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Chinese Science Bulletin © 2008
SCIENCE IN CHINA PRESS
Springer
Material differences of auditory source retrieval: Evidence from event-related potential studies NIE AiQing1, GUO ChunYan2† & SHEN MoWei1 1 2
Department of Psychology and Behavioral Sciences, Zhejiang University, Hangzhou 310028, China; Department of Psychology, Capital Normal University, Beijing 100037, China
Two event-related potential experiments were conducted to investigate the temporal and the spatial distributions of the old/new effects for the item recognition task and the auditory source retrieval task using picture and Chinese character as stimuli respectively. Stimuli were presented on the center of the screen with their names read out either by female or by male voice simultaneously during the study phase and then two tests were performed separately. One test task was to differentiate the old items from the new ones, and the other task was to judge the items read out by a certain voice during the study phase as targets and other ones as non-targets. The results showed that the old/new effect of the auditory source retrieval task was more sustained over time than that of the item recognition task in both experiments, and the spatial distribution of the former effect was wider than that of the latter one. Both experiments recorded reliable old/new effect over the prefrontal cortex during the source retrieval task. However, there existed some differences of the old/new effect for the auditory source retrieval task between picture and Chinese character, and LORETA source analysis indicated that the differences might be rooted in the temporal lobe. These findings demonstrate that the relevancy of the old/new effects between the item recognition task and the auditory source retrieval task supports the dual-process model; the spatial and the temporal distributions of the old/new effect elicited by the auditory source retrieval task are regulated by both the feature of the experimental material and the perceptual attribute of the voice.
Forgetting or false reporting the features of an event is a common experience that everyone can undergo, for example, one eyewitness can mistake a red hair criminal with a gun as a red hair standby or as a black hair criminal with a knife. These phenomena suggest that the memory about the occurrence of an event differs from the memory of the contextual details in which this event was acquired. Insofar as the first task is called the item memory, the second is referred to as the source memory[1]. On the basis of the dual-process model, the source memory is more difficult than the item memory, and two states of awareness underlie the memory judgment—— one, familiarity, a relatively automatic process; The other, recollection, is a process requiring effort and conscious deliberation. The item memory is mainly aswww.scichina.com | csb.scichina.com | www.springerlink.com
sociated with familiarity, and the source memory is mainly associated with recollection[2]. So far, evidence for the functional dissociation between the memory of an event and the remembering of the contextual details in which this event occurred come from a variety of research, which includes the behavioral data[3], the studies in the amnesic patients[4], and those in the individuals whose brain system was damaged[5] and in the aged[6]. Received March 28, 2008; accepted May 7, 2008 doi: 10.1007/s11434-008-0334-1 Corresponding author (email:
[email protected]) Supported by the National Natural Science Foundation of China (Grant Nos. 30570603, 30570604 and J0630760), the Ph.D. Programs Foundation of Ministry of Education of China (Nos. 20060335034 and 20070335172), Educational Bureau Foundation by Zhejiang Province of China (No. 20061310) and the Postdoctoral Foundation by Zhejiang Province of China and PHR (IHLB). †
Chinese Science Bulletin | September 2008 | vol. 53 | no. 18 | 2801-2812
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auditory source, item recognition, old/new effect, event-related potential, LORETA
The above-mentioned model is further reinforced by the event-related potential (ERP) studies. The so-called old/new effect is typically used as the neural mechanism to differentiate the item memory from the source memory. In ERP studies, the old/new effect associated with the item memory is well established as the ERPs differences elicited by the accurately hit old items with that of the correctly rejected new ones, and the old/new effect associated with the source memory is well established as the ERPs differences elicited by the accurately hit old items whose contexts were correctly attributed with that of the correctly rejected new ones. In one experiment on auditory source retrieval reported by Wilding et al., participants heard words spoken either by a male or by a female voice during the study phase. During the test phase, old and new words were presented visually, participants were instructed to decide whether each word was old or new, and if a word was judged as old, the gender associated with this word during the study phase was required to be retrieved subsequently. This work recorded two old/new effects maximal over the left-parietal and the right-prefrontal sites separately. Wherein the former effect was a positive going waveform occurred at approximately 400 ms post-stimulus onset and lasted for about 500 ms, and was larger over the left than the right hemisphere. This effect was significant in both tests, which showed the amplitudes of the accurately discriminated old words and the words whose contexts were accurately attributed were much larger than those of the new ones. The latter one was more sustained over time and was only reliable during the source retrieval phase, showing the waveforms elicited by the words whose auditory source were correctly attributed were much larger than those of the correctly rejected lures over the right prefrontal scalp. Therefore, Edward et al.