The tactile system, or the sense of touch, is one of several ways that human beings experience the world around them. This system has 4 different kinds of mechanoreceptors which provide information to the nervous system and brain. During the developmental stage it is important for social and emotional well-being. The tactile system in humans is one of the earliest sensory systems to develop, with responses to tactile stimulation seen as early as seven and a half weeks after conception (Cheatum & Hammond, 2000). The tactile system includes touch, pressure, vibration, itch and tickle (Tortora & Derrickson, 2009). The tactile system also includes the kinesthetic senses, which provide information on the position of the body in space by sensors related to proprioception. The tactile system continues to develop well past ten years of age as the corpus calossum is myelinated with a corresponding development of midline crossing (Galin, Johnstone, Nakell & Herron, 1979). However, there are several crucial stages of development during the infancy period of birth to 12 months that affect growth and development well into adolescence and adulthood.

The Tactile System

Movement Experience for Children
KIN 366
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Instructor:	Dr. Shannon S.D. Bredin
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Crude and Discriminative Touch

Crude touch provides little information aside from the fact that one is touching something as well as the sensation of movement. Areas such as the back or the thigh have poor spatial resolution, also known as two-point discrimination. Areas such as this have low receptor density. Discriminative touch on the other hand, includes pressure touch, perception of weight and vibratory sense. Pressure touch is essential to determine shape, size and texture. Fingertips have very fine spatial resolution, and therefore a high receptor density. Infants gain a large amount of information by simply touching and using their hands to examine objects (Berk, 2009). They are then able to match this information to what they can see, which is known as intermodal perception (Berk, 2009). Building an image based on palpation of the 3D characteristics of an object is known as stereognosis (Berk, 2009).

Mechanoreceptors

There are four mechanoreceptors worth noting:

Meissner corpuscles are rapidly adapting receptors, generating impulses on the onset of touch and are involved in sensing pressure (Tortora & Derrickson, 2009)
Ruffini receptors are sensitive to stretch that result from movement by the limbs or digits and are slowly adapting (Tortora & Derrickson, 2009).
Pacinian corpuscles are rapidly adapting mechanoreceptors that have large receptive fields and aid in sensing pressure (Tortora & Derrickson, 2009).
Merkel discs are slowly adapting receptors that are abundant in the fingertips, lips and hands and contribute to sensations of pressure (Tortora & Derrickson, 2009).

There are three steps from mechanotransduction, or application of stimulus, to a generation of an action potential. First, the stimulus is mechanically applied to the cells. Second, the deformation is converted to an electrical signal. Third, the receptor potential is encoded into an action potential to the central nervous system.

Development of the Tactile System

Early Exploration: Visual Stimuli

Berk (2009) describes a study that explored the effects of various mobiles hung over a crib on infant reaching. 3 groups of infants were assigned to one of three groups: a group that received no visual stimulation, one group that received moderate visual stimulation and a group that received heavy visual stimulation. She did not mention whether the infants were randomly assigned or not, so it is difficult to determine the level of evidence of the study and visual stimulation was mobiles of various complexity designs. It was found that those who received heavy visual stimulation reached earlier than the group that received no stimulation, but reached later than the group that received moderate stimulation. An important note is that the heavy visual stimulation group tended to cry more than other groups. Berk (2009) concludes that moderate visual stimulation, that is beginning with simple designs and progressing in complexity, yielded the best developmental benefits as infants began to reach 6 weeks earlier than the other groups. This initial visual stimulation is important to the development of the tactile system. A moderately challenging yet appropriate level of visual stimulation will motivate the infant to attempt tactile exploration.

Pain in Infancy and Development Disruption

One of the tactile systems functions is to act as a warning system (Cheatum & Hammond, 2000). Early in life, the infants central nervous system is immature, which means that preterm, younger and male babies feel pain very intensely (Berk, 2009). Physical contact with an infant may release endorphins that calms the infant and soothes this intense pain (Berk, 2009). Allowing an infant to endure severe pain will overwhelm the nervous system and lead to an abundance of stress hormones in circulation (Berk, 2009). This combination of overwhelming pain and stress will disrupt the development of the capacity of the child to handle common, everyday stressors (Berk, 2009). Berk (2009) states that this will also result in:

heightened pain sensitivity
sleep disturbances
feeding problems
difficulty calming down when upset

Children with little adult contact tend to withdraw and are typically impaired in all domains of development (Berk, 2009), so this physical contact should not be reserved for only those infants who are experiencing pain. For ethical reasons, there is little research on emotional, developmental and biochemical response of the infant to pain in both the short and long term.

Effects on other Aspects of Development

Reaching plays a very important role in infant cognitive development. By grasping, turning over and dropping objects, infants are able to learn about sights, sound and feel (Berk, 2009). Chase (1994) concluded based on a series of longitudinal studies that during infancy, the availability of play materials and the involvement of the parents led to cognitive development. The toys used should fit the interests and abilities of the child in question and a toy that is too simple or complex will lead to a decrease in exploration (Chase, 1994). 9-18 month old infants spend nearly half of the time when they are awake, looking at and playing with objects (Chase, 1994), so a variety of properly stimulating toys are necessary to allow them to develop.

