As I was researching academic studies related to processing speed (with a view to perhaps including processing speed training in the Brain Fitness program) I discovered this fascinating paper:

“A latent variable analysis of working memory capacity, short-term memory capacity, processing speed, and general fluid intelligence”

(Andrew R. A. Conway, Nelson Cowan, Michael F. Bunting, David J. Therriault and Scott R. B. Minkoff)

Conway set out to see whether working-memory, short term memory, and processing speed could be correlated to fluid intelligence. He found, somewhat surprisingly, that while working-memory capacity has a very strong correlation to fluid intelligence, neither short term memory nor processing speed has a significant correlation.

Conway discusses the significance of this result at some length. He makes some compelling points:

1. His findings strengthen the argument that working-memory can be equated to fluid intelligence. The more items of information we can hold and manipulate, the better we can arrive at intelligent analyses.

2. When testing the effect of processing speed on intelligence it is important to keep the tasks very simple, to avoid any unintended overlap with working-memory. He cites this as the reason that previous studies found a link between processing speed and fluid intelligence.

3. In young children and aging subjects, processing speed may indeed have an impact on fluid intelligence. This would call for processing speed training for the elderly.

I found Conway’s methodology quite thoughtful and sound. Overall, I’m disuaded from designing exercises that train only processing speed, but instead to continue to focus on working-memory and perhaps include an element of processing speed as a way to provide novelty and reward (a faster working-memory task, perhaps).