Stall Catchers

Some of the slowest work in Alzheimer’s research comes down to a yes-or-no question about a single blood vessel. Stall Catchers hands that question to the public. The free citizen science game comes from the Human Computation Institute, which built it for the EyesOnALZ project with Cornell University’s Schaffer-Nishimura Lab. The BrightFocus Foundation funded it. On Android, the app is listed under the developer name Games for Health.

The scientific problem is narrow. Researchers have linked capillary stalls to the reduced brain blood flow seen in Alzheimer’s disease. A stall is a tiny brain vessel clogged so that blood stops moving. Finding stalls means reviewing video from the brains of live mice, and doing that by hand is slow lab work. Each clip in Stall Catchers is a short black-and-white video with one vessel segment outlined. The player answers one question: is blood flowing, or is it stalled?

No single answer settles anything. The platform combines responses from many players into results reliable enough for research. The project’s pitch is that volunteer answers can spare lab time. The method builds on the virtual-microscope approach of UC Berkeley’s Stardust@home. That puts Stall Catchers in the tradition of crowdsourced scientific image review, a long way from the casual-games market.

That tradition defines its competition: other volunteer projects asking for the same goodwill and spare time. Its reputation fits. Cornell, UC Berkeley, Discover Magazine, Science News, NSTA and public libraries all praise it as an easy, meaningful way for anyone to help Alzheimer’s research. Feedback in app stores barely exists. The game’s main home is the web browser, on a computer, tablet or phone. The Android app is a side entrance, with sparse user feedback and a bare store listing.

• Binary Vessel Judgement: Each short black-and-white clip from a live mouse brain outlines one vessel segment. The player marks it as flowing or stalled.
• Crowd Aggregation: Answers from many players are pooled into research-grade results, so volunteer answers can spare lab time.
• Gamified Progression: Points, levels, badges and leaderboards reward players for coming back.
• Catchathon Events: Live online community events turn solo work into group sessions.
• SciStarter Account Linking: Accounts connect to SciStarter, which suits volunteers who take part in several citizen science projects.
• Proven Foundations: The platform adapts the virtual-microscope model of UC Berkeley’s Stardust@home.
• No Prerequisites: No science background is needed, and the browser version runs on computers, tablets and phones.

One Question, Asked Well

Every clip asks the same binary question, and that narrowness is the best decision in the design. Citizen science projects fail when they ask volunteers for expertise they don’t have. Stall Catchers asks for attention instead. The outline around one vessel segment tells the player exactly where to look. The question becomes “is this moving?” and never “what am I looking at?” That is why no science background is needed, and why press coverage keeps coming back to the low barrier to entry. For a task like this, onboarding friction is almost entirely about understanding the task, and the binary format removes most of it.

The Crowd Is the Instrument

Aggregation is what makes the game scientifically valid, and it shapes everything built on top of it. Answers from many players are pooled into research-grade results, so no one player has to be right every time. Newcomers can contribute without worrying that one wrong call will spoil a dataset.

Aggregation also ties engagement directly to output. More answers per clip means more reliable results, so keeping players is a scientific need as well as a community goal. That gives the engagement loop a purpose that is easy to defend. The time-saving pitch is the project’s sharpest, because it turns an abstract act of volunteering into a concrete trade of time.

Progression and Gamification

Points, levels, badges and leaderboards make up the reward layer. None of it is new. This is the standard gamification kit, applied without much ambition. For a research tool that is a fair trade, but it means the bigger draw is the intrinsic one: knowing that each answer feeds Alzheimer’s research.

Leaderboards create a tension in any crowdsourced labelling task. They reward volume, while the research needs careful answers. Pooling many responses per clip is the structural safeguard that keeps sheer volume from becoming a quality problem. That safeguard is what makes a competitive layer acceptable here.

The Repetition Problem

The design’s main strength also sets its limit. A single question, asked clip after clip, is repetitive by construction. As the project presents it, progression raises the rewards and leaves the task unchanged.

How much that matters depends on the player. For someone motivated by contribution, the repetition is the point: a steady, low-effort stream of useful judgements. For someone who wants entertainment, the loop will wear thin, and points will not hide it.

Catchathons and the Social Layer

The live online Catchathon events are the design’s best answer to repetition. They turn a solitary, monotonous task into a shared push with a set time. The work stays the same while the setting changes. They give the community a rhythm that badges alone cannot.

SciStarter linking extends that community outward. Volunteers who already track their work across citizen science projects can fit Stall Catchers into an existing habit, without starting a new one. For a project that depends on returning players, that is smart ecosystem thinking.

The data is the art direction. Black-and-white microscopy footage from live mouse brains, with one vessel segment outlined, leaves no room for decoration. That restraint is correct, because anything decorative would compete with the faint movement the player has to judge. The outline is the most important UI element, since it defines the task on every clip.

The Android storefront does the product few favours. A sparse listing makes a thin first impression for a project with this much press support.

Short video clips are a light workload by design, so the format should not strain a phone in principle. Age is the bigger concern. The Android build is long unmaintained, so how it behaves on current devices is unknown. Screen size is a design-level issue too. Judging motion in one small capillary asks more of a phone display than of a tablet or monitor.

Android is the only listed platform, but the Android app is not where the project lives.

• Input: Touch suits the task. A flowing-or-stalled decision maps cleanly to a tap.
• Browser alternative: The web version runs on computers, tablets and phones, so Android users can reach the same project without installing anything.
• Maintenance: The app is long unmaintained, so changes the project has made on the web are unlikely to appear in it.
• Footprint: Sparse user feedback and a bare store listing. The game is mostly played in the browser.
• Price: Free.

We recommend the browser over the app for Android owners. The app’s main appeal is a home-screen shortcut, and a browser bookmark does the same job while pointing at the platform the project actively maintains.

Hard to recommend for most people, Stall Catchers has a clear purpose but little polish. Its central design choice, one outlined vessel and one binary question, fits a crowdsourced research task exactly. It removes the need for expertise, leaves accuracy to aggregation, and gives the gamification layer a real job to do. The costs are just as clear. The task is repetitive by construction, the reward systems are off the shelf, and the Android app is long unmaintained. We recommend it narrowly to volunteers who want to put spare minutes toward Alzheimer’s research, played through a browser. As an Android app, it is a dated doorway to a worthwhile project.