Figure 1.

Structure of the behavioral tasks in two animals. A, Structure of the trials in ferret FerUP. The animal was trained to listen to acoustic stimuli and to withhold licking during a sequence of tone pairs with downward shifts (reference stimuli: random number of 1–5 repeats). The animal learned to approach the waterspout upon hearing an upward shifting tone pair (target) to receive a water reward. The frequencies of the tone pairs were variable, both within and between trials, and randomly shifted in frequency. In some experiments, only the tone pairs were presented (with silence between them). In others, additional spectrotemporally modulated sounds (such as TORCs or amplitude-modulated rippled noise; see Materials and Methods) were inserted between all tone pairs, and the animals learned to ignore the TORCs and continued to perform the task based on the tone pairs. B, Structure of the trials in ferret FerDN. This animal learned the same task as FerUP, except for attending to the opposite tone-pair shifts. All other details were the same. C, Behavioral performance in head-holder. The bar plot represented the average DI when the animal performed the task with its head restrained. The dashed horizontal lines indicate the threshold level defined as the mean + 2 SD of the shuffled DIs (for more details, see Yin et al., 2010). There was no difference in performance between the experimental conditions with and without the TORCs. Although both ferrets displayed significant performance, FerUP had overall a better performance in the head-holder than FerDN (Wilcoxon rank sum test, p < 0.01).