Feature Analysis of Unsupervised Learning for Multi-task Classification Using Convolutional Neural Network

Abstract

This study analyzes the characteristics of unsupervised feature learning using a convolutional neural network (CNN) to investigate its efficiency for multi-task classification and compare it to supervised learning features. We keep the conventional CNN structure and introduce modifications into the convolutional auto-encoder design to accommodate a subsampling layer and make a fair comparison. Moreover, we introduce non-maximum suppression and dropout for a better feature extraction and to impose sparsity constraints. The experimental results indicate the effectiveness of our sparsity constraints. We also analyze the efficiency of unsupervised learning features using the t-SNE and variance ratio. The experimental results show that the feature representation obtained in unsupervised learning is more advantageous for multi-task learning than that obtained in supervised learning.