We propose to finetune vision-language models to generate more pragmatically optimal referring expressions by transforming observations of incremental listener comprehension, in the form of gaze scanpaths, into learning signals. During training, referring expressions are sampled from the speaker policy being optimized, conditioned on images and target referents; then, a neural listener estimating human gaze behavior maps from images and sampled referring expressions to scanpaths, each represented by a sequence of fixations, with each fixation corresponding to a word in the referring expression. We experiment with several approaches to convert fixation sequences and target referents into token- and sequence-level rewards, which are used to optimize policy parameters. Through evaluation with human listeners, we find that speaker policies trained with gaze-estimating listeners result in significantly more pragmatically-optimal references than base models, reducing sequence length from 15.4 down to 4.0 words while increasing referential success from 75.2 up to 80.0%. Our work demonstrates a promising opportunity for learning to generate utterances through language-based interaction, not only from the explicit signal of communicative success, but also from implicitly-available observations of a listener's process of comprehension.
Figures & tables
Figure 1: Learning to refer from interaction with incremental listeners. During training, we iterate between (a) deploying a speaker policy πθS in a reference game with a listener policy πG , which is trained to estimate gaze behavior of human listeners, and (b) updating the speaker policy by transforming observations of listener gaze behavior to rewards.
Speaker
dπs (Human) ↓
dπs (Qwen) ↓
Acc. ↑
Length
Time to target (s) ↓
Molmo
1.41
1.41
75.2
15.4
0 8.22
Gaze-BeforeFirstHit
1.11
0.81
73.3
0 4.2
0 4.86
Gaze-SeqAnyHit
0.88
0.95
80.0
0 9.5
0 7.04
Gaze-SeqLPHit
1.07
1.03
77.7
11.0
0 8.29
Gaze-Shaping
0.99
0.87
75.5
0 4.0
0 5.13
REC-BeforeFirstHit
1.49
0.99
66.8
0 2.0
0 3.98
Table 1: Human evaluation averaged over all datasets with dπs from Qwen2.5-VL for comparison. Time to target refers to the average time after speech onset when the human evaluators can accurately identify the target by clicking on it.
Figure 2: Comparison of communicative success and average reference length in words with human and Qwen2.5-VL listeners with 95% confidence ellipses.
Figure 3: Examples of generated referring expressions conditioned on an image and bounding box from several different speaker policies. See Appendix D for examples from all speaker models.
Figure 4: Comparison of referential strategies utilized by different speakers. The keywords used for this analysis can be found in Appendix D.1 .
Appendix figures & tables23 assets
Supplementary material from the paper’s appendix.
Appendix
Figure 5: Example of the iterative gaze prediction for gold and finetuned Molmo. The orange sequence represents the human scanpath and the blue is that produced by our gaze predictor model. Each point indicates the location of the gaze and the word heard at the time the fixation was recorded.
Word Index
Molmo Avg Dist
ART Avg Dist
0
4.25
4.43
1
12.17
9.81
2
12.85
12.56
3
13.59
14.08
4
12.10
11.56
5
12.77
13.11
Appendix
Table 2: Average Euclidean distance per word index and total sum of distances, averaged over all gold sequences.
Word Index
Molmo Avg Dist
ART Avg Dist
0
2.04
2.01
1
10.56
6.59
2
8.63
6.54
3
9.92
8.56
4
9.39
7.70
5
11.78
9.99
Appendix
Table 3: Average Euclidean distance per word index and total sum of distances, using the closest gold path (Best Match).
Figure 6: (A) Comparison of length distributions of human and Molmo-generated references, (B) accuracy of the gaze predictor on human-generated (blue) and Molmo-generated references (red) over different reference lengths, and (C) comparison of the proportion of words not assigned fixations.
Speaker
Acc. ↑
Length
Time (s) ↓
dπs↓
RefCOCO testA
Human (Gold)
95.67
0 3.59
0 3.97
0.00
Molmo
84.17
15.15
0 7.99
1.41
REC-BeforeFirstHit
68.50
0 2.01
0 4.23
2.37
REC-SeqAnyHit
93.17
25.27
11.40
1.89
REC-Success
93.50
18.58
0 9.21
1.31
Appendix
Table 4: Full human evaluation results by dataset.
Figure 11
Speaker
Time (s) ↓
Reveal Rate ↓
Early Click Rate ↓
Overall
Human (Gold)
0 3.87
0.03
0.05
Molmo
0 8.22
0.05
0.27
REC-BeforeFirstHit
0 3.98
0.04
0.04
REC-SeqAnyHit
11.26
0.05
0.45
REC-Success
0 8.79
0.03
0.41
Appendix
Table 5: Behavioral efficiency metrics grouped by dataset, including overall averages.
