Laboratory rats (Rattus norvegicus) do not use binaural phase differences to localize sound

The ability of Norway rats to use binaural time- and intensity-difference cues to localize sound was investigated by determining their ability to localize pure tones from 500 Hz to 32 kHz. In addition, their ability to use the binaural time cues present in the envelope of a signal was determined by presenting them with a 1-kHz tone that was amplitude modulated at either 250 or 500 Hz. Although the animals were easily able to localize tones above 2 kHz, indicating that they could use the binaural intensity-difference cue, they were virtually unable to localize the lower-frequency stimuli, indicating that they could not use the binaural phase (time) cue. Although some animals showed a residual ability to localize low-frequency tones, control tests indicated that they were using the transient interaural intensity difference in the onset of a sound that exists after it reaches the near ear but before it reaches the far ear. Thus, in contrast to earlier studies, we conclude that the Norway rat is unable to use the ongoing time cues available in low-frequency tones to localize sound, raising the possibility that the rat may not use interaural time differences to localize sound.