Tactile-visual cross modal transfer after an extended period of congenital blindness

Abstract

Purpose: In underdeveloped villages of India, infants with congenital cataracts often do not undergo cataract surgery due to socioeconomic reasons. Consistent with a strict interpretation of the critical period, if congenital cataracts are treated within a few months of birth it leads to a near normal development of vision but after age 6 or 7 years there should be little or no improvement. The experiments below show that vision can be regained after the critical period. The objective of Experiment 1 is to assess the development of the tactile-visual link compared to intramodal tactile and visual object recognition while Experiment 2 assesses precision of the tactile-visual link. Methods: Subjects were between 8 and 15 years old. In Experiment 1 objects were used to assess tactile-to-tactile, tactile-to-visual, visual-to-tactile, and visual-to-visual transfer in three patients. In Experiment 2, objects of a specific length, aspect ratio, or curvature ratio were used to assess the precision of tactile-to-visual transfer in three other patients and four normally sighted control subjects. Results: In Experiment 1, tactile-to-visual transfer accuracy pre-operatively was about 20% and improved to above 50% during one week. In Experiment 2 the patients had a preoperative error range of 23-51%. There was a 25% improvement on post operation day 1 and by the day 4 there was a 50% improvement in the number of errors. Conclusion: We have demonstrated that the link between touch and vision strengthened significantly after the classic critical period.