The team has found that infants who had an opportunity to use a plastic cane to get an out-of-reach toy were better able to understand the goal of another person's use of a similar tool than were infants who had previously only watched an adult use a cane to retrieve a toy.
"Acting on the world is one way infants learn about the world, and only recently have there been studies showing that active, hands-on experience is a more effective way of learning than watching," said Jessica Sommerville, a University of Washington assistant professor of psychology and lead author of a study.
"This study indicates that there is a benefit to actual hands-on experience early in human development," she added.
For the study, UW researchers divided 51 infants - 26 boys and 25 girls - into three groups.
The first group called the 'training group' had an opportunity to use a red-striped and a green-striped cane to pull a rubber toy (such as a yellow duck and a purple hippopotamus) toward them on a table.
Then the infants were trained in how to use the crook of a cane to retrieve a toy. Finally, they were given two trials to see if they could pull the toy to them all by themselves.
The second group of infants called the 'observational group' went through the same procedure with one major difference. Instead of using the tools, the infants watched an adult mimic the babies in the first group learning how to use the cane to get a toy.
The infants in those two groups, as well as those in the third, or baseline, group individually watched training trials in which a researcher seated behind a table used one cane to retrieve a toy and then picked up the toy. Then, out of sight of the babies, the location of the toy was switched in four test trials.
In two of the trials, the crook of the same cane she had previously used was placed around a new toy. In the other two trials, crook of a new cane was placed around the same toy as in the training trials. All of the babies were filmed during the test trials to see how long they watched each trial.
The researchers found that infants in the observational and baseline groups spent equal amounts of time looking at the new cane and toys trials.
But the trained group spent more time looking at the new toy trials, suggesting they understood that the adult was using the cane as a tool.
Moreover, that infants in the training group who were the most proficient at retrieving a toy - looking at the toy, purposefully pulling the cane to bring the toy to them and then quickly grasping the toy - were more likely to look at the new toy trials for a longer time.
"We speculate that for infants to really understand the tool use event, and, in particular, for them to anticipate upcoming actions and action outcomes while watching the event, they need to be able to perform the tool use sequence themselves," said Sommerville.
"Merely watching another person perform the sequence does not appear to be enough for them to understand it.
"We think first-person experience may be particularly important for infants' understanding of an action because we need to anticipate upcoming actions and outcomes to become skillful at producing those actions," she added.
The study is published in the current issue of the journal Developmental Psychology.