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Cross-Model Circuit Analysis: Gemini vs. Gemma Comparison Framework

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by

Dan Petrovic
in , ,

1. Introduction

Understanding the similarities and differences in how different large language models represent and prioritize brand information can provide crucial insights for developing robust, transferable brand positioning strategies. This framework outlines a systematic approach for comparative circuit analysis between Google’s Gemini and Gemma model families, with the goal of identifying universal brand-relevant circuits and model-specific mechanisms.

2. Research Objectives

The cross-model analysis aims to answer several key questions:

  1. Circuit Universality: To what extent do brand-relevant circuits exist across different model architectures?
  2. Architectural Influences: How do architectural differences between Gemini and Gemma affect brand representation and mention patterns?
  3. Transfer Learning: Can insights from one model’s circuits be effectively applied to optimize prompting strategies for the other?
  4. Robustness Assessment: Which brand positioning strategies exhibit cross-model stability versus model-specific effectiveness?

3. Methodological Framework

3.1 Parallel Instrumentation

Implement consistent activation capture across both model families:

# Setup for parallel model instrumentation
def setup_dual_model_analysis():
    # Load models
    gemini_model = AutoModelForCausalLM.from_pretrained("google/gemini-1.5-pro")
    gemma_model = AutoModelForCausalLM.from_pretrained("google/gemma-3-instruct")
    
    # Initialize tokenizers
    gemini_tokenizer = AutoTokenizer.from_pretrained("google/gemini-1.5-pro")
    gemma_tokenizer = AutoTokenizer.from_pretrained("google/gemma-3-instruct")
    
    # Create activation dictionaries
    gemini_activations = {}
    gemma_activations = {}
    
    # Register parallel hooks for both models
    for i, layer in enumerate(gemini_model.model.layers):
        # Attention hooks
        layer.self_attn.q_proj.register_forward_hook(
            lambda mod, inp, out, i=i: hook_fn(mod, inp, out, f"layer_{i}_q_proj", gemini_activations)
        )
        # (Additional hooks)
    
    for i, layer in enumerate(gemma_model.model.layers):
        # Parallel hooks with same naming convention
        layer.self_attn.q_proj.register_forward_hook(
            lambda mod, inp, out, i=i: hook_fn(mod, inp, out, f"layer_{i}_q_proj", gemma_activations)
        )
        # (Additional hooks)
    
    return {
        "gemini": {
            "model": gemini_model,
            "tokenizer": gemini_tokenizer,
            "activations": gemini_activations
        },
        "gemma": {
            "model": gemma_model,
            "tokenizer": gemma_tokenizer,
            "activations": gemma_activations
        }
    }

3.2 Standardized Testing Protocol

Develop a controlled testing environment that ensures fair comparison:

  1. Prompt Normalization:
    • Standardize prompt formatting across models
    • Account for different instruction formats and system prompts
    • Create template mapping for equivalent prompting across models
  2. Activation Normalization:
    • Normalize activation values to account for scaling differences
    • Implement layer mapping between architectures (if layer counts differ)
    • Establish dimension alignment for neural activations
  3. Output Normalization:
    • Standardize token probability distributions
    • Normalize brand mention metrics
    • Implement consistent evaluation framework

3.3 Parallel Circuit Analysis

Conduct symmetrical analysis across both models:

  1. Identification Phase:
    • Run identical prompt sets through both models
    • Capture activation patterns for brand-mention and non-mention cases
    • Identify candidate circuits in each model independently
  2. Comparative Analysis:
    • Map corresponding neurons and attention heads between models
    • Calculate similarity metrics between activation patterns
    • Identify functionally equivalent circuits across architectures
# Example: Comparing attention head importance across models
def compare_attention_heads(gemini_data, gemma_data, brand_mention_positions):
    results = {}
    
    # Calculate head importance scores for both models
    gemini_scores = calculate_head_importance(gemini_data, brand_mention_positions)
    gemma_scores = calculate_head_importance(gemma_data, brand_mention_positions)
    
    # Compare distribution of important heads
    for layer_idx in range(min(len(gemini_scores), len(gemma_scores))):
        gemini_layer = gemini_scores[layer_idx]
        gemma_layer = gemma_scores[layer_idx]
        
        # Calculate correlation between head importance patterns
        correlation = scipy.stats.spearmanr(
            [gemini_layer[i] for i in range(len(gemini_layer))],
            [gemma_layer[i] for i in range(len(gemma_layer))]
        ).correlation
        
        results[f"layer_{layer_idx}_correlation"] = correlation
    
    return results

3.4 Intervention Transfer Testing

Test the transferability of circuit interventions:

