Thank you for participating in this experiment! You will be looking at stimuli 
rendered in 3d on our computer display and making judgments about the lightness 
of certain target patches. You can think of "lightness" as "what color paint the patch 
is coated with". 
 
On each trial, you will see two squares ("contexts"), each consisting of a random 
assortment of grayscale rectangles. These two contexts are at a right angle to each 
other. You will also see a patch near the center of the display. The patch will be 
oriented in one of four ways: flat in the plane of the upper context, flat in the plane 
of the lower context, rotated out of the upper context plane by 90 degrees, and 
rotated out of the lower context plane by 90 degrees. This patch is called the "target 
patch". 
 
To indicate your judgment about the lightness of the target patch, you will use the 
palette to your right. Notice how each grayscale chip has a number underneath it. By 
moving the slider (located below the wooden box), you will change the number 
appearing on the computer screen behind the palette. The number will correspond 
to one of these numbers on the grayscale chip palette. Try to find the grayscale value 
that most closely matches the target patch. When you have found the closest match, 
press the red button to lock in your match and move onto the next trial.  
 
You are encouraged to look back and forth between the computer display and the 
palette several times before locking in your match. However, if you do, please be 
sure to put your head in the chinrest when looking at the stimuli, to ensure the 
proper perception of the stimuli. 
 
There are three special values on the slider that do not appear on the palette. If you 
shift the slider all the way to the right, you will see the option "Glowing". Slightly to 
the left of that point is the option "Lighter than 9.5, but still a surface". If you think 
that the target patch appears to be self-luminous, pick the former. If you think that 
the target patch looks lighter than the palette chip corresponding to 9.5, but that it 
does not yet appear to be glowing as though it were a light itself, pick the latter. If 
you shift the slider all the way to the left, you will see the option "Darker than 0.5". 
Pick this option if you think the patch looks darker than the darkest palette chip 
corresponding to 0.5. 
 
There are a total of 108 trials in each block, and a total of 12 blocks. In some blocks 
you will look at the stimuli with both eyes; in others you will only use one eye (the 
other eye hole will be covered with a felt patch). The program will ask you to stop to 
take a break every 36 trials, or every third of the block. Please take this opportunity 
to rest your eyes for a few minutes--the experiment is taxing!  
 
If you have any questions at any point, please feel free to stop and get the 
experimenter. There is no time limit, so please try to make the most accurate match 
you can. 
 
Thanks!