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					                                Advantages and Disadvantages of a Computer




  With the development of society, Internet is stepping into our daily life. But like
everything else, it has two sides: the positive side and the negative side.
  There are several advantages about using a computer. The greatest one is that it is
an information press way. Through a computer, we can obtain various information
from the Internet. What‟s more, we can send e-mail by computers and chat with our
far away friends when we are on line. Finally, people can do business through a
computer. In a word, computers enrich our life and make our life more comfortable
and convenient.
  There is no denying that a computer offers us convenience and benefits. In spite
of its advantages, its disadvantages are also evident. First, more and more students
lose themselves in computer games, which is not only waste of money but also
waste of time. Second, there is much false information on the Internet, and
sometimes it is very difficult to distinguish what is true and what is false. Some
people even commit crimes through computers.
  Nowadays computers have played so important a role in our life that sometimes
we may find that we cannot be without our computers. So we‟d better take
advantage of its positive side and try to avoid its negative side.
                              Advantages and disadvantages of the computer

               In our accommodations, many students have computers. Also we can see in the
            electronic reading room and the cybercafés, rows of students sit in front of the
            monitors. Computers play an important role in our everyday life.

              We use computers to cope with files and photos etc. And the internet is just a large
            database and we can get on the internet to search for anything we need through the
            computers. We can keep in touch with the others with the emails, msn and QQ etc.
            Enjoying ourselves in music, games and movies can loosen us after nervous classes.

            电脑的利与弊(Advantages and disadvantages of the computer)



                                                                                                     1
电脑的利与弊(Advantages and disadvantages of the computer)

   In our accommodations, many students have computers. Also we can see in the
electronic reading room and the cybercafés, rows of students sit in front of the
monitors. Computers play an important role in our everyday life.

  We use computers to cope with files and photos etc. And the internet is just a large
database and we can get on the internet to search for anything we need through the
computers. We can keep in touch with the others with the emails, msn and QQ etc.
Enjoying ourselves in music, games and movies can loosen us after nervous classes.

  Each coin has two sides. Disadvantages of the computers can also do harm to us.
Most of us students use the computers more to play games and chat with strangers
than searching for useful information. That‟s a waste of time. There is so much
rubbish on the net, which are some medium messages about crime or sex. It does
harm to our minds.

  From all above, we should learn to use computers in our own right ways. The
computers doesn‟t have no responsibility, it depends on the way we use them.
(www.159love.com 收集整理)

电脑的利与弊(Advantages and disadvantages of the computer)
   In our accommodations, many students have computers. Also we can see in the
electronic reading room and the cybercafés, rows of students sit in front of the
monitors. Computers play an important role in our everyday life.

  We use computers to cope with files and photos etc. And the internet is just a large
database and we can get on the internet to search for anything we need through the
computers. We can keep in touch with the others with the emails, msn and QQ etc.
Enjoying ourselves in music, games and movies can loosen us after nervous classes.

  Each coin has two sides. Disadvantages of the computers can also do harm to us.
Most of us students use the computers more to play games and chat with strangers
than searching for useful information. That‟s a waste of time. There is so much
rubbish on the net, which are some medium messages about crime or ***. It does
harm to our minds.

  From all above, we should learn to use computers in our own right ways. The
computers doesn‟t have no responsibility, it depends on the way we use them.

                   Advantages and disadvantages of the computer



                                                                                         2
     In our accommodations, many students have computers. Also we can see in the
    electronic reading room and the cybercafés, rows of students sit in front of the
           monitors. Computers play an important role in our everyday life.

  We use computers to cope with files and photos etc. And the Internet is just a large
 database and we can get on the Internet to search for anything we need through the
   computers. We can keep in touch with the others with emails, msn and QQ etc.
 Enjoying ourselves in music, games and movies can loosen us after nervous classes.

  Just as the proverb says ,'Each coin has two sides'. Disadvantages of the computers
can also do harm to us. Most of us students use the computers more to play games and
   chat with strangers than searching for useful information. That's a waste of time.
 There is so much rubbish on the net, which are some medium messages about crime
                            or sex. It does harm to our minds.