Schaefer and DiGeronimo (2000) also states that if infants experience physical contact they sleep better, gain more weight and tend to be more interested in being around people. After 6 months, when reaching and grasping are sufficiently developed, touching allows infants to problem solve and so the shape and texture of an infant’s toys should be changed often (Schaefer & DiGeronimo, 2000).

Tactile Stimulation and Growth

Gentle touching, such as a soft caress, elicits a smile and draws the attention of newborns (Berk, 2009). Berk (2009) concludes that this tactile stimulation releases chemicals in humans that promote growth and are vital for proper emotional development. This provides one way to treat issues associated with preterm infant low birth weight. If preterm infants are massaged, they tend to gain weight faster and are more advanced in motor and mental development after 1 year than preterm infants without this tactile stimulation (Berk, 2009).

Tactile System Milestones

It is important to note that milestones are overall age trends, and that individual differences do exist in the development of infants. Age ranges are perhaps a more appropriate way of classifying milestones, for example: infants are able to grasp cubes on average at 3 months and 3 weeks of age, but 90 % of infants grasp a cube between 2 and 7 months (Berk, 2009).

Birth

Immediately after birth, infants respond to a touch or pain stimulus (Berk, 2009). Infants are also able to distinguish the shape of an object placed in their palm (Berk, 2009).

1-6 Months

Between 1 and 6 months, infants can be expected to explore objects by mouthing them (Berk, 2009). Mouthing involves an infant touching an object with their lips or tongues, and then moving away from it to examine it visually. At approximately 4-5 months, infants begin to transfer objects from one hand to another (Berk, 2009). This coincides with the development of the ability to sit up, which frees the hands from supporting balance and allows for exploration (Berk, 2009). Infants are able to hold an object with one hand, and scan the surface of the object with the fingertips of the other. This leads to improving object manipulation, which is a great deal of improvement before the end of the first year and which coincides with the development of the pincer grasp (Berk, 2009). Reaching in this time frame is typically guided by vision (Berk, 2009). Exploratory mouthing peaks in frequency at approximately six months and declines as more elaborate touching, which involves turning an object, poking it and generally feeling it, develops (Berk, 2009).

5-6 months

At 5-6 months, infants should be able to control reaching by proprioception, in the absence of a visual stimulus (Berk, 2009). When an infant in this age range begins to reach for an object and the lights are turned off, they should be able to continue reaching without relying on vision until they successfully reach the object guided only by the tactile system and a memory of where the object was located (Berk, 2009).

8-11 months

By this point, the ability to reach and grasp should be well practiced, which frees the attention to what occurs before and after reaching and grasping (Berk, 2009). This means that at approximately 10 months of age, infants are able to solve simple problems that involve reaching (Berk, 2009). For example, if a toy is out of their line of sight, they should be able to search for and find the toy using tactile information alone (Berk, 2009). This method of searching differs from that at 5-6 months, in that at 5-6 months, visual information is used to begin reaching and tactile information is used to complete the action. At 8-11 months, however, the infant will see that an object exists and observe it being hidden; they will then use tactile sensory information to locate it. This ability likely coincides with the stages of the development of object permanence.

Midline Crossing

Crossing the midline is one of the most important developmental milestones. Issues with crossing the midline often lead to difficulty in athletics as well as academics, from difficulty running which manifests as rotation in the torso, to difficulty reading and writing, because children allocate the task of writing on the left side of the page to their left hand and writing on the right to their right (Bredin, 2014). Crossing the midline is also vital for proper development of the tactile system. Myelination of the corpus callosum, which is heavily involved in midline crossing, begins at approximately the end of the 1st year and is substantially advanced by 4 years of age (Galin et al. 1979). The myelination of the corpus callosum continues to improve to 10 years of age and beyond (Galin, et al. 1979). Each hemisphere receives the sensory information from one side of the body and one visual field. In infants, however, there is a distinct lack of communication between the two hemispheres, similar to those with surgically disconnected commisures and a similar inability to perform crossed tactile matching (Galin et al. 1979). This capacity for simple transfer of sensory information is one of the earliest to develop in children. Galin et al (1979) found that matching tactile stimuli at the same skin site, or uncrossed testing, is easier than at different sites, known as crossed testing, though the ability to match at different sites improves significantly from 3 to 5 years old.

Intermodal Perception

Intermodal perception is the ability to receive and process sensory input from more than 1 modality and perceive things as integrated wholes. Intermodal perception is the realization that an object is the sum of all sensory information received about it. An example is an infant sees an object and is able to recognize that the shape is the same whether they see it or touch it. They are able to recognize that certain objects have an amodal sensory property, that is, parts of the objects physical structures are perceived even when only a limited part of it is triggering sensory receptors (Berk, 2009). This means that after an infant has adequately developed intermodal perception, they are able to touch an object, such as a cube, and be able to distinguish it visually from differently shaped objects, such as a sphere. This sensitivity to intermodal information is very important to perceptual development (Berk, 2009).

