Finetuning Methods

This repo includes an implementation of some recent finetuning methods. Methods include:

• LP-FT
• Surgical Finetuning
• Disciriminitive Finetuning
• Feature Extraction

LP-FT

LP-FT is a method discussed in the paper Fine-Tuning can Distort Pretrained Features and Underperform Out-of-Distribution where the authors argue for finetuning the entire network only after having a trained linear probe. This theory follows from the idea that the pre-trained model already has a good feature extractor and we should strive for minimally disturbed extractors after finetuning. We can achieve this by the proposed method.

Surgical Finetuning

Surgical finetuning methods are region specific finetuning methods. These methods were discussed in the paper Surgical Fine-Tuning Improves Adaptation to Distribution Shifts. These methods were mainly used for domain adaptation. The two implemented methods found in Finetuning.ipynb are:

• Layer Specific finetuning
  • This method requires specifying the first and last layer from a list of available layers to finetune.
• AutoRGN
  • Automatically adjust the learning rate for each layer to be finetuned by its relative gradient norm with respect to all layers

Discriminitive Finetuning

Inspired by ULMFiT and a recent post on medium discussing layer specific learning rate decay and warm-up steps, we implement these methods in the Finetuning.ipynb notebook. The methods:

• Ramp up the learning rate from 0 to the initial learning rate specified in n epochs
• The learning rate is highest for the last layers and drops by %10 for each preceeding layer

Feature Extraction

In the Data_Visualization.ipynb notebook, we use the pre-trained model as a feature extractor and plot the features in a 2D space using UMAP. We additionally compute the representation similarity of different resizing methods (using different interpolations) using Centered Kernel Alignment (CKA).