What was that thing that the writer could not forget all through her life despite her losing vision and hearing power?

In Helen Keller's The Story of My Life, she states that: But during the first nineteen months of my life I had caught glimpses of broad, green fields, a luminous sky, trees and flowers which the darkness that followed could not wholly blot out.

Thus, she would never forget the way things looked in the gardens of her infancy.