The difference between spoken language and written language is vision. Most of us learn to speak, develop adequate auditory processing, and learn the rules of our language implicitly. Spoken language is symbolic, but most children easily and rapidly absorb the symbolism because it is immediately useful and it is part of our genetic endowment. Reading is not part of our genetic endowment. It requires explicit instruction to learn letters and letter/sound relationships which do not have immediate utility. Reading requires years of practice and places extraordinary perceptual demands on the visual system. As the symbolism of algebra overwhelms some children, especially if it is presented too early, the symbolism of letters, their subtle differences, their orientation specificity, and their sequencing within words can be overwhelming. This is also exacerbated when children are pushed to read before they are perceptually ready.
Tests of visual perception which require a child to copy shapes have been accepted as an important part of a learning-related evaluation for over 50 years. They continue to be used because the ability of a child to copy shapes is predictive of their progress in reading and in math, recognizing that the predictive ability of any single test is limited. Since the differences of these tasks is great on the surface, this connection may seem surprising, but the ability to copy, read, and do math are all dependent on some of the same foundational skills; attention to detail, perseverance, patience, breaking a problem down and putting it back together, and working memory. They all involve symbols. Tasks designed to develop perceptual skills have been found to be salutary, especially when implemented early when children are still in the early stages of reading and math.
We received a video this week of our two-month-old grandson sitting in a tub of sudsy water. His lower body cannot be seen. He suddenly raises a leg and sees what appears to be his toes – and then they disappear. From this stage of perceptual immaturity, we anticipate that he will be speaking in two years and learning his letters and numerals in three or four. The development and processing that these feats represent are astounding and, to our amazement, are accomplished by almost every child. The processing of visual symbols that is necessary to read is contrary to a child’s prior perceptual learning. Young children readily learn many different categories and perceptual constancy. They know, for example, that a wide variety of different looking and different sized animals are “dogs” and that it is the same dog whether it is standing or sitting and whether we see it from the front or the back. These rules change with letters which must have a specified orientation and a precise sequence to become a word. (see Reversals)
Visual perception, eye movements, and visual span must integrate many times a second to enable reading. Early readers see individual letters in the order in which their eyes aim at them and construct words from these pieces as if the letters were presented individually. It takes years for children to see whole words as we do. The word-length effect is an example of this. Accomplished readers read words of different lengths in approximately the same time. The time to recognize words for early readers is proportional to how many letters are in the word. If their eyes do not process the letters in the correct spatial order, they will be confused and skip the word or guess based on the first letter which is the easiest letter to find.
Some children are more prone than others to interference from the surrounding letters and words, which is known as visual crowding. The auditory system is also vulnerable to crowding. Auditory crowding causes sequential sounds to run together so they cannot be discriminated. Children may have difficulty with both visual and auditory crowding. Written words may overlap and spoken words may overlap as they do when we are listening to another language. (see Visual Crowding)
We can only see a very small area clearly with each fixation (about 5 degrees which is the equivalent of 5 letters). We believe that we can see more because our eyes are constantly moving and our brains make a composite picture of the individual snapshots. Reading is visually discontinuous but is sensed as continuous when the visual system is working efficiently. Our eyes move 4 times a second when we are reading. During that ¼ second:
-we move our eyes to the target that has been selected by a shift in our visual attention
-we take in what we can see in that fixation in 1/10 second
-we integrate this information with prior information from the preceding text and from our experience
-we use this to predict the word that is most likely to come next
-we shift our attention to the next target
-our eyes make the next saccade and start the process all over
This happens four times a second and the visual system must erase the image from the prior fixation so it does not overlap with the next fixation. Vision must also be suppressed during the eye movement or the page will appear smeared. Not everyone is fortunate to have the visual agility, timing, and stamina to sustain this rapid process over extended periods of time. The conscious mind is much too slow to orchestrate this. It also does not have the bandwidth to perform all of these tasks and attend to the information that is encoded in the print on the page.
Since we cannot move our eyes faster than four times a second, to be able to read faster, we need to be able to take in information from adjacent letters that cannot be seen clearly. This bottom-up process (from eyes to brain) is assisted by the top-down process of predicting what is coming next. This breaks down if our perception is disrupted by crowding. It also breaks down and creates noise in the signals received by the brain if the eyes are not aligned within a fraction of a millimeter.
Unless we are the rare individual with eidetic imagery, we do not store what we are reading as pages of words. Most of what we read is stored as visualizations and associations.
Children with perceptual problems which make it difficult to process print have no way of knowing that how they perceive differs from how others perceive. Astute observers who are working with them may notice behaviors which make them suspect that they have visual problems and refer them for evaluation and appropriate care if indicated. Some people recognize as adults that they have a processing problem and seek care at that time. Patients whose visual processing is affected by a head injury know that they have a problem because reading is not as it was before. Insights from this population have enhanced our understanding of developmental aberrations.
In the book Range, David Epstein states that narrow specialists are needed with deep understanding, but they need to be teamed with others who have a broader perspective. Some specialists are convinced that all reading problems have the same cause. Scientists and professionals with greater range understand that it should be expected that problems in complex systems such as reading most likely have multiple causes. A restricted perspective keeps many children from receiving the help that they need to perform to their cognitive potential.