Development of perception for navigation and affordances
When infants start crawling they also start to learn that not all surfaces are equal, and that the softness, slipperiness and inclination of the surface and the presence of obstacles, steps, gaps or cliffs need to be accommodated.
Experience teaches crawling infants the associate the visual information about the structure of the he environment that they perceive with their experience of successfully navigating their way over and around surfaces and obstacles.
Crawling infants quickly learn what a particular situation will allow. In other words what is possible given their size and abilities.
The little fellow in the images below has not yet learned about navigating a step-down of the support surface. Infants are particularly sensitive to the risk of falling, so this is not a mistake he repeats.
Infants with some crawling experience have better control of their crawling actons and will happily crawl down a low step or pile of pillows
But when confronted by a higher drop, will usually decide that it is safer to turn around and go backwards.
Karen Adolph's studies
When the infant starts to walk, the relationship between their abilities and the structure of the environment needs to be learned from scratch. Karen Adolph, from the NYU Action Lab, has done a series of very elegant studies in which she demonstrates how infants learn through experience when it is safe to crawl or walk down a step, over a gap or down a steep slope.
In this set of video clips Karen demonstrates how infants use information from the environment to decide what is safe and what is not. What is particularly interesting is that once infants start to walk, they need to relearn through experience what is safe.
Affordances as possibilities for action
Gibson (1979)) coined the term affordances to describe the possibilities for action allowed by different circumstances. An affordance can be defined as as the match between the body and the environment that makes a particular action possible.
Perceiving affordances can be characterized by sensitivity, accuracy, and consistency. (Ishak et L 2014)
Sensitivity refers to the ability to detect the critical body–environment relations
Accuracy refers to the match between the actual affordance and participants' decisions.
'Accuracy is necessary to ensure that selected actions are appropriate given the properties of the body and environment. Errors in action selection, such as trying to fit through openings that are too small, can have dire consequences for safety. Accuracy can be influenced by sensitivity and by differences in response criteria such as how heavily one weights the penalty for error." Ishak et al 2014
Infants and children must learn to perceive affordances accurately. When they first acquire new skills, infants' decisions about possible and impossible actions are rife with errors, but over weeks of experience practicing their new skills, decisions become increasingly accurate.
For example, novice walkers attempted to descend impossibly steep slopes and cliffs (requiring rescue from an experimenter to prevent injury). Over weeks of walking, decisions gradually geared in to infants' actual abilities. Experienced walkers made accurate decisions by refusing to descend or by switching to an alternative sliding or backing position (Adolph, 1997; Kretch & Adolph, 2013a, 2013b).
Infants will often use touching behaviors to explore a situation when they are uncertain, such as patting a surface to find out about firm, touching the circumference of an opening before attempting to insert the hand (Ishak et al 2014).
In order to successfully move in the physical environment actions need to be scaled to the properties of the body and the environment. For example in order to step up onto a raised surface (step) the amount the foot is lifted up must be adapted to the height of the step.
This toddler has learned to step up onto a 10 cm step without support. But notice how he lifts his foot far higher than is needed for foot clearance. Over time he will scale his actions more accurately.
Forward planning for navigating the environment
Successful navigation of a physical environment requires information about the surfaces, objects, people and animals that will be encountered. It also requires the ability to predict and anticipate the path of moving objects and people, as well as adapt to sudden changes in the environment.
Visual and auditory pickup provides information about:
Objects: relative position, size, shape, static or moving
Support surfaces: rough or even, stability, slope, firmness, gaps, slipperiness
People and animals: relative position and predictable or unpredictable movement in the environment
Navigating through apertures
Extract from Wilmut, K., Du, W., & Barnett, A. L. (2016). Navigating through apertures: perceptual judgments and actions of children with Developmental Coordination Disorder. Developmental science, 20(6)
As we move around the environment we encounter many obstacles such as parked cars, pedestrians and street furniture, and navigating passed these often involves judging whether a gap is large enough to fit through. This requires the ability to visually estimate the size of the gap, integrate accurate information regarding body size and then determine whether the gap is large enough to fit through either with or without a shoulder rotation. Once this judgement has been made, we need to execute a movement which allows safe passage. Misjudgement in our perception of passability or in the execution of an adaptive movement to pass through may result in collision/injury. The constraints‐based approach to understanding motor behaviour (Newell, 1986) integrates ideas from dynamical systems theory (Thelen, 1989) and ecological psychology's direct perception (Gibson, 1979) and would suggest that a motor response emergesas a function of the perception of the environment and what it affords. Affordances are tied to the interaction between the physical properties and capabilities of the actor and the physical properties of the environment (Gibson, 1979). A decision to rotate the shoulders when passing through a gap depends on the perception of the affordances of the gap, i.e. the perception of the gap in relation to body size and action capabilities. The constraints‐based approach also states that any motor response is constrained and influenced by the task, the environment and the individual (Keogh & Sugden, 1985; Newell, 1986). Therefore, the response to walking through a gap emerges from demands of the task (e.g. the size of the gap), the environment (e.g. stability of the gap) and the individual (e.g. their ability to determine affordances and their ability to control movement). Central to this approach is the link between perception and action (Sugden & Wade, 2013).