  1. Cross-Model Patching:
    • Identify high-influence neurons in model A
    • Locate corresponding neurons in model B
    • Test whether similar interventions on these neurons produce similar effects
  2. Strategy Transfer:
    • Develop optimized prompting strategies based on model A’s circuits
    • Test effectiveness of these strategies on model B
    • Measure transfer performance ratio
# Example: Testing transfer of neuron importance
def test_neuron_importance_transfer(source_model_data, target_model_data, brand_positions):
    # Identify top neurons in source model
    source_neurons = find_brand_relevant_neurons(
        source_model_data["activations"], 
        brand_positions
    )[:20]  # Top 20 neurons
    
    # Map to corresponding neurons in target model
    # (This could use various mapping techniques - position, activation pattern, etc.)
    target_neurons = map_neurons_between_models(
        source_neurons,
        source_model_data["architecture"],
        target_model_data["architecture"]
    )
    
    # Test intervention on source model neurons
    source_results = patching_experiment(
        source_model_data["model"],
        source_model_data["tokenizer"],
        test_prompts,
        source_neurons
    )
    
    # Test intervention on mapped target model neurons
    target_results = patching_experiment(
        target_model_data["model"],
        target_model_data["tokenizer"],
        test_prompts,
        target_neurons
    )
    
    # Calculate transfer ratio
    transfer_ratio = calculate_effect_similarity(source_results, target_results)
    
    return {
        "source_neurons": source_neurons,
        "target_neurons": target_neurons,
        "source_effect": source_results["effect_size"],
        "target_effect": target_results["effect_size"],
        "transfer_ratio": transfer_ratio
    }

4. Analysis Dimensions

4.1 Architectural Comparison

Analyze how architectural differences affect brand circuits:

  1. Layer Distribution Analysis:
    • Compare at which relative depth brand-relevant circuits emerge
    • Analyze how information flows through the networks
  2. Attention Mechanism Comparison:
    • Compare multi-head attention patterns between models
    • Analyze differences in entity tracking mechanisms
  3. Feedforward Network Analysis:
    • Compare neuron specialization patterns
    • Identify differences in concept representation

4.2 Token Representation Analysis

Examine how brand tokens are represented:

  1. Embedding Space Comparison:
    • Compare brand token embeddings between models
    • Analyze neighborhood relationships in embedding space
  2. Contextual Representation:
    • Compare how brand representations evolve through layers
    • Analyze context integration patterns
# Example: Comparing brand token representations
def compare_brand_representations(gemini_data, gemma_data, brand_name):
    gemini_token_id = gemini_data["tokenizer"].encode(brand_name)[0]
    gemma_token_id = gemma_data["tokenizer"].encode(brand_name)[0]
    
    # Get embedding layer representations
    gemini_embedding = gemini_data["model"].transformer.wte.weight[gemini_token_id].detach()
    gemma_embedding = gemma_data["model"].transformer.wte.weight[gemma_token_id].detach()
    
    # Compare embedding similarity
    embedding_similarity = cosine_similarity(gemini_embedding, gemma_embedding)
    
    # Compare contextual representations across layers
    layer_similarities = []
    for layer_idx in range(min(gemini_data["num_layers"], gemma_data["num_layers"])):
        # Get contextual representations for this layer
        gemini_contextual = gemini_data["contextual_reps"][layer_idx][0, gemini_token_pos]
        gemma_contextual = gemma_data["contextual_reps"][layer_idx][0, gemma_token_pos]
        
        # Calculate similarity
        similarity = cosine_similarity(gemini_contextual, gemma_contextual)
        layer_similarities.append(similarity)
    
    return {
        "embedding_similarity": embedding_similarity,
        "layer_similarities": layer_similarities
    }

4.3 Prompt Response Analysis

Compare how prompts trigger brand mentions:

  1. Threshold Comparison:
    • Analyze differences in brand mention thresholds
    • Compare completion trajectory patterns
  2. Linguistic Trigger Analysis:
    • Identify which linguistic patterns work consistently across models
    • Catalog model-specific linguistic triggers
  3. Brand Context Analysis:
    • Compare contexts in which brands appear
    • Analyze sentiment and positioning differences

