System requirements

You can play Stall Catchers on any internet-connected device (computer, phone or tablet), running on any modern operating system and internet browser with JavaScript enabled.
Nope. Stall Catchers does not require the installation of any special software. It just runs on your web browser.
It depends on how patient you are! ;) The faster your connection, the faster each vessel movie loads. With a normal internet connection, you might not notice any delays at all. 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 1.5 Mb download).


To find a treatment for Alzheimer's disease. Researchers at Cornell University have discovered a number of important clues to understanding, preventing and reversing Alzheimer's in mice. But we must answer some key questions before we can find a treatment for humans. We need your help to answer them as fast as possible.
As long as there are unanswered questions concerning reduced blood flow in the brain and Alzheimer's disease at Cornell University, Stall Catchers will keep at it! There is still a lot to learn before we can find a functional treatment target. It doesn't look like we'll be running out of research questions to analyze any time soon!
Not at all! Anyone can contribute by watching vessel movies and searching for signs of stalls.
Nope! Everyone can play.

We've witnessed great intergenerational competitions too!
Absolutely - as long as you are able to view the vessel movies and record your answers, you can take part. We have ways to make sure we get the best out of each answer, so even if you are sundowning or have any other condition that may temporarily affect your performace, there is no way you can negatively affect the data. Every little bit helps!
Of course! You cannot hurt the research data even if you try - you can only help. We use multiple answers for each movie to generate a reliable 'crowd' answer. We also take your sensitivity into account (indicated by the blue bar next to the vessel movie), so if you're having an off day and make a few mistakes, we will interpret your answers accordingly. This way, you have no way to negatively impact the data!

Just give the best answer you can and have fun!
To find an effective treatment for Alzheimer's disease in humans, there is still a lot of data to be analyzed. In Stall Catchers you and other catchers help analyze datasets looking into various questions regarding the role of stalls in Alzheimer's. These are the 'real' or 'research' movies, which are previously unseen and don't have expert answers.

A dataset might be concerned with a particular diet, lifestyle aspect or a drug that might have a role in the disease or an ability to reduce the symptoms.

Once a dataset is analyzed, the results are sent back to the biomedical research lab to draw conclusions. We will report all the findings on our blog.

Learn more in this short video: How does playing Stall Catchers help find a cure for Alzheimer's disease?.
Even though the 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 them to analyze the data on their own. By playing this game, you can help speed up the research by orders of magnitude!
At the moment, no image processing algorithm is up to the task of determining whether blood vessels are flowing or stalled at high enough accuracy. That's why we have to rely on the human eye for now. However, we use your answers to help us develop new machine learning methods, which could soon be analyzing the easy cases, and leaving the challenging ones to humans! See this blog post for more information. In April 2021 we ran the first catchathon that included an automated bot and annotated Stall Catchers data along with human participants.
The Stall Catchers game was created by the Human Computation Institute, as part of the EyesOnALZ project, and in collaboration with the Schaffer-Nishimura Lab at Cornell University, stardust@home team at U.C. Berkeley and Previous collaborators include Sebastian Seung’s Laboratory at Princeton University, WiredDifferently and others.
BrightFocus Foundation funded the creation of Stall Catchers. The project has since been supported by donations from Microsoft and receives continuing support from the Schaffer-Nishimura Laboratory at Cornell University, as well as contributions from individual donors.
EyesOnALZ was the original name for this project because we thought we would need a second game besides Stall Catchers to help with another aspect of the research. Eventually, we figured out how to do this using only machines. For more details on the history of this, please see this blog post.

Learn more about the project and the team on the About page on this site.
Check the About page on this site, or follow our blog and social media channels. You can also find us on SciStarter. There are also many articles that have been written about Stall Catchers that do a good job of explaining it. This article in Wired Magazine is very well written and captures both the human impacts and the technical aspects of Stall Catchers. There is also an excellent PBS documentary segment that describes the project and how it got started and interviews some of the players and people impacted by Alzheimer’s disease.

If you have any questions at any time, you can ask them on our forum, or email us at

Getting started

To get started, head straight to Stall Catchers, watch a quick tutorial and register. Once you sign up, we will walk you through the interface and help you analyze the first ten movies.

If you feel you need more in-depth instructions, check out the tutorial, vessel examples and other helpful content on the Get Started page (under 'How to' in the top menu). You can also replay the tour of the interface at any time by clicking 'Replay tour'.
Once you register, we will send you a link to set your password at the email address you provided. Just follow the instructions in the email and create your password. Your password must have a minimum of 6 characters.
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.
To produce valid scientific results, we have to keep participant answers separate from each other. This also allows us to update your stats with your individual accomplishments.
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 go offline for reasons beyond our control. Do try again in a few minutes or a few hours at most! Please email us at if the problem persists.
First, make sure that you are logging in with the same email address you used to register and that it is typed correctly. If you think you might have forgotten your password, click on the 'Forgot password' link and follow the instructions in the password reset email you receive.

