"4. We think with the ideas held in working memory, which can only be accessed at high speed from the brainís stored memory. Understanding is nourished by the information you hold in working memory as you think. Without such knowledge, we have a mind full of mush."
More: Five Reasons That Memory Matters | Psychology Today
Heinle's Newbury House Dictionary of American English
Definition of mush | Collins English Dictionary
mush - definition of mush by Macmillan Dictionary
To sum up: The whole piece is about people who abandon memorization that was a prized skill in the past and disadvantage of Google.
Question: Does "a mind full of much" mean dead brain, brain that doesnít work unless external factors such as Google is available, or something empty?