I observed a few things as I was going through the trials. There was not a third option. Had I found a third option to choose if the lines were the same, I would have been more confused. However, I did sometimes have to stop and pause and see if one was really bigger than the other and at times it was easy to judge both lines.
What this lab reminded me of was being in an optometrist’s office and getting an eye exam where one has to choose between options “1” and “2” and how the doctor asks you to make a choice. In an eye exam, sometimes you get a third option of “about the same,” but here there were only two choices. Sometimes it may be that third response that complicates matters.
I also found myself wanting to select a third option that did not exist, in fact I believed in quite a few of the trials the lines appeared to be the same length. I think that the wings on the lines made those lines appear longer than they actually were, so if they appeared the same size I chose that the line without wings was longer. I like how you related it to the eye doctor, I wear contacts so I have to get an eye exam yearly, and I always struggle with this part of the exam. I think it is similar in that it is difficult to tell which option is clearer, just as it was difficult to tell which line is longer. Although at the eye doctor I am able to say the options are about the same sometimes it feels as though it is not an option, the doctor does not seem to like when I say they look the same. Although I had a similar experience with the lab I did not relate it to the eye doctor that way, I am glad you did because it made a lot of sense!
I found myself wanting to click on a third option when I did not believe that one was longer than the other.