- Email: [email protected]
Event-related potentials elicited by stimulus spatial discrepancy in humans
Neuroscience Letters 326 (2002) 73–76 www.elsevier.com/locate/neulet
Event-related potentials elicited by stimulus spatial discrepancy in humans Jing Yang, Yuping Wang* Department of Neurology, Xuanwu Hospital, Capital University of Medical Sciences, Beijing 100053, PR China Received 17 December 2001; accepted 19 February 2002
Abstract Sixteen subjects were instructed to discriminate whether the spatial locations of two visual stimuli presented in sequence were identical and event-related potentials (ERPs) were recorded from their scalps. The first and the second stimuli were presented in the same location in condition 1, but were in different locations in condition 2. ERP components of P100, N150, late positive component (LPC) and slow negative wave (SNW) were recorded in condition 1; in condition 2, N150 was enhanced and N270 was elicited before LPC. N150, N270 and SNW were all mainly distributed bilaterally over P3, P4, Pz, O1, O2, and Oz. N270 represents the brain activity for processing spatial discrepancy. There are several specialized brain areas involved in the generation of the N270. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Event-related potentials; Spatial discrepancy; Conflict; N270; Slow negative wave
Several lines of investigation have led to the proposal that there exist two distinct modes of analysis for visual information in primates and man. One is primarily concerned with the discrimination of contours and figural properties of stimuli and is hypothesized to mediate the identification of details of objects. The other is concerned with orienting towards events in visual space and the processing of information about stimulus location [17]. Cortical areas along the ‘dorsal stream’ (including the posterior parietal cortex) are primarily concerned with spatial localization and directing attention and gaze towards objects of interest in the scene. Cortical areas along the ‘ventral stream’ (including the inferotemporal cortex) are mainly concerned with the recognition and identification of visual stimuli [5]. It has been reported that an event-related potential (ERP) component N270 can be elicited on the human scalp after the onset of the second stimulus (S2) in a stimulus pair when the stimulus features show some discrepancy from the first one (S1) [1,2,6,18,19]. Under those conditions, the attribute information from the S2 conflicts with that encoded in human brain from the S1 which might be modulated mainly in the ventral stream. Therefore, this component was considered to represent the activity of a conflict processing system * Corresponding author. Tel.: 186-10-63013355x2867; fax: 186-10-63042809. E-mail address: [email protected] (Y. Wang).
[2,6,18]. In this study, subjects were asked to make a spatial discrimination and we attempted to examine whether such a wave can also be evoked by spatial discrepancy which is processed in the dorsal stream. Sixteen right-handed adults (eight males and eight females), aged 24–38 years, served as paid subjects. None of them had any history of neurologic or psychiatric diseases. All participants had reached university education level and had normal or corrected to normal vision. Visual stimuli were presented on a monitor, 100 cm in front of the subjects. The computer screen was carefully positioned so that the stimuli (presented green-on-black) occurred on the subject’s horizontal straight-ahead line of sight. A stimulus system (STIM, Neurosoft, Inc. Sterling, USA) was employed for controlling the presentation of the stimuli. S1 and S2 in a stimulus pair were green rotundities flashing 300 ms in sequence and separated by an interval of 500 ms. The interval between the end of the previous S2 and the onset of the following S1 was 5 s. The stimulus located randomly in one of five positions relative to the central fixation point: central; left-top; right-top; left-bottom; and right-bottom (1.48 lateral to the vertical meridian, and 1.48 above or below the horizontal meridian). Each stimulus subtended a visual angle of 1.78 (diameter). The stimulus pairs were divided into two conditions: in condition 1, S2 matched S1 in position; in condition 2, S2 was different from S1 in position.
0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 2) 00 20 4- 5
74
J. Yang, Y. Wang / Neuroscience Letters 326 (2002) 73–76
Subjects were seated in a dimly lit, electrically shielded and sound attenuated chamber, with response buttons under their left and right hands. They were required to discriminate whether the position of S2 was identical to S1 or not. After the onset of S2, subjects pressed the left button of the pushpad as fast and accurately as possible when S2 matched S1, and pressed the right button when S2 showed some difference from S1 in position. Hands used for response were counterbalanced in the first and the second half of the test in each subject. Following ten practice trials, the 160 stimulus trials were presented. The electroencephalogram (EEG) was recorded from 20 scalp electrodes (Fz, Cz, Pz, Oz, FP1, F3, F7, C3, T3, P3, T5, O1, FP2, F4, F8, C4, T4, P4, T6, O2) according to the International 10–20 System. The linked earlobes were used as reference. Vertical and horizontal electro-oculograms (EOGs) were recorded by electrodes situated above and below the left eye, and on the outer canthi of both eyes, respectively. Electrode impedances were kept below 5 kV. EEG was amplified with a bandpass of 0.05–100 Hz, sampled at 500 Hz and stored on a hard disk for off-line analysis. ERPs were averaged for each condition separately.
