Age-related changes in ON and OFF responses to luminance increments and decrements

Combined manifestation of two geometric visual illusions

The present study continued to investigate whether the effects of length misperception caused by cross-shaped (formed by two pairs of the oppositely oriented Müller-Lyer wings) contextual distractors can be explained by the combined manifestation of two different (i.e., the Müller-Lyer and filled-space) geometric illusions of extent. In psychophysical experiments, the luminance of one pair of wings was randomly changed, while the luminance of the other pair remained constant. Two different distractor orientations were used-when the wings with constant luminance formed the right side of the cross or the left side, otherwise. To separately evaluate the manifestation of the Müller-Lyer illusion under different luminance conditions, two distracting crosses of the same orientation were attached to the lateral stimulus terminators in the first series of experiments. In the following four series, a single distracting cross (with different orientation) was attached to one of the lateral stimulus terminators and various combinations of the constant and background luminance were used. To interpret the experimental data, we used the basic computational principles of previously developed quantitative models of hypothetical visual mechanisms underlying the emergence of the Müller-Lyer illusion and the filled-space illusion. It was shown that the results of theoretical calculations adequately approximate the experimental curves obtained for all modifications of stimuli, which strongly supports the suggestion that the joint manifestations of these two illusions can be considered among the main factors determining the features of the illusion investigated.

Contrast Increment and Decrement Processing in Individuals With and Without Diabetes

Purpose

Animal models suggest that ON retinal ganglion cells (RGCs) may be more vulnerable to diabetic insult than OFF cells. Using three psychophysical tasks to infer the function of ON and OFF RGCs, we hypothesized that functional responses to contrast increments will be preferentially affected in early diabetes mellitus (DM) compared to contrast decrement responses.

Methods

Fifty-two people with DM (type 1 or type 2) (mean age = 34.8 years, range = 18-60 years) and 48 age-matched controls (mean age = 35.4 years, range = 18-60 years) participated. Experiment 1 measured contrast sensitivity to increments and decrements at four visual field locations. Experiments 2 and 3 measured visual temporal processing using (i) a response time (RT) task, and (ii) a temporal order judgment task. Mean RT and accuracy were collected for experiment 2, whereas experiment 3 measured temporal thresholds.

Results

For experiment 1, the DM group showed reduced increment and decrement contrast sensitivity (F (1, 97) = 4.04, P = 0.047) especially for the central location. For experiment 2, those with DM demonstrated slower RT and lower response accuracies to increments and decrements (increments: U = 780, P = 0.01, decrements: U = 749, P = 0.005). For experiment 3, performance was similar between groups (F (1, 91) = 2.52, P = 0.137).

Conclusions

When assessed cross-sectionally, nonselective functional consequences of retinal neuron damage are present in early DM, particularly for foveal testing. Whether increment-decrement functional indices relate to diabetic retinopathy (DR) progression or poorer visual prognosis in DM requires further study.

Bidirectional relationships between semantic words and hues in color vision normal and deuteranopic observers

We previously showed that impressions of nine semantic words expressing abstract meanings (like "tranquil") can be expressed by 12 hues in a paired comparison method; in this study, White, Gray, and Black were added (Exp. 1) to the previous 12 hues. Color impressions were also estimated using a set of 35 paired words by a semantic differential (SD) method (Exp. 2). The data of nine color vision normal (CVN) and seven color vision deficient (CVD) observers (one protanope and six deuteranopes) were analyzed separately by principal component analysis (PCA). In the results of Exp. 1, all hues used as loadings were distributed in a hue-circle shape in the 2D color space of PC axes for both observer groups [however, the four bluish hues (Blue-Green to Violet) tended toward convergence]. One data set of five CVNs and five deuteranopes was analyzed together using PCA because of high concordance. In the word distribution of the CVDs in Exp. 1, because second PC scores tended to be smaller, the categorization of the words was not clear; the points of five word scores were approximately on one line, reflecting that the colors used in the paired comparison were treated in one-dimensional scaling (which correlates to lightness) in the CVDs. In the results of Exp. 2, the word distribution of loadings was similar between the CVNs and CVDs, and the color score distribution had a similar tendency of showing an ellipse-shaped hue circle; it was probably caused by their experience of being associated with color names rather than color appearance (although the radius of the short axis is shorter in the CVDs' data). The comparison of the word distribution between experiments suggests that two to five semantic word impressions can be stably expressed by hue, but the impression of other words, such as "Magnificent" for the CVNs and "Fine" for the CVDs, cannot. The hue circle is conceptually kept in the SD measurement for all observers; however, it was not kept in the paired comparison for the CVDs. The analysis of one combined data set suggests that the 2D color distribution is not caused by a 3D color system because the lightness scaling is involved in the 2D color distribution.