[7] proposed that the right-prefrontal old/new effect might reflect the search for and/or retrieval/evaluation of the source-specifying information, i.e., the gender of the voice, and the right prefrontal cortex (PFC) was an important neural mechanism for the auditory source retrieval task on word, and the role played by this region was the post-retrieval processing[7]. This study, together with many other works, demonstrated that the item recognition task and the remembering of the voice bound to items were functionally and neuro-anatomically dissociated processes. The relevancy between the auditory source retrieval task and the prefrontal or the frontal cortex was further 2802
strengthened by other experiments[8,9]. However, inconsistent to these works, other research demonstrated that the tight link between the anterior cortices and the auditory source retrieval task was modulated by many factors. In one study of Wilding et al., they used either a 2.5 s response–time limit or no explicit upper time limit during the auditory source retrieval test. For the no timelimited test, the old/new effect occurring at 700 ms poststimulus displayed a relatively larger positivity for the correctly judged old items than that for the new ones, and this relative positivity was maximal at the anterior scalp over the right hemisphere. For the time-limited test, by contrast, the old/new effect during the same latency window was most prominent over the central electrode locations of the right hemisphere, and comprised a relatively larger positivity for the correct judgment to the new items rather than to the old ones, suggesting that the limitation of the different response–time resulted in the involvement of the functionally distinct process during the episodic retrieval task[10]. Diane et al. examined the time course of the old/new effect for the item recognition task and the auditory source retrieval task in patients with focal lesions at lateral PFC and in healthy old and young controls. ERPs revealed notable differences among these groups. The early positive going old/new effect was prominent in the young but reduced in the patients and the old, and the old displayed a prominent left frontal negativity (600―1200 ms) not observed in the young. This left frontal effect was substantially smaller and shorter in the patients. These results indicated that the old might adopt alternate memory strategies and recruit compensatory mechanisms to fulfill the task. However, the patients were unable to use these strategies and mechanisms, and thus they had great difficulties in the memory monitoring process[11]. Relative to the controls, the participants who administrated cortisol displayed an increasing ERP voltage between 500 and 1400 ms post-stimulus onset, which was diffusely distributed for the correct rejections but of a lesser magnitude frontally for the old items whose auditory contexts were correctly attributed. These findings implicated that the cortisol administration to healthy participants would impair their performance of the auditory source retrieval task[12]. To conclude, the ERP findings suggest that the item recognition task and the auditory source retrieval task are two different processes, in addition, other factors as
NIE AiQing et al. Chinese Science Bulletin | September 2008 | vol. 53 | no. 18 | 2801-2812
1
Methods
1.1 Participants Thirty-one healthy and right-handed undergraduates (15 males and 16 females) who were not majored in linguistics or fine arts were recruited for the current experiments with 15 (7 males) for experiment 1 (Exp. 1) and others for experiment 2 (Exp. 2) and received monetary compensation. Their eyesight or corrected eyesight was above 20/40, and their age averaged 21.4 years. All participants were native Chinese speakers, who reported no major neurological or psychiatric problems, and signed informed consent in accordance with the guidelines set by the local ethics committee. 1.2 Stimuli The stimuli in Exp. 1 were 400 white meaningful line
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pictures from Snodgrass et al.[13] revised to Chinese norms. These pictures were randomly divided into 8 blocks of 50 each and were matched on familiarity, naming difficulty, visual complexity and imaging consistency. The stimuli in Exp. 2 were 400 low-frequency Chinese two-word concrete nouns been divided into 8 blocks of 50 each balanced on frequency, stroke, spelling and pronunciation[14], 50 additional nouns from the identical criterion were used for practice. All nouns were displayed in white bold face. Each block in both experiments comprised a study task and two test tasks (item recognition and source retrieval). In each block, the items during the study phase were 30 (with 2 fillers at the beginning and 2 others at the end to avoid primacy and recency effects), with half the names of the items read out by a male voice and the other names read out by a female voice. The stimuli for the item recognition task were 10 old items (5 previously associated with the male voice and 5 with the female voice) and 10 new ones, the remaining old items with 10 additional novel ones added were for the source retrieval task. All stimuli were presented at the center of a black background DELL dimension 8200 monitor with 15 inches