It has been thought that infants form categories using information from just one sense, whichever the most relevant. For example, the category of ‘faces’ result from an accumulation of visual information about what faces look like. However, an intriguing new study, involving four-month-old infants and their mothers’ smelly t-shirts, suggests that babies’ early acquisition of the face category is a truly multi-sensory process.
For the experiment, before the testing started – babies’ mothers wore the same t-shirt for three nights in a row, keeping it in hermetically sealed bag at all other times. They and their infants were then taken into a quiet, odour-free lab space where the babies were shown a series of images. Some were of faces against natural backgrounds, while the majority featured animals, plants and manufactured objects. Each image was presented for only 167 milliseconds (less than a quarter of a second), meaning that perception had to happen at a glance.
Some of the time, the babies had their mother’s odorous T-shirt placed on their upper chest. (The T-shirt was folded so that the maximally-smelly underarm, breast and neck regions were closest to their nostrils.) Other times, they had a clean, unworn T-shirt placed near their noses. Throughout the experiment, the researchers used EEG (electroencephalography, which measures electrical activity via electrodes on the scalp) to monitor how the babies’ brains responded to the images.
Results showed that the babies’ face-related brain activity in response to the images of faces was significantly greater when they could smell their mother’s well-used T-shirt at the same time, compared to when their mother’s odour was not present. This suggests that the odours strengthened their recognition of faces. This result provides strong support for the idea that multi-sensory, rather than single cases, inputs drive our acquisition of categories.
Other research supports this finding – whenever you look at a face, neurons in a region of the visual cortex called the fusiform gyrus respond with a burst of activity. This shows that a region that had traditionally been thought to be responsive only to visual data is clearly receptive to other sensory signals when they indicate that a face is likely to be in the visual scene. It makes sense that babies use odours to help them to spot faces, the researchers add. Odours are less fleeting than many visual stimuli, and of course body odours tend to co-occur with the appearance of a face.
Category(s):Child Development
Source material from Research Digest
