Complex sentence: He further pointed out that in her dissertation Curtiss wrote many of Genie's less grammatical utterances were responses to intercession in her speech, and that after these efforts stopped Genie's ungrammatical sentences ceased.
Split into simpler sentences: He further pointed out that in her dissertation, Curtiss had pointed out that many of Genie's less grammatical utterances were responses to intercession in her speech. At the time, she had said that after these efforts stopped Genie's ungrammatical sentences ceased.