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When I was in high school (30 years ago), I took a biology class, and the instructor showed us an Ishihara color test for color-blindness. (This is the "hidden numbers" test.)

What I thought I saw once or twice was two different numbers* that had been embedded in the same slide. Were there slides in the test that had two or more numbers, or was I hallucinating?

[EDIT:] * "Two different numbers" means "different numbers in different colors."

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  • $\begingroup$ We can't answer a question about whether you were hallucinating 30 years ago, or what an instructor may or may not have shown you. If you want to reformulate your question to ask if there is such a test (with numbers in two different colors), that can be answered here. $\endgroup$ – De Novo Mar 16 '19 at 6:51
  • $\begingroup$ I clarified my question. Look at the last sentence of paragraph 2, and paragraph 3. $\endgroup$ – Christopher Heckman Mar 18 '19 at 0:54
  • $\begingroup$ I got a chance to look through the actual images, and it appears I hallucinated the third number. $\endgroup$ – Christopher Heckman Jun 1 '19 at 22:15
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The Ishihara Color Test consists of plates containing one number. But that number may consist of two digits (Fig. 1). The plates may also contain one or two wiggly lines that have to be traced. So...

Were there slides in the test that had two or more numbers, or was I hallucinating?

There might have been two digits in the plate - you were not hallucinating.

number![wiggly
Fig. 1. Ishara test with a plate containing one number of two digits (left) and one or more wiggly lines (right). source: Colour Blindness

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  • $\begingroup$ I didn't make myself clear enough ... I mean numbers of two different colors, not a 2-digit number. (Sorry; I've fixed this above.) $\endgroup$ – Christopher Heckman Mar 16 '19 at 6:47
  • $\begingroup$ @Christopher - See plate 16 and 17 in the link given in the answer. $\endgroup$ – user237650 Mar 16 '19 at 7:19
  • $\begingroup$ @user237650: Once again, I consider that one number. Maybe I need to add: "the second digit wasn't lined up with the first one"? $\endgroup$ – Christopher Heckman Mar 17 '19 at 6:36

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