Computational Cognitive

Neuroscience LabToday: Second session

Computational Cognitive Neuroscience Lab

» Today:» Homework is due Friday, Feb 10» This homework has more projects than

the last, but fewer questions per project

Bias Weights» Why do we have them?» Why are some higher than others

in the transform project?

Local vs. Distributed Representations

» Counting on your fingers--how high can you count??

» 10, using a localist representation» Using a distributed representation,

such as a binary code, we can count to 1024!

What is clamping?» An analogy to cellular physiology,

where electrodes are inserted into cells to control the membrane potential

» Types of clamps: current clamp, voltage clamp

» Clamping just means to externally force a state upon the cell

Bidirectional connectivity» What we have seen so far: bottom-

up, or stimulus-driven excitation» Now: top-down, or hypothesis-

driven excitation» What does top-down mean?

Imagine

What does top-down mean?

» Customary terminology: bottom is stimulus, top is a brain-state

» Bottom-up: think about a loud noise that makes you jump

» Top-down: What if you knew to expect a loud noise? That expectation might make you jump less when you finally hear it

Inhibition» Benefits» Mechanisms» K-winners-take-all» Sparse, distributed codes