Fig. 2
From: Delta opioid receptors affect acoustic features of song during vocal learning in zebra finches
(a) Sonogram representing an exemplar of an FM syllable. These are complex syllables with intricate frequency traces. (b) Sonogram representing a harmonic stack syllable which is simpler than FM syllables and consists of frequency traces arranged in a stack above the fundamental frequency. Both these types of syllables were used to measure the motif complexity of the naltrindole-treated birds and their control siblings. Figures show average number of syllable types produced by the (c) control and (d) treated birds. Each point in the scatter plot represents data for one bird for the number of FM or H-stack type syllables per motif. (c) There was a significantly greater number of FM syllables in the songs of controls, whereas (d) songs of birds administered the δ-OR antagonist naltrindole tended to have a greater number of harmonic stacks