SpongeBob SquarePants is not the sharpest sponge in the ocean, despite his angularity. In fact it's his amiable cluelessness that probably endears him to a large segment of American TV viewers, who appear to be sustaining a robust market for T-shirts and toddler sippy cups blaring out his bright yellow spongey self.

But just because SpongeBob is a bit bumbling, don't assume that watching SpongeBob takes no brains. There are some real cognitive challenges involved. Scenes switch every 11 seconds on average. What we see isn't labeled or explained, nor does it have any connection to what we might expect in a real undersea world (pineapple houses? igloos?). Strange-looking characters arrive with no introduction – it's  assumed we already know Patrick the Starfish and Sandy Cheeks the Squirrel – and  use words that have no immediate relationship to the objects around them. They speak in snippets of conversations that require our brains to process concepts that aren't touchable or concrete: ideas about the future, references to past disagreements, and allusions to the latest American fetishes (in one episode, Sandy's TV is broadcasting the "eating channel"), often served with a side of snide.

Adults and older children seem to make sense of these rapid changes and abstract references without much mental effort. But this ability to grasp what is going on without clear stage directions isn't something we're born with. It takes years to develop the necessary cognitive equipment – the  neuronal connections and background knowledge – that  are required to make SpongeBob make sense.  (Even with all of our mental capacities in full bloom, there's a case to be made that the show feels like gobbledygook, or a bizarre dream induced by eating dinner too late, but I'll leave that for the TV critics.)

So how old must a person be to comprehend the show? A widely-noted study released in Pediatrics last week about four-year-old viewers doesn't attempt to answer that question directly, but it seems to conclude that four is too young. The study found that SpongeBob has a negative impact on four-year-old children's short-term thinking skills.

The show wasn't designed for preschoolers – Nickelodeon  says it is aiming for ages 6 to 11 – but  that hasn't stopped it from becoming part of the American media diet for children of that age. SpongeBob is perennially at or near the top of cable and broadcast ratings for two- to five-year-old viewers. I've seen the show's popularity firsthand, as a journalist who has interviewed families about their use of TV and as a mother with two girls who, long before they entered kindergarten, would point excitedly to SpongeBob's image in the supermarket as if greeting a long-lost friend.

Ever since I started digging into the science of early learning and technology, SpongeBob has represented a strange paradox in our society: American adults seem to be ignorant of what young children may be able to handle in real life at age four. Despite the push for public investments in pre-kindergarten programs, good preschools are still not the norm for most children; education policies continue to treat four-year-olds as if they aren't ready to be challenged. And yet we park those same children in front of cartoons designed for kids more than twice their age and assume they have the cognitive wherewithal to manage the flood of information streaming their way. Actually, we never think of it that way – we tend instead to feel guilty for parking our kids in front of mindless TV that we don't believe will engage their brains, when in fact this zany TV may overwhelm them.

In the study, psychologists Angeline Lillard and Jennifer Peterson of the University of Virginia randomly assigned 60 four-year-olds to one of three nine-minute activities. One group of children watched a SpongeBob episode, another group watched an episode of Caillou (a slower-paced cartoon that runs on PBS Sprout about a little boy and his family), and a third group was invited to color with crayons. Before the experiment, each group seemed pretty similar. They came from relatively well-off families, and their parents had reported no differences in their behavior or ability to pay attention. There was no significant difference in how much TV they watched at home.

Immediately after watching the shows, the children were asked to perform four tasks that tested their "executive function" – the scientific catchall term for the cognitive work involved in paying attention, focusing on and following through with activities, and being able to hold back impulses. Good executive functioning has been increasingly connected to a child's ability to do well in school, and scientists have designed some short tests to determine whether children are developing these skills. One, for example, is a "game" called Head-Toes-Knees-Shoulders, which requires a level of mental discipline. When the test administrator directs the children to touch their heads, they are supposed to touch their toes, and vice versa. Children listen and react to a repeated series of directives and are scored on their ability to follow the games' rules. It's all about paying close attention.

In this test and three others, SpongeBob watchers didn't do so well. Compared to the other two groups, the SpongeBob audience performed significantly worse on all four tasks. It was as if something had impaired their ability to focus on what they had been asked to do.