Information gathering for stepping down
Extract from Buckley
Descending a step such as a kerb is an example obstacle negotiation during ongoing gait that involves the regulation of appropriate foot placement before the kerb-edge and foot clearance over it. It also involves the modulation of gait output to ensure the body-mass is safely and smoothly lowered to a new level.
“Indeed, most of us will have experienced stepping from a kerb we had not anticipated. The shock force generated travels up the leg to the base of the spine and is experienced as an uncomfortable ‘jolt’ to the lower back. Thus predicting at what height and hence when contact with the lower level occurs are critical factors . These factors determine how and when the leading limb needs to be prepared for landing in order to safely and smoothly attenuate the increased downward momentum generated in lowering the body-mass to a new level; so that normal level walking can resume with minimal delay or perturbation."
Vision has a predominant role in determining these critical factors with vision from the lower visual field (lvf) being particularly important.
Gaze during adaptive gait is directed two or more walking steps ahead. This implies that when descending a kerb during ongoing gait, an individual is unlikely to look directly at their feet or the area on the ground they intend to step onto. Although gaze may be directed ahead, visual feedback of the lower-limb and/or floor area immediately in front/below the foot will be available from the lvf. Such feedback has been shown to be used online during obstacle crossing to update foot placement before the obstacle and toe clearance over it , as well as detect the presence of an unexpectedly appearing obstacle.
Factors that contribute to bumping and frequent falls in young children
Toddlers fall al lot
Toddlers who have recently learned to walk fall a lot. Karen Adolph counted the number of times toddlers fall per hour: 12- to 19-month-olds averaged 2,368 steps and 17 falls.
Falls will usually decrease over timee and with experience and most toddlers and young children fall infrequently.
"After walking onset, natural locomotion improved dramatically: Infants took more steps, traveled farther distances, and fell less. Walking was distributed in short bouts with variable paths—frequently too short or irregular to qualify as periodic gait. Nonetheless, measures of periodic gait and of natural locomotion were correlated, which indicates that better walkers spontaneously walk more and fall less. Immense amounts of time-distributed, variable practice constitute the natural practice regimen for learning to walk." Adolph et al 2012
One reason for a toddler falling is a decision to change direction when moving at speed. They also develop speed wobbles.
Child does not pay attention to the environment
Looking where one is going is essential for adapting one's actions to accommodate support surface characteristics, obstacles up ahead, people and animals moving about. Visual attention includes knowing what to pay attention, and selecting and interpreting this information with respect to present goals.
Picking up information, and keeping it in mind as the task unfolds also requires good working memory.
Try the following
Next time you walk out of doors, notice how frequently you look down to see what lies a few meters ahead. Notice what you do as you approach a curb, a set of steps, another person in front of you, or a door.
Children with coordination difficulties often do not look ahead and check what is coming up. As a result they do not make the adjustments needed to maintain their balance and successfully negotiate obstacles and uneven surfaces.
Adapting actions to the characteristics of the environment
One of the important abilities toddlers need to acquire when they first start to walk independently is being able to interpret available visual information about the surfaces, objects and people in the environment to make decisions about what is possible. What does the environment allow/afford?
Can I jump down from this chair, or is it too high. Can I step across the gap, or is it too wide? Can I step up onto this step, or is it better to use my hands and climb up?
Ability to negotiate obstacles: stepping over, across, down and up.
Children acquire the task specific balance, coordination and strength needed for stepping up, down and over obstacles through experience. Repeated practice allows the child to adapt their actions to the demands of the task, develop the coordination and strength needed for performing the task and use anticipatory and adaptive adjustments to maintain balance and stabilize the trunk. .
Difficulties with performing a particular task requires an assessment and intervention tailored to the of the child's ability to perform the particular task in different situations. Generic approaches to training balance do not recognize the task specific nature of balance control. Read more: Poor balance is not a thing
Difficulties with coordination (DCD)
Many children with movement difficulties have an underlying an coordination disorder (such as developmental coordination disorder) which affects the variability of their gait patterns and ability to control the COM and makes them more susceptible to trip and falls.
