Fig. 2: In hearing birds, the valence of light-off reinforcers is negative.

a, b Hearing birds change pitch in the direction of decreasing LO rate, here shown for a low-pitch light-off (LO low) bird (bird b2y2, a same bird as in Fig. 1c, d) and a LO high bird (bird p6s6, b). Legend as in Fig. 1d, f. c Histograms of average daily pitch changes in LO high (blue, n = 6), LO low (green, n = 6), and in hearing control (noLO) birds (gray, n = 12). The asterisks indicate subs birds with significant pitch changes compared to controls (two-sample, two-sided t-test, p < 0.05, see “Methods”). d The three mixed linear fixed effect terms and their standard errors. The bars indicate the daily change in pitch (d’/day) during baseline, during LO exposure in the direction of increasing LO rate (LO, ***indicates non-zero fixed effect −0.08, p = 1.4 × 10⁻⁴, df = 377, SE = 0.02, tstat = −3.85, confidence interval −0.12 to −0.04 d’/day, n = 24 birds), and in hearing control birds (noLO). e Average directed pitch changes over all days in LO (hearing, 144 days) vs subs (deaf, 102 days) birds. Hearing birds changed their pitch away from the LO zone (decreasing the number of renditions with LO) and deaf birds towards the LO zone (increasing the number of renditions with LO). The error bars indicate the standard errors of the mean. f The magnitude of average pitch change is larger in subs birds than in LO birds (0.16 d’/day, *indicates p = 0.01 for average magnitude, tstat = 2.73, df = 20, two-sample two-sided t-test, n = 12 LO and n = 10 subs birds), and much larger than in unsubs birds (0.22d’/day in time-matched periods, **** indicates p = 4 × 10⁻⁵, tstat = −5.35, df = 18, n = 20 birds, two-sample two-tailed t-test). The magnitude of average pitch change is larger by 0.10 d’/day for hearing LO than noLO birds (p = 0.02, tstat = −2.43, df = 22, two-sample two-tailed t-test, p-values are not adjusted for multiple comparisons. The error bars indicate standard errors of the mean and the dots represent individual birds (colors as in c).