Hearing, taste and smell

The infant exploits all her senses as she learns about and reacts to her world. Hearing, although not fully developed at birth, is well developed at this stage, enabling young infants to discriminate among sounds that vary in volume, duration and repetitiveness, and to organize their perception of and responses to the spatial environment (Kellman & Arterberry, 1998). So when exposed to the ‘approach’ of an illusory object (a sound increasing in volume), quite young infants lean away as the noise gets louder (Freiberg, Tually & Crassini, 2001). Perhaps one of the starkest pieces of evidence against the ‘empty vessel’ theory of human nature comes from the infant’s discrimination among tastes (Mennella & Beauchamp, 1997). Babies are not passive when it comes to food and drink, and display clear preferences. Their sucking rate increases for sweet liquids, but decreases for salty or bitter liquids (Crook, 1978). They show by their facial or vocal expressions whether they like or dislike a particular taste, and will protest vigorously if offered something they find unpalatable (Blass, 1997). These preferences are by no means arbitrary and may well have survival value. Infants do not have conscious nutritional information to help them decide whether a foodstuff is good or bad for them, but they know what they like. For example, alcohol is potentially harmful to infants, and research suggests that they would prefer not to drink it. Mennella and Beauchamp (1994) compared babies’ consumption of breast milk when their mothers had been drinking either alcoholic beer or non-alcoholic beer. In the alcohol condition, the babies drank significantly less milk. Babies’ taste preferences can also be exploited by adults – certain tastes, such as milk or sweetened drinks, help to calm down a crying infant (Blass, 1997). Infants react to smells in similar ways. Their facial expressions or head orientations reveal whether they find a smell pleasant or unpleasant (Soussignan, 1997). Again, the sensory preferences may have survival value. For instance, there is evidence that infants are attracted to the smell of amniotic fluid and to milk (Marlier, Schaal & Soussignan, 1998).