Sparing of sensitivity to biological motion after early visual deprivation

Abstract

The perception of biological motion is mediated mainly by neural networks in the posterior region of the superior temporal sulcus, an extrastriate area that receives input from both the dorsal and ventral visual cortical streams. We evaluated the functional integrity of those networks after early visual deprivation by measuring sensitivity to biological motion in six patients who had been treated for dense congenital bilateral cataracts at 2 – 10 months of age and later tested at 12 – 25 years of age. Their task was to discriminate point light biological motion displays depicting human movement from scrambled versions of the same displays and to indicate whether the person appeared in interval 1 or 2. To estimate thresholds, we added noise dots to the displays and used a staircase to estimate the number of noise dots that could be tolerated for 71% discrimination accuracy. Surprisingly, patients' sensitivity to biological motion was entirely normal: every one of the six patients had thresholds within the normal range of thresholds produced by three age-matched controls. Yet, the same deprivation causes marked deficits in the perception of global motion and global form, aspects of vision that depend on the integrity of the dorsal and ventral visual streams, respectively. We speculate that sensitivity to biological motion is spared because some of the neurons involved are stimulated by self body movement during the period of visual deprivation, perhaps via a homologue of the macaque mirror system.

Footnotes

 Support: CIHR grant MOP-36430