Reading Without a Reader: Large Language Models Collapse Reading and Writing into a Single Entangled Code

A new study from arXiv preprint 2607.24797v1 finds that decoder-only large language models (LLMs) such as GPT-2, OPT, and Pythia entangle reading and writing into a single code, unlike the human brain's double dissociation. The researchers measured an entanglement index E between 0.23 and 0.35 across models, with output-side weights drifting 3.2 times farther than input-side weights, and found behavioral coupling in all 12 non-degenerate models (sign test p<0.001), contrasting with the brain's separable systems.

arXiv:2607.24797v1 Announce Type: cross Abstract: In the literate human brain, reading and writing are two doubly-dissociable systems: a ventral decoding route impaired in pure alexia and a fronto-parietal encoding route impaired in pure agraphia , sharing a partial orthographic core. A decoder-only large language model LLM instead drives both from a single autoregressive path optimized on text, a recent cultural invention rather than an evolved instinct. We ask how entangled that one mechanism is, comparing an input-side "reading code" $W E$ with an output-side "writing code" $W U$ via an entanglement index $E \in 0,1 $ CKA, Procrustes residual, mutual $k$-NN calibrated against an independent-init floor and a tied ceiling. Across nine probes on GPT-2, OPT, Pythia 14M--1.4B , T5, and BERT/RoBERTa six consolidating established results, three introducing the read/write analysis , two complementary levels agree in direction. In the weights, untied models hold one coupled but sub-ceiling code $E=0.23$--$0.35$, far above floor on a non-monotonic couple-then-differentiate trajectory, with $W U$ drifting $\sim 3.2\times$ farther than $W E$ in every frequency decile. In behaviour, comprehension and production are positively coupled in all 12 non-degenerate models sign test $p<0.001$ , the opposite of the brain's double dissociation. This coupling is general, not decoder-only: encoder--decoders separate the two pathways representationally up to 0.96 yet stay behaviourally coupled. We report our nulls plainly the geometry $\rightarrow$ behaviour bridge is null, $\rho=0.00$ . Because a single forward path makes some coupling expected a priori, our contribution is its quantification and cross-level concordance; by analogy, not homology, this situates LLMs as a distinct point in the space of possible minds.