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A previous experiment showed that blue light (as a component of white light) protected against low temporal frequency dependent eye growth. This experiment investigated the role of temporal contrast. White leghorn chicks were exposed to white (with blue) or yellow (without blue) LED lighting modulated at either low (0.2 Hz) or high (10 Hz) temporal frequencies. Four cone contrast conditions were used: low (16%), medium (32%), medium-high (60%) and very-high (80%). Chicks were exposed to the lighting condition for 3 days (mean 680 lux). Exposure to high temporal frequencies, with very high temporal contrast, reduced eye growth, regardless of spectral content. However, at low temporal frequencies, eye growth was dependent on the illuminant. At lower temporal contrast levels, eye growth increased regardless of temporal or spectral characteristics. To conclude, very high temporal contrast, white light, provides a “stop” signal for eye growth that overrides temporal cues for growth that manifest in yellow light.

In broadband light, longitudinal chromatic aberration (LCA) provides emmetropization signals from both wavelength defocus and the resulting chromatic cues. Indoor illuminants vary in their spectral output, potentially limiting the signals from LCA. Our aim is to investigate the effect that artificial illuminants with different spectral outputs have on chick emmetropization with and without low temporal frequency modulation. In Experiment 1, two-week-old chicks were exposed to 0.2 Hz, square-wave luminance modulation for 3 days. There were 4 spectral conditions: LED strips that simulated General Electric (GE) LED "Soft" (n = 13), GE LED "Daylight" (n = 12), a novel "Equal" condition (n = 12), and a novel "High S" condition (n = 10). These conditions were all tested at a mean level of 985 lux. In Experiment 2, the effect of intensity on the "Equal" condition was tested at two other light levels (70 lux: n = 10; 680 lux: n = 7). In Experiment 3, the effect of temporal modulation on the "Equal" condition was tested by comparing the 0.2 Hz condition with 0 Hz (steady). Significant differences were found in axial growth across lighting conditions. At 985 lux, birds exposed to the "Equal" condition showed a greater reduction in axial growth (both p 0.01) and a greater hyperopic shift compared to "Soft" and "Daylight" (both p 0.01). The "High S" birds experienced more axial growth compared to "Equal" (p 0.01) but less than in "Soft" and "Daylight" (p 0.01). Axial changes in "Equal" were only observed at 985 lux with 0.2 Hz temporal modulation, and not with lower light levels or steady light. We conclude that axial growth and refraction were dependent on the lighting condition in a manner predicted by wavelength defocus signals arising from LCA.

Blur is a useful cue for depth. Natural images contain objects at a range of depths whose depth can be signaled by their perceived blur. Here, to evaluate the usefulness of blur as a depth cue, we estimate the number blur levels that observers can perceive simultaneously. To estimate this value, observers discriminated and classified dead leaves patterns that contained a controlled distribution of blur levels but are more complex or naturalistic than stimuli typically used in blur research. We used a 2-IFC discrimination task, in which observers reported the interval that contained more blur levels and a classification task, in which observers reported the number of perceived blur levels. In both tasks, observers could not discriminate or classify more than four levels of blur in the stimulus reliably. In isolation from other cues, blur may provide only a coarse cue to depth and add limited depth information when present in natural scenes with complex distributions of blur and multiple depth cues.

To evaluate the Spot Vision Screener in detecting targeted vision disorders compared to cycloplegic retinoscopy in children3 years of age.Children, ages 6 months to 36 months underwent vision screening using the Spot Vision Screener. Results were compared to results of comprehensive eye examinations. Validity of the Spot was evaluated by calculating the area under the curve (AUC); the receiver operating characteristics (ROC) were used to determine optimal sensitivity and specificity for detection of targeted vision disorders.A total of 249 children were included. The AUC for detecting targeted vision disorders as defined by the study specific criteria using the Spot was 0.790. Compared to cycloplegic retinoscopy, the Spot underestimated hyperopia by 1.02 D (95% CI, 0.86-1.17 D). For hyperopia ≥4.5 D spherical equivalent (n = 10), the mean difference between the Spot and cycloplegic retinoscopy was 3.46 D (95% CI, 1.95-4.98 D). In contrast, the Spot overestimated astigmatism compared to cycloplegic retinoscopy (-1.00 D vs -0.48 D; P 0.001) by -0.52 D (95% CI, 0.43-0.62 D).The Spot Vision Screener showed good overall validity in detecting targeted vision disorders. It was within 0.5 D and 1 D of cycloplegic retinoscopy with regard to low hyperopia and astigmatism. Higher hyperopic spherical equivalent refractive errors showed larger differences in mean values between the Spot and cycloplegic retinoscopy.

Leventhal et al. (Science, 2003, 300(5620), 812-815) reported that orientation selectivity of V1 neurons was significantly reduced in older macaque monkeys, which suggests that mechanisms that encode orientation in humans may become more broadly tuned in old age. We examined this hypothesis in two experiments that used sine-wave masking and notched-noise masking to estimate the bandwidth of orientation-selective mechanisms in younger (age approximately 23 years) and older (age approximately 68 years) human adults. In both experiments, the orientation selectivity of masking was essentially identical in younger and older subjects.

SummaryDiscriminating the direction of motion of a low-contrast pattern becomes easier with increasing stimulus area. However, increasing the size of a high-contrast pattern makes it more difficult for observers to discriminate motion. This surprising result, termed spatial suppression, is thought to be mediated by a form of center-surround suppression found throughout the visual pathway. Here, we examine the counterintuitive hypothesis that aging alters such center-surround interactions in ways that improve performance in some tasks. We found that older observers required briefer stimulus durations than did younger observers to extract information about stimulus direction in conditions using large, high-contrast patterns. We suggest that this age-related improvement in motion discrimination may be linked to reduced GABAergic functioning in the senescent brain, which reduces center-surround suppression in motion-selective neurons.