Engineers and computer experts continue to strive for new innovations to improve the quality of life for the blind. But a new research study suggests that Braille, the first great innovation for the blind – may offer more in stimulating the visual cortex that any technology incorporating only audio signals.
Background
Previous studies have previously established a physiological correlation among blind people using Braille. This relationship was verified using functional magnetic resonance imaging (fMRI), positron emission tomography (PET) and transcranial magnetic stimulation (TMS). These studies established that visual cortex, key to processing visual signals, plays a functional role enabling the blind perform Braille reading.
Controversy persists, however, concerning differences in the engagement of primary visual cortex between persons who become blind early in life versus those who acquire blindness later (e.g., before age three vs. after age 12). The differing results with early versus late onset blindness raise questions regarding the period of susceptibility for cross-modal reorganization. A previous fMRI study of verb generation for Braille nouns revealed anatomically distinct activation foci corresponding to V1, V2, V3, VP, and LO in both early blind and late blind subjects. This result, if compared to vision in sighted subjects, suggests a distributed network of specialized functional areas. However, assignment of specific functionality remains unclear.
One possibility is that blindness leads to visual cortex adaptation for the analysis of information obtained by touch. Thus the same functionality used for the analysis of print orthography in sighted persons is applied to Braille decoding in the blind.
Another possibility is that core language processes, e.g., semantic, phonological, or syntactic, acquire representation in visual cortex as a result of adaptations to blindness. A new study tests this hypothesis by studying blind individuals using a language task involving hearing instead of Braille reading. The researchers selected verb generation of "heard nouns" as the behavioral task. This potent, semantic paradigm has been extensively studied in sighted subjects.
A New Study
A new experiment can be compared to previous studies of verb generation to Braille read nouns except that the tasks are identical except for input word modality, i.e., auditory versus Braille. The authors of "Adaptive Changes in Early and Late Blind: A fMRI Study of Verb Generation to Heard Nouns," are H. Burton, A. Z. Snyder, J. B. Diamond, and M. E. Raichle, all from the Washington University School of Medicine, St. Louis, MO. Their findings appear in the December 2002 edition of the Journal of Neurophysiology.
Methodology
Eight early blind, six late blind, and eight sighted subjects participated in the study. Results were excluded from one early blind, five late blind, and three sighted individuals because of excessive head movement, abnormal brain anatomy by structural imaging, or inadequate performance on post-fMRI scan recall testing. Early blind subjects had no sight at birth or by age three. The average age at onset of blindness in the late blind group was age 19.2 (range, seven to 36). All blind subjects, but no sighted subjects, were fluent Braille readers. Average Braille reading rates for the early blind and late blind subjects were 106.3 words/min (wpm) and 79.7 wpm, respectively.
The task assigned was covert generation of a compatible verb for heard nouns (e.g., think "paint" in response to "house"). The control task was passive listening to indecipherable sounds (reverse words) matched to the nouns in sound intensity, duration, and spectral content. Functional responses were analyzed at the level of individual subjects using methods based on the general linear model and at the group level, using voxel-based ANOVA and t-test analyses. The concrete-to-abstract noun ratio was approximately 2:1.
During control blocks subjects were presented unintelligible stimuli matched to the nouns in intensity, duration, and spectral content, which they were instructed to ignore. The stimuli were created by a male voice reading nouns into a computer. Extraneous noise before and after each word was erased. Sound intensities for all words were equalized. The nouns were randomly assigned to eight different lists, one for each fMRI run. No noun was repeated within or across runs. Otherwise, unused two or three syllable nouns were time reversed to create the control stimuli, which were constant within each run but varied across runs.
Results
On average, subjects recalled more than 60 percent of covertly generated verbs from a preceding run. Early blind recalled significantly fewer verbs. The fMRI results from these two subjects were indistinguishable from other early blind subjects. Average reaction times for recalled verbs were significantly shorter for sighted subjects. This difference primarily reflected greater consistency in the performance of nearly all sighted subjects compared with several blind subjects. The predominant reaction times even in the latter were similar to those observed in the sighted group. Despite these differences, all subjects reported having no difficulty doing the task.
Conclusions
The results confirm prior reports of visual cortex activation in blind persons performing nonvisual tasks. Auditory tasks were used in several prior studies of early blind individuals. These tasks included the following:
- detecting and counting tones with a deviant frequency versus ignoring the tones during Braille reading,
- detecting a deviant tone in one ear while ignoring distracting sounds in the other, and
- sustaining attention to binaural sound localization in the azimuth domain.
Braille literacy requires associative coupling between phonics and the tactile experience of Braille. All of the subjects learned Braille after they became blind, and they had extensive experience associating the feel of the Braille fields and auditory instruction as to the lexical meaning of the tactile sensations.
Hence, the researchers suggest that Braille literacy is not primarily related to touch but rather lexical and that the lexical processor resides at least in part in left occipital. Accordingly, this leads to a belief that that acquisition of Braille literacy leads to expansion of the brain regions engaged by language during listening as well as reading. This outcome would have important implications for education in the blind, and by extension, rehabilitation in general.
Source: December 2002, edition of American Journal of Neurophysiology. The journal is one of 14 published monthly by the American Physiological Society (APS).
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.
Journal
Journal of Neurophysiology