Minimal Recurrent Behavioral Memory for Imitation under Partial Observability
Abstract
What is the least recurrent memory needed to reproduce a specified expert under partial observability? The instantaneous requirement is the conditional entropy of the expert's behavioral quotient, but recurrence must also preserve distinctions that future observations will not restore before use. We characterize this minimal recurrent behavioral memory by a compatibility relation: under transitivity its classes attain the exact minimum, while the general case is an entropy minimization over closed compatible state assignments, with exact certificates on finite instances. A sole-carrier measurement protocol separates behavioral sufficiency, excess code rate, and information carried by observations or other memory paths; experimental bit requirements refer to the induced symbolic behavioral model under the stated occupancy. Across manipulation tasks, learned code rates remain near zero- and two-bit requirements as hidden modes grow to , and anticipatory memory follows a requirement despite zero instantaneous demand during waiting. Learning this representation remains difficult: event-agnostic future-behavior supervision yields sufficient seeds with one frozen configuration and improves the longest-horizon pixel setting from to sufficient held-out seeds (closed-loop success from to ). On unmodified community benchmarks, the protocol certifies delay-independent requirements, which sufficient codes match at mid-delay. The supervision aids commitment but can induce predictive surplus; annealing it lets imitation and rate training reduce that surplus, separating the information-theoretic target from the ability to learn it.
Figures & tables
| training target | gap 6 | gap 10 | gap 20 | ||
|---|---|---|---|---|---|
| teacher internal state | |||||
| task-informed future behavior | |||||
| event-agnostic future behavior | |||||
| event-agnostic: closed-loop success |
| learner | first second gap (bits) | sufficient | closed-loop success |
|---|---|---|---|
| plain | |||
| event-agnostic, annealed | |||
| task-informed reference |
Appendix figures & tables21 assets
Supplementary material from the paper’s appendix.
Appendix
| finite toys | signpost corridor | A ′ (distortion-constrained) | A ′ (attainability) | Task A | |
|---|---|---|---|---|---|
| domain | finite POMDPs | grid navigation | Franka, kinematic attach | Franka, kinematic attach | Franka, physics-simulated kg grasp |
| regime (solver) | exact; (A2), (A4), transitive | exact at ; certified at | exact | exact | exact: transitive, (A4) fails at one step |
| learner | raw VQ, lr | raw VQ, tanh-bounded state | plain R | scaffold-RF | plain R |
| data, steps | 6k | 6k | ; 10k | k | ; 10k |
| role | exact validation | cross-domain replication | distortion-constrained | attainability only | matched performance |
| choice | premise | evidence |
|---|---|---|
| is the only carrier across time | Definition 2 | Appendix B.2 : bypass under-counts in three domains |
