Complex sentence: After several weeks, in mid-October 1971, Curtiss was reading Genie a story when she saw Genie was clearly listening and responding to her speech, and from then on Genie paid attention to people even when they were not speaking directly to or about her.
Split into simpler sentences: After several weeks, in mid-October 1971, Curtiss was reading Genie a story when she saw Genie was clearly listening and responding to her speech. After that point, Genie paid attention to people even when they were not speaking directly to or about her.