Right-hemisphere Involvement In Chinese Idiom Processing

PurposeChinese four-character idioms are phrases with metaphor meanings that cannot be directly derived from the literal meanings. Characters in an idiom were fixed and cannot be replaced by similar characters. No imaging study has been conducted with idioms, for English and Chinese. In the present study, we used different kinds of stimuli to address the neural basis analyze the idiom processing with an event-related fMRI (functional magnetic resonance imaging) design.Methods1. SubjectsSixteen native Chinese College Students (eight females; mean age, 23.0 years; age range, 22.0-25.0 years) participated in the study. All participants had normal or corrected to normal vision, and were right handed.2. Experimental design and Imaging MethodsThe experiment was carried out using a 1.5-T Philips scanner at the Medical College of Shantou University, China with a standard head coil. The functional data were recorded using a T2-weighted gradient-echo-planar imaging [EPI] sequence with echo time [TE]=45ms, flip angle=90 degrees, repetition time [TR]=2,000 ms. The matrix acquired was 64×64 with a field of view [FOV] of 230×230ms. Twenty axial slices covering the whole brain and surrounding areas were recorded (6 mm thickness, no skip).The anatomical images(acquisition matrix=256×256) were acquired with a T1-weighted spin echo pulse sequence (TR=204ms; TE=14ms).Participants were lying comfortably in the scanner and wore earphones and goggles specially designed for the MR environment (Resonance Technology Company, Los Angeles, CA). Foam padding was used to reduce head motion, and they were told to keep their head still when doing the task inside the scanner. Participants made their responses using a button box. All visual Stimuli through the goggles was in real-time using a computer with an Inquisit software package (Millisecond controlled stimulus presentation and response recording Software, Seattle, WA).In a fast, random-interval, event-related design, subjects were told that some idioms would appear false in some way, but were not told the exact nature of the anomalies nor were they given examples. They were first familiarized with the task and stimuli outside the scanner, and then went into the magnet and each completed six scanning sessions. The first session contained 20 practice trials and was excluded from later analysis. The remaining five sessions were for tests, each with twenty-four trials. In each trial, a false (either pseudo - idiom or wrong idiom) or true idiom (real idiom) was presented through the goggle. The task required participants to decide whether the idioms were true (real) or false. Participants had to indicate their decision by pressing a button. Subjects were told to decide as quickly as possible, and accuracy was also emphasized.In each session, one half of the trials were real idioms (idiom condition, metaphoric meaning) trials, one quarter were pseudo - idiom (a set of four characters literal phrases matched syntactically and semantically to the real idioms) trials and one quarter were wrong idioms (nonsense-string condition, either metaphoric or literal meaning) trials, randomly intermixed. The intertrial interval (ITI) was pseudorandomized with a mean length of 10 s and a range of 6-14s. In each trial participants carried out the semantic decision task for 240 s (24 trials with an average length of 10s). All participants were required to fixate on a central dot between two trials. Each scanning run began with a 35-s period in which participants focused their eyes and attention on a fixation cross in the center of the screen and did not do any task. Eye-movement monitoring with an eye-tracking system confirmed that participants maintained visual fixation.The experimental stimuli consisted of 120 four-character Chinese idioms, all of which were selected from the Dictionary of Chinese idioms []. We first constructed the 60 pseudo idioms with their fourth correct character replaced by a synonymous character, the pseudo-idioms follows the structure rules of Chinese idioms and could be seen as legitimate four-character literal phrases. The 60 wrong idioms without any meaning were created by substituting their forth correct character with a wrong one so there existed violations both in semantics and in structure. All Chinese characters contained in the idioms were commonly used according to the frequency corpus of Chinese Beijing Language Institute 1986. Half of the trials obtained were used for the odd-numbered participants and the other half for the even-numbered ones. Participants were told that some idioms would appear false in some way but were not told the exact nature of the anomalies, and no trial was used more than once.3. Materials1) Three kinds of stimuli:120 four-character Real idiomsFor example:安然无恙120four-character literal phrases (syntactically and semantically to the real idioms)For example:安然无病120 nonsense itemFor example:安然无的2) Imaging MethodsThe stimuli were randomly intermixed, and were given by the goggle during the scan with a 1.5T Philips scanner. They were asked to judge whether the word they see was real idiom or not by pressing corresponding button.4. Imaging post processing and Data-analysisWe aimed to use the method of subtraction with the non-idiom (literal phrases or nonsense item) conditions and the baseline. The semantic process of real idioms and non-idiom can be isolated by subtraction. Imaging analysis was done with SPM2 software following the standard two-step random effect analysis procedure. The threshold was s p=0.005 to produce maps of activation.Results1) BehaviorMean error rate and reaction time (RT) across all 16 participants were 2.92% (SE=0.71) and 2349ms(SE=85), respectively. Reaction times of pseudo-idioms and wrong idioms were similar. Real idioms consumed more time than the other two form judgment tasks, but yielding no statistically significant differences. The error rate was 2.6%(SE=0.52), 5.2%(SE=1.90)and 0.9%(SE=0.45) for real idioms, pseudo-idioms and wrong idioms, respectively. ANOVA revealed a main effect of task for error rate [F (2,30)=3.509, P＜0.05]. Paired t-tests revealed that subjects committed significantly errors during pseudo-idioms than any other judgment task. Thus, equivalence at the behavioral level is not confounding effects of relative difficulty for real idioms and pseudo-idioms.2) fMRIa. The three condition (four-character Real idioms, four-character literal phrases or nonsense item) judgment tasks as compared to rest activated extensive neuronal networks of substantial similarity.b. The comparison of interest judgments of four-character Real idioms vs. four-character literal phrases—revealed a striking dissociation between right and left hemisphere activation, interestingly, real idioms judgments produced only significant activation several areas in the right hemisphere, the right inferior frontal gyrus(BA45,47),right Angular(BA39), right Fusiform(BA37)and right superior parietal (BAT).c. Direct comparison of four-character Real idioms vs. nonsense item also showed sever clusters of reliable activity in the right hemisphere: superior frontal (BA6), middle frontal(BA8).d. pseudo idioms vs. wrong idioms just activated a couple of regions: left fusiform(BA35) and cerebellum.ConclusionMetaphorical language comprehension is supported by a mutual communication between left hemisphere and right hemisphere. We assume that right-hemisphere involvement in Chinese idiom processing.