The list was put together by Cal Tech’s Computation and Neural Systems department, and the questions are ones that they expect PhD students ought to be able to answer. This can serve two purposes, either testing yourself to make sure that you are up to speed, or testing other people to weed out imposters! Here are some of my favorite questions:
- Discuss the major features of at least two very different nervous systems (i.e. jellyfish, locust, lamprey, octopus, owl, rat, monkey). In what ways might the features of each system affect neural processing?
- Describe and discuss the two principal models of individual neurons (integrate-and-fire and mean-rate neurons). What assumptions do they make about encoding. In what way are they faithful to real neurons and how do they fall short?
- Consider a surprising visual stimulus in your animal of choice. How quickly will information arrive at various places in the brain, and what implications does this have for neural coding?
- What do you know about population coding in subcortical (e.g. superior colliculus) or cortical structures? Why would the nervous system use population rather than single cell coding? How would cross-correlation among cells affect this?
- Define a “psychometric curve.” How would it look for a spatial hyperacuity task? Can you explain the performance of the system on dot-discrimination and line-alignment (Vernier) tasks in terms of the mechanisms of the retina and the primary visual cortex?
- Discuss the role of the nonlinearity in multi-layer neural networks. Compare thresholding versus soft sigmoidal functions and bump functions in terms of network function and learning capability.
- We can read everywhere that the brain is a “complex adaptive system”. What is meant by this vague statement? Give at least two formal definitions of complexity.
- A person rolls two fair dice and records the total number of points. You can ask a sequence of yes/no questions to find out this number. The answer to a question may affect your choice of the following questions. Devise and justify a strategy that achieves the minimum possible average number of questions.
These questions are non-trivial. The last one especially is a mind bender and a fun one at that. Perhaps I will look for the answers and blog some of them; that would be an educational experience all around.