Well, if you’re reading this right now, that’s your first problem.
It turns out that your brain switches to autopilot when confronted with written words. Meaning that it becomes literally impossible to look at a word in your native language and only see it as a series of lines and dots. Your brain simply does not allow you to NOT read the word.
Identifying colors on the other hand requires slightly more attention. The brain processes this information more slowly and by time it comes up with the answer, you are already thinking about the color that you just inadvertently read.
This phenomenon is known as the Stroop effect and was first described by American psychologist John Ridley Stroop in 1935.
To give a quick demonstration, the Stroop effect is what makes it more difficult to say the font color in the second row below:
In neuroscientific terms, two areas of the brain have been implicated: the dorsolateral prefrontal cortex (DPC) and the anterior cingulate cortex (ACC). Both of these regions are responsible for conflict monitoring and resolution. The DCC attempts to allocate resources to color recognition while suppressing signals elicited by the written word. This conflict is called semantic interference. The ACC selects the correct response from the competing options and must overcome the delay between reading the word and identifying the color.
It has been said that this technique was used by the US during the Cold War to identify Russian spies (who were presumably slower at reacting when presented with color words written in their native Russian language).
The inclusion of swear words introduces even more interference. Neuroscience has shown that swear words are stored in a different part of your brain compared to the rest of your regular non-offensive vocabulary. This part of your brain is called the limbic system and it deals with emotion and instinct. It is therefore more reactionary and quicker to fire than the cerebral cortex where the majority of language processing occurs. Just think about the first words that pop into your head when you stub your toe or...spill something!
It has been proposed that there are evolutionary benefits to swearing such as providing a mechanism to relieve stress and cope with pain. As well, it has been noted that humans are unique in that they are the only species able to emote aggressively through language without resorting to violence. Anecdotally, this can be seen this in young children, who tend to demonstrate violent behavior less frequently after learning how to communicate with language.
In the context of the game, your brain does two things when faced with a swear word card: First, it reads the swear word on autopilot like any other word. Then, as the word is processed and identified as a swear word an emotional response is triggered. These two effects occur in the blink of an eye and can be strong enough to overcome the color stimuli. The result is that you inadvertently blurt out the swear word rather than identify the color.
So remember kids, when your brain gets stuck, don't say f...!