Advertising is only looked at 2-3 secs, it has to catch your attento before that.
90% of the info channeled to the brain is visual. Only 10-40 bits/sec of 11 Million bits/sec become conscious.
Now we are reminded of the physiology of the eye. You can consult the Wikipedua for this :)
The area of the image our eye sees is only really sharp in the area of one degree (3-4 letters in this text). The rest is illusion created by the brain and the re-fixating eye.
Only eye tracking can make sure that you know what your users will see. And: They won't read manuals.
You can record "gaze plots" and heatmaps and make sure that your customer has read an ad completely.
You can derive stats from that: How many have seen the product or read the slogan?
You can even show the glancepaths as a video.
Banner blindness was discovered this way.
Results are very different for the think-aloud and the retrospective (tacid) method.
Now some videos on eye-tracking in SL: Each avatar has another perspective. The measurement of the effectiveness of advertising is very difficult inthis diverse environment.
If you create special rooms and setups you can get a controllable environment for valid tracking results.
In in-game advertising threre is more experience with ad tracking. But in game people might not be open enough for advertising.
Research projects have been started in this area.