"Influence and Correlation in Social Networks" - Anagnostopoulos et al.

The authors describe a statistical test for actions in social networks.
This test helps to distinguish correlation from causality for information propagation in social networks.
Hereby, the author's test first calculates the probability for one user influencing the other user.
Afterwards, they shuffle action times of the user and test again.
To get a detailed insight into the statistical concept please take a look at the paper.

Some Links from HCI Research

Acoustic radiation pressure: Radiation pressure--the history of a mislabeled tensor by Robert T. Beyer, a summary/review paper about 100 year-old history of radiation pressure. A more simple explanation can be found on the German Wikipedia. Essentially, this effect occurs if acoustic waves in one medium shoot at another target medium. If the frequency is higher than the time a target medium needs to stretch, than air particles get reflected back to the sound source. Furthermore, you can imagine the effect better if you think about the water-air medium change. Check Paper on water-air interface experiment. 

Tangibles go on market Appmates, little racing cars for your iPad 

Think about output to your brain Switching Neurons, Research Area is called Optogenetics, might be interesting for the normal nerve system as well. 

Cheat Sheet for Statistics Just in case, you need a refresh Cheat Sheet

Hick's Law in Mortal Combat Webpage discusses the influence of choices in martial arts.