked potential (VEP) of a binocular stimulus has been shown to be generally larger than the VEP obtained monocularly. There is evidence that this effect can be considered an electrophysiological index of fusion.To study how binocular vision develops in infancy we evaluated the incremental binocular amplitude (IBA) in three infants in a longitudinal investigation during the first five months of life. The stimuli were phase-alternating square-wave gratings with spatial and temporal parameters chosen to be appropriate for neonates. IBA was defined as the percentage increment of the largest binocular response compared with the monocular response. In the first two months of life IBA values were near zero, that is, no summation occurred. Between the second and third month IBA values rose markedly and after the third month its value was greater than 100%, demonstrating binocular facilitation. Thus in the first two months of life the eyes do not seem to cooperate as in adults. By the second and third month the binocular pattern VEP reflects an increasing binocular interaction. Other studies of the development of stereopsis have also found evidence of binocularity at similar ages.     

Vernier Acuity as a Test of Magnocellular Sensitivity

Vernier acuity has been argued to provide a means to measure the integrity of the magnocellular visual pathway. This proposal is reviewed here and found to be inadequately supported for the following reasons: (1) the conditions under which Vernier acuity corresponds to magnocellular resolution differ from those used in psychophysical tests; (2) Vernier offsets can be induced by adaptation of cortical neurons; (3) factors other than the magnocellular system have the ability to interfere with Vernier acuity. Taken together, this review argues that Vernier acuity is at best limited as a selective test of magnocellular sensitivity.     

Development of contrast sensitivity over the first 3 months of life in the human infant

Contrast sensitivity functions have been obtained for infants aged 5–12 weeks. Sensitivity was derived from fixation preference for static or drifting sinusoidal gratings over a uniform field, assessed by two-alternative forced choice by a “blind” observer. In terms of acuity, extent of the low-frequency cut, and overall sensitivity, there were large differences between the 5-week group and older age groups. This difference in performance may reflect rapid neural development in the visual system over the first 3 months of life.     

Maturation of Binocular Luminance Interaction in normal young and adult rhesus monkeys

Purpose: Our aim was to answer three questions 1) Do adult rhesus monkeys have binocular luminance interactions (BLIs) similar to those found in adult humans? 2) Is BLI in very young rhesus monkeys functionally mature? 3) If not, how does it change with age? Methods: We recorded visually evoked potentials (VEPs) in response to sinusoidally modulated uniform fields. The fields were presented dichoptically by varying the relative temporal phase between the two eyes. Monkeys varied in age from 5.6 weeks to 5.25 years. Results: VEPs were Fourier analyzed and the relative second harmonic amplitudes were taken as the response measure. The second harmonic amplitudes in adult monkeys had an asymmetrical ‘V-shaped’ function as interocular phase difference (IPD) varied from 0° to 180°, as had been observed previously in adult humans [1]. The youngest monkeys exhibited a symmetrical pattern which became more asymmetrical at older ages and was adult like by about 19 wee ks. Asymmetry magnitude and log age correlated 0.97 (p < 0.05) in the monkeys younger than 19 weeks. Conclusions: The adult rhesus data are consistent with a model derived from humans which involves two types binocular luminance processing. One combines monocular responses nonlinearly (MNL) and a second combines monocular responses linearly followed by a binocular nonlinearity (MLBNL). These two processes have been associated with the parvocellular (P-) and magnocellular (M-) streams. Within this framework, the data from the youngest monkeys indicate that BLI in the P-stream is relatively less mature at birth than that in the M-stream and develops reaching functional maturity on these measures by around 19 weeks.     

