The idea behind bionic reading is similar to why I find fonts with medium-to-small x-height more readable that fonts with large x-height. Although large x-heigh

The idea behind bionic reading is similar to why I find fonts with medium-to-small x-height more readable that fonts with large x-height. Although large x-height probably makes each individual letter more readable, more pronounced ascenders and descenders allow to read words by their shape more easily, and give anchor points when reading long paragraphs. I find serif fonts found in old books to be the most readable.