Research map / Vision-language and multimodal / CLIP and zero-shot
Bridging the Semantic Latent Space between Brain and Machine: Similarity Is All You Need
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Proposes BrainSem, a self-supervised fMRI-to-CLIP joint embedding model trained with a fuzzy one-to-many matching loss and virtual fMRI augmentation, evaluated on zero-shot neural decoding of the GOD dataset.
Problem
Aligning fMRI brain responses with a semantic embedding space to decode unseen visual categories from limited fMRI-image pairs, and testing whether brain and CLIP-like networks share similar semantic (locality-sensitive) representations.
Approach
Treats fMRI-to-image matching as a fuzzy one-to-many contrastive problem where all ImageNet images of the same class serve as positives, combined with a neuro-semantic reorganization that creates virtual fMRI responses as convex combinations of real recordings.
Key results
- BrainSem averages 25.6% Top-1 and 53.6% Top-5 zero-shot accuracy on GOD across five subjects, versus 14.0% Top-1 for BraVL (the prior SOTA).
- Ablation: using both virtual brain responses and the visual semantic library raises Top-1 from 18.8% to 25.6%.
- Swapping CLIP image encoder variants changes Top-1 only between 24.8% and 25.8%.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use BrainSem instead of BraVL | zero-shot neural classification · GOD test, average | Top-1 accuracy: 14.0% -> 25.6% | Helped |
| use BrainSem instead of BraVL | zero-shot neural classification · GOD test, average | Top-5 accuracy: 53.1% -> 53.6% | Helped |
| use CLIP ViT-L/14 instead of ViT-B/16 as image encoder (ablation) | BrainSem · GOD test | Top-1 accuracy: 25.6% -> 25.8% | Helped |
| use CLIP ViT-L/14 instead of ViT-B/16 as image encoder (ablation) | BrainSem · GOD test | Top-5 accuracy: 53.6% -> 54.4% | Helped |
| add visual semantic library (ablation) | BrainSem with ViT 6 layers, batch 100 · GOD test | Top-1 accuracy: 19.4% -> 21.0% | Helped |
| add virtual brain activity (ablation) | BrainSem with ViT 6 layers, batch 100 · GOD test | Top-1 accuracy: 19.4% -> 24.2% | Helped |
| add visual semantic library and virtual brain activity (ablation) | BrainSem with ViT 24 layers, batch 200 · GOD test | Top-1 accuracy: 18.8% -> 25.6% | Helped |
| add visual semantic library and virtual brain activity (ablation) | BrainSem with ViT 12 layers, batch 100 · GOD test | Top-5 accuracy: 46.2% -> 58.4% | Helped |
| use CLIP ViT-B/32 instead of ViT-B/16 as image encoder (ablation) | BrainSem · GOD test | Top-1 accuracy: 25.6% -> 25.2% | Hurt |
| use CLIP ResNet50 instead of ViT-B/16 as image encoder (ablation) | BrainSem · GOD test | Top-1 accuracy: 25.6% -> 24.8% | Hurt |
| use CLIP ViT-B/32 instead of ViT-B/16 as image encoder (ablation) | BrainSem · GOD test | Top-5 accuracy: 53.6% -> 52.0% | Hurt |
Surprising findings
- Raw fMRI and CLIP features show weaker locality-sensitive structure than BrainSem embeddings in ISOMAP/t-SNE visualizations.
- A smaller fMRI encoder outperforms a larger one when trained only on raw annotation data, while the fuzzy matching makes performance barely sensitive to encoder size.
Limitations
- Decoding is performed per subject; group-level decoding remains difficult due to individual variability.
- Misclassification occurs mainly when test samples have large semantic gaps from known classes.
- Only the GOD dataset is evaluated, with a small number of fMRI recordings.
Experimental setup
Datasets: GOD (Horikawa and Kamitani 2017) ImageNet
Benchmarks: GOD zero-shot neural classification ImageNet-1k retrieval subset
Metrics: Top-1 accuracy Top-5 accuracy
Baselines: CADA-VAE MVAE MMVAE MoPoE-VAE BraVL
Builds on: CLIP contrastive learning mixup BraVL
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