I do this often. In my line of work I used to work with many lines of logic and nested logic programming. I find I can no longer keep these operations and their expected results in focus. It is just too much. The neuro-psych explained it this way. Because of my processing speed deficits even though I may read, hear or visually take it in, bits of info just can not make it into short term memory. When that happens I just stop or sit there like my brain is grinding away with out that crucial bit of info. His recommendation is to slow down and only do one thing at a time. Looks like multitasking is not an option for me.