Dream to Assist: Intent-Conditioned World Models for Shared Vehicle Control
Authors: Jonathan DeCastro, Thomas Balch, Emily Sumner, Deepak Gopinath, Laporsha Dees, Patricio Reyes Gomez, Elliot Weiss, Megan Applegate-Kenton, Todd Rowell, John Leonard, Avinash Balachandran, Guy Rosman
Organizations: Toyota Research Institute, Cambridge, MA 02139, USA · Toyota Research Institute, Los Altos, CA 94022, USA · Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Assistive agents in shared-control settings face a dual challenge: acting proactively to align with the human's intentions while remaining legible enough for the human to comprehend and fluently respond in real time. We present Dream2Assist, a model-based reinforcement learning framework for tightly-coupled shared decision making that addresses both sides of this challenge. Our approach extends a recurrent state-space world model with intent inference, enabling an assistive policy trained via fictitious co-play to anticipate and support discrete human objectives without overriding human agency. Beyond the computational framework, we describe the full deployment pipeline needed to translate a world-model-based policy into a safe, human-centered system in a resource-efficient way. Crucially, we address the sim-to-real-human gap via policy down-selection and reward restructuring within an iterative human-machine interface design. We validate the framework through three human-subjects studies and a preliminary on-vehicle deployment spanning two qualitatively distinct domains: high-speed racing (N=30) and urban driving with richer intent structure (N=10). Our results demonstrate that intent conditioning yields measurable improvements in torque alignment and collision rate. We surface key design insights and practices for deploying learning-based assistive agents in safety-critical, real-time human-robot teaming.
Figures & tables
Figure 1: Dream2Assist RSSM: We blend human actions linearly with the actions from an unfrozen assistive agent. For both human and assistive agents, a multi-head RSSM architecture is then used to predict the observations, reward, and human intent (assistive only), trained to maximize their log-likelihoods against samples taken from the environment. The intent head is trained to match frozen human intents, which are fixed a priori. The assistive agent’s rewards are shaped based on the optimal policy πy^A∗ and optimal predicted reward ry^A∗ for inferred intent y^A .
Figure 2: Racing (left) and urban (right) domains.
Figure 3: The GRIP physical test platform used for immersive VR-based mixed sim/real testing.
Figure 4: Overall workflow diagram. Notice the combination of iterative refinement and selection of policy choices, as well as the iterative piloting of the overall policy and interface behavior.
Study
N
Environment (map)
Comparison
Purpose
Eval 1 : Racing characterization
24
CARLA (Thunderhill)
Dream2Assist -assisted vs. unassisted driving
Characterize shared control interaction across track geometries; identify failure modes for targeted refinement
Eval 2 : Racing refinement
6
CARLA (Thunderhill)
Refined vs. earlier configuration (within-subjects)
Validate that targeted refinements (data augmentation, output smoothing, reward restructuring) improved the interaction
Eval 3 : Urban validation
10
Unreal Engine (CrazyTown)
Intent-conditioned vs. no-intent (double-blind A/B)
Controlled test isolating the contribution of intent conditioning with the complete Dream2Assist framework
Physical platform (GRIP)
3
GRIP + VR Unreal (CrazyTown)
Intent-conditioned vs. no-intent
Feasibility demonstration of policy transfer to higher-fidelity motion platform; no retraining
Table 1: Overview of human-subjects studies. Each study used a specific system and interface configuration detailed in Table 2 .
Line by policy actions (alignment); color by accel/decel; windowed smoothing
Steering setpoint of human+policy; direct pedal blending
✓
GRIP platform ( N=3 )
✗
✓
✓
✓
As urban + longitudinal behaviors (stop/go rewards in Appendix B ). Y={left,right}×{go,slow,stop} .
✓ (traj. viz. only)
As urban validation
As urban; minimal parameter adjustment for platform hardware
✓
Table 2: Configuration reference for each study (see Table 1 for study overview). Sections III and IV describe all Dream2Assist components in full generality; this table records which were active and how they were configured in each deployment. ✓ = active; ✗ = not used. In Eval 1 , D2A refers to the configuration shown in the first row. D2A and D2A -Refined are used exclusively in Eval 2 . D2A -Full , D2A -NoIntent , and No-policy are used exclusively in Eval 3 and GRIP.
