When reading, the eyes do not move continuously from left to right across the text, but rather jerkily (saccadically) from gaze target to gaze target. In 15 to 20 percent of saccades, a backward saccade, regression, is performed – usually unconsciously – because the text was not fully understood or because the eyes jumped a little too far during the last gaze target and the text could not be fully captured by the fovea centralis.
What is regression?
The concept of regression plays a role primarily in reading. During the reading process, the gaze does not glide continuously from left to right across the lines, but moves unconsciously in regular jumps, called saccades. The term regression plays a role especially in reading. During the reading process, the gaze does not glide continuously from left to right across the lines, but it moves unconsciously in regular jumps, called saccades, from fixation to fixation. Reading does not occur in a continuous process, but in choppy and successive freeze frames, each lasting about 250 milliseconds. The gaze jumps or saccades proceed very rapidly. During the saccade, visual information is largely suppressed so that the gaze jumps are not consciously perceived. It is common for about 15 to 20 percent of saccades to incorporate a backward jump of the eyes, a regression, which in most cases occurs completely unconsciously. Regressions always occur when the corresponding part of the text was not understood right away or when something has subliminally irritated so that the subconscious decides to look at the part of the text or the word again. Also a misprint perceived in the subconscious or an unfamiliar technical term that only penetrates the consciousness a saccade later can trigger a regression. It is also not consciously perceived unless the unclear or misunderstood information still cannot be resolved with the regression in the normal dwell time of the eyes. If this is the case, the normal reading process is interrupted and attention is directed to the relevant word or passage with consciousness engaged. Regressions are not unique to reading. The eyes also perform these movements unconsciously in many other everyday situations.
Function and task
Text can be clearly recognized and processed by the brain only if it is detected through the fovea, the small area of sharpest vision with color perception. The fovea, located in the yellow spot, accounts for only about 1 degree in the entire field of vision, which encompasses about 100 degrees. This means that when reading, the eye jumps saccadically from “degree to degree” and the brain can only process the area of text that falls within the fovea at a time. The advantage is that the reading process proceeds smoothly over the simultaneous acquisition of whole words. On average, 7 to 9, but at most up to 15 characters or letters are recognized simultaneously with one fixation. In case of minor problems with text recognition, a regression, a return to the previous fixation, takes place. The regression serves to solve the problem in the subconscious without decisively interrupting the reading flow. This means that a regression is normally not even noticed. The advantage is that minor problems are solved by regression during fluent reading at a slightly reduced speed. The system of stringing together fixations and regressions for solving minor problems with text recognition results in a huge increase in reading speed over text recognition via tedious, deliberate acquisition of individual letters. Incorporating regressions into text capture may reduce reading speed by 15 to 20 percent, but it has the advantage of not decisively interrupting the flow of reading. Without regression, every minute text recognition problem would have to be raised to consciousness, which would not only be time-consuming, but the usual reading flow probably could not occur.
Diseases and ailments
Specific diseases that exclusively affect regressive saccades are not known. Functional impairments in this area are usually coupled with limitations in ocular motility.The limitations may be caused by problems with the positioning muscles of the eyes, with the transmission of sensory or motor signals via afferent or efferent nerve fibers, respectively, or with the processing of the signals in the CNS. The stellate muscles of the eyes each consist of 3 pairs of muscles, each of which serves one of the three possible axes of rotation. If only one of the 6 muscles has functional limitations, problems with the exact parallel movement of the eyes usually occur. This is true for large eye movements, as well as for microsaccades and regressions. Sensory and motor transmission problems may be caused by lesions or pathologic changes in motor cranial nerves III and IV or mixed cranial nerve V (trigeminal nerve), also known as the facial nerve. Another problem area for possible functional impairment of microsaccadic regression may be in the brainstem or cerebellum. Degenerative neurological changes such as Alzheimer’s or Parkinson’s disease are the most common causes of CNS-induced ocular motility impairment. At the beginning of the impairment, a decreasing “accuracy” of a saccade can usually be observed. After a successful gaze jump – even after microsaccades and regressions – the eyes have to be readjusted almost imperceptibly. The ability to read fluently and to grasp the text quickly is lost, so that reading causes great effort and is very tiring for the affected person.