A VEP investigation of parallel visual pathway development in primary school age children

Different features of visual function mature along unique timescales through infancy and early childhood. It is not clear which functions continue to mature in school age children. Functions believed to be mediated by the Magnocellular (M) and Parvocellular (P) pathways were compared in five- (n=25), eight- (n=21) and eleven-year-old children (n=21) and young adult controls (n=20). Steady-state visual evoked potentials were recorded from occipital electrodes in response to very low spatial frequency gratings, at a series of contrasts (M), and to high contrast gratings at a series of spatial frequencies (P). No evidence was found to indicate M pathway development across these age groups. However, the youngest children demonstrated elevated VEP thresholds to the high contrast gratings compared with either the adults or eleven-year-olds. This difference in threshold implies an immaturity of the high contrast, high spatial frequency stream, i.e. the putative P pathway. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cone contrast influence on components of the pattern onset/offset VECP

Transient visual evoked cortical potentials (VECP) were recorded from the scalp of healthy normal trichromats (n = 12). VECPs were elicited by onset/offset presentation of patterned stimuli of two kinds: isochromatic luminance‐modulated, and equiluminant red‐green modulated, sine wave gratings. The amplitude and latency of the major onset components of the onset/offset VECP were measured and plotted as a function of the logarithm of pooled cone contrast. The early onset components, achromatic C1 and chromatic N1, increase linearly with log contrast, but N1 has a higher contrast gain than C1. The late onset components, achromatic C2 and chromatic N2, have similar contrast gain, and similar response as a function of contrast level: both increase in the low‐to‐medium range of contrasts and saturate at high contrast levels. In the range of pooled cone contrast tested, C1 and N1 show similar latencies, whilst C2 shows shorter latencies than N2. We suggest that C1 and N1 are generated by the same visual mechanism with high red‐green contrast gain and low luminance contrast gain, whilst C2 and N2 are generated by different visual mechanisms.     

Summation of Temporal L-Cone- and M-Cone-Contrast in the Magno- and Parvocellular Retino-Geniculate Systems in Glaucoma

PurposeThe purpose of this study was to characterize summation of temporal L- and M-cone contrasts in the parvo- (P-) and magnocellular (M-) pathways in glaucoma and the relationship between the respective temporal contrast sensitivities (tCS) and clinical parameters.MethodsPerifoveal tCS to isolated or combined L- and M-cone contrasts (with different contrast ratios, and therefore different luminance and chromatic components) were measured at different temporal frequencies (at 1 or 2 Hz and at 20 Hz) using triple silent substitution in 73 subjects (13 healthy, 25 with glaucoma, and 35 with perimetric glaucoma). A vector summation model was used to analyze whether perception was driven by the P-pathway, the M-pathway, or both. Using this model, L- and M-cone input strengths (A_L, A_M) and phase differences between L- and M-cone inputs were estimated.ResultsPerception was always mediated by the P-pathway at low frequencies, as indicated by a median phase angle of 179.84 degrees (cone opponency) and a median A_L/A_M ratio of 1.04 (balanced L- and M-cone input strengths). In contrast, perception was exclusively mediated by the M-pathway at higher frequencies (input strength not balanced: A_L/A_M = 2.94, median phase angles = 130.17 degrees). Differences in phase were not significant between diagnosis groups (Kruskal-Wallis = 0.092 for P- and 0.35 for M-pathway). We found differences between groups only for the M-pathway (L-cone tCS deviations at 20 Hz were significantly lower in the patients with glaucoma P = 0.014, with a strong tendency in M-cones P = 0.049). L-cone driven tCS deviations at 20 Hz were linearly correlated with perimetric mean defect (MD) and quadratically correlated with retinal nerve fiber layer (RNFL) thickness.ConclusionsUnaltered phase angles between L- and M-cone inputs in glaucoma indicated intact temporal processing. Only in the M-pathway, contrast sensitivity deviations were closely related to diagnosis group, MD, and RNFL thickness, indicating M-pathway involvement.     

Implicit time of pattern evoked potentials in infants: an index of maturation of spatial vision.

