It has always surprised me how little attention philosophers have paid to humor, since it is a more significant process of mind than reason. Reason can only sort out perceptions, but the humor process is involved in changing them.

This quote is suggesting that humor is a powerful tool when it comes to thinking and problem-solving. It explains that while reason can help to sort and organize your thoughts, humor has the ability to be creative, to change and modify perceptions, and is thus even more powerful. The speaker is surprised that philosophers have not paid more attention to humor, as it is an undervalued and untapped source of problem-solving.