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This article is the fifth of a series in which I explain what my research is about in (I hope) a simple and straightforward manner. For more details, feel free to check the Research section.

In my last post we faced a hard problem: If a person visits a museum, for instance, we could give them information on the piece they are looking at. But computers don't have eyes! We could use a camera, sure, but that only works if there is only one art piece nearby. If there are several paintings close to each other, how do we decide which one of them is the interesting one?

One way is through what we call eye-tracking. This technology works like a regular camera, but with a catch: it doesn't only look forward, but it also looks backwards, at you! If you wear one of these so-called eye-trackers, it follows the movement of your eyes and records not only the entire scene (like a regular camera) but also a tiny dot that points out what you were looking at. Some colleagues and I found that eye-movement gives you a very good guess at what has captured someone's attention. After all, if you are interested in something, you are probably looking at it.

But there's a complication: eye-trackers are bulky, expensive, and take a long time to set up. And most people feel uncomfortable knowing that someone is recording their activity all the time. It is safe to say that we won't be wearing eye-trackers for fun anytime soon, and that's not great: what good are our results, if no one wants to use them?

Luckily, a man named John Kelleher came up with a smart idea: whenever we are interested in an object, we look at it and get closer. He then applied this idea backwards: if we are looking in a certain direction and walking towards it, all we need to do is figure out what is right in front of us - that must be the object we care about. This technique is called visual salience, and it's a good alternative to an eye-tracker: rather than wearing expensive glasses, all we need to know is the direction in which they are walking. It might not be as effective, but it's good enough for us.

Following people's attention is important if we want our computers to cooperate with us: if a computer asks you to turn on the lights, but you start walking towards the fire alarm, it should warn you immediately that you are about to make a mistake. How to correct that mistake, however, is the topic of the next (and final) article.

# Previous posts

So, you have successfully created an online community. People seem genuinely engaged, and you have interesting discussions going on. And then one day I show up, decide that "it would be a shame if something were to happen to your little communnity", and start harrassing your users because... well, because. Call it 4chan, Gamergate, MRA or trolls, there's always a group ready to drag a community into the ground.

Like I said last time, one of the main characteristics about the internet is that you can't block me, you can only block my user. So let's focus, from the simplest to the more complex, in how could you keep me from being annoying and/or harrassing other people in your community.

## Privileged users

The first step I suggest you take is a hierarchical scale of users. It doesn't have to be too complex - I'd start with something like this:

Anonymous users are those that have not yet logged in. Usually they are allowed read-only access to the site, but in some cases not even that. As a counter-example Slashdot is known for allowing anonymous users to post and comment on the site, although with a catch that I'll discuss later.

New users should have limited posting capabilities - maybe they can only vote but not comment, or their comments are given partial visibility by default. Getting out of this category should be relatively easy for a "good" user (although time-consuming - no less than an hour, perhaps even days), but it should definitely annoy those that are only "giving the website a try".

Your regular users are the ones that actually use your site as intended. They can post and comment at will. And finally, the power users are allowed some extra permissions - usually this mean they can edit or remove other people's posts. This level should be pretty hard to achieve.

## The iron fist of justice

Now that you have user levels, new users are your main concern: it is not unusual for trolls to create thousands of accounts (automatically, of course) and use them to assault a particular user. Remember: any regular user should be able to stop the noise in a simple and straightforward way - otherwise you risk becoming an online harrassing platform, and you'll have to publicly apologize like Twitter's CEO often does.

Our first moderation tool will be karma points. Each time a user contributes to our website, other users can rate this contribution positively or negatively. Contributions with "high karma" will be given a predominant position, while contributions with "low karma" will be buried. This is how Slashdot can allow anonymous contributions without being buried in dumb comments: every comment posted anonymously will have very low karma by default, but if enough users vote it up, it will eventually be seen by everyone else. Similarly, Hacker News will not allow users to vote negatively if they haven't yet reached a certain karma threshold.

Sidenote: you don't want to rank your posts/comments simply based on who has the highest number of votes. Instead, take a look at reddit's comment sorting system.

Another tool you'll find useful is the good old ban. A temporary ban means that a given user cannot post for a given period of time, while a permaban (permanent ban) means that the user is kicked out forever. This is a standard tool in every forum, but we can still do better: given that nothing stops a banned user from creating a new account and continue their toxic behavior (and remember, now they are pissed for being banned), you can use a hellban. When a user is hellbanned, no one but them can see their activity. The user can still log in, comment and post, but this activity is invisible to everyone else. From their point of view, it looks as if no one cares about them anymore, and it's not unusual for them to just leave.

