Abstract
Frequency-difference limens (DL) were determined in a songbird, the European starling ( Sturnus rulgaris), for stimuli differing in the type of frequency change. Four different types of frequency change were studied: an increase in frequency between pulsed tones (type FSU), a single sinusoidal sweep upward (type SSU) starting in the center of an 800 ms signal, an asymmetrical periodic sinusoidal frequency modulation that extended only above the reference frequency (type ASFM), and a symmetrical periodical sinusoidal frequency modulation extending to both sides of the reference frequency (type SSFM). Frequency DLs at two reference frequencies. 1 and 4 kHz. were studied. At 1 kHz. the starling showed the lowest DL for pulsed tones (11.4 Hz), slightly higher DLs for single sweeps and asymmetrical frequency modulation at modulation frequencies of ≦ 40 Hz (15.9 Hz for stimulus SSU. and 15.3 Hz for low modulation frequencies of stimulus type ASFM). At a reference frequency of 1 kHz. the DL for symmetrical modulation (type SSFM) at modulation frequencies ≦ 40 Hz was about twice as large (21.h Hz) than for pulsed tones. Furthermore, the DLs for periodically modulated signals at a modulation frequency of 320 Hz were about twice as large as those at low modulation frequencies. At a reference frequency of 4 kHz, the differences in the DLs for various stimulus types were insignificant (27.7 Hz for type FSU, 23.3 Hz for type SSU, 28.0 Hz for type ASFM and low modulation frequencies, and 24.6 Hz for type SSFM and low modulation frequencies). Only at high modulation frequencies (≧ 320 Hz) were the DLs increased. The results are discussed with respect to similar effects of stimulus type and reference frequency on the frequency-difference limen in humans and with respect to the frequency DLs in other bird species.
Published Version
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