Ideas for next step of Machine Learning
I would suggest you to check this excellent presentation by Li Deng (Microsoft Research). Many of the slides contain references to relevant research papers and even several interesting books on the topics of interest (it should be pretty easy to find). It might be also helpful to check references, listed in this research paper by Prof. Andrew Ng and his colleagues at Baidu Research. Finally, a focused Internet search will provide you with comprehensive list of resources for further research.