Table 1.

Description of experimental conditions

Abbreviation	Condition name	Exchange	Food	Description
ETLV	Equity test, low value	Both exchange	Both low value (carrot)	Both subject and partner exchanged for low-value reward
ETHV	Equity test, high value	Both exchange	Both high value (grape)	Both subject and partner exchanged for high-value reward
FC	Food control	Both exchange	Both see high value (grape) before exchange, receive low value (carrot) following exchange	Prior to exchange, high-value reward was held in front of exchanger, then placed back in container; after successful completion of exchange, exchanger received low-value reward
IT	Inequity test	Both exchange	Subject low value (carrot); partner high value (grape)	Partner exchanged for high-value reward and subject exchanged for low-value reward
GR	Gift reward	No exchange	Subject low value (carrot); partner high value (grape)	Partner was given a high-value reward for ‘free’ (e.g. without exchange), then the subject was given a low-value reward
DT	Delay test	Both exchange, subject waits 10 s after exchange before receiving food	Both high value (grape)	Partner and subject had to exchange for high-value reward, but the subject had to wait 10 s before receiving it
DETLV	Differential exchange test, low value	Subject exchanges; partner does not exchange	Both low value (carrot)	Partner was given a low-value reward for ‘free’ (e.g. without exchange) and subject had to exchange for a low-value reward
DETHV	Differential exchange test, high value	Subject exchanges; partner does not exchange	Both high value (grape)	Partner was given a high-value reward for ‘free’ (e.g. without exchange) and subject had to exchange for a high-value reward