Albers, A. M. | Search bioRxiv

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↗

bioRxiv2017

Eye movement-related confounds in neural decoding of visual working memory representations

The study of visual working memory (VWM) has recently seen revitalization with the emergence of new insights and theories regarding its neural underpinnings. One crucial ingredient responsible for this progress is the rise of neural decoding techniques. These techniques promise to uncover the representational contents of neural signals, as well as the underlying code and the dynamic profile thereof. Here, we aimed to contribute to the field by subjecting human volunteers to a combined VWM/imagery task, while recording and decoding their neural signals as measured by MEG. At first sight, the results seem to provide evidence for a persistent, stable representation of the memorandum throughout the delay period. However, control analyses revealed that these findings can be explained by subtle, VWM-specific eye movements. As a potential remedy, we demonstrate the use of a functional localizer, which was specifically designed to target bottom-up sensory signals and as such avoids eye movements, to train the neural decoders. This analysis revealed a sustained representation for approximately 1 second, but no longer throughout the entire delay period. We conclude by arguing for more awareness of the potentially pervasive and ubiquitous effects of eye movement-related confounds.\n\nSignificance statementVisual working memory is an important aspect of higher cognition and has been subject of much investigation within the field of cognitive neuroscience. Over recent years, these studies have increasingly relied on the use of neural decoding techniques. Here, we show that neural decoding may be susceptible to confounds induced by stimulus-specific eye movements. Such eye movements during working memory have been reported before, and may in fact be a common phenomenon. Given the widespread use of neural decoding and the potentially contaminating effects of eye movements, we therefore believe that our results are of significant relevance for the field.

neuroscience↗