Biology subjects

Hopf, J.-M.

Publications and source records attributed to Hopf, J.-M..

5 recordsLinked to original sources

bioRxiv2026

Environmental color statistics shape the anisotropic geometry of human color discrimination

Hue is a powerful cue for object discrimination, but human color discrimination is anisotropic: hue thresholds are lower than chroma thresholds for orangish colors, but nearly equal for purplish colors. Here we show that this asymmetry reflects environmental color statistics rather than being a fixed consequence of cone-opponent architecture. Across fifteen image and reflectance databases, orangish hues accounted for 62.5% of chromatic samples, compared with 5.3% for purplish hues. We replicated the hue-chroma asymmetry psychophysically in 44 participants. Magnetoencephalography revealed a corresponding neural asymmetry, with superior decoding of orangish hue differences emerging around 250 ms after stimulus onset. Deep neural networks trained on naturalistic image datasets reproduced the human-like asymmetry without explicit color supervision. Critically, training on hue-inverted images reversed the asymmetry, producing greater hue sensitivity for purplish than for orangish colors. These results suggest that the geometry of color discrimination is shaped by ecological chromatic structure.

neuroscience↗

bioRxiv2026

Altered theta distribution and coherence during set-shifting in older age

Cognitive flexibility is an executive function that enables adapting behaviour to a changing environment and is thus critical for daily life. The degree of its preservation upon healthy aging and the neural mechanisms underlying it are still a matter of debate. To investigate the electrophysiological correlates of cognitive flexibility in older age, we measured cognitive flexibility in 99 young (24.75 {+/-} 4.45 years) and 83 older adults (69.19 {+/-} 6.25) using electroencephalography (EEG). Compared to young adults, older adults showed a more conservative response pattern with longer reaction times, but lower error rates (speed-accuracy tradeoff). In the EEG, both age groups exhibited increased theta-power during set-shifting, with a fronto-central peak in the young, but a more fronto-lateral topography in older adults. Importantly, both groups displayed increases in theta coherence and global efficiency during set-shifting, but coherence modulations were restricted in frontocentral areas in the young but were diminished and distributed across the scalp in the older. Better set-shifting performance was most strongly associated with high coherence and global efficiency irrespective of age group. These results point to an age-related change of cortical processing underlying cognitive flexibility which involves the employment of more distributed neural resources for successful task completion.

neuroscience↗

bioRxiv2023

Serial attentional resource allocation during parallel feature value tracking

The visual system has evolved the ability to track features like color and orientation in parallel. This property aligns with the specialization of processing these feature dimensions in the visual cortex. But what if we ask to track changing feature-values within the same feature dimension? Parallel tracking would then have to share the same cortical representation, which would set strong limitations on tracking performance. We address this question by measuring the precision of color representations when human observers track the color of two superimposed dot clouds that simultaneously change color along independent trajectories in color-space. We find (1) that tracking precision is highly imbalanced between streams. (2) Tracking precision changes over time by alternating between streams at a rate of [~]1Hz. These observations suggest that, while parallel color tracking is possible, it is highly limited, essentially allowing for only one color-stream to be tracked with precision at a given time.

neuroscience↗

bioRxiv2020

Decoding the covert shift of spatial attention from electroencephalographic signals permits reliable control of a brain-computer interface

ObjectiveOne of the main goals of brain-computer interfaces (BCI) is to restore communication abilities in patients. BCIs often use event-related potentials (ERPs) like the P300 which signals the presence of a target in a stream of stimuli. The P300 and related approaches, however, are inherently limited, as they require many stimulus presentations to obtain a usable control signal. Many approaches depend on gaze-direction to focus the target, which is also not a viable approach in many cases, because eye movements might be impaired in potential users. Here we report on a BCI that avoids both shortcomings by decoding spatial target information, independent of gaze shifts. ApproachWe present a new method to decode from the electroencephalogram (EEG) covert shifts of attention to one out of four targets simultaneously presented in the left and right visual field. The task is designed to evoke the N2pc component - a hemisphere lateralized response, elicited over the occipital scalp contralateral to the attended target. The decoding approach involves decoding of the N2pc based on data-driven estimation of spatial filters and a correlation measure. Main resultsDespite variability of decoding performance across subjects, 22 out of 24 subjects performed well above chance level. Six subjects even exceeded 80% (cross-validated: 89%) correct predictions in a four-class discrimination task. Hence, the single-trial N2pc proves to be a component that allows for reliable BCI control. An offline analysis of the EEG data with respect to their dependence on stimulation time and number of classes demonstrates that the present method is also a workable approach for two-class tasks. SignificanceOur method extends the range of strategies for gaze-independent BCI control. The proposed decoding approach has the potential to be efficient in similar applications intended to decode ERPs.

neuroscience↗

bioRxiv2020

Attention expedites target selection by prioritizing the neural processing of distractor features

Whether doing the shopping, or driving the car - to navigate daily life, our brain has to rapidly identify relevant color signals among distracting ones. Despite a wealth of research, how color attention is dynamically adjusted is little understood. Previous studies suggest that the speed of feature attention depends on the time it takes to enhance the neural gain of cortical units tuned to the attended feature. To test this idea, we had human participants switch their attention on the fly between unpredicted target color alternatives, while recording the electroencephalographic brain response to probes matching the target, a non-target, or a distracting alternative target color. Paradoxically, we observed a temporally prioritized processing of distractor colors. A larger neural gain for the distractor followed by stronger attenuation expedited target identification. Our results suggest that dynamic adjustments of feature attention involve the temporally prioritized processing and elimination of distracting feature representations.

neuroscience↗