Tactile Stimulation: Emotional and Social Development

Touch is one of several ways that infants may interact with others. Infants are able to observe someone, usually an adult, reach and develop a perception of their actions. Infants are then able to match this perception to their own active experience of reaching (Berk, 2009). Infants see someone reach and they imitate them. This observation and imitation is basic to emotional and social development as it may help with developing things such as empathy. They are gathering information through senses, which aids in cognitive development. This reaching and grasping, as well as learning through observing is one way infants gather information about the world (Berk, 2009). So, if one wants to aid a child’s developing knowledge of the world, they can repeatedly model an action until an infant imitates them. Play allows infants to grow emotionally, intellectually and socially. Adults can aid this development by demonstrating how to experience toys and physically guide the infant’s hands in the exploration of toys (Schaefer & DiGeronimo, 2000).

Practical Applications

Parents and teachers need to consider several important factors, such as culture and socioeconomic status when deciding which toy to give children (Guyton, 2001). For example, things such as cardboard boxes or pinecones are resources that are readily available to people of any socioeconomic status (Guyton, 2001). So long as the children are engaged and adequately challenged, and more importantly motivated to experience the toy using tactile receptors there is a large variety of items that will aid tactile development. Giving children various shaped toys may also aid in their perceptual development, as they will practice and associate visual and tactile stimulation. Objects that are not perfect shapes will help develop stereognosis, and through intermodal perception, aid visual development.

Caregivers should avoid attempting to prime infants with stimulation more advanced than their level. If infants are not ready for the stimulation given, it may lead to withdrawal and will result in a developmentally similar condition to stimulus deprivation (Berk, 2009). Children should be allowed to progress and develop at their own pace, and one should keep in mind that the milestones, as mentioned above, are averages and not exact schedules to follow for every child. If a child is given a novel tactile stimulus (say, a toy or a fabric) and after a short amount of time they lose interest and cease exploration, the toy was either too simple or too advanced (Chase, 1994). If this happens, the caregiver should not force the toy on them, but rather provide the option of another toy. This ability to choose should give the infant leeway to set their stimulus complexity level.

Parents and teachers should observe children and infants as they interact with their environment in order to notice issues with the development of the tactile system (Cheatum and Hammond, 2000). One should watch to see if infants are uncomfortable with contact, whether with certain types of clothing or rough carpets, as well as if they appear apprehensive when near other people (Cheatum and Hammond, 2000). Things such as restlessness, hyperactivity, a short attention span, or academic and attitude problems may be traced back to tactile system issues (Cheatum and Hammond, 2000).

References

Berk, L.E. (2009). Child development (8th ed.) Normal, IL: Pearson Education.

Bredin, S. (2014, February). Seminar 5. Movement Experiences for Young Children. Lecture conducted from University of British Columbia, Vancouver, BC.

Chase, R.A. (1994). Toys, Play, and Infant Development. Journal of perinatal education, 3(2), 7. Retrieved from: http://gw2jh3xr2c.search.serialssolutions.com/?ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=Toys%2C+Play%2C+and+Infant+Development&rft.jtitle=The+Journal+of+Perinatal+Education&rft.au=Chase%2C+Richard+Allen&rft.date=1994-06-30&rft.pub=Journal+of+Perinatal+Education&rft.issn=1058-1243&rft.eissn=1548-8519&rft.volume=3&rft.issue=2&rft.spage=7-19&rft.externalDocID=540740521&paramdict=en-US

Cheatum, B. A., & Hammond, A.A. (2000). Physical activities for improving children’s learning and behavior: a guide to sensory motor development. United States of America: United Graphics.

Galin, D., Johnstone, J., Nakell, L., & Herron, J. (1979). Development of the Capacity for Tactile Information Transfers Between Hemispheres in Normal Children. Science, 204 (4399), 1330-1332. Retrieved from: http://www.jstor.org/stable/1748770

Guyton, G. (2011). Using Toys to Support Infant-Toddler Learning and Development. YC Young Children, 66(5), 50. Retrieved from: http://gw2jh3xr2c.search.serialssolutions.com/?ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=Using+Toys+to+Support+Infant-Toddler+Learning+and+Development&rft.jtitle=YC+Young+Children&rft.au=Gabriel+Guyton&rft.date=2011-09-01&rft.pub=National+Association+for+the+Education+of+Young+Children&rft.issn=1538-6619&rft.volume=66&rft.issue=5&rft.spage=50&rft.externalDocID=2477404381&paramdict=en-US

Schaefer, C.E., & DiGeronimo, T.F. (2000). Ages and stages: a parent’s guide to normal child development. United States of America: John Wiley and Sons, Inc.

Tortora, G.J., & Derrickson, B. (2009). Principles of anatomy and physiology (12th ed.) United States of America: John Wiley & Sons, Inc.