---
language: en
license: mit
tags:
  - pytorch
  - alexnet
  - vgg16
  - squeeze-and-excitation
  - emotion-recognition
  - facial-expression
  - psychometrics
  - grad-cam
  - interpretability
datasets:
  - AffectNet
  - VGGFace2
  - ImageNet
metrics:
  - accuracy
  - rmse
  - cohens-d
model-index:
  - name: SE-AlexNet-L3-FaceBased-r32
    results:
      - task:
          type: facial-emotion-recognition
        dataset:
          name: AffectNet
          type: affectnet
        metrics:
          - type: accuracy
            value: "Best among SE variants"
---

# SE-AlexNet: Enhancing Face Perception via Dimension Reduction

A collection of 34 fine-tuned convolutional neural networks for studying how **Squeeze-and-Excitation (SE) modules** affect facial emotion recognition. This model zoo supports the psychophysical analysis pipeline described in the companion paper.

📦 **GitHub (Code & Analysis):** [SE-AlexNet](https://github.com/JyBmegan/SE-AlexNet) | [PsychometricFittingCurve](https://github.com/JyBmegan/PsychometricFittingCurve) | [GradCAM-ROI-SaliencyMapDecoder](https://github.com/JyBmegan/GradCAM-ROI-SaliencyMapDecoder)

---

## 1. Model Details

This repository contains weights for 5 model architectures, systematically varied across 3 experimental axes:

| Experimental Axis | Values |
|:---|:---|
| **Architecture** | AlexNet, VGG16, SE-AlexNet-L1, SE-AlexNet-L2, SE-AlexNet-L3 |
| **SE Reduction Ratio** ($r$) | 2, 4, 8, 16, 32 (applies to SE variants) |
| **Pre-training Basis** | **FaceBased** (VGGFace2) or **ObjectBased** (ImageNet) |

### Architecture Descriptions

| Model | SE Position | Key Characteristic |
|:---|:---|:---|
| **AlexNet** | None (baseline) | Standard 5-conv AlexNet, num_classes=11 |
| **SE-AlexNet-L1** | After last conv, before FC stack | SE on 256-channel feature maps |
| **SE-AlexNet-L2** | Between fc6 → fc7 | SE on 4096-dim feature vector, reduction fixed at 16 |
| **SE-AlexNet-L3** | As first element of classifier | **Best performing variant** — SELayer before fc6 |
| **VGG16** | None (benchmark) | Standard VGG16, num_classes=2 (binary Happy/Sad) |

> ⚠️ **Important note on SE-Location-2:** All 10 L2 variants share *identical* architecture (reduction=16). The `squeeze-{r}` label refers to a training/data configuration, not the architectural reduction ratio. This is preserved for reproducibility.

---

## 2. Intended Use

These models are designed for **visual feature interpretability analysis** in facial emotion recognition research. Specific use cases:

- **Psychophysical model comparison:** Compare model perceptual biases (Points of Subjective Equality, PSE) against human observers
- **Grad-CAM ROI analysis:** Visualize which facial regions (eyes, nose, mouth) different architectures attend to
- **Dimension reduction study:** Quantify how SE-based channel recalibration affects representational efficiency
- **Pre-training effect study:** Compare face-based (VGGFace2) vs. object-based (ImageNet) feature transfer

**Not intended for:** Production emotion recognition systems, clinical diagnosis, or surveillance applications. These are research models trained on controlled lab datasets.

---

## 3. Training Data

All models were fine-tuned on **AffectNet**, the largest facial expression dataset:

- **Training set:** 28,000 facial images (modified subset)
- **Validation set:** 1,000 facial images
- **Classes:** 8 basic emotions (Neutral, Happy, Sad, Surprise, Fear, Disgust, Anger, Contempt) — some variants use 11-class or binary labels
- **Preprocessing:** Standard ImageNet normalization (mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225])

**Pre-training sources:**
- **FaceBased:** VGGFace2 (faces only — captures facial identity features)
- **ObjectBased:** ImageNet-1K (general objects — captures generic visual features)

**Training hyperparameters:**
- Batch size: 128
- Learning rate: 1e-4 (Adam optimizer)
- Epochs: 40
- Frozen conv layers (transfer learning), only SE blocks + classifier trained

---

## 4. Evaluation & Performance

### Key Findings from Ablation Study

| Metric | Finding |
|:---|:---|
| **Best Architecture** | SE-AlexNet-L3 (SE block closest to classifier) |
| **Optimal Reduction** | $r=32$ consistently outperformed lower reductions |
| **Pre-training Effect** | Face-based pre-training improved emotion discrimination by ~12% over object-based |
| **ROI Attention** | SE models showed more focused attention on mouth and eye regions vs. baseline AlexNet |

### Psychophysical Benchmarking

Models were evaluated against human observers ($N=40$) in a 2AFC Happy/Sad discrimination task:

- **Metric:** RMSE between model PSE and human PSE distribution
- **Statistical tests:** One-sample t-tests, Cohen's *d* effect sizes
- **Full results:** See [PsychometricFittingCurve](https://github.com/JyBmegan/PsychometricFittingCurve) repository

