Asymmetries between achromatic increments and decrements: Perceptual scales and discrimination thresholds.

The perceptual response to achromatic incremental (A+) and decremental (A-) visual stimuli is known to be asymmetrical, due most likely to differences between ON and OFF channels. In the current study, we further investigated this asymmetry psychophysically. In Experiment 1, maximum likelihood difference scaling (MLDS) was used to estimate separately observers' perceptual scales for A+ and A-. In Experiment 2, observers performed two spatial alternative forced choice (2SAFC) pedestal discrimination on multiple pedestal contrast levels, using all combinations of A+ and A- pedestals and tests. Both experiments showed the well-known asymmetry. The perceptual scale curves of A+ follow a modified Naka-Rushton equation, whereas those of A- follow a cubic function. Correspondingly, the discrimination thresholds for the A+ pedestal increased monotonically with pedestal contrast, whereas the thresholds of the A- pedestal first increased as the pedestal contrast increased, then decreased as the contrast became higher. We propose a model that links the results of the two experiments, in which the pedestal discrimination threshold is inversely related to the derivative of the perceptual scale curve. Our findings generally agree with Whittle's previous findings (Whittle, 1986, 1992), which also included strong asymmetry between A+ and A-. We suggest that the perception of achromatic balanced incremental and decremental (bipolar) stimuli, such as gratings or flicker, might be dominated by one polarity due to this asymmetry under some conditions.

Poster Session: Achromatic increments and decrements are different: the relationship between scaling and discrimination.

A basic problem in psychophysics is to relate the internal representation of a stimulus to its physical intensity. In this study, we measured perceptual scales for achromatic contrast with Maximum Likelihood Difference Scaling (MLDS), using squares against a mid-grey background. Observers compared two stimulus pairs and chose the more different pair. All four squares were either achromatic increments (A+), or achromatic decrements (A-). The MLDS result was then compared with 2AFC achromatic pedestal discrimination, with pedestals and tests that were all combinations of A+ and A-. The main result is not novel: A+ and A- obey different rules. A Naka-Rushton saturating function describes the A+ MLDS result well, and the derivative of that function is proportional to the A+ pedestal discrimination for some (but not all) observers. A- MLDS and discrimination results are more complicated and are reminiscent of the classic findings of Whittle (1986, 1992). The sensitivity of A- is a cubic polynomial function of pedestal contrast. These findings will be compared with a similar study of S-cone contrast (reported at VSS 2022), which found a different type of asymmetry between S+ and S-. Presumably these increment/decrement asymmetries are due to underlying differences between ON and OFF neural pathways. One implication is that using stimuli that include both contrast signs, such as gratings and flicker, may obscure important asymmetries in the processing of contrast.

[Role of Imbalance between Th17 Cells and Treg Cells in the Pathogenesis of Children with Henoch-Schonlein Purpura].

OBJECTIVE: To explore the role of Th17 cells, CD4⁺ CD25⁺ regulatory Treg cells (Treg) and its transcription factor RORγt and FoxP3 in the pathogenesis of children with Henoch-Schonlein purpura (HSP) so as to provide a new strategy for treatment of children with Henoch-Schonlein purpura by regulating the balance of Th17 and Treg cells. METHODS: Forty children with Henoch-Schonlein purpura in acute phase admitted in our hospital from February 2012 to March 2013 were enrolled in this study, forty healthy children were simultaneously used as controls. The expression of RORγt mRNA and FoxP3 mRNA in peripheral blood mononuclear cells was detected by real-time PCR using SYBR Green I. The levels of IL-17A, TGF-ß1, IL-2 and IL-6 in serum were measured by ABC-ELISA. The ratio of Th17 cells to Treg cells in peripheral blood T lymphocytes was detected by flow cytometry. RESULTS: The levels of Th17 cells (2.75 ± 0.60%) and RORγt mRNA (1.11 ± 0.51) in HSP group were significantly higher than levels of Th17 cells (1.41 ± 0.29%) and RORγt mRNA (0.65 ± 0.24) (P < 0.01) in control group, but the levels of Treg cells (4.56 ± 1.26%) and FoxP3 mRNA (1.15 ± 0.45) in HSP group were lower than those of Treg cells (7.85 ± 1.97%) and FoxP3 mRNA (2.32 ± 1.1) (P < 0.01) in the control group. The relative levels of serum IL-17A, IL-6, TGF-ß1 (40.40 ± 11.81 pg/ml, 75.38 ± 27.19 pg/ml, 309.41 ± 81.03 pg/ml) in the HSP group were significantly higher than those in the control group [IL-17A (20.32 ± 10.70 pg/ml), IL-6 (25.16 ± 8.31 pg/ml), TGF-ß1 (236.34 ± 66.01 pg/ml)] (P < 0.01), but the level of serum IL-2 (25.60 ± 13.19 pg/ml) in the HSP group was lower than that (34.42 ± 11.69 pg/ml) in the control group (P < 0.01). The further detection demonstrated that in the children with acute HSP, the expression of Th17 cells positively correlated with RORγt mRNA, IL-17A and IL-6 with the correlation coefficients of 0.887, 0.938 and 0.934 (P < 0.01), respectively. The positive correlation was also shown between the Treg cells and FoxP3 mRNA, IL-2 with the correlation coefficients of 0.834 and 0.932 (P < 0.01), respectively. CONCLUSION: There are higher expression levels of Th17 cells, RORγt mRNA and IL-17A, and lower expression levels of Treg cells, FoxP3 mRNA of children with HSP in acute phase, which shows that Th17/Treg imbalance exists in children with HSP in acute phase. The levels of serum IL-6, TGF-ß1 increase and the serum IL-2 decrease in children with HSP in acute phase, moreover, there are the positive correlations between the levels of Th17 cells and expression of IL-6, as well as the level of Treg cells and expression of IL-2 in children with HSP in acute phase.