color display at 75 Hz refresh frequency and 800×600 resolution, the viewing distance was 60 cm. The horizontal and the vertical visual angles for pictures in Exp. 1 were 0.84°―4.72° and 0.52°―3.40°, respectively. All nouns were subtended with a visual angle of 6.82°×3.40° in Exp. 2. All items were not repeated across blocks. The fillers were assigned to the two tests randomly, not been comprised in the subsequent statistical analysis. The voice read the names was digitized at 44.1 kHz with 16 bits resolution, the mean length of each voice was 660 ms. 1.3 Procedure The presentation order for each block was a fixation cross of 0.19°×0.19° shown at the central location of the screen for 1000 ms, followed by an instruction for 10000 ms before the stimulus onset, and then the EEG was recorded for each task. The three tasks of each block were: (1) The study task. Each item was displayed for 500 ms followed by an ISI (inter-stimulus interval) of 1300±200 ms, and the name of each item was read out either by a female or by a male voice simultaneously. (2) The item recognition task. Items were presented on the monitor for 500 ms each with the ISI randomized from around 1600 to 2000 ms. The task was to differen-
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the response-time limitation, the learning style, aging, brain lesions, and medicine can regulate the spatial and the temporal distributive characteristics of the old/new effect for the auditory source retrieval task. Nevertheless, a question remains open, that is, whether the old/new effect for the auditory source retrieval task can be replicated in other stimuli, i.e., nonlinguistic stimuli and Chinese character. To solve this problem, two ERP experiments were designed using picture and Chinese character as stimuli respectively, and the exclusion paradigm was adopted as previous research[8]. Moreover, the LORETA source analysis was employed to analyze the intracranial generators of the old/new effects associated with different retrieval tasks for these two types of materials. Two hypothesis were proposed: Firstly, both experiments would record prominent old/new effects during the item recognition task and the auditory source retrieval task, and the spatial distribution of the old/new effect was much wider for the latter task than that for the former one, which might reinforce the dissociation viewpoint depicted by the dual-process model. Secondly, either the perceptual nature of the source or the attribute of the experimental material could regulate the old/new effect of the auditory source retrieval task, and if the effects of the auditory source retrieval tasks for both picture and Chinese character were consistent with that of word from previous research, it could be thus predicted that it was the perceptual nature of the voice that regulated the old/new effect for the auditory source retrieval task, otherwise it was the attribute of the experimental material that modulated this effect.
tiate the old items from the new ones by pressing two separate keys. (3) The source retrieval task. Items were displayed on the monitor for 500 ms each with the ISI randomized between 1600 and 2000 ms. Participants were required to press one key if he/she thought an item was associated with a certain voice during the study phase, which was hereafter labeled as target, and a second key for items associated with alternate voice or for new ones (hereafter designated as non-target-old or non-target-new). After each study task, a 3-digit number was presented, and participants were required to subtract 3 backwards and give vocal reports for 1 minute. The order of the trials within each task was pseudo-randomized, and the sequence of the two tests and the assignment of the responding fingers were counterbalanced among blocks. Figure 1 illustrated the procedure for Exp. 1, and the procedure for Exp. 2 was similar to that of Exp. 1 except the stimuli.
gain of 500 and were digitized at a sampling rate of 500 Hz per channel, and were filtered with a band-pass of 0.05―100 Hz. The impendence was kept below 5 kΩ. Trials were epoched off-line with 100 ms pre- and 1600 ms post-stimulus period and the baseline for ERP measures was the mean voltage of the 100 ms prestimulus interval. Trials contaminated by eye blinks and other artifacts exceeding ±75 µV were corrected using a linear regression estimate. The waveforms were filtered with a band-pass of 0.05―40 Hz. The electrodes for statistical analysis included FPz, Fz, Cz, Pz and Oz at the midline. Three time windows were selected based on previous studies: 200―600, 600―1000 and 1000― 1400 ms. During each latency window, a two-way repeated-measures ANOVA was performed with response (2 levels) and electrode (5 levels: prefrontal, frontal, central, parietal and occipital cortices) served as within-participant variables. The 2 levels of response were the accurately hit old items and the correctly rejected foils for the item recognition task, and the accurately discriminated targets or the non-target-old items and the correctly rejected non-target-new ones for the source retrieval task. The ANOVA was performed by SPSS12.0 software and the Greenhouse-Geisser epsilon (ε) corrections were used where appropriate.
2
Results
2.1 Behavioral data
Figure 1 Participants were presented with a series of pictures and were required to decide the gender of each voice during the study phase (left). The item recognition task was to differentiate the old pictures from the new ones (middle). The source retrieval task was to judge the pictures read by a certain voice as targets (right). Each picture was presented for 500 ms.
