What reading aloud reveals about speaking: Regressive saccades implicate a failure to monitor, not inattention, in the prevalence of intrusion errors on function words

Bilinguals occasionally produce language intrusion errors (inadvertent translations of the intended word), especially when attempting to produce function word targets, and often when reading aloud mixed-language paragraphs. We investigate whether these errors are due to a failure of attention during speech planning, or failure of monitoring speech output by classifying errors based on whether and when they were corrected, and investigating eye movement behaviour surrounding them. Prior research on this topic has primarily tested alphabetic languages (e.g., Spanish–English bilinguals) in which part of speech is confounded with word length, which is related to word skipping (i.e., decreased attention). Therefore, we tested 29 Chinese–English bilinguals whose languages differ in orthography, visually cueing language membership, and for whom part of speech (in Chinese) is less confounded with word length. Despite the strong orthographic cue, Chinese–English bilinguals produced intrusion errors with similar effects as previously reported (e.g., especially with function word targets written in the dominant language). Gaze durations did differ by whether errors were made and corrected or not, but these patterns were similar for function and content words and therefore cannot explain part of speech effects. However, bilinguals regressed to words produced as errors more often than to correctly produced words, but regressions facilitated correction of errors only for content, not for function words. These data suggest that the vulnerability of function words to language intrusion errors primarily reflects automatic retrieval and failures of speech monitoring mechanisms from stopping function versus content word errors after they are planned for production.