FIGURE 4. Agrammatical controls for alternative strategies.

Mean d' ( s.e.m.) values for comparisons among the AAAA, BBBB, ABBA and BAAB agrammatical stimuli, to rule out the use of alternate solution strategies. For primacy (see main text), AAAA and ABBA should be classified similarly to new n = 2 CFG and FSG patterns, respectively, presented during the same probe sessions (Methods). For recency (see main text), BBBB and BAAB should be classified similarly to new n = 2 CFG and FSG patterns, respectively. If starlings are listening for the presence of a B/A motif transition (see text), then the d' value comparing BAAB and ABBA to AAAA and BBBB should be similar to that for new n = 2 CFG and FSG patterns. d' for the new n = 2 CFG and FSG probe stimuli (dark blue) was significantly higher than that for all three control comparisons (light blue; asterisk indicates P < 0.05 for all cases, paired t-test).