"The gait pattern of children with DCD was characterised by wider steps, elevated variability in the time spent in double support and stride time and greater medio-lateral velocity and acceleration compared to their peers. An elevated variability in medio-lateral acceleration was also seen in the young but not the older children with DCD. In addition, the young children showed a greater variability in velocity and acceleration in all three directions compared to the older children. The data suggest that the high incidence of trips and falls seen in children with DCD may be due to differences in the control of the CoM. " (Wilmut et al 2016)
Weakness and fatigue
Walking on uneven ground, running,stopping and making sudden changes in direction and negotiating obstacles all require the rapid increases in muscle force in the lower extremities to accommodate the acceleration and deceleration of the center of mass (COM) and to support the body weight.
The ability to generate a rapid increase in muscle force (muscle power) depends on the force generating capacity of the LE muscles as well as the ability to rapidly recruit motor units simultaneously (motor learning component of muscle strength and power).
Children with LE muscle weakness will fall more frequently when they are fatigued and the muscles are less able to generate the forces needed for supporting the body.
Generalized joint hypermobility (GJH)
Children with GJH have less inherent stability of the musculoskeletal system, with associated weakness, sometime limited ROM of hip adduction, which affect their ability to balance on one leg, a tendency to hyperextend their knees and poor foot alignment and ankle balance responses. All of these factors can contribute to frequent tripping and falling.
Slow to respond when balance is challenged
When we move about either walking or running and encounter an obstacle, change direction or stop suddenly our balance mechanisms come into play to rapidly restore balance and stability. These balance responses need to be automatic, fast and sufficient to be effective.
|Try the following: Do 10 very fast small two foot jumps forwards and then stop suddenly. What do you notice? Even though your feet have stopped moving, momentum keeps your upper body going forwards and in order to restore your balance you need to step forwards fast with one foot.|
Children who trip and fall a lot often have not yet developed these fast and automatic responses, so they loose their balance and fall over.
Suggested Assessment and Intervention Plan
1 Identify the circumstances that lead to falls
When and under what circumstances does the child fall? Are falls related to moving around in a busy environments, moving at speed, making sudden stops and turns, negotiating obstacles, not paying attention, fatigue?
2 Observe the child moving about in different natural environments
Does the child pay attention to the environment? Does he avoid obstacles? Does he adapt his actions to the characteristics of the terrain (slope, stiffness, gaps, steps, roughness) and so on.
Observation in natural environments associated with the child's daily routines provides insight into the relationship between the child's attention and motor abilities and the physical and social environment.
3 Assess and analyze locomotor task performance
Task oriented assessment provides information about the child's ability to perform specific locomotor tasks, and an analysis of task performance gives information about factors that contribute to, or constrain success: visual pickup, adaptation to the physical environment, impact of the social environment, functional muscle strength and power, coordination, balance responses.
4 Identify general, everyday function goals
In collaboration with th child's parents and teachers, decide on a few measurable, every-day-function goals for intervention.
What is it that the child should be able to do in his natural environment that he cannot do presently?
- Walk across the classroom without bumping into people and furniture.
- Walk across the playground without falling more than twice during one recess.
- Walk 20 meters along a rough path in the park without falling
5 Select tasks to work on
6 Implement a task oriented training intervention program
Task training, to be effective needs regular training sessions, and and such must involve the parents in implementing a home program. This is best achieved if parents are involved in figuring out:
- How to practice a task using resources in the home environment;
- How to adapt the task to allow the child to succeed;
A coaching strategy for training Nick not to bump into things
Nick is an active, on the go 6-year-old who is full of bruises on his legs because he falls and bumps his shins at least once a day, and will often bump into furniture or walk into the door frame as he moves from one place to another in the house.
Today Nick and his mum are practicing a stop-look-notice-plan strategy
Nick has planned a route through the house walking from one room to another. The game is to walk through all the doorways in the house without bumping into the door frame or furniture.
Before Nick sets off he reminds himself to look ahead and notice what is in the way. He then walks at a moderate speed across a room and through the first doorway. Once through the door he stops again and looks ahead before he sets off on the next leg of his journey through the house.
Today he achieves his goal of walking through all the doorways and around all the rooms in the house.
Speeding up and planning a path
Next Nick and his mum think about ways they can make this game more difficult. Nick decides that he wants to walk a little faster and that he wants to time himself. Together they plan a course: from the kitchen to living room, then into the bathroom and from there into Nick's bedroom and back into the kitchen. They write down the plan and Nick practices remembering the sequence.
