Spaun performing silent counting. The model is shown a starting number, and then a number to count to. It internally counts from the starting number the designated number of counts, and writes the response. This is much like an adding task. The model shows Weber's law effects on this task (scaling of response time variance with mean), and has reaction times consistent with human data.
In the fourth task, Spaun counts silently. Here it starts at 4, and counts 3 positions. You can watch the silent counting by noticing that the working memory starting at four increments by one three times. When humans perform this task, the variability of their reaction time increases with the number of counts. This kind of relationship is called Weber's law in psychology, and is evident in Spaun's behaviour as well.