Frequency difference limens of pure tones and harmonics within complex stimuli in Mongolian gerbils and humans

Frequency difference limens (FDLs) for pure tones between 200 and 6400 Hz and for the first, the second, or the eighth harmonic of an 800 Hz complex in four Mongolian gerbils (Meriones unguiculatus) were determined using a Go/NoGo-procedure. The 12 harmonics of the complex started either in sine phase or at a random phase. Gerbils showed very high pure tone FDLs ranging from 17.1% Weber fraction (200 Hz) to 6.7% (6400 Hz). They performed much better in detecting mistuning of a harmonic in the complex in the sine phase condition with FDLs decreasing from 0.07% for the first harmonic to 0.02% for the eighth harmonic. FDLs were about one order of magnitude higher when temporal cues were degraded by randomizing the starting phase of every component in the harmonic complex for every stimulus. These results are strikingly different from those obtained in four human subjects who needed about four times higher frequency shifts than gerbils for detecting a mistuned component in a sine phase complex and showed similar detection of mistuning in the random phase condition. The results are discussed in relation to possible processing mechanisms for pure tone frequency discrimination and for detecting mistuning in harmonic complex stimuli.