1Department of Neural Rehabilitation, China Rehabilitation Research Center, Capital Medical University School of Rehabilitation Medicine, Beijing 100068, China
2State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, Beijing 102600, China

Luping Song☆, Ph.D., Chief physician, Department of Neural Rehabilitation, China Rehabilitation Research Center, Capital Medical University School of Rehabilitation Medicine, Beijing 100068, China

Corresponding author: Luping Song, Department of Neural Rehabilitation, China Rehabilitation Research Center, Capital Medical University School of Rehabilitation Medicine, Beijing 100068, China
songluping882002@yahoo. com.cn

Supported by: the China Postdoctoral Science Foundation, No. 2001, #14*; the Capital Medical Development Science Research Program, No. 2005-2003*

Received: 2010-05-28
Accepted: 2010-08-05
(N20091130001/ZW)

Song LP, Peng DL, Ning N. Interaction between semantic and phonological processes in stuttering: evidence from the dual-task paradigm. Neural Regen Res. 2010;5(18):1435-1440.

www.crter.cn
www.nrronline.org

doi:10.3969/j.issn.1673-5374.2010.18.013

Abstract
Stuttering is a common neurological deficit and its underlying cognitive mechanisms are a matter of debate, with evidence suggesting abnormal modulation between speech encoding and other cognitive components. Previous studies have mainly used single task experiments to investigate the disturbance of language production. It is unclear whether there is abnormal interaction between the three language tasks (orthographic, phonological and semantic judgment) in stuttering patients. This study used dual tasks and manipulated the stimulus onset asynchrony (SOA) between tasks 1 and 2 and the nature of the second task, including orthographic, phonological, and semantic judgments. The results showed that the performance records of orthographic judgment, phonological judgment, and semantic judgment were significantly reduced between the patient and control groups with short SOA (P < 0.05). However, different patterns of interaction between task 2 and SOA were observed across subject groups: subjects with stuttering were more strongly modulated by SOA when the second task was semantic judgment or phonological judgment (P < 0.05), but not in the orthographic judgment experiment (P > 0.05). These results indicated that the interaction mechanism between semantic processing and phonological encoding might be an underlying cause for stuttering.
Key Words: stuttering; semantic processing; phonological processing; interaction; dual-task paradigm
 

INTRODUCTION

Stuttering is a wide spread language production deficit affecting speakers of all languages. Stuttering is also a neurological disease, which seriously affects the physical and mental health of patients. Revelation of the barrier mechanism will help identify the cause of stuttering, formulate reasonable effective rehabilitation programs, and also provide a scientific basis for the regeneration of neural plasticity[1-9]. Studies investigating stuttering have revealed the potential aspects of cognitive mechanisms underlying this disorder. One group of studies investigating whether people who stutter (PWS) show differences compared with fluent speakers at various stages within the speech production process[10-16]. Regarding the first notion of stuttering mechanisms, it is commonly accepted that speech production involves the following stages: semantic processing, lexical retrieval, phonological encoding, and articulation[17-21]. Previous work has examined whether PWS is as efficient as people who do not stutter (PNS) in these stages and have obtained mixed results. It has been shown that PWS exhibited poor performances in verbal tasks[13, 16, 22-28]. Some studies have shown that the semantic processing in PWS might be poorer than in PNS[27, 29-31].
Much evidence for the role of the central executive control in stuttering comes from the dual task paradigm. In a dual task experiment, two stimuli are presented consecutively, and subjects respond to each of them in the order of stimuli presentation. The response performance (reaction time and accuracy) of the second task is usually inhibited. Such an interference effect is referred to as psychological refractory period and is commonly attributed to the limit of the processing bottleneck. The psychological refractory period effect is shown to be influenced by stimulus onset asynchrony (SOA), the processing difficulty of the tasks, and potentially also the extent of the common processing components shared by these tasks[32-35]. There have been debated about whether the psychological refractory period effect is due to passive queuing or active monitoring of the two events. We focused on the application of this paradigm in understanding the differences between PWS and PNS. It has been demonstrated that 
PWS shows different psychological refractory period patterns in fluent speakers[11, 36-37].
While both hypotheses have their merits, it is unknown whether stuttering symptoms are at least partly related to interaction between different components within the language processing system. Speech production is commonly perceived as an interactive process via a monitoring mechanism[19-21]. The interactions between different speech processing modalities, such as between orthographic and speech perception or between orthography and speech production, have been well studied[38-40]. Although the efficiency of the semantic, orthographic and phonological processing of PWS was not reliably found to be different from PNS, as discussed above, it is unknown whether the modulation patterns among these components are different in the two kinds of subjects. To resolve this issue, the dual task paradigm was adopted here to investigate the modulation effect between several critical components in language processing and a phonological output task, such as reading aloud. This study will provide a theoretical basis for semantic and phonological training in stuttering rehabilitation. Furthermore, the effect of such training will help reveal the neural mechanism of reorganization that the semantic component modulates the phonological component.