Posts Tagged ‘visual cortex’

A View of the Reading Brain

October 19, 2018

This post is taken from “READER COME HOME: The Reading Brain in the Digital World” by Maryanne Wolf. Please excuse the detail, but it is important to gain an appreciation of what is involved in reading. The brain’s design is with the principle of “plasticity within limits.” The brain is able to go beyond its original biological functions—like vision and language—to develop biologically unknown capacities such as reading and numeracy. To do so, it forms a new set of pathways by connecting and sometimes repurposing its older and more basic structures. Faced with something new to learn, the human brain not only rearranges its original parts, but is also able to refit some of its existing neuronal groups in those same areas to accommodate the particular needs of the new function. The brain recycles and even repurposes neuronal networks for skills that are cognitive or perceptually related to the new one, Wolf writes, “This ability to form newly recycled circuits enables us to learn all manner of genetically unplanned-for activities—from making the first wheel, to learning the alphabet, to surfing the net while listening to Coldplay and sending tweets. None of the activities is hardwired or has genes specifically dedicated to its development; they are cultural inventions that involved cortical takeovers.” As there is no genetic blueprint for reading, there is no one ideal reading circuit. There can be different ones.

In addition to neuroplasticity, there is the concept of cell assemblies formulated by the Canadian psychologist Donald Hebb. The concept is that cells that fire together wire together. These specialist groups build the networks that allow us to see the smallest features of a letter or hear the tiniest elements in the sounds of language, literally in milliseconds. Cell specialization enables each working group of neurons to become automatic in its specific region and to become virtually automatic in its connections to the other groups or networks in the reading circuit. For reading to occur, there must be sonic-speed automaticity for neuronal networks at a local level, which, in turn, allows for equally rapid connections across entire structural expanses of the brain. So, whenever we name even a single letter, we are activating entire networks of specific neuronal groups in the visual cortex, which correspond to entire networks of equally specific language-based cell groups, which correspond to networks of specific articulatory-motor cell groups—all with millisecond precision. Multiply this scenario a hundredfold when the task is to depict what you are doing when reading with complete (or even incomplete) attention and comprehension of the meanings involved.

“In essence, the combination of these principles forms the basis of what few of us would ever suspect: a reading circuit that incorporates input from the two hemispheres, four lobes in each hemisphere (frontal, temporal, parietal, and occipital) and all five layers of the brain (from the uppermost telencephalon and adjacent diencephalon below it; to the middle layers of the mesencephalon; to the lower levels of the mesencephalon and myelencephalon).” So anyone who still believes that we use only a tiny portion of our brains hasn’t yet become aware of what we do when we read.

Behavioral Training to Improve Sight

April 29, 2015

This title is the second part of the article “Improving Vision Among Older Adults:  Behavioral Training to Improve Sight,” by DeLoss, Watanabe, and Andersen in Psychological Science Online First, March 6 2015 as dii:10.1177/0956797614567510.  Age-related decline in visual function could be due to optical, retinal, cortical, or pathological changes, there also appears to be a cortical locus as a result of decreased inhibition  in the visual cortex.

This study assessed whether perceptual learning could be a possible intervention to counteract age related declines in contrast sensitivity.  Younger and older subjects performed an orientation-discrimination task using sine wave gratings that varied in contrast.  The researchers assessed whether training improved performance for targets at a specific location, transferred to targets at an untrained orientation, and transferred to other tasks ( near- and far-acuity tasks, for example).

Sixteen younger adults (mean age=22.43) and 16 older adults (mean age=71.23) participated in the experiment.  The experiment consisted of 1.5 hr per day of testing and training over 7 days.  Participants were required to complete the study within 3 weeks of their first testing session.

The major finding of the study is that five days of training for older adults resulted in performance that was not statistically different from that of younger adults prior to training.  Clearly perceptual learning  can be used to counter age-related declines in contrast sensitivity.  The authors note that a these improvements are the result of changes in sensory process and not due to the optical efficiency of the eye.

Both age groups also showed significant transfer of learning to an untrained orientation.   Another important finding is that both younger and older individuals showed significant improvement in acuity with perceptual-learning training.  These improvements  in acuity were associated with the range of acuity most problematic for each age group.  Younger individuals showed an improvement in far acuity, whereas older individuals showed improvement in near acuity.  These improvements were substantial resulting in an average of from two to three additional letters on the acuity charts after training.   So the benefits of this training is not restricted to older adults.

This research provides strong evidence of the plasticity of visual processing as we age.  Further research is needed to determine how much more improvement could be gained by additional training.  Let us hope that such research will be done expeditiously and that programs will be developed for dissemination to the general population..