Could it have been that SpongeBob was just so hysterically funny that it temporarily rewired their brains? "Everyone keeps saying, maybe the children have just been laughing so much while they've seen SpongeBob that they can't focus," Lillard said. "Trust me, they weren't laughing. Their facial expressions looked just the same as when they were watching Caillou: transfixed and serious."

The researchers didn't conduct brain scans of the children, so we only have theories about what might be going on inside their minds. We also don't know whether these same children might have performed differently on these tasks before doing one of those three activities. But one idea that has gained adherents among child development experts is that the content of what young children see on TV matters more than we think. We tend to generalize and treat most TV as interchangeable fare – TV watching is bad, we assert, or good in moderation. But not all TV, and not all kids' TV, is the same. Can we really talk of watching Sesame Street and watching Tom and Jerry – to cite two classics that date me – as the same activity?  The rapidity of scene changes, the nature of the dialogue, the way the characters interact with each other – it may all have some impact on children's behavior and understanding. In fact, it's possible that preschoolers' brains will be quite taxed if they are being asked to comprehend quick scene changes and abstract dialogue without someone making introductions to what they are seeing and why.  In the SpongeBob case, where children may have been trying to make sense of the quick pacing, not to mention absorb and understand the hyperactive thought processes of the characters, their brains may have gone into some sort of overdrive that could affect their ability to function a few minutes later.

By contrast, the two other conditions may have been working the children's brains in a different way. Coloring with crayons requires mental work too, but at a child's pace. And the Caillou show, which was designed for four-year-olds, looks and feels quite different from SpongeBob. The scenes change less frequently, and the spoken words usually refer to what actually appears on the screen at that moment. In the episode used in the experiment, Caillou's father helps Caillou learn to swim, and Caillou goes through the motions of swimming while talking up his swimming abilities. The setting – a swimming pool – is something that four-year-olds may have already seen in the real world, and Caillou's father speaks calmly.  Instead of spinning their wheels to figure out what is happening, it's likely that preschoolers are able to keep track of what is going on, and might be able to do so even if they turned off the volume.

Shalom Fisch, a developmental psychologist and former vice president for program research at Sesame Workshop, has offered what he calls a "capacity theory" for predicting when children learn from television.  A show that is designed to guide children without confusing them frees up their brain's capacity to follow the plot, he says, and, one hopes, helps them learn and retain information they can build on later. When a show taxes that child's working memory with too many cognitive demands, it may stymie the child's capacity for learning from that show.

We don't have enough information to know if Fisch's capacity theory holds in the Virginia study.  It would be fascinating to learn more about how well the SpongeBob watchers could follow what was going on – and how that capacity changes as children age.  But there is clearly something tricky about writing shows for preschoolers or designing any kind of activity that strikes a balance between challenging and comprehensible for children in their early years.  It's not easy to step inside the minds of children and see the world through their eyes.   Take those SpongeBob sippy cups: who knows what such marketing triggers in a three-year-old child's mind? Is it pure excitement over the daft character's bright yellowness and googly eyes?   Or are kids vaguely reminded of what their relatives like to watch on TV?

On the flip side, questions and concepts that we think preschoolers cannot grasp may be not only graspable, but sparking deep thoughts – if only there were adults around to help them pull those sparks into utterable sentences and expand on what they discover.  New research on mathematics is showing that three- and four-year-olds have more capacity for understanding "number sense" than we give them credit for. Studies of how children learn to read point to the importance of having adults and children talk together about what they are doing, reading, feeling, hearing and seeing. And preschool classrooms that are designed to harness children's curiosity about nature, books, music or videos have been shown, in study after study, to help children hone their minds for even more challenges.

The shame is that those high-quality environments are few and far between for many children. Although about three-quarters of three- and four-year-olds are cared for outside the home each day, good pre-kindergarten programs are either too expensive for many working families or non-existent. What do those families turn to instead? Too often they resort to mediocre childcare where adults aren't trained in how to challenge children socially and cognitively – and  where TV shows like SpongeBob are broadcast throughout the afternoon, quite possibly taking a toll on their children's executive functioning at just the age they need to develop those skills for school.