Pattern reversal visually evoked potentials (VEP) were recorded from preterm infants, term infants, young children and adults. The implicit time of the peak of the first positive wave was measured for different check sizes. The implicit time of the VEP for checks larger than 30′ of arc reaches adult levels by 16–20 weeks of age. The implicit time for checks smaller than 30′ of arc decreases rapidly up to 1 year of age and then slowly until 5–6 years of age suggesting that the plasticity of the human visual system may extend until then. Further, from early infancy to adulthood, patterns comprised of small checks (high spatial frequencies) elicit signals with longer implicit times than stimuli with large checks (low spatial frequencies).     

PRBS-determined temporal frequency characteristics of VEP in glaucoma

The purpose of this study was to determine whether the PRBS-VEP-determined temporal frequency characteristics (TFCs) of the visual pathways are useful for evaluating the properties of the visual system of glaucomatous patients. The VEPs elicited by pseudorandom stimulation (PRBS) with red LEDs were recorded from 26 eyes with primary open angle glaucoma and 11 age-matched normal eyes. The glaucomatous patients were divided into 3 groups according to the size and shape of their visual field defect; early (9), moderate (9), and severe (8). The cross-spectrum between the PRBS and PRBS-VEPs was used as the TFCs. The TFC of each glaucomatous group were compared to those of the normal controls. A depression of the TFC was found for the middle and high frequencies (18-28 Hz) in the moderate group, and the depression spread to lower frequencies (4-16 Hz) in the severe groups. The TFC values at 14-20 Hz were depressed in the moderate group and most frequencies were depressed significantly with the progression of glaucoma (p < 0.05). The sensitivity of the TFC at 18-20 Hz was 56%, 89% and 100% in the early, moderate and severe glaucoma groups, respectively, and the specificity was 82%. We conclude that the PRBS-determined TFC is altered in glaucomatous eyes, and the frequencies depressed were related to the degree of glaucoma. These findings indicate that the PRBS-determined TFC can be useful for evaluating visual function of glaucomatous eyes.     

Development of spatial resolution, contrast sensitivity and binocularity in normal and strabismic kittens

The purpose of the present experiment was to evaluate visual acuity, contrast sensitivity and binocularity in teno-tomized, strabismic kittens of various ages.     

Fluctuations of visual evoked potential amplitudes and of contrast sensitivity in Uhthoff's symptom

Visual evoked potentials (VEPs) to pattern reversal and psychophysical contrast sensitivity (CS) were tested in five patients with Uhthoff's symptom before and after exercise. Four of the cases were related to a demyelinating disease and one patient had a severe brain injury. Uhthoff's symptom occurred also in neuropathies without previous clinical neuritis and in eyes with normal latency time of the VEPs. A depression of CS was observed by all five patients after exercise; a transient overshoot of CS following the depression was present in three of the patients. VEP amplitudes were reduced by exercise in three cases. Responses by stimulation with small checks were more affected. Paradoxical increased VEP amplitudes after exercise in the presence of a loss of psychophysical CS were found in one case.     

Flash visual evoked potentials in patients with periventricular leucomalacia in children less than 1 year of age

Background and Aim:

Children with periventricular leucomalacia (PVL) are known to have visual impairment of various forms starting from reduced vision, field defects, congnitive problems, and problems with hand eye coordination. There is very scant data/literature on the visual evoked potentials (VEPs) at an early age in children with PVL. We did a study to evaluate the flash visual evoked potentials (fVEPs) in children with PVL less than 1 year of age.

Materials and Methods:

A total of nine children diagnosed as having PVL on magnetic resonance imaging were included in the study. The mean age was 9.7± 3.5 months. All children underwent handheld fVEPs under sedation at two different flash frequencies 1.4 and 8 Hz.

Results:

The mean latency of N1 and P1 on stimulation with 1.4 Hz was 47.9± 15.2 and 77.7± 26.0 ms, respectively. However, on stimulation with 8 Hz the mean latency of N1 and P1 was 189.8± 25.6 and 238.4± 33.6 ms, respectively. The mean amplitude with 1.4 Hz and 8 stimulation frequency was 5.6± 4.5 and 5.59± 3 mV, respectively.

