Why do we make doubling error typos when typing?

Doubling errors occur in handwriting but are less frequent. Representative photo.
| Photo Credit: Cytonn Photography/Unsplash

A: Analyses of large corpora of typed text reveal that these doubling errors are a common class of typographical errors. They only arise in words that have adjacent double letters, or geminates, and are attributed to a special repetition marker in the brain. This marker is associated with a particular position in a word and causes immediate repetition of the letter at that position. Sometimes the marker may be triggered too early or too late, causing incorrect repetition of a nearby letter. Thus, ‘between’ appears as ‘betwwen’.

Repetition markers are assumed necessary by the suppression of actions during the production of a well-learned sequence. The temporary suppression of each action immediately after its execution prevents it from persevering or competing with subsequent action. This suppression is problematic when immediate repetition is required, which explains the need for the special repetition marker.

Doubling errors occur in handwriting but are less frequent. This probably reflects the slower pace of handwriting and the fact that repeated letters don’t necessarily arise from the same, single action. The exact form of each handwritten letter depends on the context of surrounding letters, suggesting several component actions in the writing of a letter, in contrast to the single depression of a key on a keyboard.

— Rik Henson, Cambridge