Most adults read automatically - taking note of key words or phrases, but inherently taking in the shapes, lines, and colors of text effortlessly, and using the "leftover" space in our minds to mull over the implications of the words we are reading. Language is an innate human ability - when exposed to other conversational humans, we will learn to speak and communicate as we grow and learn. Reading, however, is a learned skill, not unlike learning how to use a computer, or how to play a musical instrument. Early childhood is an ideal time to expose a new reader to letters, shapes, words, and sounds, the ability to read develops easily as the brain develops and language acquisition takes place; by adolescence and early adulthood, a new reader will require increased effort in order to build to an advanced reading level, (Johnson, quoting Sousa (2005), 2010).
Learning to read is equatable to training our visual system to understand how lines and shapes build to form "patterns of characters" (Johnson, 2010), or morphemes. Morphemes can be combined to form recognizable clusters that we know as words; words combine together in various ways to form phrases, idioms, and sentences, and sentences merge together to form texts of larger meaning, such as paragraphs, from which we can learn to extract nuanced symbolism and meaning.
Johnson (2010) describes the eye patterns (saccades) and how they flow across pages of text, picking out the important words, that our brains then extract further meaning from. He also goes on to explain the distinctions between feature-driven ("bottom-up") or context-driven ("top-down") reading approaches that determine whether a reader has to analyze the subtle differences in line and shape, like, for example, in ideographic scripts such as Chinese, or if the reader is learning a foreign language, or if the reader is able to quickly glance at a line of text and gather the meaning, even if the words are obscured or misspelled.
All of this careful consideration of language quickly becomes moot in the online environment when reading is disrupted through texts that are too small or two large, the use of all caps, undecipherable fonts, and unfamiliar vocabulary. Even strong readers can become frustrated by loud or bright fonts, especially overlaid onto "noisy" backgrounds, with excessive and unnecessary blocks of text. Even the use of centered or right-aligned text can disrupt the automatic eye movements that allow readers to scan text easily from left to right. Poor readers can become even more discouraged, and the ultimate conclusion would be to minimize the need for excessive, difficult reading. Designers should "support reading" and understand the flow natural linguistic processes of how we read and take in information, "not disrupt it", (Johnson, 2010).
Designers should ensure the use of controlled vocabularies, and, whenever possible, plain or natural language; avoid distracting flaws such as difficult to read text sizes and fonts, indecipherable colors and noisy backgrounds, excessive use of blocks of text, and center and right-aligned text; create formats that allow for natural visual hierarchies, making text easily scannable and, (Johnson, 2010).
Johnson, J. (2010). Designing with the Mind in Mind: Simple Guide to Understanding User Interface Design Rules. Amsterdam: Morgan Kaufmann /Elsevier.