 When access to digital computers became possible in the middle fifties , a few scientists instinctively recognized that a machine that could manipulate numbers could also manipulate symbols and that the manipulation of symbols could well be the essence of human thought . This was a new approach to creating thinking machines . 
 When access to digital computers became possible in the middle fifties , a few scientists instinctively recognized that a machine <a href='null_relcl' title='1'><mark>that</mark></a>could manipulate numbers could also manipulate symbols and that the manipulation of symbols could well be the essence of human thought . This was a new approach to creating thinking machines . 
When access to digital computers became possible in the middle fifties , a few scientists instinctively recognized dat a machine could manipulate numbers could also manipulate symbols and that da manipulation of symbols could well be the essence of human thought . This was a new approach to creating thinkin machines .