Note that if you used Facebook or Google+ to register, you need to follow the respective Facebook/Google+ links on the login page as well (typing your email address & password will not work).

If you are still having trouble logging in, please email us at and we will resolve it for you!
You can get further support by reporting issues via email -, or 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.
You can watch video tutorials and can find more in depth info on the Get Started page. You can reach it at any time by clicking 'How to' on the main menu, and clicking 'Getting started'.
Click 'How to' on the main menu, and click 'Replay the tour'. You can replay the tour as many times as you want!

Vessel movies

The Virtual Microscope (VM) is a special tool developed by the 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.
Researchers at Cornell University, Schaffer-Nishimura Lab are using two-photon microscopes to look into live mouse brains and acquire high-resolution vessel images. These are then processed to produce vessel movies, and fed into our system for you to annotate!
Stall Catchers analyzes Cornell University’s Alzheimer’s research data. This research is approved by the Institutional Animal Care and Use Committee, and the lab makes extensive efforts to minimize the pain and distress of the mice used in research, while simultaneously seeking to gain as much valuable data from each animal used.
Some of them. We call these 'training' or 'calibration' movies. They have been fully annotated by researchers at Cornell University, so we know which of them are flowing or stalled. Answering training movies right or wrong determines your score. The vast majority of movies, however, have not been seen by experts yet. We call these 'research' or 'real' movies. Real movies are entirely up to the crowd to annotate!
Each dataset can contain anywhere between several thousand to 100,000 real movies. We are adding new movies from the Schaffer-Nishimura Lab as soon as they are ready to be analyzed.
If you see at least one dark spot in the vessel that doesn't move, it's probably stalled. Check the Get Started page under 'How to' in the top menu for more tips and vessel examples.
The Get Started page under 'How to' in the top menu contains examples of stalled and flowing vessels, and more tips for analyzing movies.
One. Each movie should contain a single vessel segment enclosed within an outline and following the shape of the outline. 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.
They are probably the 'training' movies. We introduce enough of them to make sure you learn to recognize stalls, measure your "sensitivity" (represented by the blue bar next to the vessel movie) and award you with points.

The key, however, is the 'real' movies which have not been seen by experts. You should see each real movie only once, and your answer will be recorded and used with other catchers' answers to draw crowd answers.

Once we finish analyzing a dataset, we send the results back to the biomedical researchers to draw conclusions. Each dataset is concerned with a particular question regarding the role of stalls in Alzheimer's disease, and gets us closer to finding an effective treatment.
Vessel movie frames correspond to images of mice brains taken via a microscope. Each frame is 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.
Yes. Most movies in the game are research movies. The quality of the movies will vary depending on the animal being studied, the method of taking the images etc. Some datasets might have better or worse quality movies. This is completely normal, and the movies still need to be analyzed!

Some movies may also appear out of focus, have misaligned frames or 'bad outlines'. In all cases, always do your best to give an answer, even if a movie is unclear. If it is particularly problematic, simply tick the 'Flag movie' box, record your best guess and move on. We will look at all flagged movies and resolve or remove them from Stall Catchers.
Some movies may have misaligned frames or 'bad outlines': outlines that are missing, do not align with a vessel, or jump to a new spot in the same movie. These movies occasionally result as a side-effect of the pre-processing of the vessel movies.

In all cases, always do your best to give an answer, even if a movie is unclear. If it is particularly problematic, simply tick the 'Flag movie' box, record your best guess & move on. We will look at all flagged movies & resolve or remove them from Stall Catchers.
It usually takes less time for an expert to just look at a bad outline and make a final determination about the vessel (whether it is flowing or stalled). So in most cases, bad outlines will not be fixed. Instead, the expert will simply remove the movie from Stall Catchers and, if there is indeed a vessel in the outline, the expert will annotate it.
When dealing with real research movies, a lot of them may seem blurry, grainy and/or otherwise unclear. However, even in the difficult cases, it is usually possible to determine whether the vessel is flowing or stalled. Each answer is valuable to us, so just try to give it your best guess! Don't worry about making a mistake either - other catchers will look at the same movies, and we have ways to determine reliable crowd answers.