| persistence (residual proposal) | recurrence | non-persistent code: sufficient (trivial) |
| discrete codebook | directly measurable accounting | continuous: KL upper bound bit, not comparable (Table 17 ) |
| prior conditioned on | matches the conditional-rate objective | no empirical advantage over an unconditional prior in these families |
| forecaster used at training only | sole carrier at evaluation | forecaster removed before every reported rate and rollout; is the only cross-time variable (§ 5 ) |
| phase | (0.50) | (0.50) | (0.03) | mass bin (0.25) | distractor (0.25) |
|---|---|---|---|---|---|
| identification (scan) | 1.00 | 1.00 | 0.10 | 0.26 | — |
| gap 1 | 0.53 | 0.51 | 0.04 | 0.23 | — |
| grasp | 0.99 | 0.47 | 0.05 | 0.24 | — |
| gap 2 | 0.51 | 0.46 | 0.03 | 0.18 | 0.99 |
| place | 0.49 | 1.00 | 0.04 | 0.26 | — |
| gap | architecture | sufficient | first-gap rate | post-use rate | behav. error | closed-loop success | |
|---|---|---|---|---|---|---|---|
| 6 | hierarchical | 0 | 8/8 | 1.00 | 0.000 | 1.00 | |
| 6 | hierarchical | 8/8 | 1.00 | 0.000 | 1.00 | ||
| 6 | intent | 0 | 8/8 | 1.09 | – | 0.96 | |
| 6 | intent | 8/8 | 1.00 | – | 0.94 | ||
| 20 | hierarchical | 0 | 8/8 | 1.00 | 0.027 | 0.96 | |
| 20 | hierarchical | 8/8 | 1.00 | 0.000 | 1.00 |
| (mm) | 0 | 0.5 | 1 | 2 | 4 | 8 |
|---|---|---|---|---|---|---|
| closed-loop success | ||||||
| slot accuracy | ||||||
| held-out action error (MSE) | ||||||
| behaviorally correct seeds | ||||||
| seeds passing the sufficiency gate | ||||||
| flag A: correct, rate bit |
| CPU, batch 1 (ms) | GPU, batch 64 (ms) | |||||
|---|---|---|---|---|---|---|
| Transformer | GRU | DIACRITIC | Transformer | GRU | DIACRITIC | |
| 33 | 1.13 | 0.55 | 0.54 | 1.77 | 1.12 | 1.18 |
| 128 | 1.78 | 0.55 | 0.55 | 1.83 | 1.18 | 1.17 |
| 256 | 3.51 | 0.56 | 0.53 | 2.12 | 1.15 | 1.18 |
| 512 | 9.03 | 0.55 | 0.54 | 5.45 | 1.10 | 1.13 |
| 1024 | 29.3 | 0.56 | 0.55 | 16.8 | 1.13 | 1.17 |
| parameters | training time | at deployment: carried state / per-step latency | |
|---|---|---|---|
| forecaster, 3000 steps (default) | – M | – s | removed |
| random-offset forecaster, 100 steps (timing only) | M | s | removed |
| compact student, 10 000 steps, with or without the auxiliary head | M | s | bytes / ms |
| full-history Transformer baseline, 10 000 steps | M | s | floats / – ms for – |
| sufficient seeds / closed-loop success | ||||
|---|---|---|---|---|
| ours, | 8/8 / 0.91 | 8/8 / 0.96 | 8/8 / 0.98 | 8/8 / 0.98 |
| ours, | 8/8 / 1.00 | 8/8 / 1.00 | 8/8 / 0.99 | 8/8 / 1.00 |
| sys-ID, | 1/8 / 0.11 | 0/8 / 0.08 | 0/8 / 0.06 | 0/8 / 0.07 |
| sys-ID, | 8/8 / 0.71 | 3/8 / 0.18 | 0/8 / 0.08 | 0/8 / 0.09 |
| sys-ID, | 8/8 / 0.79 | 8/8 / 0.34 | 0/8 / 0.12 | 0/8 / 0.16 |
| objective | sufficient (place) | grasp rate (bits) | success | ||
|---|---|---|---|---|---|
| 128 | ours, , | 8/8 | 0.03 | 0.01 | 0.99 |
| 128 | ours, , | 8/8 | 0.18 | 0.02 | 0.99 |
