Infants are superior in implicit crossmodal learning and use other learning mechanisms than adults

摘要

On a crowded city street, we automatically attribute the sounds of cars to the cars we see driving past, and not to the motorcycles or trucks on the same road. Similarly, we assign the voices we hear to the pedestrians around us, and not to the dogs those pedestrians are walking. As adults, we cope with these everyday challenges effortlessly, but how do infants first learn to match what they see with what they hear? When young animals are exposed to new stimuli, their brains undergo changes. Similar changes only occur in adult animals if they deliberately pay attention to the stimuli and if they are associated with rewards. Rohlf, Habets et al. therefore predicted that human infants would automatically learn to associate sights and sounds upon being passively exposed to them. Adults, on the other hand, would learn these associations only if explicitly asked to do so. To test this prediction, Rohlf, Habets et al. presented tones and colored shapes to 6-month-old infants and healthy adult volunteers while using scalp electrodes to monitor the electrical activity in their brains. Certain shapes and tones occurred frequently together, whereas other combinations of the same stimuli were rare. The 6-month-olds consistently outperformed the adults in associating the tones and shapes the electrical activity in the infant brains reliably distinguished between common versus rare combinations. Adult brains made this distinction only when the adults were asked to pay attention to the tone-shape combinations as part of a task. This high sensitivity to combinations of sights and sounds that regularly occur together enables infants to quickly learn about the world around them. As adults will have done this previously, the most effective strategy for adults is to update their existing knowledge only when such learning enables them to achieve a goal. Further research is needed to find out what happens in the brain to cause this change in learning strategy. Understanding how learning differs in infants and adults will help identify stages of development in which the brain learns particularly easily. This may ultimately help us optimize learning strategies for individuals of different ages.