5. Implementation Strategy

5.1 Technical Setup

  1. Unified Testing Platform:
    • Develop standardized testing infrastructure
    • Implement consistent metrics and evaluation
  2. Parallel Computing Framework:
    • Setup efficient parallel processing
    • Implement synchronized experiment execution
  3. Visualization Dashboard:
    • Create comparative visualization tools
    • Implement side-by-side circuit analysis views

5.2 Experimental Design

  1. Comprehensive Prompt Matrix:
    • Design a systematic matrix of prompt variations
    • Cover diverse domains, styles, and structures
  2. Controlled Variable Testing:
    • Isolate specific variables for testing
    • Implement factorial experimental design
  3. Statistical Validation:
    • Implement rigorous statistical testing
    • Control for multiple comparisons

6. Expected Insights

6.1 Universal Brand Circuits

Identify circuit patterns that appear consistently across models:

  1. Common Attention Mechanisms:
    • Entity-tracking attention heads
    • Category-instance relationship patterns
  2. Shared Neuron Functionalities:
    • Quality assessment neurons
    • Domain expertise neurons
  3. Cross-Architectural Patterns:
    • Common information processing sequences
    • Shared decision boundaries

6.2 Model-Specific Mechanisms

Catalog differences in how models process brand information:

  1. Architectural Influences:
    • How scaling differences affect brand representation
    • Impact of training methodology on brand preferences
  2. Specialization Differences:
    • Model-specific circuit organizations
    • Unique brand-evaluation pathways
  3. Contextual Integration Patterns:
    • Differences in how brands are integrated into responses
    • Variations in contextual appropriateness judgments

6.3 Applied Strategy Implications

Develop practical insights for brand positioning strategies:

  1. Cross-Model Prompt Templates:
    • Design prompts that work effectively across model families
    • Identify universal linguistic triggers
  2. Model-Specific Optimization Guidelines:
    • Create targeted strategies for each model
    • Leverage unique architectural features
  3. Robustness Planning:
    • Develop approaches that maintain effectiveness across model versions
    • Create adaptive prompt strategies

7. Case Study: Luxury Brand Positioning

To illustrate this cross-model approach, consider a case study for a luxury fashion brand:

7.1 Initial Findings

  1. Common Circuits:
    • Both models showed strong luxury-category circuits in middle layers
    • Quality assessment neurons appeared in similar relative positions
    • Brand-category association mechanisms showed high similarity
  2. Key Differences:
    • Gemini showed stronger sensitivity to brand heritage signals
    • Gemma exhibited more pronounced price-quality association circuits
    • Contextual appropriateness thresholds differed significantly

7.2 Optimized Cross-Model Strategy

Based on these insights, an optimized strategy might include:

  1. Universal Elements:
    • Quality-signaling terminology that activates shared circuits
    • Category framing that works across models
  2. Model-Specific Adjustments:
    • Heritage emphasis for Gemini-optimized prompts
    • Value proposition emphasis for Gemma-optimized prompts
  3. Adaptive Components:
    • Dynamic adjustment based on detected model features
    • Flexible positioning elements

8. Future Research Directions

8.1 Longitudinal Analysis

Track circuit evolution across model versions:

  1. Version Comparison:
    • Compare circuit stability across model updates
    • Track emergence and disappearance of brand-relevant circuits
  2. Training Influence Analysis:
    • Analyze how different training approaches affect brand circuits
    • Identify relationships between training data and brand positioning

8.2 Extended Model Coverage

Expand analysis to additional model families:

  1. Architecture Comparison:
    • Extend to different architectural families (e.g., Llama, Claude, Mistral)
    • Identify architecture-specific versus universal patterns
  2. Scale Comparison:
    • Compare circuit development across model scales
    • Analyze emergence of brand circuits as function of parameter count

8.3 Multi-Modal Extension

Expand analysis to multi-modal models:

  1. Text-Image Integration:
    • Analyze how brand circuits connect with visual processing
    • Identify cross-modal brand representation patterns
  2. Multi-Modal Prompt Optimization:
    • Develop strategies for optimizing brand presence in multi-modal outputs
    • Identify synergies between textual and visual brand positioning

9. Conclusion

Comparative circuit analysis between Gemini and Gemma models offers unprecedented insights into how language models process and represent brand information. By identifying both universal and model-specific circuits, this approach enables the development of robust, transferable brand positioning strategies while highlighting model-specific optimization opportunities.

This framework not only advances our understanding of language model mechanics but also provides practical tools for brand strategists navigating an increasingly AI-mediated information landscape. As language models continue to evolve and diversify, cross-model circuit analysis will become an essential component of effective digital brand strategy.

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