Science says that our sensory memory system is very large but very brief. We have very brief photographic memory called Iconic Memory. This lab explores this phenomenon. It is based on the work of Dr. Sperling.
I use this activity in conjunction with my Memory unit and specifically Module 21 in the Myers text.
It is based on an activity at this link so try the link before you buy in case it is dead.
The website basically replicates a classic experiment in Psychology.
NOTE: Your kids need headphones if they are doing this activity in your computer lab. I have my students bring their own.