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Motor Development.pdf

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University of Toronto Scarborough
Mark Schmuckler

PSYB20 Motor Development - Lecture 04 & 05  Beginning for Midterm #2  Human infants are particular disadvantage compared to many other species – especially in the motor ability , in terms of longer gestation st  By end of 1month – infants reach their 1 milestone of lifting their chin up and from which progressive motor achievement begins  Motor milestone represent average age norm ( what a child should be able to do in terms of his age)  though definite sequential & age can vary & variation in development of motor milestone is not connected to other development aspect (e.g. intelligent)  Motor development continue into adulthood (e.g. driving a car)  2 Special issue : o 1) Development of Reaching o 2) Walking/Mobility – Development of locomotion Development of Reaching  There are necessary skills needed for visually-guided reaching  Visually guided reaching implies the ability to accurately reach & grasp for object  seem to develop w/in ½ year of life (which rely on development of other skills  `1) Perceptual Skills o Need to be able to recognize object o To understand figure-ground separation  able to pick object from background in order to reach for it  2) Motor Skills o Need gross motor coordination in terms of arm & hand coordination o Also need fine-motor coordination & control in order to close hand around the object & control grasp  3) a combination of 1& 2 = Visual-Motor integration & coordination o Visual guidance of hand – arms out there going towards the direction of object o Timing of the grasp  able to close hand at right time to grasp object  e.g. moving object – more complex to grasp the object  Classic Study w/ infants  use brightly colour object & see how they reach (using fishing lure)  1-2 months  Glance at objects when present ( see it in isolated parts) & begin to fixate objects  Arm (motor) movement but is not coordinated w/ vision  Seeing grasping reflex  2-3 moths  Isolation of component breaks down  begin to show visual-motor coordination  Focus on object & begin prehensory behaviour - meaning they accurately swipe at object, often hitting the object  Raise hand towards object ( not grasping it )  3-4 moths  Begin to see grasp (mutual grasping w/ 1 or 2 hands)  Orient their body towards object ( turn torso toward object)  4-5 months  Visual – motor integrated  integrated looking & grasping  “top level” reaching  finger start to close before they are touching the object which shows fine motor movement  Good grasping of object  Reaching for moving object  much more difficult have to put other perceptual skills – so the Question is when do they start to do this  Van Hofsten & Lindhagen (1979) – Type of Contact With a Moving Object The Number of reaches at each speed and age  expressed as proportion of maximum number of possible reaches ( 3 per condition)  Is Longitudinal study @ 3 week interval until 30 week of age , then @ 3  object moving speed of : slow, medium or fast  Looked & reached for object (at the same time fixate)  found more reaches toward slower than medium and fast objects  w/ increasing age  began to converge at all speed – so at older age – they reach for objects that were moving at slow, medium or fast speed The type of contact with the object  proportion of total number of reaches grasp, touch and miss  its coded for success in 3 way: Miss, Touch or Grasp   result showed: o Infant rarely miss the object o At young age – they made contact (touch) but didn’t grasp & w/ age touch goes down o Because  at age 18-21 weeks – grasping outperform touching  showing infants grasp at the same time for stantionary objects as for moving object as well o Galloway & Thelen (2004)  looked at different type of reaching : Reaching with hands vs. feet  In terms of body dimension & physiology  arm control is difficult than leg control because leg don’t have many freedom of movements  longitudinal study (8-15 weeks) - comparing timing for reaching with hands vs. feet  presented toy at midline b/w shoulders & midline of hips (= toys to upper torso vs. toys at lower torso) & looked at what they reached for and which limb they reached w/  Result showed – they are much more likely to reach w/ leg around 11.7 weeks compared to reaching w/ hands around 15.7 weeks on average  Also more co-ordinated w/ their leg  extended contact w/ objects w/ leg 11.8 weeks vs. w/ hands 16 weeks  This shows an EXCEPTION to physical growth rule  Is Visually-Guided Reaching a MYTH? The notion of reaching is visually guided comes w/ assumption that vision gives us special skills/ ability needed to reach for object o Cliffton et al (1993) – tested this assumption  reaching w/ light vs. dark (individual subjects)  they argued that infant will be more likely to reach in light vs. dark and be more successful at it too o Result looked at age they reach for object, made contact and grasp  if argument were to be true more bars (during light condition) should be more  Found – is that bars at top and bottom ( looked at slide 8 – top = light and bottom= dark) are the same  indication no difference b/w 2 condition  Seems that proprietary sense are enough o Vision is IMPORTANT for motivation , anticipation trajectory  e.g. see a object – get the motivation to get that object (e.g. candy)  Also blind infant reach for later than sighted infant maybe because sighted infant
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