Burton M W, Small S L, Blumstein S E
Department of Neurology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
J Cogn Neurosci. 2000 Jul;12(4):679-90. doi: 10.1162/089892900562309.
Phonological processes map sound information onto higher levels of language processing and provide the mechanisms by which verbal information can be temporarily stored in working memory. Despite a strong convergence of data suggesting both left lateralization and distributed encoding in the anterior and posterior perisylvian language areas, the nature and brain encoding of phonological subprocesses remain ambiguous. The present study used functional magnetic resonance imaging (fMRI) to investigate the conditions under which anterior (lateral frontal) areas are activated during speech-discrimination tasks that differ in segmental processing demands. In two experiments, subjects performed "same/ different" judgments on the first sound of pairs of words. In the first experiment, the speech stimuli did not require overt segmentation of the initial consonant from the rest of the word, since the "different" pairs only varied in the phonetic voicing of the initial consonant (e.g., dip-tip). In the second experiment, the speech stimuli required segmentation since "different" pairs both varied in initial consonant voicing and contained different vowels and final consonants (e.g., dip-ten). These speech conditions were compared to a tone-discrimination control condition. Behavioral data showed that subjects were highly accurate in both experiments, but revealed different patterns of reaction-time latencies between the two experiments. The imaging data indicated that whereas both speech conditions showed superior temporal activation when compared to tone discrimination, only the second experiment showed consistent evidence of frontal activity. Taken together, the results of Experiments 1 and 2 suggest that phonological processing per se does not necessarily recruit frontal areas. We postulate that frontal activation is a product of segmentation processes in speech perception, or alternatively, working memory demands required for such processing.
语音处理过程将声音信息映射到更高层次的语言处理中，并提供将言语信息临时存储在工作记忆中的机制。尽管大量数据表明左侧化以及在外侧裂周围前语言区和后语言区的分布式编码，但语音子过程的性质和大脑编码仍不明确。本研究使用功能磁共振成像（fMRI）来研究在语音辨别任务中，当节段处理需求不同时，前侧（额叶外侧）区域被激活的条件。在两个实验中，受试者对单词对的第一个音进行“相同/不同”判断。在第一个实验中，语音刺激不需要将初始辅音与单词的其余部分进行明显分割，因为“不同”的单词对仅在初始辅音的语音浊音方面有所不同（例如，dip - tip）。在第二个实验中，语音刺激需要进行分割，因为“不同”的单词对不仅在初始辅音浊音方面不同，还包含不同的元音和结尾辅音（例如，dip - ten）。将这些语音条件与音调辨别控制条件进行比较。行为数据表明，受试者在两个实验中都具有很高的准确性，但揭示了两个实验之间不同的反应时潜伏期模式。成像数据表明，与音调辨别相比，两种语音条件都显示出更好的颞叶激活，但只有第二个实验显示出额叶活动的一致证据。综合来看，实验1和实验2的结果表明，语音处理本身不一定会激活额叶区域。我们推测额叶激活是语音感知中分割过程的产物，或者是这种处理所需的工作记忆需求的产物。
