Scientist raises concerns about impact on child development, saying toymakers' themes are increasingly based on conflict

The number of happy faces on Lego toy mini-figures is decreasing and the number of angry faces is increasing, a robot expert at the University of Canterbury in New Zealand has discovered

Dr Christoph Bartneck – who studied all 6,000 Lego mini-figures – said his findings could give rise to concern about he frowning faces' impact on child development and the manufacturer appeared to be moving towards more conflict-based themes in its toys.

"It is important to study how to create appropriate expressions and how these expressions are perceived by the users. Children's toys and how they are perceived can have a significant impact on children,'' Dr Bartneck says.

"We cannot help but wonder how the move from only positive faces to an increasing number of negative faces impacts on how children play.

Bartneck said the study considered the distribution of faces across emotional categories in the context of the Lego themes. Most mini-figures were released in sets that belong to a certain theme, such as Pirates or Harry Potter.

"It is our impression that the themes have been increasingly based on conflicts. Often a good force is struggling with a bad one," he said.

"The number of new faces that the Lego company introduces every year is increasing steadily. Lego started producing a greater variety of faces in the 1990s. Happiness and anger seem to be the most frequent emotional expressions.

"But the facial expressions are not directly matched to good and evil. Even the good characters suffer in their struggle and the villains can have a smug expression. In any case, the variety of faces has increased considerably.''

Bartneck said the upshot was that children growing up with Lego today would remember not only smileys but also anger and fear in the mini-figures' faces. Designers of toy faces should take great care to design the expressions and to test their effect since toys played an important role in the development of children, he said.

"The example of the mini-figures show that to appeal to users it is necessary to offer a wide range of emotional expressions for today's users. Instead of focusing on realistic expressions, it may be worthwhile to increase the variability of expressions. A comic style expression is sufficient to convey a full spectrum of emotions and intensities."

Bartneck will present the paper on his findings [PDF] at the First International Conference on Human-Agent Interaction in Sapporo, Japan, starting on 7 August. © Guardian News and Media 2013

[Angry lego faces via Flickr user joriel]