     From all above, we should learn to use computers in our own right ways. The
    computers doesn't have no responsibility, it depends on the way we use them.

Man and the internet- -

   My first time of touching internet is about 7 years ago. When I first surfing
  on the internet, I was so excited, just like Columbus found the new continent.
  Now, I want to talk about the cyber-culture.
   The most influenced our life by cyber-culture is the way of our communicat
ion. In those days without internet, we communicated through mail, telephone,
telegraph. Internet offers us a lot of chooses of communication. ICQ, QQ, ema
il, etc. Internet convenient our communication, at the same time, it changed ou
r literature.
   For its convenience, people often use self-created short words, such as “thx”,
 it means thanks. People use some numbers stand for their words. For some i
nstances, “886” means Bye, “520” means I love you. If a man sends numbers
 “5201314” to his lover, that is the man telling his honey, he will love her th
rough his whole life. I think Chinese could be the genius of communication lit
erature.
   When we talk about the cyber-communications, we should not forget the cyb
er-love. I think love could not exist without communications, especially in the
cyber-space. Many people think cyber-love is unbelievable, „cause they thing as
 many other people think “you could not know whether your chart on the inte
rnet is a dog.” But life is full of magic, the man or woman you passing by i
n the street could be the lover you meet through the internet. No matter you

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believe it or not, I think the true love could exist in cyber-love. One of my fr
iends proved it, she met his husband on the internet and after four years, and
they decided to get married. They are married in Chinese Valentine‟s Day. I
wandered how she could marry a man, who met on the internet; she answered
  “It is a secret with a little magic and a little lucky.”
   When we look back on our life, we could find that the internet and cyber-c
ulture are truly influence our life-style.
Student‟s use of computer
     With computers becoming more and more easily accessible on the
campus ,college students are spending more time than ever doing routine tasks
electronically in the last decade ,in 1990,for example, the average number of hours a
student spent on the computer per week was less than 2 hours ,up to
2000 ,however ,time spent on the computer increased suddenly to almost 20 hours a
week.

   Many reasons account for this      growing trend .the last decade has witnessed an
astonishing development in it industry; the uses of computers are more diversified,
their cost are significantly cut down and the software is becoming more and more
user-friendly on the campus, for example students may study many courses on
computers , surf online for the latest information in their fields, and contact the
outside world through web more frequently and conveniently.

  The easy access     to computers on the campus may also bring about some
problems. the research-and-education-based use accounts for      smaller portion of the
whole use, either because the development of subject-related software lag behind, or
because students are more caught up in computer entertainment such as playing video
games, and chatting online ,. therefore, more attention should be called to the wise
and academic use of computers on the campus.


Human-computer interaction



From Wikipedia, the free encyclopedia

Jump to: navigation, search
   This article is about the interaction between users and computers at the user
interface. For direct communication pathway between a human or animal brain (or
brain cell culture) and an external computer or machine device, please see
Brain-computer interface.

Human–computer interaction (HCI) is the study of interaction between people
(users) and computers. It is often regarded as the intersection of computer science,

                                                                                        4
behavioral sciences, design and several other fields of study. Interaction between
users and computers occurs at the user interface (or simply interface), which includes
both software and hardware, for example, general-purpose computer peripherals and
large-scale mechanical systems, such as aircraft and power plants. The following
definition is given by the Association for Computing Machinery[1]:

           "Human-computer interaction is a discipline concerned with the design,
         evaluation and implementation of interactive computing systems for human
         use and with the study of major phenomena surrounding them."

   Because human-computer interaction studies a human and a machine in
conjunction, it draws from supporting knowledge on both the machine and the human
side. On the machine side, techniques in computer graphics, operating systems,
programming languages, and development environments are relevant. On the human
side, communication theory, graphic and industrial design disciplines, linguistics,
social sciences, cognitive psychology, and human performance are relevant. And, of
course, engineering and design methods are relevant.
HCI is also sometimes referred to as man–machine interaction (MMI) or
computer–human interaction (CHI).