Then he sets out on his journey using the stopwatch on mum's cell phone to time himself. The first trial he sets off at speed and develops a speed wobble turning into the passage and bumps into the doorway.
The next trial he goes a little slower and finishes the the whole course without bumping into anything.
What has Nick learned and what next?
Nick is learning to look ahead, moderate his speed and change his expectations. Falling is an error and he should stop and consider what went wrong. Now he expects to walk around the house without falling.
In the days that follow Nick and his mum create new games - they add extra obstacles to walk around and over. They go for a walk in a busy mall where Nick practices not bumping into people.
At school Nick's teacher introduces a game for the whole class that involves all the children moving around the classroom and not bumping into or even touching each other.
What can be learned from this coaching example
- Select an activity that the child needs to improve
- Think about how the activity can be made more simple or easier so that it can be performed successfully
- Involve the child in planning practice sessions
- Provide incentives and rewards
- Teach the child to recognize error and expect to succeed
- Practice the simplifies task until it can be done successfully
- Next make the task a little more difficult and provide opportunities for practice
- Provide opportunities for performing the task in different places and spaces
References and suggested reading
Adolph KE, Cole WG, Komati M, Garciaguirre JS, Badaly D, Lingeman JM, Chan GL, Sotsky RB. How do you learn to walk? Thousands of steps and dozens of falls per day. Psychol Sci. 2012;23(11):1387-94. doi: 10.1177/0956797612446346. Epub 2012 Oct 19. PubMed PMID: 23085640; PubMed Central PMCID: PMC3591461.
Buckley, J. G., Timmis, M. a, Scally, A. J., & Elliott, D. B. (2011). When is visual information used to control locomotion when descending a kerb? PloS one, 6(4), e19079.
Franchak JM, van der Zalm DJ, Adolph KE. Learning by doing: action performance facilitates affordance perception. Vision Res. 2010 Dec;50(24):2758-65. doi: 10.1016/j.visres.2010.09.019. Epub 2010 Sep 19. PubMed PMID: 20858512; PubMed Central PMCID: PMC3013505.
Gentle J, Barnett AL, Wilmut K. Adaptations to walking on an uneven terrain for individuals with and without Developmental Coordination Disorder. Hum Mov Sci. 2016 Oct;49:346-53. doi: 10.1016/j.humov.2016.08.010. Epub 2016 Sep 1. PubMed PMID: 27591489.
Wilmut K, Du W, Barnett AL. (2016) Gait patterns in children with Developmental Coordination Disorder. Exp Brain Res. 2016 Jun;234(6):1747-55. doi: 10.1007/s00221-016-4592-x. Epub 2016 Feb 15. PubMed PMID: 26879769.
Comalli DM, Persand D, Adolph KE. Motor decisions are not black and white: selecting actions in the "gray zone". Exp Brain Res. 2017 Jun;235(6):1793-1807. PDF
Franchak, J. M., & Adolph, K. E. (2012). What infants know and what they do: Perceiving possibilities for walking through openings. Developmental Psychology, 48(5), 1254–1261. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3584587/
Franchak, J., & Adolph, K. (2014). Affordances as Probabilistic Functions: Implications for Development, Perception, and Decisions for Action. Ecological Psychology : A Publication of the International Society for Ecological Psychology, 26( 1-2), 109–124. http://doi.org/10.1080/10407413.2014.874923
Ishak, S., Franchak, J. M., & Adolph, K. E. (2014). Perception–action development from infants to adults: Perceiving affordances for reaching through openings. Journal of Experimental Child Psychology, 117, 92–105. http://doi.org/10.1016/j.jecp.2013.09.003
Keogh J., & Sugden D. (1985). Movement skill development. New York: Macmillan.
Newell K.M. (1986). Constraints on the development of coordination In Wade M.G., editor; & Whiting H.T.A., editor. (Eds.), Motor development in children: Aspects of coordination and control (pp. 341–361). Amsterdam: Martinus Nijhoff Publishers.
Oudgenoeg-Paz O, Boom J, Volman MC, Leseman PP. (2016)Development of exploration of spatial-relational object properties in the second and third years of life. J Exp Child Psychol. 2016 Jun;146:137-55. doi: 10.1016/j.jecp.2016.02.005. Epub 2016 Mar 4. PubMed PMID: 26950506.
Sugden D.A., & Wade M.G. (2013). Typical and atypical motor development. New York: MacKeith Press
Thelen E. (1989). Self‐organization in developmental processes: Can systems approaches work? In Gunnar M., editor; & Thelen E., editor. (Eds.), Minnesota Symposia on Child Psychology, Vol. 22 (pp. 77–117)., Systems and development Hillsdale, NJ: Erlbaum.