Coherence Viewer: A Beginner’s Guide to Visualizing Model AttentionUnderstanding how large language models arrive at their outputs can feel like peering inside a black box. Coherence Viewer is a tool designed to make that process more transparent by visualizing where a model “looks” when it generates text. This guide explains what Coherence Viewer is, why model attention matters, how to use the viewer step-by-step, practical examples, common pitfalls, and next steps for deeper analysis.
What is Coherence Viewer?
Coherence Viewer is a visualization tool that maps model attention and intermediate signals to human-readable elements, helping researchers, engineers, and curious users inspect how a model processes input and constructs output. It typically displays attention weights, token-level activations, and other interpretability metrics across layers and heads, often aligned with the generated tokens or input context.
Why this matters: seeing which tokens influence a model’s decisions can help diagnose failure modes, reveal biases, verify that a model is using intended context, and guide fine-tuning and prompt design.
Key concepts you should know
- Attention: In transformer models, attention determines how much each token considers other tokens when computing its representation. Visualizing attention helps identify influential tokens.
- Heads and layers: Transformers are organized into layers, each with multiple attention heads. Different heads can specialize (e.g., syntactic relations, coreference).
- Tokens and subwords: Tokenizers split text into tokens; attention and activations are reported at the token level. Subword tokens can make visualization look fragmented.
- Sparsity vs. density: Attention matrices can be dense (many small weights) or sparse (few strong connections). Interpreting both patterns is important.
- Attribution vs. correlation: Attention weights correlate with influence, but they are not a perfect causal attribution. Coherence Viewer may combine attention with other metrics (gradients, integrated gradients, attention rollout) to strengthen claims.
Interface overview (typical components)
A Coherence Viewer UI generally includes:
- Token timeline: a horizontal sequence of input and output tokens.
- Attention matrix heatmaps: showing weights between tokens per head or averaged across heads.
- Layer/head selector: choose which layer or head to inspect.
- Token-focused pane: click a token to highlight incoming/outgoing attention.
- Aggregate views: mean attention across heads/layers, or focused diagnostics like attention to special tokens (e.g., [CLS], [SEP], or BOS).
- Additional diagnostics: gradient-based attributions, logit changes, or hidden-state similarity.
Step-by-step: How to use Coherence Viewer
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Prepare your example
- Choose an input prompt and model output you want to analyze.
- Keep examples focused (1–3 sentences) for clearer visual patterns; longer passages still work but are visually denser.
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Load data into Coherence Viewer
- Paste the prompt and generated text or load a saved inference trace (attention matrices, hidden states).
- Ensure you use the same tokenizer the model uses so tokens align with attention indices.
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Start at a high level
- View averaged attention across heads and layers to spot general patterns: is attention concentrated locally (nearby tokens) or globally (distant tokens)?
- Check which tokens receive the most attention overall.
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Drill down by layer and head
- Select individual layers to see how attention evolves from early to late layers.
- Inspect specific heads — some will show clear linguistic roles (e.g., copying, positional tracking, coreference).
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Token inspection
- Click a token in the timeline to highlight which source tokens it attended to most when produced.
- Compare attention during generation vs. attention during encoding (if model is encoder-decoder).
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Use attribution overlays
- If the viewer supports gradients or logit attribution, enable those to cross-check attention-based interpretations.
- Look for agreement between different attribution methods; strong agreement increases confidence.
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Save findings and iterate
- Export images or notes. Run additional prompts that vary a single factor (e.g., remove a specific token, rephrase) to test hypotheses about the model’s reliance on certain tokens.
Practical examples
Example 1 — Pronoun resolution
- Prompt: “Samantha gave her book to Jordan because she was leaving.”
- Use Coherence Viewer to inspect which tokens “she” attends to when the model resolves the pronoun. If attention strongly favors “Samantha,” that suggests the model resolves pronoun to Samantha; if it favors “Jordan,” the resolution differs.
Example 2 — Factual recall
- Prompt: “What year did the Apollo 11 mission land on the Moon?”
- Inspect whether the token generating the year attends to tokens in the prompt or to internal memory-like patterns. Strong attention to tokens like “Apollo 11” suggests retrieval conditioned on prompt; dispersed patterns may indicate memorized knowledge activation.
Example 3 — Hallucination diagnosis
- When a model asserts an incorrect fact, use the Viewer to see whether the model was attending to unrelated tokens or to prompt tokens that contain ambiguous phrasing. This can highlight prompt errors or model overconfidence.
Common pitfalls and how to avoid them
- Overinterpreting raw attention: attention is informative but not definitive; corroborate with other attribution methods.
- Tokenization confusion: subword tokens can split a word across multiple tokens; sum or aggregate attention across subwords when interpreting word-level behavior.
- Visualization bias: averaging attention hides specialized heads; always inspect both aggregate and specific-head views.
- Confirmation bias: form hypotheses before inspecting to avoid cherry-picking visual patterns that fit expectations.
Tips for clearer analyses
- Use minimal, controlled prompts to isolate behaviors.
- Compare multiple examples to detect consistent head specializations.
- Use contrastive prompts (small edits) and observe changes in attention and output to test causal influence.
- Aggregate across multiple runs or seeds to ensure patterns aren’t stochastic artifacts.
When to go beyond Coherence Viewer
Coherence Viewer is best for exploratory, human-interpretable inspection. For stronger causal claims or model editing, consider:
- Causal interventions (ablation of activations or attention).
- Fine-grained attribution methods (integrated gradients, influence functions).
- Probing classifiers trained on hidden states.
- Mechanistic analysis combining activation patching and causal experiments.
Resources and next steps
- Start by analyzing short prompts that highlight a behavior you care about (coreference, factual retrieval, token copying).
- Combine attention visualization with attributions (gradients, logits) to strengthen conclusions.
- If you find a problematic behavior, design controlled tests and, if possible, run causal interventions (disable a head, patch activations) to confirm responsibility.
Coherence Viewer makes model attention accessible and actionable: think of it as a microscope for transformer internals. Use it to generate hypotheses, guide debugging, and design experiments — but pair visual inspection with causal and quantitative methods before drawing firm conclusions.