Contents

[hide]

        1 Goals
        2 Differences with related fields
        3 Design Principles
        4 Design Methodologies
        5 Display Design
        6 Future Developments in HCI[6]
        7 Some Notes on Terminology
        8 Human Computer Interface
        9 Academic conferences
             o 9.1 Special Purpose
             o 9.2 Regional and General HCI
        10 See also
        11 Footnotes
        12 Further reading
        13 External links


[edit] Goals


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  A basic goal of HCI is to improve the interactions between users and computers by
making computers more usable and receptive to the user's needs. Specifically, HCI is
concerned with:

      methodologies and processes for designing interfaces (i.e., given a task and a
       class of users, design the best possible interface within given constraints,
       optimizing for a desired property such as learnability or efficiency of use)
      methods for implementing interfaces (e.g. software toolkits and libraries;
       efficient algorithms)
      techniques for evaluating and comparing interfaces
      developing new interfaces and interaction techniques
      developing descriptive and predictive models and theories of interaction

  A long term goal of HCI is to design systems that minimize the barrier between the
human's cognitive model of what they want to accomplish and the computer's
understanding of the user's task.

  Professional practitioners in HCI are usually designers concerned with the practical
application of design methodologies to real-world problems. Their work often
revolves around designing graphical user interfaces and web interfaces.

   Researchers in HCI are interested in developing new design methodologies,
experimenting with new hardware devices, prototyping new software systems,
exploring new paradigms for interaction, and developing models and theories of
interaction.

[edit] Differences with related fields

  HCI differs with human factors in that there is more of a focus on users working
with computers rather than other kinds of machines or designed artifacts, and an
additional focus on how to implement the (software and hardware) mechanisms
behind computers to support human-computer interaction. HCI also differs with
ergonomics in that there is less of a focus on repetitive work-oriented tasks and
procedures, and much less emphasis on physical stress and the physical form or
industrial design of physical aspects of the user interface, such as the physical form of
keyboards and mice. More discussion of the nuances between these fields is at [2]



[edit] Design Principles

  When evaluating a current user interface, or designing a new user interface, it is
important to keep in mind the following experimental design principles:




                                                                                        6
       Early focus on user(s) and task(s): Establish how many users are needed to
        perform the task(s) and determine who the appropriate users should be;
        someone that has never used the interface, and will not use the interface in the
        future, is most likely not a valid user. In addition, define the task(s) the users
        will be performing and how often the task(s) need to be performed.
       Empirical measurement: Test the interface early on with real users who come
        in contact with the interface on an everyday basis, respectively. Keep in mind
        that results may be altered if the performance level of the user is not an
        accurate depiction of the real human-computer interaction. Establish
        quantitative usability specifics such as: the number of users performing the
        task(s), the time to complete the task(s), and the number of errors made during
        the task(s).
       Iterative design: After determining the users, tasks, and empirical
        measurements to include, perform the following iterative design steps:

   1.   Design the user interface
   2.   Test
   3.   Analyze results
   4.   Repeat

Repeat the iterative design process until a sensible, user-friendly interface is
created.[2]

[edit] Design Methodologies

   A number of diverse methodologies outlining techniques for human–computer
interaction design have emerged since the rise of the field in the 1980s. Most design
methodologies stem from a model for how users, designers, and technical systems
interact. Early methodologies, for example, treated users' cognitive processes as
predictable and quantifiable and encouraged design practitioners to look to cognitive
science results in areas such as memory and attention when designing user interfaces.
Modern models tend to focus on a constant feedback and conversation between users,
designers, and engineers and push for technical systems to be wrapped around the
types of experiences users want to have, rather than wrapping user experience around
a completed system.

       User-centered design: user-centered design (UCD) is a modern, widely
        practiced design philosophy rooted in the idea that users must take
        center-stage in the design of any computer system. Users, designers and
        technical practitioners work together to articulate the wants, needs and
        limitations of the user and create a system that addresses these elements. Often,
        user-centered design projects are informed by ethnographic studies of the
        environments in which users will be interacting with the system.



