As the patients became sleepier, they were less accurate at correctly identifying the pictures and their response times were slower.
To try and work out why the sleepy patients were performing poorly, the researchers used implanted electrons to measure signals from individual neurons in their brains during the test.
They found that in the tired patients, their neurons responded more slowly, fired signals more weakly and transmitted for longer compared with the brain cells from well-rested brains.
They also found evidence that suggested parts of the tired brain were trying to take localised naps, with areas firing more slowly and showing sleep-like slow brainwaves.
This regional brain napping has been seen before in sleep-deprived rats whose brains also seemed to show localised slow brain cell firing and a reduced ability to perform cognitive tasks.
Knowing that tired brains reduce our reaction time and danger identification accuracy, as well as make us perceive and react to the world more slowly, opens up questions around the potential dangers of driving or using machinery while tired.
We already know that the performance of the brain declines with alcohol consumption, and these new results show that tiredness while driving could be just as deadly.
If it takes your tired neurons more time to respond to a simple photo identification game, imagine the consequences of a slower reaction response if a pedestrian walked out in front of your car.
Sadly, unlike a breath-alcohol test, there is no easy test to externally measure how tired a person's brain is, so the responsibility lies on the individual to make good decisions about their mental clarity before driving.
There is no set number for the amount of quality sleep we need to function properly.
Studies suggest it hovers around eight hours for most of us, with some needing more and some needing less. The general rule is that if you wake up tired and spend the day longing for a nap then you are probably not getting enough sleep.
Wearable technologies such as smart watches can help us to monitor our sleep cycles and track them against our mood to determine individual preferences.
Unlike eating and breathing, we still don't fully understand why people need to sleep, but we do know that sleep is essential and getting enough sleep is important for your health.
Some theories link sleep to the time our brain needs to store its memories from the day, others link sleep to hormone regulation. Whatever it is, sleep deprivation has been linked to weight gain, inflammation, diabetes and heart disease.
Life is busy, and getting enough sleep is tough, but prioritising sleep could actually help you to live longer, healthier and less grumpy lives.
Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science. Tweet her your science questions @medickinson
