In the second example ("Ascend. 7ths #2"), try to hear the sequence as three descending minor 2nds. To assist in this hearing, click on the "Desc. 2nds" button, which will play the sequence C5-B4-Bb4: a sequence of the three descending minor 2nds that begins to be suggested by the the second example.
In the following examples, this ambiguity is emphasized further. In the first of these ("Ascend. 7ths #3"), we hear a sequence of ascending 7ths using sine tones, as heard before. In the 2nd example ("Desc. 2nds"), we hear the descending 2nds again, in order to acustom the ear to this possible way of hearing. In the third and final example ("Ambiguous"), the spectra (that is, the "overtone" structure) of each of the tones is constructed in order to more strongly emphasize the aspect of chroma over height. When listening to this sequence, we really begin to ask ourselves: is it a sequence of ascending major 7ths beginning on C4, or is it a sequence of descending minor seconds (half-steps) beginning on C6? You will note that context is important here: if you repeatedly play the ascending 7ths sequence, it is easier to hear the ambiguous tones as ascending 7ths. If you repeatedly play the descending 2nds sequence, it becomes easier to hear the ambigous tones as descending 2nds.