Perceptual Development: Touch and Pain

Touch Perception in the Neonate

Research suggests that touch discrimination by mouth and by hands occurs as early as the newborn period. Different texture nipples (nubby versus smooth) can be discriminated by the newborn's mouth and by their hands. Using a habituation/recovery paradigm, the newborn explored the different texture nipples by their mouths and by their hands. After experience with one nipple, they habituated or stopped sucking. When the new texture nipple was presented, they started to suck again, indicating that they discriminated between the first and second nipple.

Texture perception has also been investigated in three-day-old infants using a habituation paradigm with a smooth or granular object. After holding the object, babies were given either a familiar or a new textured object. Two dependent measures were recorded: (1) holding time was used to assess habituation as well as reaction to novelty, and (2) hand pressure frequency exerted on the object was used to examine the neonates' ability to adjust their manipulation to the texture of new objects. Both measures revealed perception of the texture of objects.

Weight perception has also been studied in young infants. Light-weight (two grams) or heavier-weight (eight grams) objects (vials of cotton or pellets, respectively) were placed in the right hand of full-term newborns of depressed or nonde-pressed mothers. After the infants habituated one weight by hand, they were tested with the opposite [Page 766]weight object. The infants of the depressed mothers did not respond to the novel weight, and only 15% of those infants showed hand movements that might have facilitated their perception of the object's weight (e.g., hand-to-mouth or hand-to-face, turning/moving of the wrist or hand). In contrast, 78% of the infants of nondepressed mothers showed hand activity that would lead to weight perception, and, as a group, they held the novel weight longer, suggesting that they had perceived the weight change, whereas the infants of depressed mothers failed to make that discrimination.

Another group of investigators studied weight perception in older (one-year-old) infants. The authors not only documented weight perception by one-year-old infants but also the ability to adjust their hand manipulation of the weights. Two dependent measures were recorded: (1) holding times in order to assess habituation as well as reaction to novelty, and (2) manual pressure exerted on the object to investigate the infants' ability to adjust their manipulation to the object's weight. Both measures revealed infants' haptic perception of weight, but the second measure suggested that the one-year-olds had developed manual manipulation as another indicator of their weight perception.

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