FIGURE 4.

Across all HVC_X neurons tested for responses to accelerated trills (N = 14 cells, 6 birds), the strength of auditory response became weaker with progressive acceleration of trill rates, but cells retained their relation to specific features within the song syllable. a) The responses of individual neurons became weaker as trill rates were accelerated, with responses becoming less than that evoked by reversed presentation of the primary song type (horizontal dotted line) at even moderately accelerated conditions (triangles indicate antidromically identified HVC_X cells; open symbols indicate the cells shown in Figure 3; square symbols illustrate the diversity of responses among 3 cells that responded to the same primary song type in the same bird). At trill rates where broken syntax emerges behaviorally (> 156% of natural trill rate, shaded region), few HVC_X neurons expressed a reliable auditory representation of each syllable in those accelerated trills. b) Despite those changes in response strength, activity of HVC_X neurons was generally unchanged in its temporally precise association with specific features of the song syllable (symbols as in panel a).