Str.
Turn
All
vs. Neutral
Question
M±SE
M±SE
M±SE
t(23)
p
AI knew my intent to pass ↑
5.49±.09
5.09±.13
5.33±.08
10.63
<.001 ***
AI helped me perform the maneuver ↑
4.01±.13
3.16±.14
3.67±.10
0.44
.666
AI’s action was safe ↑
4.55±.11
3.80±.14
4.25±.09
3.60
.002 **
Better off without AI ↓
4.82±.11
5.12±.12
4.94±.08
3.57
.002 **
Table 3: Post-drive survey ratings for Eval 1 ( N=24 ), Likert 1–7 (Neutral = 4). One-sample t -tests against neutral (two-tailed, df=23 ). ↑ higher is better; ↓ reverse-coded. *** p<.001 ; ** p<.01 . Straight vs. turn breakdowns: intent recognition higher on straights ( p=.001 ); helpfulness above neutral on straights ( p=.054 ) but below on turns ( p=.025 ); safety above neutral on straights ( p<.001 ) but not turns ( p=.057 ).
Outcome
Track
No-policy
D2A
Δ
M±SE
M±SE
Overtake Rate ↑
Straight
0.810±.034
0.899±.027
+8.9%
Turn
0.547±.058
0.274±.046
−27.3%
Spinout Rate ↓
Straight
0.146±.030
0.132±.030
−1.4%
Turn
0.293±.053
0.326±.048
+3.3%
Off-Track Rate ↓
Straight
0.073±.022
0.070±.023
−0.3%
Table 4: Behavioral Outcomes by Track Type: D2A vs. No-policy ( N=24 ). Values are proportions pooled over trials; the paired tests in the text use per-participant proportions.
Outcome
No-policy
D2A
Δ
M±SE
M±SE
Overtake Rate ↑
0.721±.031
0.630±.032
−9.0%
Spinout Rate ↓
0.195±.027
0.209±.027
+1.3%
Off-Track Rate ↓
0.088±.019
0.104±.020
+1.6%
Collision Rate ↓
0.014±.008
0.026±.011
+1.2%
Right-Side Pass
0.376±.037
0.465±.038
+8.9%
Table 5: Overall Behavioral Outcomes: D2A vs. No-policy ( N=24 ). Values are proportions pooled over trials; the paired tests in the text use per-participant proportions. Note that overall this initial policy inhibited the driver.
Metric
No-policy
D2A
Δ
M±SE
M±SE
Mean Overtake Speed (m/s) ↑
26.39±.29
26.27±.28
−0.13
Min Opp. Clearance (m) ↑
1.62±.10
1.77±.48
+0.14
Table 6: Overtake Quality Metrics: D2A vs. No-policy (Overtaking Trials Only). Values are means ± SE over overtaking trials.
Metric
Track
No-policy
D2A
Δ
M±SE
M±SE
Mean O/T Speed (m/s) ↑
Straight
27.89±.22
27.44±.22
−0.46
Turn
22.67±.51
21.06±.36
−1.62
Min Opp. Clearance (m) ↑
Straight
1.50±.11
1.97±.59
+0.47
Turn
1.99±.21
1.01±.22
−0.98
Table 7: Overtake Quality Metrics by Track Type: D2A vs. No-policy (Overtaking Trials Only)
Figure 5: Aligned minus misaligned AI steering per participant under D2A and D2A -Refined ( n=5 ; P106 excluded for missing steering data). Higher values mean more steering in the driver’s intended direction. Thin lines are participants, the thick line the mean; paired t -test p=.28 .
Figure 6: AI steering around overtake onset ( t=0 ), all participants and segments ( D2A : 52 passing events; D2A -Refined : 50). Top: steering magnitude. Bottom: signed steering. Lines show mean ± SEM; individual events dimmed.
Figure 7: Policy preferences between the initial vs. updated policy faceted by position where the overtake occurred.
