Instructions: No instructions condition

In the No Instructions condition, instructions to participants were as for any standard other-race effect experiment (and also the same as used by Hugenberg et al., 2007). That is, participants were simply informed they would see faces that they would be asked to learn for a memory test, and there was no mention of race or different types of faces being presented.

3.4.1.4  Instructions: Motivation-to-individuate condition

In the Motivation condition, we used Hugenberg et al.'s (2007) wording adapted for our specific races (Caucasian and Asian). See Supplementary Materials Appendix 1 for the exact instruction wording that appeared on the screen. These onscreen

instructions were presented before learning began, and repeated before each CFMT task. We also added some additional information to further motivate participants: the session began with the tutor/experimenter providing a verbal explanation that the lab was about the ORE, and about whether we could improve it by warning observers about the importance of attending to aspects of the faces that differentiate between different people; and we also included information about the negative practical consequences of the ORE to eyewitness testimony in real-world cases.

3.4.1.5  Face recognition tasks

Caucasian and Asian faces were presented in separate tasks: the CFMT-

Australian for Caucasian faces (McKone et al., 2011) and the CFMT-Chinese for Asian faces (McKone et al., 2012). Each task followed the standard CFMT procedure (full description in Duchaine and Nakayama, 2006). Briefly, in Stage 1 (learning), each of 6 targets is learned in 3 views (each shown for a fixed 3s), followed by immediate tests of that target presented in the learned image against 2 distractors on each trial (3 trials per target; 18 trials total for Stage 1); in Stage 2 (novel images), the task becomes more difficult by requiring recognition of the target, again from 2 distractors per trial, in a new image of the target person (specifically, new viewpoint and/or lighting; 5 trials per target; 30 trials total for Stage 2); in Stage 3 (novel images in noise), the task becomes more difficult again by requiring recognition from degraded images, using new images of each target different from those used in any previous stage (4 trials per face; 24 trials

total for Stage 3). On each test trial, the 3AFC display stays on the screen until the participant responds. Instructions emphasise accuracy rather than speed of response. Hair and clothing are occluded in all images. Face images averaged 5.2° vertical visual angle (5.5 cm tall viewed at 60 cm).

Scoring. For accuracy, we scored percent correct (out of all 72 trials). For reaction time, we calculated mean reaction time for each participant, excluding trials where the response was incorrect, or the response time was an outlier (defined as RT faster than 300ms indicating pre-emptive response, or slower than mean+2.5SDs of correct-response RTs for that participant in that stage).

3.4.1.6  Effort rating task

Following the memory tests, each participant was asked: "On a scale of 1-7, how much special effort did you put into telling apart the faces of the Caucasian people you saw?" followed by "On a scale of 1-7, how much special effort did you put into telling apart the faces of the Asian people you saw?" Endpoints were 1 = "just normal effort, nothing special"; and 7 = "a lot of special effort". We chose these endpoints, rather than "none" for the lower endpoint, to avoid participants using only a small region of the scale (e.g., no-one wishing to say they had applied "no" effort during a teaching lab class).

3.4.1.7  Task order

Task order was as follows: instructions; one of either CFMT-Aus or CFMT- Chinese (with order counterbalanced across participants as far as possible given the constraints on numbers for each order arising from the lab-class testing); same instructions repeated; the other of either CFMT-Aus or CFMT-Chinese; same instructions repeated and face-picture task (described in Study 4); effort rating questions; demographic questions (age, sex, race, details of race and countries of ancestry of participant's parents, time spent living in majority-Caucasian and majority- Caucasian countries, date of moving to Australia for overseas students); then childhood and adult variants of the Hancock and G. Rhodes (2008) interracial contact

questionnaire (see Study 5 for details). In total, this sequence took approximately 1.25 hrs per participant.

Regarding the order of the CFMT-Aus and CFMT-Chinese tasks, a preliminary ANOVA showed order did not influence the effects of motivation-to-individuate instructions on the ORE (no task order x instructions condition interaction, p = .185), and thus analyses in the results section are presented collapsed across task order.

3.4.2  Results

3.4.2.1  Matching of CFMT tasks for stimulus set difficulty

Importantly, the Caucasian and Asian CFMT face stimulus sets were matched for intrinsic difficulty (i.e., demonstrating equal homogeneity within the sets), as assessed by comparing the two sets for own-race performance in the 'standard' no instructions condition. This revealed no difference between memory performance for CFMT-Australian faces learned by Caucasian observers and CFMT-Chinese faces learned by Asian observers, on either accuracy (M = 79.1% correct vs M = 81.2% respectively, t(193) = 1.287, p = .200), or reaction time (2995ms vs 3111ms, t(193) = 0.854, p = .394). This means that the ORE can be validly assessed not only as an overall ORE including both races of observer (i.e., calculated as a two-way interaction between race-of-face and race-of-observer), but also for each race of observer taken separately (see Figure 1); that is, the difference in performance for own and other race faces for a single observer group provides a pure measure of the ORE in that group (rather than a confound between of the ORE and effects of differences in set difficulty).