1.4 Electrophysiological data recording and analysis The electroencephalogram was recorded continuously with synamp amplifers from 64 Ag/AgCI electrodes extended from the 10/20 system (Jasper, 1958). Vertical EOG was recorded bipolarly from electrodes placed on the supra- and infra-orbital ridges of the left eye, and horizontal eye movements were monitored via a bipolar montage at the external canthi of both eyes. Reference electrode was located on the right mastoid online and re-referenced by both mastoids offline. The ground was between FPz and Fz. All signals were amplified with a 2804
The reaction times (RTs) and the accuracy ratios (ARs) during the test phases were displayed in Table 1. In both experiments, the RTs did not differ reliably between the accurately hit old items and the correctly rejected new ones, and the RTs differences between the accurately discriminated targets and the correctly rejected nontarget-new items also did not reach statistical significance. 2.2 ERPs characteristics In Exp. 1, the ERPs of the hit pictures were more positive going than those of the new ones during the item recognition task. P116 (the averaged latency was 116 ms), N162 and P222 could be observed at the parietal-occipital site (PO7), and P56, N116 and P174 could be observed at the central site (Cz), and N112 and P156 could be detected at the prefrontal site (AF7). During the source retrieval task, the ERPs of the target pictures were more positive going than those of the non-target-
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could be observed at the parietal-occipital site, and N90, P160, N200, P236 and N322 could be observed at the central site, and N96, P170 and N316 could be detected at the prefrontal site.
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new ones. P118, N158 and P214 could be observed at the parietal-occipital site, and N114, P172 and N232 could be observed at the central site, and P58, N110 and P156 could be detected at the prefrontal site. In Exp. 2, the waveforms of the hit nouns were more positive going than those of the rejected new ones. P62, N74, P98 and N164 could be observed at the parietal-occipital site, and P50, N90 and P160 could be observed at the central site, and N94, P220 and N324 could be detected at the prefrontal site. During the source retrieval task, the ERPs of the target nouns were more positive going than those of the non-target-new ones. N54, P106 and N164
2.3 Statistical analysis for the old/new effects (i) The old/new effects in Exp. 1. The grand average ERPs produced by the old pictures and the foils during the item recognition task were displayed in the left column of Figure 2. The ANOVA revealed that the main effect of response was significant during 200―600 ms, F(1,14) = 22.53, P < 0.001. For the second latency win-
Table 1 Behavioral data during the test phases for both experimentsa) Item recognition Old Exp.1 Exp.2
Source retrieval New
Target
Non-target-old
Non-target-new
ARs (%)
79(1.7)
96(2.2)
84(2.2)
81(1.5)
93(2.6)
RTs (ms)
760(32.9)
743(28.9)
797(35.3)
773(35.2)
755(26.9)
ARs (%)
79(4.1)
97(0.5)
78(2.3)
76(3.8)
93(1.2)
RTs (ms)
851(15.1)
878(11.8)
847(11.1)
941(14.9)
839(16.8)
PSYCHOLOGY
a) The standard derivations were shown in the parentheses.
Figure 2 Grand average ERPs elicited by the old (solid lines) and the new (dashed lines) pictures during the item recognition task (left), and the ERPs produced by the target or the non-target-old (solid lines) and the non-target-new (dashed lines) pictures during the source retrieval task (middle and right) in Exp. 1. Data were depicted at 5 scalp electrodes: FPz, Fz, Cz, Pz and Oz. Amplitudes were displayed in µV. NIE AiQing et al. Chinese Science Bulletin | September 2008 | vol. 53 | no. 18 | 2801-2812
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dow, the ANOVA demonstrated that response interacted with electrode, F(4,56) = 5.09, P < 0.01, ε = 0.96. Subsidiary analyses indicated that the effect of response was significant over the prefrontal site (P < 0.05), indicating that the ERPs of the old pictures were much larger than those of the new ones at this area. The amplitudes of these two types of items did not differ reliably for the last interval. These findings were similar to the surface potential maps based on the difference waveforms of the old/new effect as illustrated in Figure 3(a). The main effect of electrode was not described as, by itself, it did not reflect memory-related difference.
Figure 3 Surface potential maps based on the difference waveforms of the old/new effects during the item recognition phase (a) and also those during the source retrieval phase ((b) for the target pictures and (c) for the non-target-old ones) for 200―600, 600―1000 and 1000―1400 ms in Exp. 1. Red and blue regions reflected the positive and the negative activity, respectively. Dots represented the 62 scalp electrode positions. And the activities were displayed in µV.
