Erroneous artifacts in 3D display

Having recently finished annotating all of the video for the second user study, I noticed a few issues.
None of the issues I saw in the second user study were as severe as the first user study, but they are interesting.
Two people, that with my subjective judgment were complete novices to robot control and interpreting 3D information on a 2D display, mistook some artifacting in the 3D model as the deposit box, and so repeatedly dropped blocks on the artifacts.
The artifacts were showing because of an imperfect filter that is supposed to remove all parts of the 3D model that are not relevant to the task (that is, the blocks, pipes, and deposit box).
Some of the floor was showing up in the model, and these two subjects seemed to think it looked like the box.
If I were designing an interface to cater specifically to this task, I can think of ways to support the operator that would really make the deposit box stand out.
I don't think that's really what I'm researching, though, so I'm not going to change the interface design in that way, especially since 30 out of 32 people had no trouble finding the deposit box.
Most likely nobody will want to use a mobile manipulator for this particular task, since it's really mostly a toy world.

Another problem is a remnant from the first user study.
Yes, we're coming back to the alignment issue.
For one target block in one particular layout, the alignment was off by enough that at least half of the people had trouble getting it.
There were a couple other blocks that were slightly off, but most people got them as long as they followed the instructions in the training.
What it amounts to is that the calibration was slightly off for those couple of regions.
It's a little disappointing, but not too much so, since I can filter out the problem blocks to look at what happens with the well-aligned blocks.
Since there are 6 layouts and 3 blocks per layout, that means that only 1 or 2 block samples out of 18 is bad.
I think it's still plenty usable and will give some interesting insights.