Finally, you might also want to consider a "report" button, through which users can report unruly behavior. This should be more or less automated, but you cannot blindly trust these reports: you risk trolls banding together and reporting users at will. To prevent this, an automated recourse method should be enough - a moderator is notified, and the user is not fully banned until a final decision is reached. And finally, if you want to go the extra mile, you could have a "protected" flag that keeps certain users from being reported.

That's about all you can do at this level. There are no new ideas here, which is good - now you know that these concepts have been tried and tested before. In next two posts I'll be discussing about things that might not make as much sense, so stay tuned.

Once upon a time, you would create an e-mail account and use it for a long time without receiving spam. In fact, whenever you received your first spam message, you'd know exactly who to blame: that one cousin of yours who'd send you every single motivational powerpoint she came across, along with a list of 1500 other e-mail addresses. We could argue about who's the spammer in this situation, but that discussion will have to wait.

That kind of control over your account is no longer possible: even if you never share your account with anyone, you will at some point get spam. It's just the way things are, the "background radiation" of the internet. Luckily for us, things got so bad that a lot of smart people sat down to think really hard about this, and came up with Bayesian filtering, a technique so effective that most of us don't even bother checking our Spam folders anymore.

So we1 succeeded once. It's a good thing to remember, because we have a much harder battle to fight now: trolling, and it's ugly cousin, online harrasment.

Let's say you post a message on an online board. These are some of the things that could happen, in no particular order:

• You could get an interesting, well thought reply (note that "well thought" doesn't mean "agrees with you"). It happens.
• You could be modded down by people that disagree with what you just posted, even if the rules say they shouldn't.
• You could be flooded by negative messages, because a certain group decided to impose their point of view. This is called brigading, by the way, and it's usually not personal - they oppose your point of view, but not you.
• You could be flooded by negative messages, because a group has decided to target you online for something you said, or did, or are.
• You could be posting in behalf of a company, in order to speak in favor of your products posting as anyone-but-an-employee. This is called being a shill, and most websites either pretend that it doesn't happen or they don't care.
• You could be trying to derail a discussion, in order to make sure a certain point is not brought to light, or is drowned in the noise. This usually implies that you work for a government agency, it's being done right now, and it works.

We used to believe that everyone on the internet would eventually behave nicely, and that we could build our services based on trusting the 95% of users that have no hidden agenda. This is sadly not so, because

1. ... people have not behaved nicely on the Internet since September 1993.
2. ... 5% of very loud users are a lot more noticeable than 95% of the quiet ones. A post-mortem of a DARPA Challenge showed that a single person can sabotage the work of thousands of well-meaning volunteers.

In the follow-up articles I'm going to comment on what I perceive to be three main points in which this issue could be attacked. They are

• Anonymity: there's no way of taking measures against a person, only against a user. This is by design, and I'm not arguing that we should get rid of anonymity. We should instead focus on identifying toxic users, which I think can be done implementing user groups.
• Flamewars: derailing discussions in order to kill them. This may be a job for pattern matching, identifying when the shape of a discussion is tending towards known anti-patterns. We might also want to add clustering, in order to identify brigades.
• Harrassment: perhaps the harder one, requires sentiment analysis techniques to identify negative comments and kill them before they reach their destination.

In the follow-up essays I'll present some papers about how one would go about attacking each point. I have no reason to believe that this techniques are unknown (some of them are already implemented), but I post them hoping that, much like Bayesian filtering, someone will read them and have an "oh, wait" moment).

Coming up next: anonymous users and user groups.

I'm the proud owner of a Genius MousePen i608 graphic tablet (also known as UC-LOGIC Tablet WP8060U). This tablet is quite old and cheap, which is more often than not a recipe for headaches.

One very specific problem that I have: my tablet has an aspect ratio of 4:3, like old computers did, but both my desktop and laptop's screens have an aspect ratio of 16:9. Why is this a problem? Because my computer believes that the tablet and screen have the same aspect ratio, and whenever I draw a circle on my tablet it comes up on screen as an oval.

There are two possible solutions to this issue. One is changing my screen's resolution to match the 4:3 aspect ratio, which is annoying: I have to change the screen settings, then fiddle with my actual, physical screen so it doesn't stretch the image, and then I have to undo both steps once I'm done. The second solution requires a bit more calculations, but it's the right way: we'll configure the tablet in such a way that Linux recognizes the difference in ratios.

