Task-determined strategies of visual process.

Lateral masking in the peripheral field of vision obscures letter recognition and is not accounted for by diminished acuity. In measuring lateral masking between letters in the peripheral visual field we accidentally discovered that ordinary readers and severe dyslexics differ markedly in tachistoscopic letter recognition tasks. Tests were devised to measure the differences accurately. Ordinary readers recognize letters best in and near the center of gaze. Recognition falls off rapidly with angular distance in the peripheral field. Severe dyslexics recognize letters farther in the periphery in the direction of reading (English-natives to the right, Hebrew-natives to the left). They have marked lateral masking in and near the center of the field when letters are presented in aggregates. With dyslexia as an example, we proposed that the distribution of lateral masking is a task-dependent strategy in visual perception. To test this notion we designed an active practise regimen for 4 severe adult dyslexics, who within a few months improved sharply in reading. At the same time their test results changed to those of ordinary readers. We conclude that there are switchable task-determined pre-cognitive strategies of vision that can be learned and that the distribution of lateral masking may be part of what is learned.