Does learning to sit help babies see which shape is in front?
Babies of the same age who could already sit on their own treated a symmetrical shape as the object in front, while babies who could not yet sit showed no such preference.
Source
The Relationship between Sitting and the Use of Symmetry As a Cue to Figure-Ground Assignment in 6.5-Month-Old Infants
Study at a glance
- Design
- Other — Two infant preferential-looking experiments comparing naturally occurring groups (sitters vs non-sitters); the stimulus contrast is within-subject but sitting status is not manipulated.
- N
- 36 infants in Experiment 1 (sitting by parent report) and 44 infants in Experiment 2 (23 sitters and 21 non-sitters by a lab sitting test).
- Population
- Healthy full-term 6.5-month-old infants from mostly middle-class, mostly White US families.
- Outcome
- Proportion of looking time directed to the display where motion and symmetry agreed on which region was the figure; habituation measures as a control.
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What they did
Infants aged about six and a half months watched pairs of animated displays, each made of a symmetrical region joined to an asymmetrical one. After a 2-second still period one region slid in front of or behind the other, so that in one display motion and symmetry agreed on which region was the 'figure' and in the other they conflicted. Experiment 1 grouped 36 infants as sitters or non-sitters by parent report; Experiment 2 tested 44 infants, checked sitting with a 30-second lab test, and added an unrelated habituation task to see whether sitters were simply more advanced overall.
What they found
In Experiment 1, sitters looked longer at the consistent display when both displays used the same kind of motion (a large effect, d = 2.18), while non-sitters looked at chance; sitters beat non-sitters on these trials (d = 1.28). Experiment 2 replicated the sitters' preference (d = 0.94) and again found none in non-sitters, although the direct sitter-versus-non-sitter difference was not significant this time (p = 0.19). Sitters and non-sitters did not differ on the habituation task, and parent report matched the lab sitting test 100% for sitters.
The limits
What it doesn't show
Sitting was not manipulated, so the study cannot show that sitting causes the new sensitivity; some other change that happens alongside sitting could explain it. The groups were small and demographically narrow, the sitting test was a simple 30-second check rather than a standardised motor scale, and in Experiment 2 the between-group comparison itself was not significant. The preference only appeared when both displays used the same type of motion, and the authors acknowledge they cannot be sure why infants preferred the consistent displays.
Key terms
- Figure-ground assignment
- The visual process of deciding which region is an object in front (the figure) and which is background, including which region 'owns' a shared edge.
- Gestalt cue
- A regularity in an image, such as symmetry or convexity, that the visual system uses to group parts and decide what is an object.
- Preferential looking
- An infant method that shows two displays side by side and infers discrimination or expectation from which one the baby looks at longer.
- Habituation
- A drop in looking to a repeated stimulus; how quickly it happens and how much looking recovers to a new stimulus index infant processing speed and memory.
- Developmental cascade
- The idea that a new motor skill, like sitting, opens up new experiences that in turn drive changes in perception and cognition.
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Quiz yourself
What did 6.5-month-old sitters prefer to look at?
Common questions
Why would sitting have anything to do with vision?
Sitting frees both arms for reaching and gives an upright view, so infants get much more practice handling and looking at objects, most of which are symmetrical; the authors think this experience teaches that symmetry signals 'object'.
Couldn't sitters just be more advanced babies in general?
That was tested in Experiment 2: sitters and non-sitters performed the same on an unrelated habituation task, which argues against a simple general-maturity explanation, although it cannot rule out every alternative.
Why compare displays with the same kind of motion?
When both displays moved in the same way, the only difference was whether symmetry agreed with the motion cue, which made the comparison easier; sitters showed no preference when the motions were mismatched.
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