# Twenty-two divers played a gambling game 100 feet underwater and the deeper group kept picking the losing decks while previous dive count offered no clear protection, a sign that nitrogen narcosis may bend judgment before people notice it

> Twenty-two divers went underwater with a tablet and a card game, then split into two very different patterns of choice. The group working at 30 metres, close to 100 feet, scored far worse than the group at 5 metres. The difference did...

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Byline: ARGO.net Editorial Team
Published: 2026-08-15T00:55:02+00:00
Categories: Explainer, Humans

![Two scuba divers capturing the vibrant marine life near an underwater wreck in crystal clear waters](https://www.argo.net/wp-content/uploads/2026/08/scuba_diver_underwater_tablet.jpg)

**Twenty-two divers** went underwater with a tablet and a card game, then split into two very different patterns of choice. The group working at **30 metres**, close to 100 feet, scored far worse than the group at 5 metres. The difference did not come from age, body size, sex, or the number of earlier dives. It appeared during a task built to test how people handle risk, reward and delayed consequences.

The work came from **Pauliina Ahti** and Jan Wikgren at the **University of Jyvaskyla** and it was reported in [**Diving and Hyperbaric Medicine**](https://doi.org/10.28920/dhm53.4.306-312). Their study suggests that breathing **compressed air** at a depth many recreational divers still recognize as routine can affect *decision-making* in a way that is hard to detect from confidence alone.

Divers often describe narcosis as a fuzzy, drink-like feeling, but the new result points to a more practical danger. A person can keep moving, reading instruments and following a plan, while doing a worse job of learning which choices lead to losses. In open water, that kind of slip could affect timing, gas use, route changes, or responses to a small problem before it grows.

## Why a card game matters underwater

The researchers used the [**Iowa Gambling Task**](https://dictionary.apa.org/iowa-gambling-task), a standard psychology test in which people choose from decks that look similar at first but reward very different habits. Some decks give tempting short-term wins and larger long-term losses. Other decks pay more slowly and end up safer over time. Good performance depends on noticing the pattern and changing behavior as the game unfolds.

That setup fits diving better than a simple reaction-time test. Deep dives rarely fail because a diver cannot tap a screen quickly enough. Trouble is more likely when someone feels calm, sees several acceptable options and has to choose the one that protects the rest of the dive. The task asks whether a person can move away from bad options before the cost becomes obvious.

The study speaks to a part of human behavior that people often trust too much: the feeling that experience will rescue judgment. Divers learn procedures, repeat drills and build comfort in the water. The game tested whether those strengths still hold when depth changes the way the brain weighs risk and reward.

## What happened at 5 metres and 30 metres

The experiment divided the volunteers evenly between shallow water and deeper water. One group completed the task at 5 metres, while the other did the same work at 30 metres. Both groups used underwater tablets, which helped keep the test environment close to real diving conditions instead of shifting part of the job back to dry land.

The deeper group scored much lower. According to the study abstract, divers at 30 metres had a mean score of 1,584.5, while divers at 5 metres reached 2,062.5. The same report says that age, body mass index, gender and previous dive count did not explain the gap.

**Nitrogen narcosis** has been discussed for decades, yet many divers think of 30 metres as a threshold where effects are mild and manageable. The authors argued that higher cognitive functions needed closer study at that depth, because a multitasking diver can face several decisions in quick order. Their result supports that concern.

The design also matters because it asked both groups to do the same kind of mental work under water rather than comparing a dry-land test with a submerged one. That choice reduces a simple objection that any score drop came from handling a device in the water, wearing gear, or dealing with the odd feel of a tablet during a dive. The study cannot remove every source of noise, but it does make the depth contrast more meaningful because the shallow group faced the same broad setting without the extra pressure load of 30 metres.

## Why experience did not cancel the effect

One of the most striking details is what failed to help. More dives in the logbook did not predict better choices on the task. The study therefore points to a deeper-water weakness that experience alone may not cancel when divers have to sort good decks from bad ones.

That does not mean experience loses all value underwater. Training still helps with buoyancy, gas checks, teamwork and emergency habits. The narrower lesson is that practice may not fully protect the part of the mind that updates a choice strategy while a person is under pressure, distracted, or feeling unusually sure of themselves.

A related [20-meter study](https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2017.01000/full) found selective drops in some [**executive functions**](https://dictionary.apa.org/executive-function), even when simple reaction time held up. Put together, the two papers point in the same direction: underwater impairment may spare basic speed while weakening the mental control needed for flexible choices.

## What narcosis may be doing to judgment

The exact mechanism was not measured directly in this study, so caution is needed here. The broad diving explanation is that increased pressure raises the narcotic effect of gases such as nitrogen. Divers may feel relaxed, unusually confident, or slightly detached and those states can make a poor option look acceptable for too long.

Judgment in the card task depends on learning from a string of wins and losses, then resisting the lure of a deck that offers a quick payoff. A diver under narcosis may still understand the rules, yet respond less effectively to the slow accumulation of evidence. That is the kind of change that can slip past self-awareness because the person often feels able to continue.

A short [diving medicine commentary](https://www.ddrc.org/snippets-from-the-research-world-dont-gamble-at-depth-nitrogen-narcosis-and-decision-making/) on the paper described the result in practical terms for working divers. The concern is straightforward: a person can stay functional enough to keep diving, while the quality of choice behind the dive becomes less reliable.

## What the study can and cannot tell divers

The paper is informative, but it is still a small study with 22 people split into two groups. It compared one shallow depth with one deeper depth and it looked at a single kind of task. The result suggests a real risk signal, yet it does not map every kind of underwater decision or show the exact depth where each diver's judgment starts to drift.

Even with those limits, the message is useful. Divers and instructors often plan around obvious failures such as panic, equipment trouble, or loss of visibility. The study points toward a quieter weakness: a person may stay calm and still make poorer choices. That possibility argues for conservative planning on air at depth, simple task loading and team habits that catch bad calls early.

Another implication concerns how divers talk about feeling fine. Confidence is a weak safety test when the ability under pressure is the very thing being altered. The study adds weight to a practical rule already familiar in diving culture: deeper air dives deserve respect even when the diver feels normal.

Researchers will need larger groups, repeated dives and perhaps designs that follow the same people across several depths before stronger claims are justified. For now, the clearest takeaway is behavioral. At about 100 feet, some divers may keep choosing the wrong option for longer than they realize, which is exactly the kind of error that can matter underwater.

There is also a human-factors lesson beyond scuba itself. People often judge their own readiness by how steady they feel, how routine the task seems and how many times they have done it before. The study pushes against that habit. A diver can feel settled, keep a normal pace and still update choices less effectively when conditions change the brain's response to risk. In safety terms, that means checklists, buddy cross-checks and conservative depth planning are useful because they reduce the number of moments when private confidence is asked to carry the whole decision.