Effect of cumulative distance in motor space on segment-sized slips in 3-word phrases

Abstract

Slips, or speech errors (e.g., “teep a cape” for “keep a tape”), have been described as the disordered arrangement of discrete elements, giving rise to the hypothesis that these arise from misordering during phonological encoding. An alternative hypothesis is that slips are articulatory timing errors, conditioned by the same motor factors that underlie coarticulation. This hypothesis motivates the present study, which used a modified slip procedure to elicit errors from 40 native English-speaking adults. Participants spoke 3-word phrases that were constructed as mini tongue twisters, with alternating word onsets and repeating rhymes. These phrases were designed to condition slips to a greater or less extent according to coarticulatory-adjacent processes (e.g., palatalization). A metric of cumulative distance-traveled in motor space during phrase production was also calculated: the degree of change in vocal tract shapes across the phrase, estimated using data generated within the tubesounds model in ArtiSynth. Phrases designed to more strongly condition slips were expected to cover less cumulative distance in motor space than phrases designed to less strongly condition slips. The distance-traveled metric did not always align with this expectation, but was nonetheless a better predictor of presence/absence of slips than phrase condition in analyses on preliminary data.