System requirements

Q: What kind of computer or mobile device do I need to play Stall Catchers?

A: Stall Catchers is designed to work on an Internet-connected computer running any modern operating system and internet browser with JavaScript enabled.

Q: Do I have to install any software?

A: Nope. Stall Catchers does not require the installation of any special software. It just runs on your Web browser.

Q: Do I need a fast Internet connection to play this?

A: It depends on how patient you are ;) The faster your connection, the less time you will have to wait for each vessel movie to load. With a normal Internet connection, you might not notice any delays at all (and we load the next movie in the background to help). But with a very slow internet connection (~40 kbps) it could take up to 90 seconds for each movie to load. (Each movie is about a 0.5 Mb download).


Q: Do I need to be a scientist to contribute to Stall Catchers?

A: Not at all! Anyone can contribute by watching vessel movies and searching for signs of stalls.

Q: Is there an age limit to participate?

A: Nope!

Q: I have doubts about my ability to annotate movies correctly. Can I still participate?

A: Absolutely! Your answers will be combined with those of other participants to produce a “crowd” answer, so you have no reason to worry about getting each answer right. Just give the best answer you can, and have fun!

Q: What do I need to play the game? Does Stall Catchers download anything to my device?

A: All you need is a browser and an internet connection. The game does not require installation of any software.

Q: Why can't scientists do this themselves?

A: Even though scientists at Cornell University have powerful tools to acquire Alzheimer’s research data, the analysis step is so time consuming that it would take decades for a small group of researchers to analyze the data on their own. By playing this game, we could speed up the research by orders of magnitude!

Q: How do I start?

A: View the tutorial video (under “Tutorial”) and, if you feel you need a more in-depth instruction, you can read the written description of “Finding Stalls” on the same page. Then go ahead and Register! You’ll be taken straight to the game after you click on the email confirmation.

Q: Why do I have to register to play the game?

A: In order to produce valid scientific results we have to keep participant answers separate from each other. This also allows us to update your personalized dashboard with your online accomplishments.

Q: How do I change my password?

A: Click the login link at the top of the page and then click the “Forgot password” link. You will receive a password reset email. Just follow the instructions in the email to create a new password.

Q: What is EyesOnALZ, and what does it have to do with Stall Catchers?

A: EyesOnALZ is a citizen science project run by the Human Computation Institute, and supported by the BrightFocus Foundation. EyesOnALZ team includes collaborators from The Schaffer-Nishimura Lab at Cornell University, The Space Science Laboratory at U.C. Berkeley, Sebastian Seung’s Laboratory at Princeton University, WiredDifferently, and SciStarter.

Q: Where do I find more information about the game and the project?

A: Check the “About” section on this site, visit the EyesOnALZ project page, and follow our Blog! You can also find us on

Q: Where can I get support and report any problems?

A: You can get further support by posting on the relevant sections on our Forum. Don’t forget to check the existing threads to make sure nobody else has reported the same issues! We do not provide telephone support, but our active forum will provide quick answers.

Vessel movies

Q: What is the Virtual Microscope?

A: The Virtual Microscope (VM) is a special tool developed by stardust@home citizen science project team. The VM downloads vessel movies from the database and allows you to look into real movies of mouse brain vessels via your web browser.

Q: Where are the vessel movies coming from?

A: Researchers at Cornell University, Schaffer – Nishimura Lab are using two-photon microscopes to look into live mouse brain and acquire high-resolution vessel images. These are then processed to produce vessel movies, and fed into our system for you to annotate!

Q: Have any of the movies been annotated by experts?

A: Some of them. We call these “calibration movies”. They have been fully annotated by researchers at Cornell University (so we know which of them are flowing and stalled). Answering calibration movies right or wrong determines your score. The vast majority of movies, however, have not been seen by experts yet. We call these “real” movies. Real movies are entirely up to the Crowd to annotate!

Q: How many vessel movies are there in the game?

A: We are starting with several thousand vessel movies, but we will add new movies all the time from the Schaffer–Nishimura Lab!

Q: What are “layers” in the vessel movies? What is “layer number”?

A: “Layers” correspond to individual frames in the vessel movies, each corresponding to a layer of brain tissue at a different depth. Therefore, as you scroll through the movie, you are looking at deeper and deeper layers of the brain tissue and the vessel. “Layer number” indicates which layer you are looking at. This is especially useful to track the beginning and the end of the movie while Autoscrolling. It is also useful when commenting on a vessel to let other people know which layer(s) might be relevant to your comments.

Finding Stalls

Q: How can I tell if a vessel is stalled?

A: If you see at least one dark spot in the vessel that doesn't move, then it is probably stalled. Check also the “Tutorial” section for more tips and examples.

