Table 1.

Coding Definitions for Sharing and Non-sharing Behaviors

Behavior	Definition
Shares	Actively gives at least one item to AE (assistant experimenter/playmate) by placing it on AEs table within her reach and leaving it there, or by handing an item to AE & releasing it into her hand; returns to own play(or eating) afterwards; looks at AE before, during, or immediately after sharing
Imitates	Imitates AEs verbal, vocal, or gestural behavior
Social-affiliative	Looks at AE while directing other social behavior toward her, i.e., gestures, vocalizes, or speaks to AE; shows own things to AE; brings own thing(s) over to AE and plays next to her without offering any
Gives All	Puts all of the items on AEs table all at once. Does not interrupt this behavior to return to own play or eating. Does not request or try to take things back. Looks like compliance, not sharing.
Hypothesis-testing	Stares fixedly at AE for at least 4 continuous seconds, or glances repeatedly at AE while stopping own play or eating; may seem confused or tense; may look repeatedly back & forth between own items and AE; social referencing to parent or E
Refuses	Overt refusal, either verbally or gesturally (“no;” “mine;” shakes head ‘no’); guarding, hoarding, or hiding own things; fake-out or take-back (offers or hands item then changes mind and reclaims it before releasing it)
Self-focus	Doesn’t visibly respond to AE’s cue; may occasionally glance at AE’s things or may glance at AE briefly, but returns to own play or eating; can include apparently deliberate ignoring of AE; predominantly playing with (or eating) own things