Assignment 1: The basics of the brain: the numbers, the basics of neural firings, reaction times, etc.
Assigned Tuesday, 1/29.
Due Tuesday, 2/5 by 5pm - submit electronically.
Part A. Online reaction time experiments.
You will test your reaction time for a number of related visual tasks, at the web site http://www.uwm.edu/~johnchay/. This site requires Adobe Shockwave Player, available at http://www.adobe.com/shockwave/download/. If you have difficulty getting Shockwave working with this site from the computer you normally use, the Macs in Soda 349 are set up to work fine.
Your assignment involves Experiment A4, visual search. First compare your average reaction time (10 trials) for finding a black T in black L's when there are 5 versus 30 distractors. As you would expect, we are rather slower with more distractors. Now do the same comparison on trials each with a red T among (5 or 30) black L's. (Note: all told, you will have done 4 experiments, each with 10 trials.)
Note: you may have a hard time finding the file created by running a 10-trial experiment. In our experiments, it was found in "C:\Documents and Settings\
Turn in your results and also answers to the following questions; you may want to search for the answers.
a) Is there a systematic relation between the average reaction time and the number of distractors for the case of distractors of the same color - if so what is the relation?
b) Is there a systematic relation between the average reaction time and the number of distractors for the case of distractors of a different color - if so what is the relation?
c) What would happen if we had used black T's against distractors of black U's?
d) Which ex-UCB faculty member is famous for this kind of experiment?
Part B. This is a hand calculation exercise to help familiarize you with some of the most basic computational properties of the brain. You may need to do some hunting in books or the WWW for facts and numbers. Listening carefully during class and section will also help you find the answers. Note: many of the answers may be inexact. We are not looking for essays, but rather for short, insightful answers.
1.
a. What is the minimum time interval between firings of cortical neurons? Identify two factors that govern this number.
b. What is the minimum time for a person to give a forced choice response to a simple stimulus?
c. What do these facts suggest about the number of steps in a minimal neural computation?
d. What is the speed of neural signal transmission? How does this compare to the speed of a computer?
e. How does spike wave theory modify the basic story of neural computation? * It may help you look this up to know that Simon Thorpe developed this theory and founded the company SpikeNet, which is based on this theory.
2.
a. About how many neurons are in the human brain?
b. What is the fan-out of cortical neurons (on the average, to how many other neurons is each neuron directly connected)?
c. From these two numbers, estimate the number of synapses crossed that suffice to connect any two neurons in the brain. (Note: [fan-out] ^ [# of synapses] should be greater than or equal to the [# of neurons].)
d. About how many synapses are there in the brain?
e. At about what age is the number of synapses at its maximum.
f. About how many synapses per second are generated to this point.
3.
a. About how many genes are in the human genome? Why is this controversial?
b. Since there are vastly more neural connections than genes, it has been claimed that very little of our brain is pre-specified. Show that this argument fails if one takes into account the fact that much of cortex is laid out in systematic maps with regular connection patterns.
c. What is fMRI , functional Magnetic Resonance Imaging?
d. What has been discovered about political thinking using fMRI?
4.
a. Why does an action potential not go backward on a neuron?
b. What is the role of myelin in propagating the action potential?
c. When is the myelinization process complete in development?