Biology subjects

Gegenfurtner, K.

Publications and source records attributed to Gegenfurtner, K..

3 recordsLinked to original sources

bioRxiv2023

Oculomotor routines for perceptual judgments

In everyday life we frequently make simple visual judgments about object properties, e.g., how big or wide is a certain object? Our goal is to test whether there are also task specific oculomotor routines which support perceptual judgments, similar to the well-established exploratory routines for haptic perception. In a first study, observers saw different scenes with two objects presented in a photorealistic virtual reality environment. Observers were asked to judge which of two objects was taller or wider while gaze was tracked. All tasks were performed with the same set of virtual objects in the same scenes, so that we can compare spatial characteristics of exploratory gaze behavior to quantify oculomotor routines for each task. Width judgments showed fixations around the center of the objects with larger horizontal spread. In contrast, for height judgments, gaze was shifted towards the top of the objects with larger vertical spread. These results suggest specific strategies in gaze behavior that presumably are used for perceptual judgments. To test the causal link between oculomotor behavior and perception, in a second study, observers either could freely gaze at the object or we introduced a gaze contingent set up forcing observers to fixate specific positions on the object. Discrimination performance was similar between free gaze and the gaze contingent conditions for width and height judgments. These results suggest that although gaze is adapted for different tasks, performance seems to be based on a perceptual strategy, independent of potential cues that can be provided by the oculomotor system.

neuroscience↗

bioRxiv2023

Color appearance of iridescent objects

Iridescent objects and animals are quite mesmerizing to look at, since they feature multiple intense colors whose distribution can vary quite dramatically as a function of viewing angle. These properties make them a particularly interesting and unique stimulus to experimentally investigate the factors that contribute to single color impressions of multi-colored objects. Our stimuli were 3D printed shapes of varying complexity that were covered with three different types of iridescent coatings. For each shape-color combination, participants performed single- and multi-color matches for different views of the stationary object, as well as single color matches for a corresponding rotating stimulus. In the multi-color matching task, participants subsequently rated the size of the surface area on the object that was covered by the match-identified color. Results show that single-color appearance of iridescent objects varied with shape complexity, view, and object motion. Moreover, hue similarity of color settings in the multi color match task best predicted single color appearance, however this predictor was weaker for predicting single color matches in the motion condition. Taken together our findings suggest that the single color appearance of iridescent objects may be modulated by chromatic factors, spatial-relations and the characteristic dynamics of color changes that are typical for this type of material.

neuroscience↗

bioRxiv2022

Color Constant Representations in Early Visual Cortex

The light entering our eyes is the product of the illumination and the surface reflectance of an object. Although this light changes considerably when the illumination changes, we are usually able to perceive objects as stable in color. To investigate how the brain achieves color constancy, we measured BOLD fMRI while 19 participants either observed patches of light that appear colored (yellow, blue) under a spectrally neutral illuminant, or spectrally neutral gray patches that appear colored under simulated blue and yellow illumination conditions. Under bluish illumination, the neutral gray patches appeared yellow; under yellowish illumination, the same gray patches appeared blue. We successfully trained a classifier to discriminate between the blue- and yellow-colored patches in V1-V4. Crucially, we then tested whether this same classifier could also distinguish between the apparent blue and yellow induced by the illuminants. The neural representations for apparent blue and yellow resembled colorimetric blue and yellow in V1, V3 and V4. A control experiment showed that apparent lightness cannot explain these effects. These findings suggest that not only colorimetric, but also apparent color is represented to some degree in retinotopic visual cortex, as early as in V1. Furthermore, a small frontal region, the Rolandic operculum, showed activation for apparent color, possibly playing a role in color constancy.

neuroscience↗