SD of Area as a function of number of samples

This graph shows just the decrease in the standard deviation of the area as a function of samples added. As you can see the variability drops suddenly as a function of samples added. However, it is a bit hard to see the area of interest - samples of under 5000 so I re-plotted the sample graph but with the number of samples on a logarithmic scale.

This curve indicates that after a point there will not be much more improvement if more stimuli are added.

There are two questions that can be asked:

Firstly, what is the relationship between signal-to-noise ratio and the standard deviation of the area?