Backpropagation destroys V1 brain alignment in one epoch, tracking RSA alignment to fMRI across training for BP, FA, predictive coding, and STDP [R]

Third in a series of papers tracking learning rules vs. human fMRI (THINGS dataset, V1–IT, N=3 subjects). Previous finding: untrained CNNs match backprop at V1. This paper asks: when does training break that, and does the learning rule matter? Setup: RSA alignment measured at 8 checkpoints (epochs 0, 1, 2, 5, 10, 20, 30, 40), 5 seeds per rule, same architecture throughout. Main findings: BP drops 90% of V1 alignment after one epoch (r: 0.102 → 0.011, p = 0.031, consistent across all 5 seeds). FA drops 49%. PC and STDP drop only 25–31% and stabilise. By epoch 40: PC (r = 0.064) > STDP (0.059) >> BP (0.022) ≈ FA (0.019). Cohen's d > 5 for PC/STDP vs BP: extremely consistent across seeds. Opposing trend at LOC: BP shows a small increase in object-selective cortex alignment (+0.011) while local rules show nothing. Suggests a fundamental trade-off: global error signals build higher representations but destroy early ones. Degradation rate tracks error signal globality: exact gradients (BP) > random feedback (FA) > local prediction errors (PC, STDP). Limitations worth noting: 5 seeds caps permutation test resolution at p ≈ 0.031 Training on 32×32 CIFAR-10, evaluated on 224×224 THINGS, resolution/domain shift is a confound LOC increase not tested for significance, treated as suggestive Paper: arxiv.org/abs/2605.30556 Companion: arxiv.org/abs/2604.16875 Code: github.com/nilsleut Curious whether anyone has seen similar dynamics in larger architectures, the prediction would be that deeper models show the same pattern but more slowly. submitted by /u/ConfusionSpiritual19 [link] [留言]