Figure 8: Averaged torque traces for participant 03 in the oncoming car event. About 2.3 to 1.5 s before closest approach ( t=0 ), D2A -Full steers away from the oncoming car, in line with the driver’s avoidance, while D2A -NoIntent steers toward it (bottom trace). In the final second the pattern reverses: D2A -Full turns toward the car and D2A -NoIntent is near neutral.
Figure 9: (a) Overall torque alignment counts, (b) torque magnitude, as defined in Eq. ( 9 ), and (c) aligned torque, as defined in Eq. ( 10 ) for the oncoming car event, where each point represents one participant. Higher values indicate a higher average torque in alignment with the driver’s intent to pass left or right around the oncoming car. Lines connect each participant’s two conditions. Panel (a) counts all 12 sessions: P04, drawn hollow, has no D2A -NoIntent trials, and P12, excluded from the subjective analysis, is included. D2A -Full had more alignment events for 8 participants, tied for 2 and fewer for 1. Of the 11 participants with both conditions, 7 received higher overall torque under D2A -Full (b) and 8 experienced more intent-aligned torque (c).
Metric
D2A
D2A -Refined
Δ
p
M±SE
M±SE
Likability ↑
2.95±.42
3.31±.39
+.36
.108
Helpfulness ↑
2.80±.33
2.85±.20
+.05
.887
Table 8: Subjective ratings: D2A vs. D2A -Refined ( N=6 ). Likert 1–7. Paired t -tests ( df=5 ). This pilot targeted directional trends rather than statistical significance. Five out of six participants rated D2A -Refined to be higher on likability.
Metric
D2A -Full
D2A -NoIntent
Δ
p
M±SE
M±SE
Directionality ↑
4.92±.32
4.65±.29
+.27
.528
Timing ↑
5.10±.17
5.05±.30
+.05
.891
Adapting Dir. ↑
4.90±.36
4.55±.33
+.35
.368
Fight Dir. ↓
3.62±.48
3.62±.27
+.00
1.00
Safety ↑
4.38±.40
4.45±.23
−.07
.870
Table 9: Paired comparison of subjective ratings: D2A -Full vs. D2A -NoIntent ( N=10 ). Likert 1–7; Overall Rating 1–10. Two-tailed paired t -tests ( df=9 ); none reached significance. ↑ higher is better; ↓ lower is better (less resistance from AI). Participants qualitatively distinguished the two policies despite non-significant ratings (Sec. 6.4 ).
Participant
D2A -Full
D2A -NoIntent
Δ
P01
5.75
4.00
+1.75
P02
4.75
5.75
−1.00
P03
7.50
4.75
+2.75
P05
7.25
6.50
+0.75
P06
5.50
6.50
−1.00
P07
5.75
8.25
−2.50
Table 10: Per-Participant Overall Ratings: D2A -Full vs. D2A -NoIntent . Overall Rating on a 1-10 scale; values averaged across trials.
Figure 10: Two examples from GRIP experiments: an oncoming car scenario where lateral assistance can be observed (top) and a roundabout-approach scenario where longitudinal assistance is observed (bottom).
Appendix figures & tables14 assets
Supplementary material from the paper’s appendix.
Appendix
Component
Architecture
Output
Encoder qϕκ
MLP: 2 layers × 512 units
Input to posterior
Recurrent model fϕκ
GRU w/ LayerNorm, 512 hidden
htκ∈R512
Posterior qϕκ(zt∣ht,xt)
MLP: 1 layer × 512 units
ztκ (Cat. 32×32 )
Prior pϕκ(z^t∣ht)
MLP: 1 layer × 512 units
z^tκ (Cat. 32×32 )
Decoder pϕκ(x^t∣st)
MLP: 2 layers × 512 units
x^tκ (symlog MSE)
Reward head pϕκ(r^t∣st)
MLP: 2 layers × 512 units
symlog disc.
Appendix
Table 11: RSSM component architecture. All MLP layers use SiLU activations and LayerNorm. “Cat.” denotes a categorical distribution parameterized by logits.
