The answer to the blank part of the statement is vision.
When you consume alcohol, your pupils would react slower; you would be less likely to contrast dark and light objects well; your eyes would twitch if your consumption is excessive; and you have dry eye, your symptoms would be exacerbated. This is one of the reasons why people who are drunk aren’t allowed to drive, since they cannot accurately perceive the things around them due to being impaired by alcohol.