The grand average ERPs elicited by the target pictures whose contexts were correctly attributed and the non-target-new ones during the source retrieval phase were illustrated in the middle column of Figure 2. For the 200―600 ms latency window, the main effect of response was significant, F(1,14) = 34.18, P < 0.001. And the two-way interaction also reached statistical significance, F(4,56) = 11.76, P < 0.001, ε = 0.74. Post-hoc testing revealed that the old/new effects were significant over all the five cortices (Ps < 0.05). During the 600― 1000 ms latency window, the two-way interaction was pronounced, F(4,56) = 13.53, P < 0.001, ε = 0.88. Posthoc testing discovered much greater amplitudes for the target pictures than those for the non-target-new ones 2806
over the prefrontal and the frontal cortices (Ps < 0.05). The main effect of response during the last interval was prominent, F(1,14) = 5.81, P < 0.05, and also the two-way interaction, F(4,56) = 8.85, P < 0.001, ε = 0.63. Subsidiary analyses indicated that the amplitude differences of these two types of items reached statistical significance over the prefrontal, frontal and central sites (Ps < 0.05), showing the ERPs of the target pictures were more positive going than those of the non-target-new ones. Topography depicted in Figure 3(b) added further evidence for these findings. The grand average ERPs elicited by the non-targetold and the non-target-new pictures during the source retrieval phase were depicted in the right column of Figure 2. For the first latency window, the main effect of response reached statistical significance, F(1,14) = 22.99, P < 0.001, and also the response by electrode interaction, F(4,56) = 6.43, P < 0.01, ε = 0.69. Subsidiary analyses identified that the effect of response was quite marked over all the five cortices (Ps < 0.05), showing the ERPs of the non-target-old pictures were more positive going than those of the non-target-new ones. During the second interval, the analyses revealed significant interaction between response and electrode, F(4,56) = 8.89, P < 0.001, ε = 0.71. Post-hoc testing revealed much greater amplitudes of the non-target-old pictures than those of the non-target-new ones over the prefrontal and the frontal sites (Ps < 0.005). For the 1000-1400 ms latency window, the main effect of response could be detected, F(1,14) = 20.05, P < 0.001, and also the reliable twoway interaction, F(4,56) = 5.01, P < 0.05, ε = 0.56. Aside from the occipital cortex, the effect of response was pronounced over all the other cortices during this interval (Ps < 0.05), indicating that the amplitudes of the non-target-old pictures were more positive going than those of the non-target-new ones. The surface potential maps based on the difference waveforms of the old/new effect displayed in Figure 3(c) added further evidence for the above data. (ii) The old/new effects in Exp. 2. The ERPs elicited by the old nouns and those by the foils during the item recognition task and the associating surface potential maps were illustrated in the left column of Figure 4 and Figure 5(a), respectively. In a similar vein, the twoway repeated-measures ANOVA for the 200―600 ms latency window identified significant main effect of response, F(1,15) = 11.08, P < 0.005. The amplitudes of
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The grand average ERPs elicited by the non-targetold and the non-target-new nouns during the source retrieval test were depicted in the right column of Figure 4. For the first latency window, the main effect of response reached statistical significance, F(1,15) = 53.37, P < 0.001, and also the response by electrode interaction, F(4,60) = 4.41, P < 0.05, ε = 0.72. Aside from the PFC, subsidiary analyses identified that the effect of response was quite marked over all the other four sites (Ps < 0.05), which was similar to the data in Exp. 1. For the last two latency windows, only significant main effect of response was confirmed, F(1,15) = 15.87, 5.27, both Ps < 0.05, showing the amplitudes of the non-target-old nouns much larger than those of the non-target-new ones. These findings were similar to the topography as illustrated in Figure 5(c). (3) The comparison of the old/new effects between Exp. 1 and Exp. 2. As shown in Figure 3 and Figure 5, the brain activity was much stronger for the auditory source retrieval task than that for the item recognition task in both experiments. For example, during the 200― 600 ms latency window, the difference waveforms of the
PSYCHOLOGY
these two types of items did not differ reliably for the last two intervals. The middle column of Figure 4 displayed the grand average ERPs elicited by the target nouns whose contexts were correctly attributed and the non-target-new ones during the source retrieval test. During the 200-600 ms latency window, the two-way repeated-measures ANOVA confirmed significant main effect of response, F(1,15) = 76.51, P < 0.001, and also the two-way interaction, F(4,60) = 6.57, P < 0.01, ε = 0.75. Similar to the data of picture, subsidiary analyses identified reliably greater amplitudes of the target nouns than those of the non-target-new ones over all the sites (Ps < 0.05). The interaction between response and electrode approached significance for the second analytic interval, F(4,60) = 4.86, P < 0.01, ε = 0.60. Post-hoc testing identified that the waveforms of the target nouns were more positive going than those of the non-target-new ones at PFC (P < 0.05). For the last latency window, significant main effect of response was validated, F(1,15) = 6.12, P < 0.05. Topography as depicted in Figure 5(b) added further evidence for these findings.