Racing (CARLA)
Urban / GRIP
Num. agents in env
2
up to 10
Max. opponents in obs
1
3
Action repeat
2
2
Episode time limit
1000 steps
1000 steps
Observation components (ego-centric)
Ego state
position, velocity, heading (rel. to track)
Appendix
Table 12: Observation and action spaces by domain. All observations are expressed in the ego vehicle’s body frame.
Hyperparameter
Value
World model
Batch size
16
Sequence length
64
Train ratio
512
Learning rate
1×10−4
Optimizer
Adam ( ϵ=10−8 )
Appendix
Table 13: Training hyperparameters. All values are shared between the racing and urban configurations unless marked.
Parameter
Racing
Urban
Collision penalties
Inner collision
−5,000
−10,000
Outer collision
—
−10,000
Boundary violation
−100
−10,000
Intent rewards (human training)
Pass/left reward scale
10
αlat+
Appendix
Table 14: Key reward scalars by domain and training role. “Human” denotes training of FCP sub-populations; “AI” denotes training of the assistive policy.
Reward term
Type
Racing
Urban
GRIP
Collision Eq. ( 17 )
rtask
✓
✓
✓
Boundary Eq. ( 18 )–( 19 )
rtask
✓
✓
✓
Smoothness Eq. ( 20 )–( 21 )
rtask
✓
✓
✓
Speed / progress Eq. ( 22 )–( 23 )
rtask
✓
✓
✓
Finish-line bonus
rtask
✓
✗
✗
Pass / stay Eq. ( 12 )–( 14 )
ry
✓
✗
✗
Appendix
Table 15: Mapping of reward terms to the general framework (Eqs. ( 1 ) and ( 5 )) and to each domain. ✓ = active; ✗ = not used.
Name
Description
Domain
Platform
Policy Training
Real human data augmentation
20% of replay buffer replaced with relabeled real human driving data to reduce sim-to-real gap.
Racing Urban
Sim
FCP population diversity
Synthetic humans sampled at varying training checkpoints (suboptimal to optimal) to expose the assistant to diverse behaviors.
Racing Urban
Sim
Action smoothing
Causal moving-average (window =10 ) applied to synthetic human and AI outputs to suppress physically unrealistic jitter.
Racing Urban
Sim GRIP
Intent class re-balancing
Training reweights intent classes to prevent mode collapse toward a dominant intent.
Urban
Sim
Pass/stay reward restructuring
Bounded per-intent indicator reward plus speed progress term, capped to prevent single-mode collapse (Eq. ( 12 )–( 14 )).
Racing
Sim
Appendix
Table 16: Design variables and human factors considered in Dream2Assist , organized by category. Domain and platform indicate where each factor was actively applied. Factors marked (excluded) were considered but rejected during piloting.
Figure 11: Interfaces tested during iterative piloting for the racing domain, showing variations in trajectory line color, length, and style.
Figure 12: Final trajectory visualization used in Eval 3 (Urban Validation). Line length scales with assistance magnitude; green indicates acceleration, red indicates deceleration.
Figure 13: Driving flow for Eval 1 (Racing Characterization). Each block consists of two follow laps and two overtake-attempt laps, with difficulty increasing via a staircase design.
Figure 14: Per-participant overtake rate by track type, without and with the policy, in Eval 1 ( n=23 participants with both conditions). Thin lines are participants, colored by the direction of change; the thick line is the mean. p -values are paired t -tests.
Figure 15: Driving flow for Eval 3 (Urban Validation).
Figure 16: Averaged torque traces across all participants and all (a) straight and (b) turn trials for Eval 2 . On turns, D2A applies larger steering 4–3 s before overtake onset ( t=0 ) than D2A -Refined ; on straights the two are similar. Traces show raw signed steering, not steering relative to the driver’s intent.
Figure 17: Event-locked traces for the roundabout-approach scenario on GRIP, aligned to the roundabout-gate crossing ( t=0 ). Top: vehicle speed. Bottom: distance to the crossing vehicle. Lines show mean ± SEM with individual trials dimmed; n = trials per condition.