                                                                                         7
      Principles of User Interface Design: these are seven principles that may be
       considered at any time during the design of a user interface in any order,
       namely Tolerance, Simplicity, Visibility, Affordance, Consistency, Structure
       and Feedback.[3]

      See List of human-computer interaction topics#Interface design methods for
       more



[edit] Display Design

   Displays are human-made artifacts designed to support the perception of relevant
system variables and to facilitate further processing of that information. Before a
display is designed, the task that the display is intended to support must be defined
(e.g. navigating, controlling, decision making, learning, entertaining, etc.). A user or
operator must be able to process whatever information that a system generates and
displays; therefore, the information must be displayed according to principles in a
manner that will support perception, situation awareness, and understanding.


THIRTEEN PRINCIPLES OF DISPLAY DESIGN[4]

   These principles of human perception and information processing can be utilized to
create an effective display design. A reduction in errors, a reduction in required
training time, an increase in efficiency, and an increase in user satisfaction are a few
of the many potential benefits that can be achieved through utilization of these
principles.

   Certain principles may not be applicable to different displays or situations. Some
principles may seem to be conflicting, and there is no simple solution to say that one
principle is more important than another. The principles may be tailored to a specific
design or situation. Striking a functional balance among the principles is critical for an
effective design. [5]


Perceptual Principles

1. Make displays legible (or audible)

   A display‟s legibility is critical and necessary for designing a usable display. If the
characters or objects being displayed cannot be discernable, then the operator cannot
effectively make use of them.

2. Avoid absolute judgment limits


                                                                                             8
  Do not ask the user to determine the level of a variable on the basis of a single
sensory variable (e.g. color, size, loudness). These sensory variables can contain many
possible levels.

3. Top-down processing

  Signals are likely perceived and interpreted in accordance with what is expected
based on a user‟s past experience. If a signal is presented contrary to the user‟s
expectation, more physical evidence of that signal may need to be presented to assure
that it is understood correctly.

4. Redundancy gain

   If a signal is presented more than once, it is more likely that it will be understood
correctly. This can be done by presenting the signal in alternative physical forms (e.g.
color and shape, voice and print, etc.), as redundancy does not imply repetition. A
traffic light is a good example of redundancy, as color and position are redundant.

5. Similarity causes confusion: Use discriminable elements

   Signals that appear to be similar will likely be confused. The ratio of similar
features to different features causes signals to be similar. For example, A423B9 is
more similar to A423B8 than 92 is to 93. Unnecessary similar features should be
removed and dissimilar features should be highlighted.


Mental Model Principles

6. Principle of pictorial realism

  A display should look like the variable that it represents (e.g. high temperature on a
thermometer shown as a higher vertical level). If there are multiple elements, they can
be configured in a manner that looks like it would in the represented environment.

7. Principle of the moving part

   Moving elements should move in a pattern and direction compatible with the user‟s
mental model of how it actually moves in the system. For example, the moving
element on an altimeter should move upward with increasing altitude.


Principles Based on Attention

8. Minimizing information access cost



                                                                                        9
  When the user‟s attention is averted from one location to another to access
necessary information, there is an associated cost in time or effort. A display design
should minimize this cost by allowing for frequently accessed sources to be located at
the nearest possible position. However, adequate legibility should not be sacrificed to
reduce this cost.

9. Proximity compatibility principle

   Divided attention between two information sources may be necessary for the
completion of one task. These sources must be mentally integrated and are defined to
have close mental proximity. Information access costs should be low, which can be
achieved in many ways (e.g. close proximity, linkage by common colors, patterns,
shapes, etc.). However, close display proximity can be harmful by causing too much
clutter.

10. Principle of multiple resources

   A user can more easily process information across different resources. For example,
visual and auditory information can be presented simultaneously rather than
presenting all visual or all auditory information.


Memory Principles

11. Replace memory with visual information: knowledge in the world

   A user should not need to retain important information solely in working memory
or to retrieve it from long-term memory. A menu, checklist, or another display can aid
the user by easing the use of their memory. However, the use of memory may
sometimes benefit the user rather than the need for reference to some type of
knowledge in the world (e.g. a expert computer operator would rather use direct
commands from their memory rather than referring to a manual). The use of
knowledge in a user‟s head and knowledge in the world must be balanced for an
effective design.

