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Lecture 4

PSYB20 - Lecture 4.docx

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Mark Schmuckler

PSYB20 – Lecture 4 Prof’s Speech - Purple Slide 2 – Age Norms for Important Motor Milestones - Motor capabilities are probably the most obvious and present indicator of helplessness of an infant - Newborns at best move head, kick; have uncoordinated motor skills - Human newborn motor milestones occur within the first few months - Motor skills development takes place in fairly definitive stages - Achievement of motor milestones is not related to intellectual development - Body dimensions of infants typically play a role in their motor milestone achievement - Motor development doesn‟t stop at 24 months, but continues into adulthood; throughout entire lives, which means that there are many motor skills we can talk about, but we will focus on walking and reaching Slide 3 – Necessary Skills for Visually-Guided Reaching - Visually-guided reaching occurs when we can accurately reach for and grasp an object in our visual field - Prominent skill that develops in first months - Perceptual skills o Object recognition  Have to be able to perceive objects  Depth perception requires motor skills o Figure-ground separation - Motor skills o Arm and hand coordination o Fine-motor coordination and control - Visual-motor integration and coordination o Involves Visual guidance of the hand o And the right Timing of the grasp  For moving objects, we have to perceive and predict where it will move; reach for where you think the object will be Slide 4 – The Normative Sequence of Reaching - 1 – 2 Months o Begin to see isolated components, i.e. perceptual components are fixated o Glance at objects when present o Begin to fixate objects for 5-10 sec o Arms not organized with vision  Motor abilities do not necessarily coordinate with vision - 2 – 3 Months o Isolation of components breaks down  Visual-motor coordination appears o Focus on objects o Beginning of prehensory behavior o Raise hand towards object  Can make relatively accurate swipes at an object  Can hit and bat, maybe not grasp  Being to see raising of hand, but not actually trying to grasp - 3 – 4 Months o Mutual grasping, 1 or 2 hands  Grasping is seen – just as likely with 2 hands as it is with 1 hand o Sometimes turn torso towards object  Begins to orient body toward object - 4 – 5 Months o Integrated looking and grasping o “Top-level” reaching  Even timing is accurate o Good grasping of object  Good hold of object (stationary object) Slide 5 – Type of Contact with a Moving Object - Von Hofsten & Lindhagen (1979) o Carried out a longitudinal study with 12-24 week old babies at 3 week intervals until 30 weeks and then at 36 weeks o Von Hofsten - reaching for a moving object is much more difficult because you have to extend the arm with a trajectory of the object is moving - Graph: The number of reaches at each speed and age, expressed as a proportion of the maximum number of possible reaches (3 per condition). o Had the infants reach for moving objects at different speeds – slow, medium, fast o Researchers looked at reactions – reaches occurred at the same time as when the infant started to fixate o Infants are more likely to reach for slower moving objects, but the graph doesn‟t show successful reaching Slide 6 – Type of Contact with a Moving Object - Graph: The type of contact with the object. Proportion of total number of reaches for “grasp,” “touch,” and “miss.” o Infants rarely miss o “touch” but no grasp – goes down with age o Touch and grasp – goes up with age o At 18-20/21 weeks, grasping outperforms touching o Grasping of stationary and moving objects occurs at the same age Slide 7 – Reaching with hands vs. feet - Esther Thelen o Noted that while reaching with the arm is interesting, it is difficult for infants to control their arms and much more so than their legs – partly because of body dimensions, partly because of physiology o legs are capable of fewer movements o If body constraints are important, infants should be better at reaching with their legs o Compared timing for reaching with the hands versus reaching with the feet  Tested 8-15 week olds longitudinally (weekly)  Presented with toy at midline between shoulders, and midline of hips to see which (arms or legs) they used to reach o Timing of reaching with hands and feet:  Average age of first contact: Hands: 15.7 weeks; Feet: 11.7 weeks  More likely to contact object with their feet  Extended contact with object: Hands: 16, Feet: 11.8  Extended contact was more likely with feet than with hands, which suggests that infants are more coordinated/organized with their feet Slide 8 – Is Visually-Guided reaching a Myth? - Clifton, Muir, Ashmead, & Clarkson (1993) - Visually-guided reaching reflects that there is something special in vision with reaching; we use vision to guide our hands to the object - Rachel Clifton (aka Rachel Keen) – if vision is more important to reaching, reaching should be more successful in the light than in the dark - Reaching in the light vs the dark graphs: if vision is important
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