Hemispheric Specialization for Linguistic and Nonlinguistic Tactual Perception Using a Dichotomous Stimulation Technique

The present study was undertaken to assess the relative participation of the left and right hemispheres in processing nonlinguistic and linguistic stimuli presented in the tactual modality in neurologically intact individuals. Two tests involving dichotomous tactile stimulation, one using nonsense shapes and the other letters, were given to 47 normal right-handed boys between the ages of 6 and 14 years. It was found that nonlinguistic tactile information was more efficiently processed in the right (nonspeech) hemisphere in neurologically intact individuals as had been previously inferred on the basis of the study of individuals with unilateral brain damage. The right hemisphere specialization for nonlinguistic tactual perception was found to be present as early as six years of age.It was also found, contrary to expectation, that simple tactile linguistic stimuli such as letters were not processed more efficiently by the left hemisphere. The results were interpreted as indicating that linguistic stimuli presented tactually must be analyzed first in a spatial code and then translated into a linguistic code. This suggests that there is no direct link between input and linguistic analysis in the tactual modality as there appears to be in the visual and auditory modalities.The role of environmental factors, both present and past, such as response mode and previous similar experience, in priming particular central processes and consequently modifying left-right perceptual asymmetries was also noted.