The averaging epoch was 1700 ms, and the 200 ms before the onset of S1 served as baseline. Trials containing incorrect responses, EOG artifacts or amplifier saturation were excluded from the averages. ERPs for each of the two conditions were averaged over 30 trials. To investigate the neurophysiologic correlates of visual position processing, we compared the amplitude of ERPs in each of the two conditions using a within subject repeated measures of analysis of variance. The reaction time and correct rate (mean ^ SD) were 502.7 ^ 142.7 ms and 98.9 ^ 2.2 for condition 1, and 582.4 ^ 118.4 ms and 98.1 ^ 1.9 for condition 2. There was no difference between the two conditions in correct rate (P . 0:05), while there was a significant difference in reaction time (P , 0:01). In condition 1, ERPs evoked by the S2 consisted of P100, N150, late positive component (LPC) and slow negative wave (SNW). On the other hand, ERPs consisted of P100, N150, N270, LPC and SNW in condition 2 (Fig. 1). In both conditions, P100 and N150 were recorded mainly on the posterior scalp areas. In condition 1, the LPC was recorded broadly on the scalp. In condition 2, the potentials following
Fig. 1. ERPs from stimulus spatial discrimination task. The two vertical dotted lines represent the onset of the S1 and S2. The solid line indicates the discrepancy condition (condition 2) and the dashed line indicates the match condition (condition 1). P100, N150, LPC and SNW were evoked by S2 in condition 1. ERPs evoked by S2 in condition 2 consisted of P100, N150, N270, LPC and SNW.
J. Yang, Y. Wang / Neuroscience Letters 326 (2002) 73–76
the enhanced N150 went continuously to negativity and formed another component named N270. The N270 component was distributed with the most negative amplitude at the central, parietal and occipital regions. Following that component, LPC and SNW were recorded broadly on the scalp. In the first 140 ms following the onset of the S2, the mean amplitude showed no significant difference between the two conditions. P100 components were included in this time segment. In the time window between 142 and 220 ms (N150 was in it), the mean amplitude of condition 2 was significantly more negative than condition 1 at Cz, P3, P4, Pz and O2 (P , 0:05; Table 1). In the interval of 222–320 ms (N270 was in it), the mean amplitudes of condition 2 were more negative than those of condition 1, primarily at C4, Cz, P3, P4, Pz, O1, O2, and Oz. No asymmetry was observed. From 322–460 ms (LPC was in it), the mean amplitudes of condition 2 were more positive than condition 1 at frontal areas (F4, F8, Fp1, Fp2, and Fz). From 462 to 640 ms (SNW was in it), the ERP amplitudes of condition 2 at O1, O2, Oz, P3, P4, Pz and T5 were more positive. No significant difference was found in amplitude between the two conditions after this time window. Previous studies showed that attribute difference between two successively presented stimuli is important for the generation of N270. N270 can be elicited by the conflict of stimulus attributes such as digit value [6], color [1], and shape [2]. N270 can also be evoked by the conflict of mental mismatching such as arithmetic conflict [18]. The results of the present study demonstrate the presence of ERP
75
