The segment as the minimal planning unit in speech production and reading aloud: evidence and implications

Alan H. Kawamoto, Qiang Liu, Christopher T. Kello

Speech production and reading aloud studies have much in common, especially the last stages involved in producing a response. We focus on the minimal planning unit (MPU) in articulation. Although most researchers now assume that the MPU is the syllable, we argue that it is at least as small as the segment based on negative response latencies (i.e., response initiation before presentation of the complete target) and longer initial segment durations in a reading aloud task where the initial segment is primed. We also discuss why such evidence was not found in earlier studies. Next, we rebut arguments that the segment cannot be the MPU by appealing to flexible planning scope whereby planning units of different sizes can be used due to individual differences, as well as stimulus and experimental design differences. We also discuss why negative response latencies do not arise in some situations and why anticipatory coarticulation does not preclude the segment MPU. Finally, we argue that the segment MPU is also important because it provides an alternative explanation of results implicated in the serial vs. parallel processing debate.