Speaker
Acc. ↑
Length
dπs↓
RefCOCO testA
Human (Gold)
94.60
0 3.51
0.00
Molmo
48.20
15.71
1.41
REC-BeforeFirstHit
40.07
0 3.03
1.18
REC-SeqAnyHit
60.20
25.81
1.97
REC-Success
62.85
20.27
1.53
Appendix
Table 6: QwenVL-based evaluation results by dataset.
Speaker
Acc. ↑
Length
dπs↓
Overall (Averaged)
Molmo
45.65
16.35
1.41
REC-BeforeFirstHit
46.18
0 3.05
0.99
REC-SeqAnyHit
57.96
25.29
1.84
REC-Success
61.94
19.70
1.41
REC-Shaping
52.12
0 5.17
0.86
Appendix
Table 7: QwenVL-based evaluation results averaged across all datasets.
Figure 7: Comparison of REC results with QwenVL and CogVLM-Grounding.
Figure 8: Comparison of Gaze-BFH training performance with and without the KL penalty. Red shows training with a KL penalty ( β=0.02 ) and blue shows the ablated training run. For comparison, we include Molmo and human speakers in the rightmost chart.
Speaker
Acc. ↑
Length
dπs↓
Overall (Averaged)
Molmo
45.65
16.35
1.41
REC-BeforeFirstHit
46.18
0 3.05
0.99
REC-SeqAnyHit
57.96
25.29
1.84
REC-Success
61.94
19.70
1.41
REC-Shaping
52.12
0 5.17
0.86
Appendix
Table 8: QwenVL-based evaluation comparing standard models against the length-penalized REC-Success variant.
Speaker
Acc. ↑
Length
dπs↓
Overall (Averaged)
Molmo
45.65
16.35
1.41
REC-BeforeFirstHit
46.18
0 3.05
0.99
REC-SeqAnyHit
57.96
25.29
1.84
REC-Success
61.94
19.70
1.41
REC-Shaping
52.12
0 5.17
0.86
Appendix
Table 9: Evaluation comparing speakers trained on full incremental gaze versus models predicting only the final gaze point.
Speaker
Acc. ↑
Length
dπs↓
Overall (Averaged)
Molmo
45.65
16.35
1.41
REC-BeforeFirstHit
46.18
0 3.05
0.99
REC-SeqAnyHit
57.96
25.29
1.84
REC-Success
61.94
19.70
1.41
REC-Shaping
52.12
0 5.17
0.86
Appendix
Table 10: Performance comparison when training the speaker against a listener finetuned directly on RefCOCO.
Speaker
Acc. ↑
Length
dπs↓
Overall (Averaged)
Molmo
45.65
16.35
1.41
REC-BeforeFirstHit
46.18
0 3.05
0.99
REC-SeqAnyHit
57.96
25.29
1.84
REC-Success
61.94
19.70
1.41
REC-Shaping
52.12
0 5.17
0.86
Appendix
Table 11: Comparison of Supervised Finetuning (SFT) baselines and SFT+RL hybrid models against the default RL/Gaze speakers.
Speaker
Acc. ↑
Length
dπs↓
Human (Gold)
88.98
0 3.52
0.00
Molmo-7B
Molmo
45.65
16.35
1.41
REC-BeforeFirstHit
46.18
0 3.05
0.99
REC-SeqAnyHit
57.96
25.29
1.84
REC-Success
61.94
19.70
1.41
Appendix
Table 12: Cross-architecture evaluation using LLaVA-1.5-7B and PaliGemma-3B as speaker backbones.
Figure 9: Mention frequency of the red bounding box across speaker models.
Figure 10: Analysis of ambiguity and incorrect reference rates across four selected speaker models.
Figure 11: Examples of generated references from all speaker models.
Speaker Model
Gaze Retention Rate (%)
REC-Success
100.0%
REC-BFH
90.6%
REC-Shaping
90.4%
REC-SeqAnyHit
85.7%
Gaze-Shaping
54.3%
Gaze-SeqLPHit
52.8%
Appendix
Table 13: Gaze trajectory retention metrics across speaker model configurations, demonstrating post-hit retention across reward setups.
Speaker Model
Mid-Ref Period Rate (%) ↓
Double Space Rate (%) ↓
Mean Periods
Molmo
18.58
0 0.00
1.22
REC-BeforeFirstHit
0 0.78
0 0.00
0.02
REC-Shaping
0 6.93
53.17
0.84
REC-Success
17.12
0 0.00
1.20
REC-SeqAnyHit
39.31
0 0.00
1.46
Gaze-BeforeFirstHit
0 0.52
0 0.00
0.04
Appendix
Table 14: Frequency of mid-reference period punctuation, double spacing, and mean period counts across speaker model configurations.
Speaker Model
Coordinate Occurrence Rate (%) ↓
Molmo
0.00%
REC-BeforeFirstHit
0.78%
REC-Shaping
0.02%
REC-Success
0.00%
REC-SeqAnyHit
0.01%
Gaze-BeforeFirstHit
0.00%
Appendix
Table 15: Frequency of coordinate artifact occurrences across speaker model outputs.