What difference does it make if we read texts displayed on a computer screen instead of on paper printed with ink? The computer certainly does not guarantee deeper comprehension, greater subtlety of mind, or a wider range of imaginative reference. The mediation of a computer, however, puts new powers at the disposal of intelce. For one thing, the computer itself can do reading--as I have noted, it can 'read' an immense body of literature in search of designated(指定的)words. As anyone knows who has ever spent days in libraries in search of errant information, simply identifying relevant sources absorbs inordinate amounts of time in research. The objection may be raised that a search of texts by computer may block the occasional(偶然发现的)discoveries that occur while browsing in the stacks of great libraries. No member of the academy need fear that the use of a computer will keep him from the stacks, but browsing is, if anything, easier if texts can be called up on a screen in the serenity(宁静)of one's chosen surroundings. The great deficiency of libraries, as we know them, is that while titles are catalogued, the libraries have no indexes of the contents of books. Individual volumes, it is true r have indexes, often of inferior quality, but even the best indexes must be examined one at a time. The great advantage of the electronic library is that a computer could search and yze its contents without proceeding volume by volume. As work in artificial intelce develops, computer systems may also become adept at more complex tasks, such as summarizing texts, which has been accomplished experimentally. What does the writer mainly talk about in this passage?