I think most of us parents already suspected this.
From CBS News:
A new study says watching Nickelodeon’s popular cartoon, “SpongeBob SquarePants”, can negatively affect a 4-year-old’s focus and memory – and it only takes less than 10 minutes of tube time.
For the study – published in the September 12 issue of Pediatrics -60 four-year-old kids were assigned to either draw, or watch nine minutes of a “fast-paced” cartoon “featuring an animated kitchen sponge,” or a slower-paced educational cartoon, “Caillou.” Seventy percent of the kids who drew passed the problem-solving tests with flying colors, compared with 35 percent who watched “Caillou.” Only 15 percent of the fast-paced cartoon viewers passed.
Nickelodeon responded that there were not enough kids in the study to make such a definite claim and that the show is unfairly being compared.
Jane Gould, Nickelodeon senior vice president:
“It made me scratch my head and feel confused,” Gould said. “I couldn’t understand the logic of including a program like ‘SpongeBob,’ which is expressly designed to entertain 6-to-11-year-olds and have that program be compared to a slow-paced educational program for preschoolers. ‘SpongeBob’ is not designed to educate preschoolers. It’s designed to entertain kids.”