| 128 | sys-ID, | 0/8 | 3.73 | 0.62 | 0.04 |
| 128 | sys-ID, | 3/8 | 6.84 | 1.40 | 0.17 |
| 512 | ours, , | 8/8 | 0.03 | 0.01 | 0.99 |
| 512 | ours, , | 8/8 | 0.10 | 0.02 | 0.98 |
| task | learner | sufficient | first-gap rate | transport rate | closed loop |
|---|---|---|---|---|---|
| readout-2 | R | 8/8, 7/8, 8/8 | 2.00, 2.02, 2.03 [2.00] | 1.10, 1.23, 1.06 [1.00] | 0.94, 0.85, 0.87 |
| readout-2 | forecast | 8/8, 8/8, 8/8 | 2.02, 2.08, 2.03 [2.00] | 1.11, 1.27, 1.09 [1.00] | 0.95, 0.90, 0.96 |
| readout-2 | sys-ID, largest | 4/8, 6/8, 1/8 | 4.82, 5.56, 7.49 | 4.49, 4.74, 7.93 | 0.25, 0.26, 0.19 |
| readout-3 | forecast | 6/8, 5/8, 4/8 | 3.03, 3.09, 3.17 [3.00] | 3.06, 3.01, 3.09 [3.00] | 0.25, 0.28, 0.15 |
| readout-3 | forecast, | 0/8, 0/8, 0/8 | 2.73, 2.92, 2.87 | 2.49, 2.46, 2.76 | 0.05, 0.05, 0.05 |
| readout-3 | sys-ID, largest | 6/8, 0/8, 0/8 | 4.83, 5.78, 7.94 | 4.78, 5.78, 8.31 | 0.32, 0.07, 0.03 |
| configuration | success | ||||
|---|---|---|---|---|---|
| , (every mass in training) | |||||
| DIACRITIC ( ) | 0.34 | 0.01 | – | – | 0.99, 0.88 |
| shared, weight 1 ( ) | 2.83 | 0.73 | – | – | 0.07, 0.05 |
| shared, weight 0.1 ( ) | 4.52 | 0.80 | – | – | 0.38, 0.23 |
| dual carrier ( ) | 0.46 | 0.03 | 4.12 | 2.73 | 0.90, 0.84 |
| dual, stop-gradient | 0.29 | 0.00 | 4.35 | 2.45 | 0.93, 0.88 |
| sufficient seeds | gap 6 | gap 10 | gap 20 | ||
|---|---|---|---|---|---|
| EA, anneal (frozen) | ( ) | ( ) | ( ) | ( ) | ( ) |
| EA, anneal | — | — | ( ) | — | ( ) |
| EA, not annealed | ( ) | ( ) | ( ) | ( ) | ( ) |
| TI | (—) | ( ) | ( ) | ( ) | ( ) |
| teacher state | |||||
| rate / closed loop | gap 6 | gap 10 | gap 20 |
| horizon | learner | sufficient | rate (bits) | success | slot accuracy |
|---|---|---|---|---|---|
| gap 6 | plain R | ( ) | |||
| gap 6 | task-informed forecast | ||||
| gap 20 | plain R | ( ) | |||
| gap 20 | event-agnostic, not annealed | ||||
| gap 20 | event-agnostic, annealed from | ||||
| gap 20 | event-agnostic, annealed from |
| target | gap 6 | gap 10 | gap 20 | ||
|---|---|---|---|---|---|
| task-informed forecast of pending behavior | 8/8 | 8/8 | 8/8 | 8/8 | 5/8 |
| teacher’s internal state | 2/8 | 0/8 | 0/8 | 0/8 | 1/8 |
| unsupervised (best variant) | 3/8 | 2/8 | 1/8 | 0/8 | 0/8 |
| forecast: rate before use (theory 2.00) | 2.01 | 2.05 | 2.09 | 2.08 | 2.13 |
| forecast: rate after use (theory 1.00) | 1.07 | 1.06 | 1.10 | 1.09 | 1.11 |
| forecast: closed-loop success | 0.95 | 0.89 | 0.92 | 0.84 | 0.73 |
| variant | sufficient | post-use rate (bits) | rate measurement | success |
|---|---|---|---|---|
| DIACRITIC ( R, ) | ✓ | (near) | ✓ | |
| scaffold DIACRITIC ( k) | ✓ | – on (strongest) | ✓ ( at evaluation) | – |
| ✓ | (redundant) | ✓ | ||
| continuous bottleneck | possible | KL bound ; nuisance | upper bound only | — |
| GRU bypass | ✓ | (apparent under-rate) | (not the sole carrier) | – |
| system identification | budget-dep. | – (learned rate) | ✓ | – |
| policies | (gap 2 ) | slot accuracy | success | action error (cm) | |
