This 2013 human study provided further details of critical periods in human development. The study subjects were:

“11 children enrolled in a humanitarian and scientific effort in India that provides corrective surgery to children with treatable cataracts and subsequently studies their visual abilities.”

The researchers found:

“The human visual system can retain plasticity beyond critical periods, even after early and extended blindness.

We define “early-onset” blindness as occurring before 1 y of age. We define “extended” blindness as lasting at least until early childhood, when many visual abilities in normally developing children reach adult levels. Contrast sensitivity in particular develops until approximately age 7 in normally sighted humans.

Of the 11 children, five had no discernible improvement, whereas one child’s vision grew worse, probably because of post-surgical complications. Five of the patients showed remarkable enhancement, however, and of these, an 11-year-old and a 15-year-old showed 30-fold improvement in contrast sensitivity.

“The visual brain can be plastic for longer than we originally thought,” concludes Kalia. “Many of the kids dramatically improve their quality of life.”

http://www.pnas.org/content/111/5/2035.full “Development of pattern vision following early and extended blindness”