Fig. 1.

Sound stimuli and behavioral apparatus. A: waveform envelope of the artificial vowel stimulus 1. B: power spectra of all 4 stimuli. Stimuli 1 and 3 (formants at 1,520 and 3,420 Hz) were associated with turns to the right and stimuli 2 and 4 (2,280 and 5,130 Hz) with turns to the left. C: to initiate a trial, the rat had to enter the nose poke. D: immediately after its entry in the nose poke, 1 of the 4 sounds was played through both speakers. E: the rat had to recall whether the left or right water spout was associated with the sound vowel sounds to obtain a water reward. The opposite platform, where the identical behavior was performed, is depicted at the top of C–E.