effects related to the conflict processing on spatial discriminating tasks. The characteristic of N270 in the spatial discrepancy task can be summarized. First, the N270 in spatial discrimination tasks was found showing its main peaks in the 220–320 ms period, therefore presenting a timing similar to that of the N270 for color (about 242–336 ms), although slightly earlier. Second, the N270 in this study is recorded at the central, parietal and occipital regions, while the N270 in previous studies was distributed widely on the scalp [1,2,6]. Numerous studies have shown that the visual system involves different cortical pathways in the perception of object (ventral visual pathway) and spatial (dorsal visual pathway) information [16,17]. The notion of separable working memory systems for object forms and spatial locations was also confirmed by recent neuroimaging studies [13,15]. Some reports support a temporal advantage of the dorsal stream relative to the ventral stream [11]. An earlier peak amplitude of N270 might indicate that spatial discrepancy analyses in the dorsal stream were completed earlier than feature discrepancy analyses in the ventral stream. The ventral stream in relation with the temporal lobe is responsible for the processing and storage of the information about discernment of objects; and the dorsal stream in relation with the parietal lobe is concerned with the analysis of the locations of objects, and their movements in space [4]. This is in accordance with our finding that N270 distribution in spatial discrepancy differed from that elicited by stimulus attribute conflict. N2b was usually elicited in a stimulus feature relevant
Table 1 The mean amplitude of ERP in spatial discrimination tasks a Time window
142–220 ms
Sites
Condition 1
Condition 2
Condition 1
Condition 2
Condition 1
Condition 2
Condition 1
Condition 2
Fp1 Fp2 F3 F4 Fz C3 C4 Cz P3 P4 Pz O1 O2 Oz F7 F8 T3 T4 T5 T6
3.0 ^ 5.5 3.3 ^ 5.0 21.1 ^ 5.9 22.4 ^ 6.1 21.7 ^ 5.6 22.7 ^ 5.4 23.6 ^ 4.4 22.7 ^ 6.4 23.7 ^ 5.6 24.4 ^ 5.2 22.2 ^ 5.8 24.5 ^ 4.9 24.1 ^ 5.0 24.2 ^ 5.2 0.8 ^ 5.9 20.4 ^ 4.0 22.6 ^ 5.3 23.2 ^ 3.7 27.1 ^ 5.5 27.1 ^ 4.4
2.4 ^ 5.0 2.6 ^ 4.8 21.1 ^ 6.3 23 ^ 6.3 23.1 ^ 7.1 23.3 ^ 6.1 25.2 ^ 5.5 25.5 ^ 7.9 b 25.8 ^ 6.8 b 27.0 ^ 6.5 b 25.9 ^ 7.3 b 26.1 ^ 6.1 26.0 ^ 5.7 b 25.6 ^ 5.5 0.7 ^ 5.3 0.1 ^ 3.6 21.8 ^ 4.5 23.3 ^ 4.1 27.6 ^ 6.3 28.5 ^ 6.1
5.2 ^ 6.1 5.6 ^ 6.0 3.7 ^ 5.6 3.6 ^ 5.4 4.1 ^ 6.2 3.3 ^ 4.5 3.2 ^ 4.1 4.1 ^ 5.8 5.1 ^ 4.6 4.4 ^ 5.3 6.4 ^ 5.7 3.3 ^ 5.4 3.6 ^ 5.6 3.2 ^ 5.3 2.7 ^ 5.5 2.1 ^ 3.4 0.7 ^ 4.3 0.6 ^ 2.5 0.1 ^ 4.5 0 ^ 4.3
5.1 ^ 6.2 5.4 ^ 5.6 2.9 ^ 6.1 2.8 ^ 6.3 2.1 ^ 7.1 1.3 ^ 6.1 0.6 ^ 5.9 b 0.6 ^ 8.1 b 1.6 ^ 7.4 b 0.8 ^ 7.6 b 1.4 ^ 8.2 b 1.2 ^ 7.4 b 1.0 ^ 7.2 b 0.9 ^ 6.8 b 2.6 ^ 5.4 2.6 ^ 3.9 0.1 ^ 4.3 20.2 ^ 4.0 21.2 ^ 6.4 21.3 ^ 6.5
20.2 ^ 4.8 1.1 ^ 5.0 20.3 ^ 5.1 0.7 ^ 3.9 21.3 ^ 4.1 0.7 ^ 3.7 1.8 ^ 3.2 20.7 ^ 4.6 3.7 ^ 3.5 3.0 ^ 3.8 4.3 ^ 4.3 2.8 ^ 3.2 3.0 ^ 4.0 2.7 ^ 3.5 0.1 ^ 4.7 1.3 ^ 2.5 0.4 ^ 3.4 1.7 ^ 2.0 0.9 ^ 3.5 0.6 ^ 3.3
2.1 ^ 4.8 b 3.6 ^ 5.2 b 1.8 ^ 3.5 3.2 ^ 4.6 b 0.7 ^ 5.1 b 1.5 ^ 3.7 2.8 ^ 5.0 20.3 ^ 6.2 4.1 ^ 6.0 3.7 ^ 6.9 4.5 ^ 7.1 3.0 ^ 6.4 2.8 ^ 6.6 2.8 ^ 6.3 1.4 ^ 3.3 3.7 ^ 3.0 b 1.2 ^ 2.4 2.7 ^ 3.0 1.2 ^ 5.1 1.3 ^ 5.2
20.5 ^ 3.0 21.0 ^ 3.4 21.3 ^ 2.9 21.9 ^ 3.8 23.1 ^ 3.3 21.0 ^ 2.9 21.5 ^ 3.0 22.6 ^ 4.0 20.4 ^ 3.9 21.4 ^ 3.4 20.3 ^ 3.5 20.6 ^ 3.1 20.8 ^ 3.7 20.8 ^ 3.8 20.3 ^ 3.1 20.7 ^ 2.8 21.1 ^ 2.8 21.3 ^ 2.4 21.6 ^ 3.6 21.9 ^ 3.0
0.2 ^ 3.0 0.7 ^ 4.7 20.4 ^ 3.0 20.3 ^ 2.9 22.2 ^ 4.3 0.5 ^ 3.3 0.3 ^ 2.6 21.0 ^ 5.5 2.8 ^ 4.2 b 1.5 ^ 3.8 b 3.3 ^ 4.8 b 2.0 ^ 3.6 b 1.3 ^ 3.9 b 1.7 ^ 4.0 b 20.1 ^ 1.9 0.8 ^ 1.9 0.3 ^ 1.5 0.4 ^ 1.6 0.6 ^ 3.6 b 20.4 ^ 3.4
a b
222–320 ms
Mean amplitude ^ SD (mV). