研究議題

I. Inhibition and Intentional Forgetting

Forgetting unwanted or irrelevant information is crucial for maintaining the functionality of memory. Intentional forgetting is often investigated with the directed forgetting paradigm, which instructs subjects to remember some study materials but to forget others. In a series of studies we used event-related brain potentials to show that active inhibition is involved in intentional forgetting. First, the Remember/Forget cues gave rise to ERPs that were predictive of the subsequent recognition performance to the study items preceding the cues. The subsequent memory effect elicited by the Remember cues was more sustained than that elicited by the Forget cues and showed distinct scalp distribution during the extended period (Hsieh et al., 2009) Second, employing a procedure that combined semantic priming and item-method directed forgetting, we demonstrated that targets preceded by Forget cues yielded a smaller P200 wave than those preceded by Remember cues. Furthermore, the topography of the N400 effect was different for targets preceded by Remember and Forget cues. (Liu et al., 2012). In addition, the N400 effect, thought to reflect semantic processing, was greatly reduced for targets preceded by Forget instructions in comparison to Remember instructions. These findings therefore support the role of active inhibition in the intentional forgetting of unwanted memories.

Lin, W.-J., Kuo, Y.-C., Liu, T.-L., Y.-J. Han, & Cheng, S.-k.* (2013). Intentional forgetting reduces the semantic processing of to-be-forgotten items: An ERP study of item-method directed forgetting. Psychophysiology, 50,1120-1132. (corresponding author , SCI, IF=3.26, 13/83 in Experimental Psychology).

Cheng, S.-K.*, Liu, I.-C., Lee, J. R., Hung, D. L., & Tzeng, O. J.-L. (2012). Intentional forgetting might be more effortful than remembering: An ERP study of item-method directed forgetting. Biological Psychology 89, 283-292. (corresponding author, SCI, IF=4.337, 7/71 in Psychology; 5/49 in Behavioral Sciences)

Hsieh, L.-T., Hung, D.L., Hung, O.J.-L. Tzeng, Lee, J.R., & Cheng, S.-k*, (2009). An event-related potential investigation of the processing of Remember/Forget cues and item encoding in item-method directed forgetting. Brain Research, 1250, 190-201. (corresponding author, SCI, IF=2.551) (NSC 96-2413-H-008-002)

II. Word Learning and Episodic Memory

Words with different characteristics can be viewed as mini-events that are analogous to various types of episodes experienced in real life. In a study we demonstrated that semantic transparency as a linguistic property modulates the recognition memory for two-character Chinese words, with opaque words (i.e., words whose meanings cannot be derived from constituent characters, e.g., “光[/guang/, light]棍[/gun/, stick]”, bachelor) remembered better than transparent words (i.e., whose meanings can be derived from constituent characters, e.g., “茶[/cha/, tea]杯[/bei/, cup]”, teacup). We argued that the conceptual incongruence between the meanings of a whole word and its constituent characters made opaque words more distinctive and hence better remembered than transparent words. (Han et al, in press).

Han, Y.-J, Huang, S.-c, Lee, C.-Y., & Cheng, S.-k.* (accepted). The modulation of semantic transparency on recognition memory for Chinese two-character words. Memory & Cognition, in press. (correspondent author, SSCI, IF=2.049, 32/83 in Experimental Psychology)

III. Mismatch Negativity and Cochlear Implant Simulation

We recorded ERPs when normal-hearing participants passively listened to speech sounds of two tones and their CI simulations in different numbers of channels. The MMN responses elicited by the speech sounds and those elicited by the CI simulations were compared. we demonstrated that spectral resolution plays an important role in the processing of Mandarin Chinese tones. In order to effectively transmit Chinese tonal information, speech signals must be divided into more than 8 frequency channels in CI devices. The constraint of spectral resolution on the transmission of tonal information should be taken into account in the design of cochlear implants. The presence of both positive and negative mismatch response in adults to the low- and high-resolution CI simulations sounds implicates that there are multiple mechanisms underlying auditory mismatch responses (Kuo et al, 2014).

