ESOMAR, the global market research industry association, has addressed ethical practice issues in a series of publications over the years.  Its "Codes and Guidelines" library can be found here.

A new Guideline entitled "Passive Data Collection, Observation, and Recording," most recently revised in February 2009, addresses a number of observational techniques, including

• Audio and video recordings of interviews and group discussions
• Observation of human behavior in public and private places
• Incidental data
• Retail tracking
• Physical monitoring

The complete guideline can be viewed online and downloaded here.  The section on physical monitoring includes specific guidelines for neural and physiological data collection.  Lucid Systems subscribes to these guidelines in full and further recommends that buyers insist on Independent Review Board (IRB) approval for all research performed using any of these techniques.