To be more precise: We will define a rectangle with the same height as the screen and a proportional width (sticking to the 4:3 ratio between width and height), we will position that rectangle in the center of the screen, and all movements in our tablet will only apply to that section of the screen. All movements on the tablet will translate to this rectangle without distortion, and if we need to interact with the screen outside this area we can still use our mouse.

The following code will run all the numbers for us. In essence, it will calculate the required set of parameters, and then it will modify the property Coordinate Transformation Matrix of xinit accordingly:


# Get the current screen resolution
resolution=xrandr | grep '*' | cut -f 4 -d ' '
width=echo ${resolution} | cut -f 1 -d 'x' height=echo${resolution} | cut -f 2 -d 'x'

# Get the proper tablet width, according to the 4:3 proportion
tablet_width=echo "${height} 3 / 4 * n" | dc # We need to calculate four parameters c0, c1, c2, c3. For that, we use the # 'dc' utility, which uses postfix notation (i.e., you write "7/3" as "7 3 /"). # # Note: if you want to move the usable section of the screen left or right, # take a look at the 'x offset' value. Also note that, since we are using the # entire height of the screen, the 'y offset' is simply 0. # Touch area width / width c0=0echo "7 k${tablet_width} ${width} / n" | dc # Touch area x offset / width c1=0echo "7 k${width} ${tablet_width} - 2 /${width} / n" | dc
# Touch area height / height
c2=1.0
# Touch area y offset / height
c3=0.0

# Obtain the device ID for the graphics tablet. Note that UC-LOGIC is my device
# ID, but yours may be different
device=xinput | grep UC-LOGIC | head -n 1 | cut -f 2 -d '=' | cut -f 1
# Set the Coordinate Transformation Matrix
xinput set-prop ${device} --type=float "Coordinate Transformation Matrix"${c0} 0 ${c1} 0${c2} \${c3} 0 0 1


And that's it! It happens to me often that the transformation doesn't work straight away, in which case unplugging and plugging the tablet again solves the problem. A second issue with every reinstall is that the X server sometimes refuses to recognize my tablet. I solved that problem by adding the following lines to the /etc/X11/xorg.conf file:


Section "InputClass"
Identifier "evdev tablet catchall"
MatchIsTablet "on"
MatchDevicePath "/dev/input/event*"
Driver "evdev"
EndSection


There's a popular song, written by an Argentinean musician called Charly García, called "Los Dinosaurios" ("The Dinosaurs"). The song was released in 1983 in the album "Clics Modernos", and you can listen to it in all its vinyl glory here.

This song represents for me an interesting problem: it is by far my favourite song from this author, and I would like to listen to something similar. But so far all recommendation systems have failed me. Here are some of the reasons why.

A first approach could be to pick something from the same author, or even the same album. This approach, sadly, doesn't work: while Charly García is certainly a prolific author, with 41 published records and countless guest appearances, his main style is oriented towards electronic music, and it doesn't really fit the style of this specific song. If anything, this song is more fitting for his earlier albums, which limits us quite a bit - out of those 41 soloist albums, "Clics Modernos" is the second one.

We could instead assume that this song was written in a certain context, and that looking at authors from a similar context we can obtain similar music. Again, this doesn't entirely work: if we pick "Argentinean songs from the 80's", we would end up with a list of songs that fit perfectly the style of the other 8 songs on this album, but not this one specifically1. Grouping the song into "Latin American music", as some systems do, only exacerbates the problem: there is no relation at all between this song and, say, a Cuban bachata.

If we look at the actual lyrics, the situation gets even worse: "Los dinosaurios" is a thinly veiled critique of the military dictatorship that ruled the country between 1976 and 1983. A lyrics-based systems would most likely fail on two fronts: either it wouldn't understand the references made in the song and label it as "nonsense/fantastical", or it would understand the reference and recommend politically charged songs. Neither approach seems really right - while "The times they are a-Changin" could be a viable candidate for a recommendation, neither "The Revolution will not be televised" nor "Redemption song" fit the bill.

All of these approaches fail for the same reason: they apply a network-oriented measure to a song that doesn't fit the popular rhythm of the time and place in which it was produced, and which doesn't fit the overall style of the author either.

So what exactly am I looking for? A non-technical answer would be "I need a song that contains simple vocals, a piano as it's main instrument, and with raising tension towards the end". Or in the words of the author, a song that "adapts the English sound to Tango". As far as I know, the only system that applied a similarity measure capable of detecting this would be Pandora, but with their system closed to Europe, I cannot tell whether this works or not.

Related reading: The Napoleon Dynamite problem.