Figure 4 Grand average ERPs elicited by the old (solid lines) and the new (dashed lines) nouns during the item recognition task (left), and the ERPs produced by the target or the non-target-old (solid lines) and the non-target-new (dashed lines) nouns during the source retrieval task (middle and right) in Exp. 2. Data were depicted at 5 scalp electrodes: FPz, Fz, Cz, Pz and Oz. Amplitudes were displayed in µV. NIE AiQing et al. Chinese Science Bulletin | September 2008 | vol. 53 | no. 18 | 2801-2812
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Figure 6 The amplitudes of the old/new effects during 200―600 ms for picture (a) and Chinese noun (b).
Figure 5 Surface potential maps based on the difference waveforms of the old/new effects during the item recognition phase (a) and also those during the source retrieval phase ((b) for the target nouns and (c) for the non-target-old ones) for 200―600, 600―1000 and 1000―1400 ms in Exp. 2. Red and blue regions reflected the positive and the negative activity, respectively. Dots represented the 62 scalp electrode positions. And the activities were displayed in µV.
old/new effects were much larger for the target and the non-target-old pictures during the source retrieval task than that for the old ones during the item recognition task in Exp. 1 (Figure 6(a)). Aside from the occipital
cortex, similar trends could be detected from Exp. 2 (Figure 6(b)). Results from the intracranial source analyses for the difference waveforms using the LORETA (Low Resolution Electromagnetic Tomography) method via Curry 6.0 were shown in Figure 7. In this method, the grand average ERPs of the old/new effects for different tasks were put into a standardized realistic volume conductor MRI model derived by using a boundary element method with three layers, and each source localized region was made at the time point where the MGFP (Mean Global Field Power) was the largest post-stimulus onset,
Figure 7 Results of the intracranial source analysis of the old/new effects for the item recognition task and the auditory source retrieval task in Exp. 1 (up) and in Exp. 2 (bottom).
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3
Discussion
As expected, the current two experiments identified not only the significant old/new effects during the item recognition tests and the auditory source retrieval tests for both picture and Chinese noun but also the relation of the spatial and the temporal distributive characteristics for these effects. During the first latency window, the main effect of response for the item recognition task in Exp. 1 reached statistical significance, and notable old/new effect was recorded at PFC for the 600―1000 ms interval. In Exp. 2, the old/new effect for the item recognition task was similar to that of picture during 200―600 ms, and this effect did not approach statistical significance for the last two latencies. Intracranial source analyses demonstrated that the activated regions were wider for picture than those for Chinese character, suggesting that the item recognition task was more difficult for the former stimuli. The potential possibility for this distinction Table 2 Exp. 1
The Talairach coordinates of the intracranial generators for the old/new effects during the test phases Comparison Times Brain regions BA Old>New
430 ms
Target>Non-target-new
Exp. 2
384 ms
x
y −67
z
RD(%)
42.9
8.61
R precuneus
19
31.1
R fusiform gyrus
20
50.4
−5.6
−23.7
L superior frontal gyrus
10
−20.6
51.4
5.2
R middle temporal gyrus
21
45.2
2.3
−22.8
R lingual gyrus
17
1.3
−-88.9
5.2
6.91
Old>New
506 ms
L occipital lobe
18
−0.4
−86.3
12.2
8.01
Target>Non-target-new
506 ms
L superior frontal gyrus
10
−18.8
54.0
0.8
7.84
L occipital lobe
18
−18.8
−83.6
22.8
BA, Brodmann area; L, left; R, right; RD, residual deviation. NIE AiQing et al. Chinese Science Bulletin | September 2008 | vol. 53 | no. 18 | 2801-2812
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might rest with the difference of the encoding mode. In general, the encoding of word was mainly top-down and the encoding of picture was mainly bottom-up[15,16], thus the processing rate was distinct between different materials, which induced that the resources transferred and assigned to picture were different from those to Chinese character and this might result in the different retrieval effect. From Exp. 1, the spatial distribution of the old/new effect for the auditory source retrieval task was much wider than those of the item recognition task, and the effect for the former task was more sustained over time than that of the latter one. The frontal old/new effect during 600―1000 ms and the prefrontal, frontal, central old/new effects during 1000―1400 ms only approached statistical significance for the auditory source retrieval task. Similar to that of Exp.1, the second experiment discovered significant PFC old/new effect during the 600―1000 ms latency window and the pronounced main effect of response for the last analytic interval. These data implicated that the item recognition task and the auditory source retrieval task were two dissociated processes that occurred sequentially for both picture and Chinese character, which was consistent with the results — on word[7 9]. These findings also validated the notion from the dual-process model, indicating that the item recognition task was associated with the relatively automatic process——familiarity, and the auditory source retrieval task was associated with the process requiring effort and conscious deliberation——recollection[2]. Surface potential maps based on the difference waveforms of the old/new effects also confirmed these data for both experiments. The longer lasting old/new effect for the auditory source retrieval task than that of the item recognition task was consistent with the model proposed by Burgess et al., wherein they claimed that episodic re-
