Schematic illustrations of the experimental apparatus and an alternating block stimulus.

<p>A) The apparatus used in behavioural experiments. The ferret moved freely in the lower semicircular region of the arena. B) Example showing trials presented in alternating blocks of 8 trials with easy (blue) and hard (pink) detection conditions. Each block contains four no-sound trials and four sound trials (unfilled and filled squares, respectively), and two tones at two stimulus levels (dots, easy: s1, s2; hard: s3, s4). For blocks of 24 trials, there are 12 sound trials in a block, 6 at each of two levels.