The three physiological brakes

How the eye actually reads

The eye does not glide along the line. It moves in saccades, abrupt jumps of twenty to forty milliseconds during which you see nothing, separated by fixations, stops of two hundred to two hundred and fifty milliseconds during which information is taken in.

So your speed depends on three variables only.

1. The duration of each fixation.
2. The number of words taken in per fixation, the span.
3. The number of useless fixations, the backtracks.

The three brakes correspond exactly to those three variables.

Brake number 1: subvocalisation

This is the small voice that pronounces the words in your head. It caps you at speaking speed, 150 to 250 words per minute. Conversational English runs at about 150 words a minute, and read-aloud English at about 180, which is where the ceiling comes from.