Moving Dot Coherence Task

Background

How do our brains make decisions about the things we see? In order to study the neural basis of decision making, Shadlen and Newsome devised an experiment in which nonhuman primates were trained to make decisions about whether a cloud of moving dots was moving to the left or the right. They changed the proportion of dots moving to the left or right from 100% left, to 50% left and 50% right, and 100% right. They recorded from neurons in a brain region called MT, and found that MT neurons encoded the subject's choice by a simple voting method. In particular, they found that individual neurons in MT responded either to rightward motion or leftward motion. When the dots were all moving to the right, only the rightward motion neurons responded. Similarly, when all the dots were moving to the left, only the leftward neurons responded. When half the dots were moving to the right and half the dots were moving to the left, however, Shadlen and Newsome found that they could predict the choice the monkey was going to make based on how many rightward neurons were responding compared to leftward neurons.

In the moving-dot coherence task, when 50% of the dots are moving to the left and 50% of dots are moving to the right, theoretically one has no idea which direction the dots are moving as a whole. Neurons in MT, however, can have a bias towards one particular direction. Thus, if you choose left or right over 50% of the time when the dots are moving evenly in both directions, this suggests that you have a preference for movement to the right or left. If 55% of dots are moving in one direction, it may still be difficult to discern which direction the dots are moving in. As the proportion of dots moving towards a particular direction increases, however, you become more and more certain of the direction. Try it yourself below!

Instructions

First, a screen with a cross will be presented. Focus on the cross for several moments. After this, a screen of moving dots will appear for several seconds, after which you will see a cross that is green. When the cross is green, press "l" if the dots you saw were moving to the left, and press "r" if the dots were moving to the right. The plot below will show you the proportion of trials you indicated were rightward for each proportion of dots moving rightward (0% rightward means that 100% of the dots were moving to the left).