Time course of simultaneous masking in the starling's auditory forebrain.
Simultaneous masking of pure tones was studied in the primary auditory forebrain of a songbird species, the European starling (Sturnus vulgaris). The responses of 32 multi-unit clusters in the input layer of the auditory neostriatum (field L2a) were recorded via radiotelemetry from freely moving birds. The probe was a 10-ms tone burst at the units' characteristic-frequency (CF) presented 20 dB above the threshold. The masker was an 80-ms tone burst presented either at the units' CF (excitatory masker) or at a frequency located in inhibitory side-bands (inhibitory masker) of the units' tuning curves. The probe was presented either 3 ms or 63 ms after masker onset. Probes presented at a 3-ms delay were influenced at significantly lower levels of an excitatory masker than probes presented at a 63-ms delay. The mean difference in masker level at the detection thresholds for both probe delays was 8 dB. No difference in masker level was observed for inhibitory-frequency maskers. The observed neural masking effects may be explained by at least four mechanisms: (1) swamping of the probe response by the response to the masker, (2) a reduction of the probe response during neural adaptation of the response to the masker, (3) a reduction of the probe response during side-band inhibition in the central nervous system, and (4) suppression originating in the cochlea.
Nieder
A
A
Institut für Zoologie, Technische Universität München, Garching, Germany. nieder@corvus.bio2.rwth-aachen.de
Klump
G M
GM
D000161:Acoustic Stimulation; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001717:Birds / Q000502:physiology*; D005260:Female; D008297:Male; D010470:Perceptual Masking / Q000502:physiology*; D016548:Prosencephalon / Q000502:physiology*; D013686:Telemetry; D013997:Time Factors