If a movie seems particularly problematic, simply tick the 'Flag movie' box, record your best guess & move on. We will look at all flagged movies and resolve or remove them from Stall Catchers.
At the moment there is no in-game feature to increase the movie size (they are at their maximum resolution), but you can always try zooming a bit in your browser (Control + Plus sign usually works, or Command + Plus sign on Mac). Also see below for tips on changing contrast to see movies better.
There is no in-game feature to change these parameters for the movies, but you could also try changing the contrast of your screen itself to make the movies stand out a little better. A more long-term solution could be inverting the colors in your browser for the Stall Catchers window. Most browsers have plugins for that, e.g. 'Invert Colors' on Firefox, 'Invert Page Colors' on Chrome etc.

Scoring and stats

Your score is roughly a function of the vessel difficulty and your proven ability to detect stalls.
Your score will never go down!
In general, the number of points depend on the participant’s sensitivity level (represented by the blue bar) and on the type of movie:

For calibration movies you receive your total points immediately, and depending on the correctness of your answer your blue bar may rise or fall. The number of points you can earn for a correct answer to a calibration vessel ranges from 1 to 2320, depending on the height of your blue bar. For more difficult movies, these points might be doubled, tripled, or even quadrupled!

For “real” movies, which are the unanswered vessel movies being evaluated from the current dataset: depending on your current skill level, which is depicted by the height of the blue bar, you will immediately receive between 1 and 116 points regardless of your answer. “Redeem later” means that we won’t know if your answer is considered correct or not until we establish a final crowd answer, which is based on your answer combined with the answers of other participants who evaluated the same movie. Once this happens, if your answer agrees with the crowd’s answer, you will receive up to 2320 more points, depending on your skill level, when you click the redeem button.
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.
This tells you how high your score needs to get to advance to the next level.
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.
The 'Movies' number indicates how many movies you have annotated in Stall Catchers to date. 'Movies (research)' indicates the movies that represent brand new research data, while 'Movies (training)' indicates movies previously answered by experts that are used to help assess and train catchers.
This indicates the number of stalls you have correctly identified as verified by an expert.
'Lab time' indicates the lab-equivalent research time that your contribution in Stall Catchers has helped achieve so far. Note that exact lab time is tricky to calculate, and the final results depend on the contributions of many catchers, but that should give you a rough idea!
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.
There is a timesheet option in the profile menu, which you can access by clicking on your username in the upper right. From the Timesheet page you can specify the dates for which you want to list your Stall Catchers contributions. Feel free to print this timesheet and share it as needed to verify your volunteer activities.


'Movie frame' indicates which layer 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.

This is useful to track the beginning and the end of the movie while autoscrolling (autoplaying). It is also very important when commenting on a vessel to let other people know which layer(s) might be relevant to your comments.
When 'autoscroll' is checked, the vessel movies will play automatically and repeatedly so you don't have to use the slider.
When 'show answer' 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.
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.
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 'research' or 'real' movies, and we don't immediately know 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 once it has been answered by multiple catchers. You get points for your contribution in any case!
Check this box if the expert feedback seems wrong or confusing, or if there is inappropriate community feedback.
The redeem button allows you to claim back the points you earned for the research movies answered correctly. Since research movies have not been seen by experts, we rely on the crowd to determine whether they are flowing or stalled.

When you annotate a research 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 your answer agreed with the crowd.

Click on the Redeem button when the message changes to 'Redeem points!' to get the full points you earned for redeemable research movies (the amount per movie will compare to that earned for training movies). After you have redeemed your points the message will change back to 'No points yet', until at least one more of your annotated research 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'.
The tribar indicate the progress on the current dataset. It has three colors that represent completion of three separate phases of our data analysis in Stall Catchers: “Analyze" (yellow, first pass), "Validate" (green, second pass), and "Verify" (blue, third pass). The analysis of each dataset in Stall Catchers occurs in three phases: we collect a first pass of crowd answers for all vessels in a dataset before beginning a second pass, and a second pass on all vessels before we begin a third pass. More information about the multicolor tribar can be found here.
An upward directed arrow next to a username on the leaderboard indicates that this participant is currently climbing the leaderboard. Once it appears the arrow will stay for about five minutes.
The circles next to usernames on the leaderboard indicate whether a user is currently online or offline. The circle is green whenever a participant is playing Stall Catchers and turns off after 5 minutes of inactivity.
The bot icon next to a username indicates that this is not a “human” player but an AI-powered bot that is catching stalls alongside humans. Such bots were taught to play Stall Catchers using data generated by human catchers!

