Internal Oppenheim-Lim test reveals phase/sign identity codes shared across image classifier architectures
A new arXiv preprint applies a causal intervention inspired by Oppenheim and Lim (1981) to probe whether trained image classifiers encode identity in Fourier phase rather than magnitude within their hidden layers. By transplanting phase or sign components between images at chosen layers in PRISM2D, GFNet, ViT-B/16, and ResNet-50, the authors find that predictions follow the phase/sign donor across all tested architectures, with image-specific magnitude largely dispensable. ResNet-50 requires a pre-ReLU intervention to reveal a latent sign code, exposing how rectification and readout geometry shape the basis in which the code is expressed. The findings offer a mechanistic account of the texture–shape gap between CNNs and attention-based models.
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Label-Free Bias Identification in Vision Models via Gradient Probes on Concept Decompositions
This paper introduces a post-hoc, label-free method for identifying spurious correlations in frozen vision classifiers without requiring bias annotations, group labels, or retraining. The approach applies non-negative matrix factorization to intermediate activations to extract interpretable concept vectors, then ranks them using a gradient-based bias estimator derived from misclassified examples. On Colored MNIST, Waterbirds, and CelebA benchmarks, the method recovers known spurious cues and improves worst-group accuracy by up to 17.9 percentage points on Waterbirds by suppressing top-ranked concepts at inference time. Notably, the method surfaces decision-relevant directions that do not always coincide with annotated attributes, offering both an auditing tool and a debiasing handle for deployed models.
Expressivity Limits of Congruence-Based Architectures for Neural Networks on Positive-Definite Matrices
This paper analyzes neural network architectures designed to classify symmetric positive-definite (SPD) matrices, focusing on congruence-like layers as used in SPDNet. The authors prove that imposing semi-orthogonality constraints on weight matrices limits expressivity, causing deep architectures to collapse to single-hidden-layer equivalents due to spectral diversity loss—a consequence of Poincaré's separation theorem. The work also compares Riemannian classifiers for compatibility with congruence-based feature maps.
Visual instruction tuning aligns modalities in intermediate LLM layers, not early ones
A new arXiv paper investigates how visual instruction tuning embeds image features into the layer-wise hierarchy of LLM backbones across diverse vision-language architectures. Using probing analyses and causal interventions, the authors find that instruction tuning routes visual features into intermediate semantic layers, bypassing early unimodal-processing layers. They further show that fine-tuning restricted to these intermediate layers alone preserves full fine-tuning performance on vision-centric benchmarks while reducing training time, suggesting multimodal integration is a localized phenomenon.
Phase diagram framework for choosing between cross-modal alignment and prediction in multimodal learning
A new arXiv preprint develops a unified linear framework to determine when cross-modal alignment (CA) versus cross-modal prediction (CP) is the better objective for multimodal representation learning. Under a spiked signal-plus-noise model, the authors derive separation ratios that expose complementary failure modes for each paradigm, producing a four-regime phase diagram (Both, CA only, CP only, Neither). A data-driven procedure lets practitioners locate their dataset in this diagram using a small labeled subsample before committing to training. Experiments on synthetic data, stereo-vision, image-caption pairs, and astrophysical data validate the framework, including a 'Neither' regime where cross-modal training is actively harmful.
Multimodal neurons in artificial neural networks
OpenAI researchers discovered neurons in CLIP that respond to the same concept across literal, symbolic, and conceptual representations. This finding parallels multimodal neurons previously observed in biological brains and helps explain CLIP's ability to classify unusual visual renditions of concepts. The work is presented as a step toward understanding the associations and biases learned by CLIP and similar vision-language models.
Social Gaze Consistency as a Semantic Cue for AI-Generated Image Detection
This paper introduces Social Gaze Consistency (SGC), a high-level semantic detection axis based on the mutual coherence of gaze direction, head-eye alignment, and pupil placement between interacting individuals in images. The authors construct a controlled diagnostic dataset with region-specific gaze perturbations and a Block-Compositional Caption Supervision scheme to train detectors without generator-fingerprint memorization shortcuts. Cross-architecture validation shows +3.7 pp improvement on the COCOAI Interaction subset when applied to FakeVLM, with gains transferring from a single inpainter (FLUX.1-Fill) to multi-generator suites. The work argues that diffusion models share a spectral weakness in periocular structure, making gaze coherence a robust, backbone-agnostic detection signal orthogonal to existing low-level artifact methods.
Beyond Prediction Accuracy: Target-Space Recovery Profiles for Evaluating Model-Brain Alignment
This paper introduces a framework for evaluating alignment between artificial vision models and the human visual cortex that goes beyond scalar prediction accuracy. Using repeated fMRI data from the Natural Scenes Dataset, the authors decompose brain response spaces into reproducible dimensions and measure which of these dimensions are recovered by model predictions. A key finding is that pretrained and randomly initialized models can achieve similar prediction accuracy while showing distinct recovery profiles, revealing that accuracy alone can mask fundamental model-brain mismatches. The framework also enables brain-to-brain comparisons as a diagnostic human reference baseline.
Stable Recovery Manifold hypothesis: catastrophic forgetting as accessibility problem, not information destruction
A new arXiv preprint investigates the geometric structure of recoverability in continual learning using Split CIFAR-100 and a sequentially trained ResNet-18. The authors introduce Recovery Subspace Dimensionality (k_t) and find that recovery dimensionality remains stable across tasks (mean k_t = 8.0) despite substantial representational drift, with principal-angle drift strongly predicting recoverability (r = -0.862). The findings support the Stable Recovery Manifold hypothesis: forgotten knowledge remains compactly decodable, reframing catastrophic forgetting as a manifold-alignment and accessibility problem rather than true information loss.