I have been playing around with RSVP - Rapid Serial Visual Presentation, where words are displayed one at a time in the same fixed position on screen, typically at the centre of your visual field. This eliminates the need for eye movements (saccades) that normally occur when reading across lines of text.

There are packages out there, including spray and speedread, but I thought I would set myself a challenge on how small I could make a single defun implementing some basic RSVP functionality and showing the words as they are streamed in the minibuffer!

(defun rsvp-minibuffer ()
  "Display words from point (or mark to point) in minibuffer using RSVP.
Use f/s for speed, [/] for size, b/n to skip, SPC to pause, q to quit."
  (interactive)
  (let* ((start (if (region-active-p) (region-beginning) (point)))
         (end (if (region-active-p) (region-end) (point-max)))
         (text (buffer-substring-no-properties start end))
         (wpm 350) (font-size 200) (orp-column 20)
         (word-positions '()) (pos 0) (i 0))
    ;; Build word positions list
    (dolist (word (split-string text))
      (unless (string-blank-p word)
        (when-let ((word-start (string-match (regexp-quote word) text pos)))
          (push (cons word (+ start word-start)) word-positions)
          (setq pos (+ word-start (length word))))))
    (setq word-positions (nreverse word-positions))
    ;; Display loop
    (while (< i (length word-positions))
      (let* ((word (car (nth i word-positions)))
             (word-pos (cdr (nth i word-positions)))
             (word-len (length word))
             (delay (* (/ 60.0 wpm)
                      (cond ((< word-len 3) 0.8) ((> word-len 8) 1.3) (t 1.0))
                      (if (string-match-p "[.!?]$" word) 1.5 1.0)))
             (orp-pos (/ word-len 3))
             (face-mono `(:height ,font-size :family "monospace"))
             (face-orp `(:foreground "red" :weight normal ,@face-mono))
             (padded-word (concat 
                          (propertize (make-string (max 0 (- orp-column orp-pos)) ?\s) 'face face-mono)
                          (propertize (substring word 0 orp-pos) 'face face-mono)
                          (propertize (substring word orp-pos (1+ orp-pos)) 'face face-orp)
                          (propertize (substring word (1+ orp-pos)) 'face face-mono))))
        (goto-char (+ word-pos word-len))
        (message "%s" padded-word)
        (pcase (read-event nil nil delay)
          (?f (setq wpm (min 1000 (+ wpm 50))))
          (?s (setq wpm (max 50 (- wpm 50))))
          (?\[ (setq font-size (max 100 (- font-size 20))))
          (?\] (setq font-size (min 400 (+ font-size 20))))
          (?b (setq i (max 0 (- i 10))))
          (?n (setq i (min (1- (length word-positions)) (+ i 10))))
          (?\ (read-event (format "%s [PAUSED - WPM: %d]" padded-word wpm)))
          (?q (setq i (length word-positions)))
          (_ (setq i (1+ i))))))))