Teams and Leagues

A team is absolutely any group of Stall Catchers players, who choose to pool their scores together and compete with other teams or with each other within a team. Anyone can form a team, although note that you can only belong to one team at a time, so if you create a new team, your membership in the former team will be lost (though you can always rejoin later).
Team Humanity is the team which all Stall Catchers belong to - aren’t we all in this for humanity’s sake? Team Humanity does not compete with other teams, and represents the pooled achievements of all players.
You can contribute to only one team at a time, which is why if you join or create another team, your active membership in the former team will be lost. However, the original team will still retain all the points you contributed, and you can start where you left off if you ever go back. In the meantime, you will have to start contributing points to the new team from scratch. Your individual all-time score will not be affected.
Click on your username and select 'Teams'. This will take you to all teams page. Click on 'Create a new team', fill in a short team registration form, upload a logo, click 'Create' and you’re done!
Click on your username and select 'Teams'. This will take you to all teams page. Browse the available teams by scrolling, switching through pages or searching by keywords in the search box. If you click on team titles you will be taken to their full pages. Click 'Join' to join the team you like.
Click on your username and select 'Teams'. This will take you to all teams page. You can leave your current team by navigating to it on the list and clicking the "Leave" button without selecting a new team. To switch teams instead, choose the one you like from the list and click 'Join'.
In your team page you can copy & share the link that will lead new Stall Catchers players to register and then automatically join your team. Players who have already registered will be invited to join your team. Otherwise, you can advertise your team (and lure the best players from other teams!) in the Stall Catchers topic at .
A league is a group of teams united under one topic, agenda, level or goal - whatever you can think of. E.g., 'Fourth graders' league might be formed by multiple 4th grade classrooms that each form a separate team in Stall Catchers, and compete with each other within the league. Anyone can create a league, and teams can join and switch leagues anytime.
Only one. Any team can choose to compete in one league, and can change it at any time.
Only team owners can do this. Navigate to your Team page and click 'Edit team'. You will see a dropdown menu for 'League' - select the one you want and click 'Save'.
Only team owners can do this. Navigate to your Team page and click 'Edit team'. You will see a dropdown menu for 'League' - select 'No league' and click 'Save'.
The Team score is the sum of points of all its former and current members, contributed while part of that team. The individual scores of a player are added to the team score only as long as that player is a member of the team. Once they leave the team, their newly gained points are no longer added to the team score, but the team retains all the points that the player contributed during the period of membership.
League rank is the position of a team in the leaderboard relative to other teams that are part of the same League.
Overall team rank is the position of a team in the overall team leaderboard. This compares all teams to each other regardless of league membership.
Today/This week/All time team leaderboards list teams that are in the lead during the specified time periods. The daily leaderboards reset at 0:00 UTC every day, weekly - 0:00 UTC every Sunday.


To open the chatbox on a laptop, click on the arrow next to 'Online: X catchers' at the bottom right of your screen. On a phone or tablet, tap the bubble icon in the top menu.
To post a message, open the chatbox, type your message and click 'Send'.
To hide your message, click on you message and select 'Hide'. Your message won't appear in the public history, but it will still be accessible in chat history in the database (visible to admin only ).
All messages are kept in the database with no expiration date.
At the moment, admin is fully controlled by our internal team. We don’t have any other roles at the moment, but those might come with future updates (e.g. moderator).
The chatbox is public and visible to all logged in Stall Catchers users. When using the chatbox, please have in mind Stall Catchers is an international and multicultural community with different tolerances and sensitivities. Be kind and respectful. Here are a few additional rules:
  • no swearing
  • no spamming or scamming
  • don't impersonate admin
  • no cursing or profanity
  • no discrimination
  • no advertising
  • no arguments with others or admin
We reserve the right to hide messages, mute and ban users if these rules are disrespected.
For now, we rely on catchers like you to alert us about any inappropriate content so we can address it immediately. Automated filtering is also coming in future updates.
To report abuse, send an email to . Please add the username of the abusive user, the date and time of the post. That will help us find the post in the database and act upon it. Note that we never discuss our interventions.
Admin messages are shown in green. Admin will post official information about the project, event announcements and so on. Always remember that admin will never ask for personal information or login information.
Those are “sticky posts” - messages by admin that remain at the top of the chatbox until admin “unpins” them. These posts are meant to provide useful and timely information about Stall Catchers.
We are always working to add new features and improve the chatbox, so there’s a chance we released something, but haven’t covered it in this FAQ yet! If you have an urgent question about it, or would like to nudge us to write it up here, you can reach us at

We would like to thank all Stall Catchers participants who gave feedback on the FAQ and an extra thanks to caprarom for the extensive contributions!