12. Principle of predictive aiding

   Proactive actions are usually more effective than reactive actions. A display should
attempt to eliminate resource-demanding cognitive tasks and replace them with
simpler perceptual tasks to reduce the use of the user‟s mental resources. This will
allow the user to not only focus on current conditions, but also think about possible
future conditions. An example of a predictive aid is a road sign displaying the
distance from a certain destination.

13. Principle of consistency

                                                                                      10
   Old habits from other displays will easily transfer to support processing of new
displays if they are designed in a consistent manner. A user‟s long-term memory will
trigger actions that are expected to be appropriate. A design must accept this fact and
utilize consistency among different displays.

Future Developments in HCI[6]

  The means by which humans interact with computers continues to evolve rapidly.
Human-computer interaction is affected by the forces shaping the nature of future
computing. These forces include:


* Decreasing hardware costs leading to larger memories and faster systems
* Miniaturization of hardware leading to portability
* Reduction in power requirements leading to portability
* New display technologies leading to the packaging of computational devices in new
forms
* Specialized hardware leading to new functions
* Increased development of network communication and distributed computing
* Increasingly widespread use of computers, especially by people who are outside of
the computing profession
* Increasing innovation in input techniques (i.e., voice, gesture, pen), combined with
lowering cost, leading to rapid computerization by people previously left out of the
"computer revolution."
* Wider social concerns leading to improved access to computers by currently
disadvantaged groups

The future for HCI is expected to include the following characteristics:

Ubiquitous communication Computers will communicate through high speed local
networks, nationally over wide-area networks, and portably via infrared, ultrasonic,
cellular, and other technologies. Data and computational services will be portably
accessible from many if not most locations to which a user travels.

High functionality systems Systems will have large numbers of functions associated
with them. There will be so many systems that most users, technical or non-technical,
will not have time to learn them in the traditional way (e.g., through thick manuals).

Mass availability of computer graphics Computer graphics capabilities such as
image processing, graphics transformations, rendering, and interactive animation will
become widespread as inexpensive chips become available for inclusion in general
workstations.

Mixed media Systems will handle images, voice, sounds, video, text, formatted data.
These will be exchangeable over communication links among users. The separate

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worlds of consumer electronics (e.g., stereo sets, VCRs, televisions) and computers
will partially merge. Computer and print worlds will continue to cross assimilate each
other.

High-bandwidth interaction The rate at which humans and machines interact will
increase substantially due to the changes in speed, computer graphics, new media, and
new input/output devices. This will lead to some qualitatively different interfaces,
such as virtual reality or computational video.

Large and thin displays New display technologies will finally mature enabling very
large displays and also displays that are thin, light weight, and have low power
consumption. This will have large effects on portability and will enable the
development of paper-like, pen-based computer interaction systems very different in
feel from desktop workstations of the present.

Embedded computation Computation will pass beyond desktop computers into
every object for which uses can be found. The environment will be alive with little
computations from computerized cooking appliances to lighting and plumbing
fixtures to window blinds to automobile braking systems to greeting cards. To some
extent, this development is already taking place. The difference in the future is the
addition of networked communications that will allow many of these embedded
computations to coordinate with each other and with the user. Human interfaces to
these embedded devices will in many cases be very different from those appropriate
to workstations.

Group interfaces Interfaces to allow groups of people to coordinate will be common
(e.g., for meetings, for engineering projects, for authoring joint documents). These
will have major impacts on the nature of organizations and on the division of labor.
Models of the group design process will be embedded in systems and will cause
increased rationalization of design.

User Tailorability Ordinary users will routinely tailor applications to their own use
and will use this power to invent new applications based on their understanding of
their own domains. Users, with their deeper knowledge of their own knowledge
domains, will increasingly be important sources of new applications at the expense of
generic systems programmers (with systems expertise but low domain expertise).

Information Utilities Public information utilities (such as home banking and
shopping) and specialized industry services (e.g., weather for pilots) will continue to
proliferate. The rate of proliferation will accelerate with the introduction of
high-bandwidth interaction and the improvement in quality of interfaces.

