@inproceedings{grewal-2026-decodability,
title = "Decodability Is Not Computation: Examining Probing Claims",
author = "Grewal, Kabir Singh",
editor = "Arad, Dana and
Belinkov, Yonatan and
Chen, Hanjie and
Feldhus, Nils and
Mueller, Aaron and
Mohebbi, Hosein and
Sarti, Gabriele and
Tutek, Martin",
booktitle = "Proceedings of the 9th {B}lackbox{NLP} Workshop: Analyzing and Interpreting Neural Networks for {NLP}",
month = oct,
year = "2026",
address = "Budapest, Hungary",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.blackboxnlp-1.14/",
pages = "201--219",
ISBN = "979-8-89176-476-7",
abstract = "High probe accuracy does not by itself establish that a language model computes and uses the decoded value. We examine this inference in a syntax-sensitive arithmetic testbed: Llama-3.1-8B often fails multiplication when an operand is wrapped in parentheses or an additive identity. In the primary operand band, an input-only linear baseline nearly matches the original hidden-state probe{'}s regression $R^2 \approx 0.96$. A classical variance decomposition gives an analytical headroom of only 0.031 for this baseline class. In wider bands, selection-separated reanalysis instead finds positive activation advantages, which increase with regularization tuning; joint input-and-activation probes also improve over the baseline. These predictive gains are distinct from exact integer recovery and causal use. In the primary band, tested answer-site steering and state transplants produce small average output shifts and no observed donor-answer emissions, whereas operand-site interventions produce large effects. Operand access is necessary, with a strong bottleneck at one attention layer. The causal tests do not cover the wider-band predictive gains. We advocate explicit input baselines, matched causal tests, and positive controls, with conclusions restricted to the distributions, representations, and interventions actually examined."
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%0 Conference Proceedings
%T Decodability Is Not Computation: Examining Probing Claims
%A Grewal, Kabir Singh
%Y Arad, Dana
%Y Belinkov, Yonatan
%Y Chen, Hanjie
%Y Feldhus, Nils
%Y Mueller, Aaron
%Y Mohebbi, Hosein
%Y Sarti, Gabriele
%Y Tutek, Martin
%S Proceedings of the 9th BlackboxNLP Workshop: Analyzing and Interpreting Neural Networks for NLP
%D 2026
%8 October
%I Association for Computational Linguistics
%C Budapest, Hungary
%@ 979-8-89176-476-7
%F grewal-2026-decodability
%X High probe accuracy does not by itself establish that a language model computes and uses the decoded value. We examine this inference in a syntax-sensitive arithmetic testbed: Llama-3.1-8B often fails multiplication when an operand is wrapped in parentheses or an additive identity. In the primary operand band, an input-only linear baseline nearly matches the original hidden-state probe’s regression R² \approx 0.96. A classical variance decomposition gives an analytical headroom of only 0.031 for this baseline class. In wider bands, selection-separated reanalysis instead finds positive activation advantages, which increase with regularization tuning; joint input-and-activation probes also improve over the baseline. These predictive gains are distinct from exact integer recovery and causal use. In the primary band, tested answer-site steering and state transplants produce small average output shifts and no observed donor-answer emissions, whereas operand-site interventions produce large effects. Operand access is necessary, with a strong bottleneck at one attention layer. The causal tests do not cover the wider-band predictive gains. We advocate explicit input baselines, matched causal tests, and positive controls, with conclusions restricted to the distributions, representations, and interventions actually examined.
%U https://aclanthology.org/2026.blackboxnlp-1.14/
%P 201-219
Markdown (Informal)
[Decodability Is Not Computation: Examining Probing Claims](https://aclanthology.org/2026.blackboxnlp-1.14/) (Grewal, BlackboxNLP 2026)
ACL