Created for Eliza Yujun Ng December 2018

Numbers are presented at a rate of one per second. The first digit cannot be 0 Following digits can be 0 but cannot be the same as the previous digit.

If the answer is correct the span is increased for the next trial If the answer is wrong the span is decreased for the next trial

If there are at least two errors at a given span and that represents more than half of the total attempts at that span then the experiment ends, returning a span of one less than the final span attempted.