An SLP asks a listener to identify the word “pie” when presented with words that start with different voice-onset-times. Six responses are obtained for each of the following VOTs: VOT = −20, 0/6 = pie; VOT = −10, 0/6 = pie; VOT = 0, 1/6 = pie; VOT = +10, 2/6 = pie; VOT = +20, 4/6 = pie; VOT = +30, 6/6 = pie. What VOT value corresponds to this listener’s perceptual category boundary between “pie” and “bye”?

• A. −20 ms VOT
• B. 0 ms VOT
• C. 15 ms VOT
• D. +30 ms VOT

Answer: (C)

Perceptual category boundary is the VOT where the listener is equally likely to hear either category, here pie or bye. Looking at the data, pie responses are 2 out of 6 at +10 ms and 4 out of 6 at +20 ms. The 50% point lies halfway between these two, so the boundary occurs at +15 ms VOT. This is the VOT value where the listener would be about equally likely to identify the sound as pie or bye.