Kuo, Y.-C., Lee, C.-Y., Chen. M.-C., Liu, T.-L., & Cheng, S.-k.* (2014). The impact of spectral resolution on the mismatch response to Mandarin Chinese tones: An ERP study of cochlear implant simulations. Clinical Neurophysiology, 125, 1568-1575. (corresponding author, SCI, IF=3.707, 110/252 in Neurosciences)

IV. Phonological processing in Chinese reading

The aims of this project are threefold: 1. to acquire the event-related potential (ERP) data that are correlated with word identification and speech perception; 2. to explore the ERP correlates of phonological processing, particularly rhyme processing, and their relationships with reading ability; 3. to investigate the temporal dynamics of Chinese word identification with MEG data. During the past year, we conducted experiments that use mismatch negativity (MMN) and picture identification task to identify the electrophysiological correlates of speech perception that differentiate dyslexic children from skilled readers. The materials for the MMN experiment included verbal sounds of Chinese, English, and Finnish syllables. Reliable MMNs were observed when college students and elementary school children were presented with these materials. Moreover, in college students, we found correlations between naming RT and MMN magnitude, suggesting that indeed phonological processing could be indexed by the MMN.

Chen, Y., Lee, J.R., Kuo, W.-J., Hung, D. L., & Cheng, S.-k.* (2010). An ERP study of Chinese speakers’ rhyme judgment to Chinese and English words. Neuroreport 21, 636-640. (Corresponding Author, SCI).

V. The Formation and Retrieval of Erroneous Memory

We employed a procedure that incorporated two types of memory errors: ‘source memory errors’ and ‘gist-based false recognition’, and investigated their underlying mechanisms by recording the ERPs associated with these errors. The results showed that recollection is involved in source judgment errors when the rearranged pairs correspond to the gist of study pairs formed during encoding. Moreover, although correctly classified old pairs and incorrectly classified rearranged pairs appear to engage equivalent processes at the time of retrieval, these two classes of memory judgment appear to depend on qualitatively distinct encoding operations. (Rugg and Cheng, 2004; 2010).

Cheng, S.-k*. & Rugg, M. D. (2010). Event-related potential correlates of gist and verbatim encoding. International Journal of Psychophysiology 77, 95-105. (corresponding author, SCI, IF=3.314)

Cheng, S.-k*. & Rugg, M.D. (2005). An event-related potential study of two kinds of source judgment errors. Cognitive Brain Research, 22, 113-127. (corresponding author , SCI, IF=3.77)

VI. Using tDCS and rTMS to examine the role of LPPC in episodic memory retrieval

Although functional neuroimaging studies of recognition memory consistently report activations in the left posterior parietal cortex (LPPC), very few neuropsychological or brain-stimulation studies provide evidence for a causal relationship between LPPC and memory retrieval. This study employed transcranial direct current stimulation (tDCS) to examine whether LPPC is required for memory retrieval. Anodal and cathodal tDCS stimulation are known to increase and decrease neuronal excitability respectively and it was predicted that, if LPPC is required for successful memory retrieval, such stimulation over this region with anodal or cathodal currents should lead to a concomitant increase or decrease in memory performance. Participants in the present experiment visited the laboratory twice for two source memory tests. In one visit, all participants received sham stimulation over the LPPC scalp region for a 10-minute interval between study and test phases. For the other visit, half of the participants received anodal stimulation and the other half received cathodal stimulation. The old/new recognition performance was found to increase after anodal stimulation and decrease after cathodal stimulation. No such effects were found in a control experiment where left primary motor cortex was stimulated. These findings provide evidence for the causal relationship between LPPC and retrieval processes in recognition memory.

Chen, N.-F., Lo, C.-M., Juan, C.-H., Muggleton, N., & Cheng, S.-k. (under review) Source Memory Performance is modulated by Transcranial Direct Current Stimulation over the Left Posterior Parietal Cortex.

Chen, N.F., Juan, C. -H, Hung, D.- L., & Tzeng, O.J.-L., Cheng, S.-K., (2014). Post-retrieval monitoring in episodic memory is modulated by transcranial direct current stimulations over the left posterior parietal cortex. Cognitive Neuroscience Society 2014 Annual Meeting, Boston, USA.