Thursday, March 3, 2011

Human or Computer?

“Can machines think?”
This is the question posed by Alan Turing in his article “Computing Machinery and Intelligence” which appeared in the British journal Mind in 1950. His question is one that lies at the heart of the ongoing dialectical engagement between our understandings of life and machinery.
 In the article, he proposes a test to find the answer to this question. The essence of the test is that a computer could be said to "think" if a human interrogator could not tell it apart, through conversation, from a human being. Having discussed the test, he remarks-
The original question “Can machines think?” I believe to be too meaningless to deserve discussion. Nevertheless, I believe that at the end of the century the use of words and general educated opinion will have altered so much that one will be able to speak of machines thinking without expecting to be contradicted.
He went on to predict that by 2000, computers would be able to fool the average interrogator over five minutes of questioning at least 30 percent of the time. After sixty years of tremendous progress in Computer Science and Artificial Intelligence, Turing’s words seem to have been almost prophetic. But although the Turing test, as it is now called, spawned a vibrant field of research known as artificial intelligence, his prediction has proved false. Today's computers are capable of feats Turing never imagined, yet in many simple tasks, a typical 5-year-old can outperform the most powerful computers.
Indeed, the abilities that require much of what is usually described as intelligence, like medical diagnosis or playing chess, have proved far easier for computers than seemingly simpler abilities: those requiring vision, hearing, language or motor control. It is this limitation to the abilities of artificial intelligence that allows us to devise ways of telling it apart from human intelligence.
Today we are all familiar with a reversed form of the Turing Test, namely, the CAPTCHA, or "Completely Automated Public Turing test to tell Computers and Humans Apart".

 Internet bots, also known as web robots, WWW robots or simply bots, are software applications that run automated tasks over the Internet. Typically, bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human alone. The largest use of bots is in web spidering, in which an automated script fetches, analyzes and files information from web servers at many times the speed of a human. But internet bots may also be used for more malicious purposes, and it is this problem that scientists at Yahoo had to face at the start of the millennium.

 Rogue computer programs masquerading as teenagers were infiltrating Yahoo chat rooms, collecting personal information or posting links to Web sites promoting company products. Spam companies were creating havoc by writing programs that swiftly registered for hundreds of free Yahoo e-mail accounts then used them for bulk mailings.

 What they needed was a simple way of telling a human user from a computer program. In their quest for a solution, Yahoo called a conference with a group of computer science researchers at Carnegie Mellon University. Dr. Manuel Blum, a professor of computer science at Carnegie Mellon who took part in the Yahoo conference, realized that the failures of artificial intelligence might provide exactly the solution Yahoo needed. Why not devise a new sort of Turing test, he suggested, that would be simple for humans but would baffle sophisticated computer programs.

Yahoo liked the idea, so with his Ph.D. student Luis von Ahn and others Dr. Blum devised a collection of cognitive puzzles based on the challenging problems of artificial intelligence. The puzzles have the property that computers can generate and grade the tests even though they cannot pass them. The researchers decided to call their puzzles CAPTCHAS, an acronym for Completely Automated Public Turing Test to Tell Computers and Humans Apart

A CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. CAPTCHA tests are based on open problems in artificial intelligence (AI): decoding images of distorted text, for instance, is well beyond the capabilities of modern computers.

Some researchers promote image recognition CAPTCHAs as a possible alternative for text-based CAPTCHAs. Computer-based recognition algorithms require the extraction of colour, texture, shape, or special point features, which cannot be correctly extracted after the designed distortions. However, human can still recognize the original concept depicted in the images even with these distortions.

A recent example of image recognition CAPTCHA is to present the website visitor with a grid of random pictures and instruct the visitor to click on specific pictures to verify that they are not a bot. (such as “Click on the pictures of the airplane, the boat and the clock”)

Another CAPTCHA, called Sounds, consists of a distorted, computer-generated sound clip containing a word or sequence of numbers. To solve the puzzle, a user must listen to the clip and type the word or numbers into the box provided.

The different types of CAPTCHAS in use today illustrate some of the limits of mainstream artificial intelligence today. But already researchers, including von Ahn, one of the creators of the CAPTCHA, have started experimenting with an idea that will help AI overcome these deficiencies.
 In 2007, Von Ahn launched a set of games designed to get humans to ‘teach’ computers. This is "human computation," the art of using massive groups of networked human minds to solve problems that computers cannot. Ask a machine to point to a picture of a bird or pick out a particular voice in a crowd, and it usually fails. But even the most dim-witted human can do this easily. Von Ahn has realized that our normal view of the human-computer relationship can be inverted. Most of us assume computers make people smarter. He sees people as a way to make computers smarter. 


              CAPTCHAs have several applications for practical security, such as:
·         Preventing Comment Spam in Blogs. Most bloggers are familiar with programs that submit bogus comments, usually for the purpose of raising search engine ranks of some website. By using a CAPTCHA, only humans can enter comments on a blog.

·         Protecting Website Registration. Several companies (Yahoo!, Microsoft, etc.) offer free email services. Up until a few years ago, most of these services suffered from a specific type of attack: "bots" that would sign up for thousands of email accounts every minute. The solution to this problem was to use CAPTCHAs to ensure that only humans obtain free accounts.
·         Online Polls. In November 1999, released an online poll asking which the best graduate school in computer science was (a dangerous question to ask over the web!). As is the case with most online polls, IP addresses of voters were recorded in order to prevent single users from voting more than once. However, students at Carnegie Mellon found a way to stuff the ballots using programs that voted for CMU thousands of times. CMU's score started growing rapidly. The next day, students at MIT wrote their own program and the poll became a contest between voting "bots." MIT finished with 21,156 votes, Carnegie Mellon with 21,032 and every other school with less than 1,000. Can the result of any online poll be trusted? Not unless the poll ensures that only humans can vote.

·         Preventing Dictionary Attacks. CAPTCHAs can also be used to prevent dictionary attacks in password systems. The idea is simple: prevent a computer from being able to iterate through the entire space of passwords by requiring it to solve a CAPTCHA after a certain number of unsuccessful logins. This is better than the classic approach of locking an account after a sequence of unsuccessful logins, since doing so allows an attacker to lock accounts at will.

1. Gödel, Escher, Bach: an Eternal Golden Braid – Douglas Hofstadter

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