In our daily activities, we encounter numerous objects that we successfully distinguish and recognize within a fraction of a second. This holds for coarse distinctions (e.g., cat vs. hammer) but also for more challenging distinctions that require fine-grain analysis (e.g., cat vs. dog). The efficiency of this recognition depends on how the brain organizes object-related information. While several attempts have focused on unraveling large-scale organization principles, research on fine-grained knowledge organization is rather limited. Here, we explored the fine-grain organization of object knowledge and investigated whether manipulable objects are organized and represented in terms of their similarity. To accomplish this, different groups of individuals participated in a behavioral and functional magnetic resonance imaging (fMRI) release from adaptation experiment. Adaptation was induced by presenting different exemplars of a particular object, and release from adaptation was elicited by the presentation of a deviant object. The relationship between adaptation and deviant objects was manipulated into four levels of similarity, measured by feature overlap between these objects. Our findings revealed that increasing object similarity provoked slower reaction times and weaker fMRI release from adaptation. Specifically, we identified similarity-driven tuning curves for the release from adaptation in the medial fusiform, collateral sulcus, parahippocampal gyri, lingual gyri, lateral occipital complex, and occipito-parietal cortex. These results suggest that the processing and representation of objects in the brain and our ability to perform fine discriminations between objects reflect real-world object similarity in a relatively parametric manner.

Scan site harmonization is a crucial part of any neuroimaging analysis when data have been pooled across different study sites. Zhang and colleagues recently introduced the multivariate harmonization method RELIEF (REmoval of Latent Inter-scanner Effects through Factorization), aiming to remove explicit and latent scan site effects. Their initial validation in an adult sample showed superior performance compared to established methods. We here sought to investigate utility of RELIEF in harmonizing data from the Adolescent Brain and Cognitive Development (ABCD) study, a widely used resource for developmental brain imaging. We benchmarked RELIEF against unharmonized, ComBat, and CovBat harmonized data and investigated the impact of manufacturer type, sample size, and a narrow sample age range on harmonization performance. We found that in cases where sites with sufficiently large samples were harmonized, RELIEF outperformed other techniques, yet in cases where sites with very small samples were included there was substantial performance variation unique to RELIEF. Our results therefore highlight the need for careful quality control when harmonizing data sets with imbalanced samples like the ABCD cohort. Our comment alongside shared scripts may provide guidance for other scholars wanting to integrate best practices in their ABCD related work.