Some Notes on Terminology




                                                                                          12
      HCI vs MMI. MMI has been used to refer to any man–machine interaction,
       including, but not exclusively computers. The term was used early on in
       control room design for anything operated on or observed by an operator, e.g.
       dials, switches, knobs and gauges.

      HCI vs CHI. The acronym CHI (pronounced kai), for computer–human
       interaction, has been used to refer to this field, perhaps more frequently in the
       past than now. However, researchers and practitioners now refer to their field
       of study as HCI (pronounced as an initialism), which perhaps rose in
       popularity partly because of the notion that the human, and the human's needs
       and time, should be considered first, and are more important than the
       machine's. This notion became increasingly relevant towards the end of the
       20th century as computers became increasingly inexpensive (as did CPU time),
       small, and powerful. Since the turn of the millennium, the field of
       human-centered computing has emerged with an even more pronounced focus
       on understanding human beings as actors within socio–technical systems.

      Usability vs Usefulness. Design methodologies in HCI aim to create user
       interfaces that are usable, i.e. that can be operated with ease and efficiency.
       However, an even more basic requirement is that the user interface be useful,
       i.e. that it allows the user to complete relevant tasks.

      Intuitive and Natural. Software products are often touted by marketers as
       being "intuitive" and "natural" to use, often simply because they have a
       graphical user interface. Many researchers in HCI view such claims as
       unfounded (e.g. a poorly designed GUI may be very unusable), and some
       object to the use of the words intuitive and natural as vague and/or misleading,
       since these are very context-dependent terms. See [7] for more discussion.



Human Computer Interface

  The human/computer interface can be described as the point of communication
between the human user and the computer. The flow of information between the
human and computer is defined as the loop of interaction. The loop of interaction has
several aspects to it including:

      Task Environment: The conditions and goals set upon the user.
      Machine Environment: The environment that the computer is connected i.e a
       laptop in a college student's dorm room.
      Areas of the Interface: Non-overlapping areas involve processes of the
       human and computer not pertaining to their interaction. While the overlapping
       areas, only concern themselves with the processes pertaining to their
       interaction.

                                                                                         13
          Input Flow: Begins in the task environment as the user has some task that
           requires using their computer.
          Output: The flow of information that originates in the machine environment.
          Feedback: Loops through the interface that evaluate, moderate, and confirm
           processes as they pass from the human through the interface to the computer
           and back.

    Human or Computer? Take This Test



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    By SARA ROBINSON
    Published: December 10, 2002

      As chief scientist of the Internet portal Yahoo, Dr. Udi Manber had a profound
    problem: how to differentiate human intelligence from that of a machine.

       His concern was more than academic. 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 we needed,'' said Dr. Manber, ''was a simple way of telling a human user
    from a computer program.''

       So, in a September 2000 conference call, Dr. Manber discussed the problem with a
    group of computer science researchers at Carnegie Mellon University. The result was
    a long-term project that is just now beginning to bear fruit.

      The roots of Dr. Manber's philosophical conundrum lay in a paper written 50 years
    earlier by the mathematician Dr. Alan Turing, who imagined a game in which a
    human interrogator was connected electronically to a human and a computer in the
    next room. The interrogator's task was to pose a series of questions that determined
    which of the other participants was the human. The human helped him, while the
    computer did its best to thwart him.


                                                                                           14
   Dr. Turing suggested that a machine could be said to think if the human
interrogator could not distinguish it from the other human. 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.

  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 Dr. 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.

   ''Abilities like vision are the result of billions of years of evolution and difficult for
us to understand by introspection, whereas abilities like multiplying two numbers are
things we were explicitly taught and can readily express in a computer program,'' said
Dr. Jitendra Malik, a professor specializing in computer vision at the University of
California at Berkeley.

  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.

   Dr. Manber 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 (on the Web at www.captcha.net).

  One puzzle, called Gimpy, consists of a display of seven distorted, overlapping
words chosen at random from a dictionary of simple words. Solving the puzzle
requires identifying three of the seven words and typing them into the box provided.
The Carnegie Mellon group also created a simplified version of Gimpy -- a single
distorted word displayed against a complicated background. It is now part of Yahoo's
registration process.

