Sadato et al. (1996)

From Psy3242

Activation of the Primary Visual Cortex by Braille Reading in Blind Subjects

The paper explains that the primary visual cortex receives input from the eyes up through the geniculate nuclei. This area is not known to receive input from other sensory modalities. Therefore, Sadato wonders whether the PVC could have non visual functions. To determine whether or not the PVC has input from the samato sensory system, they use PET (Positron Emission Tomography). The following subjects studied were non blinded, genetically blinded, or blinded at an early part of his/her life. To begin they study eight Braille readers. Eight character, non-contracted Braille letter strings were presented every 2.4 seconds with 41 words and 3 non words. Subjects are to read these words and utter “num” if they encounter non words and were to react only when they read real words. These subjects were compared with six other blind subjects and ten other sighted subjects in order to determine non-discrimination and discrimination groups. Generally, if both sides of the subjects are shown, the results can easily determine whether the primary visual cortex receives input from other sensory modalities. These subjects were given one non-discrimination ‘sweep’ task and three discrimination tasks including the ‘angle’, ‘width’, and ‘character’ tasks. In the ‘sweep’ task, the subjects were to move their index fingers among a line of Braille dots without responding. In the ‘angle’ task, the subjects were presented pairs of Braille dots and were required to say “num” when they were the same. In the ‘width’ task, the subject were to respond when the vertical grooves (or width) of the Braille were the same. Last of all with the ‘character’ task, the subjects were given three upper case Braille letters and were to respond if all of these letters were the same. There was no mental or spatial imagery needed. Through these tasks we learned that the non discrimination task didn’t activate the primary visual cortex. However, the discrimination tasks did not only because there were two more tests, but because of the variety of subjects. We also learned that selective attention does not affect the PVC the same way with blind subjects that it does with sighted subjects. Also, the congenitally blind subjects who performed Braille reading tasks showed the same activation of the PVC as other blind subjects.