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Visual guidance in infants' reaching toward suddenly displaced targets
D H Ashmead1, M E McCarty, L S Lucas
1Bill Wilkerson Hearing and Speech Center, Vanderbilt University, Nashville, TN 37212.
Insights
Infants
Area of Science:
- Developmental psychology
- Motor control
- Human factors
Background:
- Reaching behavior is a fundamental motor skill.
- Visual feedback is crucial for refining movements.
- Understanding developmental changes in visually guided reaching is important.
Purpose of the Study:
- To investigate how visual information about target and hand location influences reaching in infants and adults.
- To determine the developmental trajectory of visually guided reaching.
- To examine the role of visual guidance during the approach phase of reaching.
Main Methods:
- Participants included 5-month-olds, 9-month-olds, and adults.
- Experiments were conducted in a dark room with illuminated toys.
- Trials involved either a static target (no-switch) or a target that changed position mid-reach (switch).
- A luminescent marker was used on the reaching hand for some trials.
Main Results:
- Adults fully compensated for target changes.
- 9-month-olds partially adjusted to target changes when using a hand marker, but not without it.
- 9-month-olds showed no difference in accuracy with or without the hand marker on no-switch trials.
- 5-month-olds were generally inaccurate and unaffected by the hand marker.
Conclusions:
- Visual guidance during reaching increases with development.
- 9-month-olds utilize visual feedback to adjust reaches, particularly when their hand's position is marked.
- 5-month-olds show limited visual guidance in their reaching behavior.
Abstract:
This experiment evaluated the role of visual input about the location of a target object and the location of the hand in reaching by infants and adults. 5- and 9-month-old infants were presented with illuminated toys to reach for in a dark room. On no-switch trials, the toy remained illuminated throughout the infant's reach, whereas on switch trials the first-lit toy was replaced during the reach by a second-lit toy at a different position. On approximately half of the trials of each type a luminescent marker was attached to the reaching hand. Adult subjects (tested without the hand marker) fully compensated to the second-lit toy on switch trials, during a second reaching segment. On switch trials, 9-month-olds partially adjusted to the second-lit toy when wearing the hand marker and did not adjust without it. On no-switch trials, 9-month-olds reached just as accurately with or without the hand marker. 5-month-olds were generally inaccurate in their reaching and were unaffected by the presence or absence of the hand marker. The findings suggest that during the development of reaching there is an increase in visual guidance during the approach phase of reaches.