---------- 12/14/2015 ---------- Jack Ryan created this fork to document the recent decision to allow the recruitment of 18 - 24 year olds in this study. Given recent difficulty in recruiting subjects aged 25 - 40 years, we have decided to recruit from a second, younger pool. This will expedite data collection and will allow us to check for differences in nulling reliability between the two age groups. - Note we are still collecting 16 25 - 40 year old subjects but now we are collecting an additional 16 18 -24 group. - We will compare the within subject nulling reliability of the two groups - All other parameters remain the same as Fork 2 of the Control Population Stimulus Nulling Experiment. Edits to the preregistration document: 1. Age ranged changed from 25 - 40 to 18 - 24. 2. Added: **"Compare both the within session test / re-test reliability of the nulling measures and the standard deviation across subjects between subjects aged 18 - 24 and subjects 25 - 40."** to the list of goals.