PSYCHOLOGY
which could be seen via the color scale of F values in Figure 7. Table 2 displayed the Talairach coordinates of each source generator based on the low-resolution current density reconstruction. As illustrated in Figure 7, the parietal lobe was activated during all the tests in both experiments; Left superior frontal gyrus showed strong activation during the auditory source retrieval tasks alone; The temporal lobe, by contrast, only activated in Exp. 1. These data demonstrated that the auditory source retrieval task needed more regions to be involved than the item recognition task, which was consistent among different materials; And the appearance of the MGFP was earlier for picture than that for Chinese character, indicating that the variation in topography was the function of both the experimental material and the source required to be retrieved.
trieval was a reconstructed process based on two specific stages. The first stage specified the searching of parameters and cues, and updated and maintained the contents for working memory. The second stage manipulated and monitored the products of memory search. If the monitoring process discovered the retrieved information was inappropriate or incomplete, then these two stages were required to be re-performed till the exact decision was made[17]. According to this model, the old/new effect for the source retrieval task might last longer than that for the item recognition task. Despite the attribute difference of the experimental materials, the current two experiments recorded prominent old/new effects maximal at the prefrontal and the frontal cortices during the auditory source retrieval phases, which further replicated and extended the con— clusion drawn by Wilding et al. on word[7 9]. And the intracranial source analysis also confirmed the relevancy between the frontal scalp and the auditory source retrieval task, indicating that the regulation role played by the experimental material for the involvement of the anterior cortex in the auditory source retrieval task was less, and it was the nature of the source that modulated this linkage. Moscovitch had discussed the important role that the frontal (or the prefrontal) cortex played in the source retrieval task and raised an important model, wherein he claimed that the PFC operated the products of the MTL (medial temporal lobe), and initiated and directed the search process, and monitored and verified the memories, and placed the products in the appropriate spatial-temporal context. The model held that the process of the MTL was relatively automatic and non-strategic, and the manipulation of the output from the MTL by the PFC was conscious and strategic[18]. It was evident that the function of the anterior old/new effect played during the auditory source retrieval task in the current experiments highly resembled the notion proposed by Moscovitch. As Wilding et al. demonstrated, the role of the right prefrontal old/new effect played in the source memory was post-retrieval processing, and this effect was the neural basis that distinguished the item recognition task from the source retrieval task[7,19]. Other research indicated that the anterior prefrontal regions might be specifically related to the evaluation of the source nature[20]. Here, in the current two experiments, the functional role that the prefrontal and the frontal cortices played might be the post-retrieval moni2810
toring or the evaluation of the perceptual characteristic of voice. — Contrary to the data on word[7 9], the picture elicited marked old/new effect at the central cortex during the auditory retrieval phase from around 1000 till 1400 ms, and Chinese noun recorded the main effect of response during this interval. Take together, these results indicated that the old/new effect of the auditory source retrieval task might be evident aside from the anterior regions, and there was some identical component of the old/new effect for this task and also some distinction among different experimental materials, implicating that this effect was a bigger family[21]. The possible explanation for the notable old/new effect besides the PFC could be threefold. The first might be the encoding style, specifically, the lower the encoding level, the more effort was needed during the retrieval phase and the more brain areas were required. However, this explanation was not the exclusive one, for the presentation modality of the stimuli in the current experiments was both aural and visual, and the modality in previous experiments ― was aural alone[7 9]. Therefore, although the task in these researches was to judge the gender of each voice, the encoding level of picture and Chinese noun should be much higher than that of word. The second was the material-specific. As had been known, the cognitive manner of different material differed reliably[15,16], which might be owing to the features of different stimuli. The features of word are phonography and ideography, and picture has the characteristics of ideography and morphology, and Chinese character has the attributes of phonography, ideography and morphology. These differences might induce the different storage regions for these three types of materials, and hence would in reverse activate distinct scalp during the source retrieval task. However, the material-specific was also not an exclusive answer, for there were reports of the bilateral prefrontal effects for picture in prior works[22,23]. The third was the conjunction of the material with the context. As the judgment of the target was made on the basis of the decision on whether an item was learned or not, the process of binding an item to its auditory source during the retrieval phase was an essential reason for the distinct results among different experimental materials. To put it differently, both the perceptual attribute of the source and the characteristic of the stimuli could regulate the old/new effect of the source retrieval task, which
