Table 1. Sequence of isolated and covered face regions presented to each dog in the training phases of Experiment 1.

	Order of presentation
Dog ID	1st	2nd	3rd	4th	5th	6th
1	E-R	N-R	M-R	E-R covered	M-R covered	N-R covered
2	M-R	E-R	N-R	N-R covered	E-R covered	M-R covered
3	N-R	M-R	E-R	M-R covered	N-R covered	E-R covered
4	E-R covered	N-R covered	M-R covered	M-R	N-R	E-R
5	M-R covered	E-R covered	N-R covered	N-R	E-R	M-R
6	N-R covered	M-R covered	E-R covered	M-R	N-R	E-R
7	E-R covered	M-R covered	N-R covered	E-R	M-R	N-R

Once dogs reached the learning criterion with a given stimulus type, they proceeded to the next stimulus until the sixth training phase.

E-R  =  eyes region, N-R  =  nose region, M-R  =  mouth region.