Activity patterns of cochlear ganglion neurones in the starling

1. Spontaneous activity and responses to simple tonal stimuli were studied in cochlear ganglion neurones of the starling. 2. Both regular and irregular spontaneous activity were recorded (Figs. I to 5). Non-auditory cells have their origin in the macula lagenae. Mean spontaneous rate for auditory cells (all irregularly spiking) was 45 spikes s-1. 3. In half the units having characteristic frequencies (CFs) <1.5 kHz, time-interval histograms (TIHs) of spontaneous activity showed regularly-spaced peaks or 'preferred' intervals. The spacing of the peak intervals was, on average, 15% greater than the CF-period interval of the respective units (Fig. 11). 4. In TIH of lower-frequency cells without preferred intervals, the modal interval was also on average about 15% longer than the CF-period interval (Fig. 11). Apparently, the resting oscillation frequency of these cells lies below their CF. 5. Tuning curves (TCs) of neurones to short tone bursts show no systematic asymmetry as in mammals. Below CF 1 kHz, the low-frequency flanks of the TCs are, on average, steeper than the high-frequency flanks. Above CF 1 kHz, the reverse is true (Fig. 15). 6. The cochlear ganglion and nerve are tonotopically organized. Low-frequency fibres arise apically in the papilla basilaris and are found near non-auditory (lagenar) fibres (Figs. 2 and 19). 7. Discharge rates to short tones were monotonically related to sound presure level (Fig. 20). Saturation rates often exceeded 300 spikes s- 1. 8. 'On-off' responses and primary suppression of spontaneous activity were observed (Figs. 22 and 23). 9. A direct comparison of spontaneous activity and tuning-curve symmetry (Fig. 15b) revealed that, apart from quantative differences, fundamental qualitative differences exist between starling and guinea-pig primary afferents

Temporal scales of auditory objects underlying birdsong vocal recognition

Vocal recognition is common among songbirds, and provides an excellent model system to study the perceptual and neurobiological mechanisms for processing natural vocal communication signals. Male European starlings, a species of songbird, learn to recognize the songs of multiple conspecific males by attending to stereotyped acoustic patterns, and these learned patterns elicit selective neuronal responses in auditory forebrain neurons. The present study investigates the perceptual grouping of spectrotemporal acoustic patterns in starling song at multiple temporal scales. The results show that permutations in sequencing of submotif acoustic features have significant effects on song recognition, and that these effects are specific to songs that comprise learned motifs. The observations suggest that (1) motifs form auditory objects embedded in a hierarchy of acoustic patterns, (2) that object-based song perception emerges without explicit reinforcement, and (3) that multiple temporal scales within the acoustic pattern hierarchy convey information about the individual identity of the singer. The authors discuss the results in the context of auditory object formation and talker recognition