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from that of the targets. Nevertheless, participant could exclude the non-target-old items based on guess[22]. For the three analytic latency windows, the current two experiments discovered that the temporal distribution of the old/new effects for the non-target-old items and the target ones was similar, suggesting the discrimination of the non-target-old items was more difficult than that of the item recognition, and that these two tasks occurred sequentially. One reason for this difference might be the familiarity/response conflict, which described that the familiarity of the non-target-old items was much higher than that of the old ones during the item recognition task. When the multiple features of a non-target-old item was relatively familiar, it might cause conflict between different responses associated with the testing tasks, and also might influence the brain regions involved during the discrimination of the non-target items[27]. During the 1000-1400 ms latency, the old/new effect was only prominent for the non-target-old pictures but not for the target ones over the parietal cortex in Exp.1, and the distributive features of the old/new effects were different between the non-target-old nouns and the target ones in Exp. 2. These data suggested that the task orientation and the strategies for these two types of items that the participants enforced differed reliably in both experiments, which was an open issue merited further evaluation. In summary, the current two experiments recorded reliable old/new effects for both the item recognition task and the auditory source retrieval task. The scalp distribution of the old/new effect for the latter task was wider than that for the former one, and the old/new effect for the latter task was more sustained over time than that of the former one. These findings were consistent with the notion depicted from the dual-process model; moreover, the brain regions involved during the auditory source retrieval tasks for picture and Chinese character were identical in some aspects and there were also some distinctions, demonstrating that the distributive characteristics of the old/new effect for the auditory source retrieval task were mostly regulated by both the perceptual attribute of the source and the nature of the experimental materials.
PSYCHOLOGY
might induce markedly distinct brain regions for the source storage of different materials, and participants would retrieve the information from where the stimuli were initially processed[24]. Therefore, additional experiments were needed to fully clarify the hypothesis of the combination role of these two factors to elucidate the neural mechanism of the source retrieval task. The current density maps analysis suggested that the temporal lobe was activated obviously during both the item recognition task and the auditory source retrieval task in Exp.1 but not in Exp. 2. Similar results were recorded in patients. In an fMRI investigation, Haist et al. recorded strong activation of the bilateral superior temporal gyrus during the auditory source retrieval task in ASD (autism spectrum disorders) compared with the healthy controls using picture as stimuli. The author considered the activity of this area as the functional offset for the source retrieval task[25]. It was evident that the activity of the temporal lobe was specific to picture and its activity did not differ along with the task requirement. Similarly, in one study on working memory conducted by Guo et al., they repeated the pictures with different numbers of other pictures intervened, and the times of the repetition also varied momentarily. The intracranial source analysis also observed notable activation at the temporal lobe for the repetition effect, and this activation was not varied with the numbers of the pictures intervened and also not with the repetition times of the analytic pictures themselves[26]. These data implicated that the relevancy between the activity of the temporal lobe and the retrieval of the picture was pronounced not only in the long-term memory but also in the working memory, and the activation of this area for other materials was only effective under the condition of functional compensation. The old/new effect of the non-target-old items was rarely reported in previous experiments. The occurrence of this effect was different from those of the item recognition task and the source retrieval task. The item recognition task could be performed based on familiarity without retrieval of any contextual detail, and the valid judgment of the non-target-old items required to decide the context in which these items occurred was different
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