Fig. 1: Light-off stimuli are positive reinforcers of vocal pitch in deaf songbirds.
a Schematic of the experiment. A singing deaf bird inside a sound-isolation chamber (left) experiences a light-off (LO) stimulus for a duration in the range of 100–500 ms (right) when the pitch of one of its song syllables (red note) exceeds a given threshold (Credit: Sarah Steinbacher, MELS UZH). b Example picture of a pair of surgically removed cochleas. Complete deafness was confirmed by the presence of the osseous spiral lamina and by verification of an intact loop including the lagena. c, e Example song spectrograms in birds b2y2 (c) and b2p19 (e) with substituted feedback for low-pitched (c) and high-pitched (e) syllable renditions. The time points of pitch measurement are indicated by white dashed lines and the LO stimuli by green (c) and blue (e) bars. d, f Pitch values for syllable renditions without substitution (black dots) and with substitution (green dots: low-pitch subs, d); blue dots: high-pitch subs, (f)). The birds adapted the pitch in the direction of increasing LO rate. g Histograms of average daily pitch changes during substitution in birds with high-pitch substitution (subs high, blue, n = 5 birds, the first bar corresponds to b2p19 shown in (e) and (f)), low-pitch substitution (subs low, green, n = 5 birds, the 8th bar corresponds to b2y2 shown in (c) and (d)), and in deaf control birds without substitution (unsubs, dark gray, n = 10 birds). The light gray bar to the left of each colored bar indicates the average daily pitch change in that bird during the last 5 baseline days. The asterisks indicate subs birds with significant pitch changes compared to controls (two-sample, two-sided t-test, p < 0.05). h Subs birds, as a population, adapt pitch in the direction of substituted feedback. Shown are the three fixed-effect terms of a mixed linear-effect model and their standard errors (282 observations from n = 10 subs and n = 10 unsubs birds). The bars indicate the daily change in pitch (d’/day) during baseline, during substitution in the direction of increasing light-off rate (subs, **** indicates nonzero fixed effect 0.19 d’/day, p = 3.0 × 10−6, SE = 0.04, tstat = 4.77, df = 279, confidence interval 0.11–0.27 d’/day, n = 20 birds), and in control (unsubs) birds.