Figure 18: Averaged torque traces for selected participants in the oncoming car event in Eval 3 . Top: torque magnitude. Bottom: signed torque, positive away from the oncoming car (aligned with the driver’s avoidance). From 3 to 1.5 s before closest approach, D2A -Full is less misaligned than D2A -NoIntent for all seven participants shown; in the final second, D2A -Full is the more misaligned of the two for five of them (P01, P02, P03, P05, P12).
We introduce DreamFormer, a model-based agent that acquires language-conditioned, multi-task skills by imitating expert demonstrations within the latent imagination of a learned world model. DreamFormer first learns a task-agnostic Transformer world model from unstructured play data, then acquires task-specific behaviors by optimizing an intrinsic reward that aligns agent-generated rollouts with expert demonstrations in latent space. Since the policy is trained on-policy inside imagination, it is exposed to its own errors during training, mitigating the covariate shift inherent to offline behavioral cloning. To make long-horizon imagination affordable, DreamFormer encodes a high-resolution multi-view robotic observation into a single input token, avoiding both spatial downsampling and the multi-token representations used by prior Transformer world models. On the long-horizon CALVIN benchmark, DreamFormer outperforms LUMOS, the comparable model-based agent, on single-environment evaluation (2.52 vs 2.34 average tasks completed per chain of five) while keeping imagination rollouts tractable. Against HULC, the behavior cloning baseline, it nearly doubles performance on zero-shot transfer to an unseen environment (1.30 vs 0.67), indicating that dynamics learned by the world model transfer more readily than a directly cloned policy. This is consistent with the role attributed to internal models in biological agents, where a model of environment dynamics supports behavior in situations not previously encountered.
Mostafa Kotb, Cornelius Weber, Muhammad Burhan Hafez +1
Knowledge Technology Group, Department of Informatics, University of Hamburg, 20146 Hamburg, Germany · Mathematics Department, Faculty of Science, Aswan University, 81528 Aswan, Egypt · School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK
In cooperative multi-agent reinforcement learning (MARL), agents must coordinate with partners whose internal policies and intentions are not directly observable. While world models such as Dreamer have demonstrated strong generalization and sample efficiency in single-agent settings, their application to MARL remains limited by an inability to handle teammate-induced uncertainty. We propose a new perspective: treat teammates as structured, learnable components within the agent's world model. We introduce an architecture that factorizes the latent state of a Dreamer-style recurrent state-space model (RSSM) into environment and teammate components, and learns an auxiliary Theory-of-Mind (ToM) head to infer latent embeddings of partner behavior such as character, intent, and predicted actions from partial trajectories. These teammate latents condition the actor and critic, enabling the agent to imagine and adapt to diverse collaborators. We outline how this approach can support zero-shot and few-shot coordination in partially observable settings and propose a set of benchmarks and evaluation protocols to assess its impact. This work positions world models as not only predictors of environmental dynamics, but as simulators of social behavior, opening new directions for generalizable, human-compatible AI.
A common approach for shared autonomy blends human inputs with autonomous assistance based on the human's likely goal. However, most existing approaches assume that a static set of possible goals is known a priori, which limits the use of such methods in unstructured assistive settings. We instead investigate how to enable shared autonomy with open-ended and dynamically changing goals. We formulate goal-oriented shared autonomy as a particle filter in which particles represent candidate human goals. Unlike conventional approaches with a fixed goal set, our transition model dynamically proposes new candidate goals as the interaction evolves, and human actions update the belief over these goals in real time. We instantiate this framework with foundation models (e.g., vision grounding and large language models) that propose context-relevant semantic goals, generate goal-conditioned assistance from low-level skill primitives, and refine those skills from human corrections. We assess our approach through a user study where 12 participants perform a variety of tabletop manipulation tasks with our method and state-of-the-art shared autonomy baselines. The results show that our particle filter-based approach reduces the amount of time users spend teleoperating the system and improves user satisfaction. User study videos: https://youtu.be/Ii26XuRqm9c
Mengxue Fu, Ethan Xu, Sam Iyer-Singh +3
Collaborative Robotics Lab (Collab), Dept. of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061 · RT2 Lab, Dept. of Computer Science, UW-Madison