Q: Where can I find more examples of stalled and flowing vessels?

A: The “Tutorial” section contains more examples of stalled and flowing vessels, and tips about annotating movies.

Q: How many vessels am I annotating in each movie?

A: One. Each movie should contain a single vessel segment enclosed within a green outline and following the shape of the outline. If you think the area contains more than one vessel, you can notify us via the Forum. Sometimes more than one vessel appears within an outlined area. When this happens, the vessel you should be annotating is the one that most closely follows the shape of the outline.

Q: Where can I review the tutorial video?

A: Under “Tutorial” tab at the top panel. You can view the tutorial as many times as you like, and there is an in-depth written tutorial there too!


Q: How is my score determined?

A: Your score is roughly a function of the vessel difficulty and your proven ability to detect stalls.

Q: Can my score go down?

A: Your score will never go down :)

Q: What does "level" mean?

A: Level indicates how experienced you are as a stall catcher. Each time your score gets high enough, you go up another level. It takes more points to get promoted at higher levels than at lower levels.

Q: What does "next" indicate?

A: This tells you how high your score needs to get to advance to the next level

Q: How is my rank determined?

A: Your rank is based on your score relative to other participants. The best possible rank is 1. The lowest possible rank depends on the number of participants.

Q: What does the "movies" statistic refer to?

A: The number of vessel movies you have annotated since you became a Stall Catcher

Q: What does the "stalls" number mean?

A: This indicates the number of stalls you have correctly identified as verified by an expert.

Q: What does sensitivity mean?

A: Your sensitivity indicates your ability to distinguish between flowing and stalled vessels. When your sensitivity is higher, you will get more points for each correct annotation. Your more recent activity has a greater impact on this number than your past performance. In general, your sensitivity will fluctuate depending on how alert you are on a given day, and may increase as you become more experienced.

Q: What does the layer number represent?

A: This indicates which layer of brain tissue you are looking at at any given moment. When you move the slider back and forth to watch the vessel movie, you are not only moving backward and forward in time, but also moving upward and downward through layers of brain tissue. These layers are numbered such that layer 1 is at the top of the stack.

Q: What does the "autoscroll" checkbox do?

A: When "autoscroll" is checked, the vessel movies will play automatically and repeatedly so you don't have to use the slider.

Q: What does the "feedback" checkbox do?

A: When "feedback" is checked, each time you give an answer, you will see feedback about how your answer compares to answers from experts or other stall catchers.

Q: What does the "flag movie" checkbox do?

A: When you check the "flag movie" checkbox, that lets our experts know there is something wrong with the vessel movie. Please do not use this box to indicate that the movie is too difficult. It should be used to flag a technical issue; for example, to indicate that the movie did not load properly. It lets us know that we need to look into something related to that movie.

Q: What does a “Maybe!” answer mean? Why is it “up to the Crowd”?

A: Since vessel data analysis is so time-consuming, experts cannot analyze all the movies by themselves. That‘s why some movies in Stall Catchers have not been answered by experts. We call them “real” movies, and we cannot tell you whether you answered correctly, i.e. whether they are flowing or stalled.

This is where the Crowd comes in. We will use the crowd consensus to determine the flowing/status of the movie, when it has been answered by multiple stall catchers! You get points for your contribution in any case!

Q: What does a "flag feedback" mean?

A: Check this box if the Expert feedback seems wrong or confusing, or if there is inappropriate community feedback.

Q: I continue to get a message "wrong reCAPTCHA" while registering. What do I do?

A: If you are sure your input is correct, and you have tried several times without luck, it is possible that reCAPTCHA is not working at the moment. reCAPTCHA is an external service that might come offline for a reason beyond our control. Do try again in a few minutes or a few hours at most! Email us at if the problem persists.

Q: Redeem button. What do the messages “No points yet” and “Redeem points!” mean?

A: The redeem button allows you to claim back the points you earned for the real movies answered correctly. Since real movies have not been seen by experts, we rely on the crowd to determine whether they are flowing or stalled. When you annotate a real movie you will most often get a “Maybe!” answer, and a few points as a reward. However, as soon as we accumulate enough crowd annotations to know the answer for certain, you will be able to redeem the full points you earned, if you answered the movie correctly. Click on the Redeem button when the message changes to "Redeem points!" to get the full points you earned for redeemable real movies (the amount per movie will compare to that earned for calibration movies). After you have redeemed your points the message will change back to "No points yet", until at least one more of your annotated real movies becomes available to redeem again. If you click on the “No points yet” message, you will be able to see how many movies are in the queue to be redeemed, e.g. "5 movies pending".