Bridging the gap: Infants’ sensitivity to bridge width and drop-off height Kari S. Kretch, Jennifer L. Quon, Jennifer Kung, & Karen E. Adolph New York University

NICHD R37-33486 to KEA

ATTEMPTS TO CROSS

RESEARCH QUESTIONS

GAIT MODIFICATIONS WALKERS

Do infants take bridge width & drop-off height into account when deciding whether to cross bridges?

0.75

Ppn of Trials

Ppn of Trials

1.00

0.50 0.25

Cm

10 Large Drop-off

Small Drop-off

-6

0

+6

+12 +18

Cm from Threshold

2

-12

Cm

-6

0

+6

+12 +18

Cm from Threshold

25

25

20

20

Latency

15 10

Latency (s)

Latency (s)

30

20

0.75 0.50 0.25

Time to Cross (s)

0.00 +6

+12

Cm from Threshold

+18

0

50

Cm

+6

+12

Cm from Threshold

+18

Cm

VISUAL ATTENTION

10 5

0

0 -12

-6

0

+6

+12 +18

Cm from Threshold

2

50

Cm

Cm

1.00

1.00

0.75

0.75

Exploring Bridge

0.50 0.25 0.00 2

Ppn of Trials

Cm

2 walkers wore wireless head-mounted eye-tracker to calculate point of gaze

1.00

15

5

-12

-6

0

+6

+12 +18

Cm from Threshold

50

Cm

-12

-6

0

+6

+12 +18

Cm from Threshold

0.50 0.25 0.00

50

2

Cm

Cm

1.00

1.00

0.75

0.75

0.50 0.25 0.00 2

Cm

-12

-6

0

+6

+12 +18

Cm from Threshold

50

Cm

Exploring Drop-off

-12

-6

0

+6

+12 +18

Cm from Threshold

50

Cm

0.50 0.25 0.00 2

Cm

-12

-6

0

+6

+12 +18

Cm from Threshold

50

Cm

Latency & touching vary with bridge width, not drop-off height

50

Cm

50

S#1: Large Drop-off

25

Assessed motor decisions & exploration on safe and risky bridges relative to individual thresholds

Cm from Threshold

+18

CRAWLERS

30

Cm

Small Drop-off

+12

Infants modify their gait on smaller bridges, but do not distinguish between drop-off conditions

WALKERS

2

Large Drop-off

+6

EXPLORATION

30

10

0

0.25

Infants attempt to cross large bridges and refuse small bridges, but do not distinguish between drop-off conditions

35

15

5

Cm

0.50

0

0.25

Cm

10

50

Stepping Strategies

0.50

50

Cm from Threshold

+18

S#2: Small Drop-off

1.00

1.00

0.75

0.75

Ppn of Time

15

-12

+12

0.75

Ppn of Time

20

0.75

0.00 2

+6

15

0

0.00

Ppn of Trials

25

Small Drop-off

Ppn of Trials

30

CRAWLERS

Large Drop-off

1.00

Ppn of Trials

Affordance Threshold (cm)

Affordance Threshold (cm)

35

Crawling Thresholds

5

1.00

Ppn of Trials

WALKERS

Determined each infant’s motor threshold—narrowest bridge crossed successfully on 2/3 trials Walking Thresholds

Time to Cross

10

0

0.00

Infants crossed 2-60 cm wide bridges, over large (71 cm) & small (17 cm) drop-offs

15

0

How do infants deploy visual attention while deciding whether to cross?

37 14-mos walkers & 18 11-mos crawlers

20

Ppn of Trials

Time to Cross (s)

20

Crawlers’ posture may make drop-off height more salient; are they more sensitive to drop-off than walkers?

METHOD

CRAWLERS

0.50

0.50

0.25

0.25

0.00

0.00

10

22

30

50

Bridge Width (cm)

60

bridge drop-off landing other

10

22

30

50

Bridge Width (cm)

60

Infants look at both the bridge and the drop-off while making decisions Indifference to drop-off height is not due to lack of visual information

50

Cm