Modelling incomplete chromatic adaptation on a display under different ambient illuminations

The purposes of this study was to investigate the chromatic adaptation and adaptive whites on a display under various ambient lighting conditions with different chromaticity and illuminance. An image including black text and white background was rendered by means of the CAT02 chromatic adaptation transform, into 42 different white stimuli varying at 6 CCTs and 7 Duv levels. Twenty observers assessed the neutral white evaluations of each color stimulus via psychophysical experiments. The optimization based on the neutral white stimulus under each ambient lighting condition suggested a lower degree of chromatic adaptation under the conditions with a lower CCT and a lower illuminance level. The results were used to model the adaptive display white and the incomplete adaptation factor (D) for CAT02 under different ambient illumiantions.

A Perception-Based Model of Complementary Afterimages

Complementary afterimages are often modeled as illusory Hering opponent hues generated by the visual system as a result of adaptation. Yet, the empirical evidence suggests a different picture—Complementary afterimages are localized RGB filtered perception based on complementary color pairs. The article aims to bring to the fore an ongoing ambiguity about red/green afterimages and then to address all cases of complementary afterimages. A simple model of afterimages based both on empirical data and the available literature is reconsidered and discussed: The afterimage color A depends both on the color stimulus S and on the ensuing background color B as estimated by the relation, A = B – kS.

Visualization of IOL Material-Induced Changes in Retinal Color Stimulus

Purpose. Different IOL materials, particularly blue-light filtering materials, have different spectral transmittance characteristics. The color stimuli, which influence retinal receptors objectively, have consequently implications for color perception. We report on the quantitative determination of IOL-specific transmittance characteristics and present a method visualizing the resultant changes in color stimulus.Methods. A setup was realized to quantify IOL-absorption in a range of 390–780 nm. To visualize the influence of the different spectral transmittance characteristics an algorithm was developed, which converts RGB-pixel values of images into spectra, which performs the corresponding transmittance correction, reconverts to RGB, and reconstructs the image. IOLs of hydrophobic acrylate and hydrophilic acrylate with a hydrophobic surface in each case with/without blue-light filter were examined.Results. Assessment of the reference images verifies the suitability of the pipeline. Evaluation of the transmittance spectra reveals differences of material- and manufacturer-specifics, which are capable of inducing considerable changes in color perception, particularly in the blue color range and mixed colors involving blue.Conclusions. The developed technique provides an approach for determining IOL-specific transmittance behavior and subsequently its influence on the retinal color stimulus. Problems of altered color perception are occasionally reported after cataract surgery and these become obvious with the visualization procedure developed here.

Role of Color on the Production of Responses in Children’s Rorschach Protocols

Previous studies have shown that, while color has the property to increase the production of responses to the Rorschach, such an effect is not present in children’s protocols. Based on a review of the literature, the author highlights the characteristic of high reactive demand of the subject to color stimulus and traces its evolution to the preoperational period, where color nominations and the incongruent use of color, especially of pure color, are frequent. With the entry in the period of concrete operations such responses become rare or even disappear. In turn, the mean number of responses to color cards decreases between 5 to 6 and 11 years, and their form quality goes down as well. The cause of this change is the emergence and development of logical thinking. Given the intensity of color stimulus, the child does not yet have the equipment that will allow her to later integrate color and object as they really are.

Prefrontal Activity During Serial Probe Reproduction Task: Encoding, Mnemonic, and Retrieval Processes

To study the prefrontal neuronal mechanism for the encoding and mnemonic processing of multiple objects, the order of object presentation, and the retrieval of an object among objects in the working memory, we recorded neuronal activity from the lateral prefrontal cortex while two monkeys performed the serial probe reproduction task. In the task, two objects (C1 and C2) were presented sequentially interleaved with a delay (D1) period, and after the second delay (D2) period, a color cue was presented. Monkeys were trained to select one target object on the basis of the color stimulus. During the C1 and C2 periods, we found responses that depended on the order of presentation (order-selective response). During the D1 and/or D2 periods, two-thirds of the neurons with object-selective delay-period activity showed order-selective activity coding either C1 or C2. Neurons with larger response magnitudes during the C2 period showed order-selective delay-period activity during the D2 period. These order-selective responses during the C2 period could also contribute to order-selective delay-period activity, and order-selective delay-period activity during the D1 and D2 periods could play an essential role in storing information on both the object and the temporal order of presentation. During the color cue period, two-thirds of the neurons with responses showed target object selectivity (CT and T responses), although the target object was not presented during this period. The CT and T responses could play a critical role in the retrieval of an item among various items in the working memory.