On the emergence of the in-out effect across trials: two items do the trick

Individuals prefer letter strings whose consonantal articulation spots move from the front of the mouth to the back (e.g., BAKA, inward) over those with a reversed consonant order (e.g., KABA, outward), the so-called in-out effect. The present research explores whether individuals hold an internal standard or scheme of consonant order that triggers this effect. If this were the case, the in-out effect should already occur in one-trial between-subjects designs. If not, the in-out effect should emerge over the course of trials in within-subjects designs. In Experiments 1a-e (1b-e preregistered; total N = 2973; German, English, and Portuguese samples) employing a one-trial between-subjects design, no in-out effect was found. In Experiment 2 (N = 253), employing within-subjects designs with either 1, 5, 10, 30, or 50 trials per consonant order category (inward vs. outward), the in-out effect was absent in the first trial, but already surfaced for the first 2 trials, reached significance within the first 10 trials and a solid plateau within the first 20 trials. Of the four theoretical explanations, the present evidence favors the fluency/frequency and letter-position accounts and is at odds with the eating-related embodiment and easy-first accounts.