In research on speech perception much use has been made of continua of synthetic speech items. These can be used to investigate the boundary between different elements, and how those boundaries may be modified. The elements are normally presented in random order.
In this simple example you will first hear three synthetic /3:/ vowels with no consonant. You will then hear eight CV syllables, each with a slightly different F2 onset transition (approximately as shown in the first eight items in the figure below). The first one should sound like /b3:/. At which point do you hear a change to /d3:/?