Some readers need to hear every word with their inner voice, this limits reading speed to around 400 wpm. In such cases, auditory brain areas pace reading. This is called the sound barrier. Functional images of the brain show that a concrete word like ‘book’ preferentially activates visual areas. While an abstract word like ‘efficiency’ is processed by the auditory areas. So words do not always require sound to produce meaning. Not faced with this sound barrier and without special training deaf people often read above 1000 wpm.