|---|---|---|---|---|---|
| teacher-forced sufficient ( R, seeds 0, 6) | 2 | , | , | , | , |
| insufficient, R | 6 | – | – | – | |
| insufficient, scaffold-R | 8 | – | – | – |
| cue bits, variant | |||||
|---|---|---|---|---|---|
| 1 bit, R | 8/8 / 1.25 | 8/8 / 1.19 | 7/8 / 1.00 | 3/8 / 1.00 | 5/8 / 1.00 |
| 1 bit, RF | 8/8 / 1.12 | 8/8 / 1.50 | 8/8 / 1.38 | 5/8 / 1.10 | 6/8 / 1.17 |
| 1 bit, scaffold-RF | 8/8 / 1.17 | 8/8 / 1.00 | 8/8 / 1.06 | 8/8 / 1.19 | 6/8 / 1.08 |
| 2 bits, R | 6/8 / 2.00 | 4/8 / 2.00 | 1/8 / 2.00 | 0/8 / — | 0/8 / — |
| gap 6 | gap 20 | |||
|---|---|---|---|---|
| learner | sufficient | closed loop | sufficient | closed loop |
| plain R | / | / | / | / |
| task-informed forecast | / | / | / | / |
| task-informed forecast from step 0 | / | / | / | / |
| event-agnostic, not annealed | / — | / | / — | / |
| system identification | / — | / | / — | / |
| learner | ||||
|---|---|---|---|---|
| GRU policy, continuous state | 8 (1.00) | 8 (1.00) | 8 (1.00) | 7 (0.93) |
| compact carrier, plain imitation | 1 (0.53) | 1 (0.53) | 0 (0.46) | 0 (0.46) |
| compact carrier, event-agnostic forecast | 8 (1.00) | 7 (0.94) | 5 (0.80) | 0 (0.48) |
| compact carrier, RF (decoder sees future observations) | — | 1 (0.53) | 0 (0.46) | 0 (0.46) |
| compact carrier, annealed continuous scaffold | — | 0 (0.46) | 0 (0.47) | 0 (0.47) |
| GRU policy, 8-dimensional state | — | 0 (0.47) | 0 (0.41) | 0 (0.35) |
| task | delay | certified | suff., plain | suff., event-agnostic | learned rate |
|---|---|---|---|---|---|
| MemoryChain, 1 bit | 10 | ||||
| MemoryChain, 1 bit | 30 | ||||
| MemoryChain, 1 bit | 100 | ||||
| MemoryChain, 2 bits | 10 | ||||
| MemoryChain, 2 bits | 30 | ||||
| MemoryChain, 2 bits | 100 | — |
| method | target representation | F | S | E | B | rate of the target’s fixed-demonstrator form under our solver |
|---|---|---|---|---|---|---|
| bisimulation ( Zhang et al., 2021 ) ; -bisimulation ( Castro, 2020 ) | value / dynamics equivalence (policy-specific for -bisim.) | policy | – | – | – | not implemented |
| -irrelevance ( Li et al., 2006 ) ; support sufficiency ( Walsh, 2026 ) | optimal-action equivalence (single decision) | optimal act. | – | rate–regret | – | single-decision quotient : 0 bit in the gaps (Fig. 7 ) |
| causal states / PSR ( Shalizi and Crutchfield, 2001 ; Littman et al., 2001 ) | sufficiency for predicting observations | – | – | stat. complexity | – | observation-predictive form: bit on the re-reveal toy vs. for (App. D.3 ) |
| multi-step inverse / ACSD ( Mhammedi et al., 2023 ; Lamb et al., 2023 ) | control-endogenous latent | – | – | – | – | – bit of drift on the corridor, never sufficient (App. C.4 ) |
| approximate information state ( Subramanian et al., 2022 ) | sufficiency for reward and next observation | – | – | – | – | not implemented |
| stable quotients ( Zhang et al., 2026 ) ; Nerode quotient ( Nixon, 2026 ) | minimal Markov / controller-equivalent state | – | – | – | – | not implemented |