Yaocong Duan¹ (), Jiayu Zhan², Joachim Gross³, Rachael E. Jack¹, Robin Ince¹, Philippe G. Schyns¹; ¹University of Glasgow, ²Peking University, ³University of Muenster

The occipital cortex is crucial for early visual feature representation during categorization tasks. Task-irrelevant features are quickly reduced within 120–150ms, while task-relevant features are selectively transmitted into the ventral visual pathway for further processing that influences behavior. The transformation of these task-relevant feature representations along the occipito-ventral pathway, however, remains unclear. To investigate this, a 10-participants study was conducted, where they performed four different 2-Alternative-Forced-Choice categorizations using the same set of 64 base images depicting a realistic city scene over 1,536 trials. These images included embedded targets such as eight face identities varying by gender and expression, and the presence of vehicles and pedestrians. Each trial began with a fixation cross followed by a 150ms presentation of a base image with randomly sampled features using the Bubbles technique to identify critical features for categorization. Participants' brain activity was recorded using MEG, alongside their categorization responses. Using information-theoretic co-information, we examined whether features are represented similarly or differently in MEG activity as they evolve dynamically across occipito-ventral pathway sources. Occipital cortex sources that maximally represented each stimulus feature were identified within 50–120ms and 160–200ms post-stimulus. Co-information was computed to determine if features were represented redundantly (similarly) or synergistically (complementarily) across source pairs over time. We found that task-relevant feature representations change dynamically across space-by-time. Around 100ms, features are redundantly represented across occipital cortex sources. By ~180ms, a new redundant representation of the same features emerges at the junction of occipital, ventral, and parietal regions, indicating a dynamic transition in feature representations. The initial representations interact with parietal regions, while the second set interacts with the ventral pathway, peaking ~300ms, suggesting that only the second representation is involved with internal decision-making. These results highlight the dynamic nature of feature transformation for flexible, task-specific visual categorization decisions in the brain.

Acknowledgements: This research was funded by the Wellcome Trust [Senior Investigator Award, UK; 107802] awarded to PGS; the European Research Council (ERC) grant [759796] awarded to REJ; the Wellcome Trust [214120/Z/18/Z] awarded to RI.