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   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 idea of using puzzles to prevent automated registrations was not new. Other
e-commerce sites, including the AltaVista search engine and eBay's PayPal service,
were experiencing problems like Yahoo's and independently came up with
Captcha-like puzzles. Through its acquisitions, Hewlett-Packard holds a patent on
text-based Captchas.

  Still, researchers credit Dr. Blum for the breadth of his vision. Dr. Blum ''did a
great thing by recognizing that this problem is much more than solving a nuisance for
Yahoo and AltaVista,'' said Dr. Andrei Broder, who helped develop the AltaVista
puzzle and is now at I.B.M.

  As a cryptographer, Dr. Blum was familiar with the constant efforts of
cryptographic researchers to advance the field by cracking codes to discover their
weaknesses.

   He hoped to start a similar dynamic for Captchas, spurring researchers to try to
create better Captchas while building computer programs that crack existing ones.

  ''Captchas are useful for companies like Yahoo, but if they're broken it's even more
useful for researchers,'' Dr. Blum said. ''It's like there are two lollipops and no matter
what you get one of them.''

  In October Dr. Blum got his wish. Dr. Malik of Berkeley and Greg Mori, a student,
devised a computer program that could crack Gimpy -- both the simple version used
by Yahoo and the harder one on Captcha's Web site.

   Since its inception two years ago, the Captcha effort has been building. Several
research teams have joined the Captcha effort, trying to make and break Captchas and
even using the ideas behind Captchas for new lines of research.

  Researchers at the Palo Alto Research Center modified a program used for
scanning text to create a program that could solve certain types of Yahoo-Gimpy
puzzles, says Dr. Henry Baird, who was in charge of that effort. The group is also
developing a new text-based Captcha called Baffletext that it hopes to license to
e-commerce sites.



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   Inspired by the themes behind Captchas, Dr. Doug Tygar, a professor of computer
science at Berkeley, and his student Monica Chew are developing alternatives to
passwords that are tailored to human skills. Humans have trouble remembering long,
random strings of characters, yet they excel at remembering faces and objects, noted
Dr. Tygar.

  Dr. Malik said he first became interested in the effort after attending a Captcha
conference at the Palo Alto center in January. After he and his former student Dr.
Serge Belongie, now at the University of California at San Diego, developed a new
object recognition technique modeled to have some of the properties of human vision,
Dr. Malik decided that Captchas were ideal for testing their method.

  The Yahoo-Gimpy cracking program, written by Mr. Mori, takes a version of the
easy Gimpy, a distorted word displayed in a cluttered background, and finds some
points along the boundary of each letter, using standard techniques of computer vision
theory.

  Then, applying the Malik-Belongie method, it makes a radial chart for each point
indicating where the other boundary points are in relation to it. The charts of
boundary points for that letter are compared with the charts of boundary points for all
26 possible letters. The closest match is usually the correct answer.

  Using various tricks to make it run faster, the program can crack an easy Gimpy
puzzle in a few seconds, and it gets the right answer over 80 percent of the time.

  For the harder version of Gimpy, the researchers devised a program that examines
entire words instead of individual letters, so its performance is in minutes rather than
seconds, and it gets the puzzle right only about a third of the time. Still, the program
will need on average only three tries to get the right answer.

  Dr. Malik and Mr. Mori are exploring ways of improving the performance of their
program on Gimpy that will also improve their general technique of recognizing
objects in a cluttered background.

    ''We want to keep working on this in a principled way so we can use the same
technique on an outdoor scene with buildings, trees and cars,'' Dr. Malik said.

  The general technique, he said, will have many practical applications, like
automated recognition of military targets or detection of trademark infringements on
the Internet.

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  Meanwhile, Yahoo will have to install a new Captcha that is resistant to Dr. Mori's
program. This task will fall to Dr. Manber's successor, since Dr. Manber moved to a
new position last month as chief algorithms officer for Amazon.com. There, he said,
he plans to continue his collaborations with academic researchers.

  ''I'd love to foster more cooperation between industry and academica,'' he said. ''It's
great for everybody.''




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