Tactile vision in the blind: An fMRI experiment on pattern recognition and brain plasticity

Citation: 
Giudice, N.A., Madison, C.M., Zhuang, J.C., Costello, P.A., Legge, G.E., Hu, X., & He, S. (2000). Tactile vision in the blind: An fMRI experiment on pattern recognition and brain plasticity. Annual Meeting of the Association for Research in Vision and Ophthalmology, Supp. IOVS, 40, S49, Ft. Lauderdale, FL.
Abstract: 
Purpose. It is unclear exactly what information processing is occurring in the visual cortices of blind people. Several studies using Positron Emission tomography and Transcranial Magnetic Stimulation (Sadato, 1996 & 1998, Buchel, 1998, Hamilton, 1998) have demonstrated functional activation in primary and secondary visual areas of blind subjects performing tactile tasks. In contrast, sighted controls did not show significant activation in these areas. The purpose of the current study is to further investigate the role of the visual cortices in tactile shape discrimination across blind and sighted populations. We are particularly interested in the participation of the inferior temporal cortical areas in tactile shape recognition of these groups. Methods. Seven blind and five sighted subjects were studied using a 1.5 Tesla magnet. Stimuli were all composed of embossed Braille dots and included, Braille, Roman Letters, simple geometric shapes, and random dot patterns. A smooth surface served as a baseline control. Whole brain activity was recorded while subjects performed various tactile discrimination tasks. Results. Not surprisingly, strong activation was observed in the somatosensory areas in both groups. However, Temporal cross correlation analysis showed highly significant activation in the early visual cortical areas (V1/V2) and inferior temporal areas (IT) in the blind population in response to the meaningful tactile stimuli. In contrast, the sighted controls showed minimal or no activation in the early visual areas and much weaker activation in the inferior temporal areas in response to the same tactile stimuli. Conclusions. These results replicate the early PET studies showing functional reorganization in primary and secondary visual cortices in blind subjects. Our findings further demonstrate the participation of IT areas in tactile shape recognition. The recruitment of visual cortical regions in tactile tasks may explain the enhanced tactile pattern recognition and discrimination ability of blind subjects over their sighted counterparts found in previous behavioral studies (Madison & Legge, 1998).

Comments

This conference presentation

This conference presentation was based on extremely novel work, which ended up not progressing because of an unfortunate conjunction of factors (probably the study which I am most disappointed about in my career). Except for one single patient account by Sadato in 1999, this study was the first fMRI multi-subject project to show cross-modal plasticity of Occipital regions by touch in the blind. Importantly, it showed differential activation as a function of stimulus complexity. Finally, to my knowledge it was the first study to demonstrate cross-modal plasticity in people with usable residual vision as well as those who were totally blind (something which remains poorly studied.