Conclusion:

We have found for the first time that there is a change in the latency and the delay occurs at 8 Hz frequency but not at 1.4 Hz. We also conclude that amplitudes by fVEPs may be normal even in presence of periventricular changes. The amplitudes of fVEPs are not reliable in children with PVL.     

The technique, validity and clinical use of the sweep VEP

Vision scientists have concentrated on studying two visual functions when it comes to assessing the sensory visual development in human: visual acuity and contrast sensitivity. The methods used to measure these visual functions can be either behavioral or electrophysiological. A relatively new technique for measuring the visual acuity and contrast sensitivity electrophysiologically is the sweep visual evoked potential (sVEP). This paper is a review of the literature on the sVEP technique: stimulus parameters, threshold determination, validity and reliability of sVEP are discussed. Different studies using the sVEP to study the development of visual acuity, contrast sensitivity, and vernier acuity are presented. Studies have demonstrated that the sVEP is a potentially important tool for assessing visual acuity and contrast sensitivity in non-verbal individuals with disorders affecting their visual system.     

Visual evoked potentials during the early phase of optic nerve compression in the orbital cavity

We obtained case histories and electrophysiologic recordings from four patients with transient vision impairment due to acute orbital compression. The visual evoked potentials (VEPs) displayed alterations that depended on the size and consistency of the compressing pathology and also on the duration of the compression. This study provides evidence of the utility of the VEP in the assessment of the severity and reversibility of optic nerve lesions. The case histories also emphasized the necessity to elucidate the pathologic process of compressive lesions of the optic nerve.     

Contrast sensitivity of the human infant for moving and static patterns

A fixation preference method was used to assess contrast sensitivity of 1–3-month infants for stationary and drifting (3-Hz) sinusoidal gratings. The infants showed greater sensitivity for moving gratings at low spatial frequencies, but at their acuity limits there was no difference between static and moving stimuli. We conclude that the advantage of moving stimuli at low spatial frequencies reflects a differential sensitivity similar to that of the adult.     

Assessment of visual acuity by evoked potential recording: Ambiguity caused by temporal dependence of spatial frequency selectivity

The spatial-frequency selectivity of pattern evoked potentials depends on the stimulus repetition rate: responses to low spatial frequencies are emphasized by stimulating at 16–20 Hz, while responses to high spatial frequencies are emphasized at 5–8 Hz. These findings are consistent with the suggestion that pattern EP's are a mixture of pattern responses and responses to local flicker. To a first approximation the “local flicker” responses resemble EP's produced by flickering a light similar to the patterned stimulis in all respects except for absence of pattern. Any developmental changes in the temporal tuning of pattern responses and/or local flicker responses might distort the results of studies in which pattern EP's have been used as an index of either (a) the development of visual acuity or (b) acuity changes due to visual deprivation. Methods of minimizing this problem are suggested.     

视觉诱发电位检查在婴幼儿眼眶蜂窝组织炎的临床应用

目的：通过监测婴幼儿眶蜂窝组织炎患眼在治疗前、中、后的视觉诱发电位变化,探讨视觉诱发电位检查在婴幼儿眼眶蜂窝组织炎的临床应用价值。 方法：对23例眼眶CT确诊的单眼眶蜂窝组织炎患儿进行视觉诱发电位检查,以患眼作为观察组,健眼作为对照组。比较观察视觉诱发电位在治疗前、中、后的变化。 结果：观察组与对照组相比,其视觉诱发电位有明显改变。随着治疗的进行,观察组患儿视觉诱发电位振幅提高,潜伏期缩短。 结论：在婴幼儿眼眶蜂窝组织炎的治疗过程中,采用视觉诱发电位检查对患儿的视功能进行监测是简便、可行、有效的方法。