---

## 5. How to Get Started

### Installation

```bash
pip install -r requirements.txt
```

### Quick Start — Forward Pass in 10 Lines

```python
from inference import SEModelPipeline

# Load the best model (SE-Location3, FaceBased, r=32)
pipe = SEModelPipeline('se-location3/facebased/squeeze-32')

# Run inference
probs = pipe.predict('path/to/face_image.jpg')
print(f'Prediction shape: {probs.shape}')  # (1, 11)
```

### List Available Models

```python
import os, json

for root, dirs, files in os.walk('.'):
    if 'config.json' in files:
        with open(os.path.join(root, 'config.json')) as f:
            cfg = json.load(f)
        print(f"{root}: {cfg['model_type']} | {cfg['pretraining']} | {cfg.get('reduction', 'N/A')}")
```

### Load a Specific Model Programmatically

```python
import json
from modeling import load_model_from_config

# Load config
with open('se-location3/facebased/squeeze-32/config.json') as f:
    config = json.load(f)

# Build model with weights
model = load_model_from_config(
    config,
    weights_path='se-location3/facebased/squeeze-32/model.safetensors',
    device='cpu'
)

# Forward pass
import torch
x = torch.randn(1, 3, 224, 224)  # dummy input
output = model(x)
```

### Use for Grad-CAM Visualization

```python
from modeling import load_model_from_config
import json

# Load any model
with open('se-location3/facebased/squeeze-32/config.json') as f:
    config = json.load(f)
model = load_model_from_config(
    config,
    'se-location3/facebased/squeeze-32/model.safetensors'
)

# Target the last conv layer for Grad-CAM
target_layer = model.features[-3]  # Last Conv2d in features
# ... apply standard Grad-CAM pipeline
```

---

## 6. Repository Structure

```
SE-AlexNet/
├── README.md                    # This Model Card
├── requirements.txt             # Python dependencies
├── modeling.py                  # Exact model architecture definitions
├── inference.py                 # Universal inference pipeline
├── convert_weights.py           # .pth → .safetensors conversion script
├── generate_configs.py          # Config file generator
│
├── alexnet/                     # Standard AlexNet baseline
│   ├── facebased/
│   │   ├── config.json
│   │   └── model.safetensors
│   └── objectbased/
│       ├── config.json
│       └── model.safetensors
│
├── vgg16/                       # VGG16 benchmark
│   ├── facebased/
│   └── objectbased/
│
├── se-location1/                # SE after all convolutions
│   ├── facebased/
│   │   ├── squeeze-2/ → squeeze-32/  (5 reduction ratios)
│   └── objectbased/
│       └── squeeze-2/ → squeeze-32/
│
├── se-location2/                # SE between fc6 → fc7
│   ├── facebased/
│   └── objectbased/
│
└── se-location3/                # SE in classifier (BEST)
    ├── facebased/
    └── objectbased/
```

---

## 7. Citation & Related Repositories

### Companion Code Repositories

| Repository | Role | Link |
|:---|:---|:---|
| **SE-AlexNet** | Training code, ablation scripts, raw results | [GitHub](https://github.com/JyBmegan/SE-AlexNet) |
| **PsychometricFittingCurve** | MATLAB psychometric curve fitting, PSE calculation, human comparison | [GitHub](https://github.com/JyBmegan/PsychometricFittingCurve) |
| **GradCAM-ROI-SaliencyMapDecoder** | Grad-CAM heatmap generation & ROI statistical decoding | [GitHub](https://github.com/JyBmegan/GradCAM-ROI-SaliencyMapDecoder) |

### Technical Architecture

SE-AlexNet extends the classic AlexNet by inserting Squeeze-and-Excitation blocks at strategic locations:

- **Squeeze:** Global Average Pooling compresses spatial information into channel descriptors
- **Excitation:** A bottleneck MLP learns channel-wise scaling factors
- **Recalibration:** Feature maps are re-weighted by learned importance scores

The three location variants test the hypothesis that SE blocks are most effective when placed closer to the decision boundary (classifier), where channel-wise feature importance directly impacts classification.

---

## 8. Limitations

- **Dataset bias:** Trained only on AffectNet (posed + spontaneous expressions). Performance may degrade on in-the-wild or cross-cultural expressions.
- **Image resolution:** Input fixed at 224×224. Smaller or lower-quality faces may reduce accuracy.
- **Binary vs. Multi-class:** VGG16 models use binary classification (Happy/Sad); AlexNet/SE variants use 8-11 classes. Not directly comparable without task alignment.
- **Transfer learning only:** Convolutional layers are frozen. Models are not trained end-to-end from scratch.
- **Architecture age:** AlexNet and VGG16 are now classic architectures. These models are for scientific comparison, not state-of-the-art emotion recognition.

---

## 9. License

MIT License. See companion GitHub repositories for full license details.

---

*Trained weights converted from original PyTorch .pth checkpoints. For questions about the training methodology or experimental design, please refer to the companion paper and GitHub repositories.*