How did the "AI winter" of the 1970s and 1980s impact the progress of neural network research? How did the "AI winter" of the 1970s and 1980s impact the progress of neural network research? How did the "AI winter" of the 1970s and 1980s impact the progress of neural network research? How did the "AI winter" of the 1970s and 1980s impact the progress of neural network research?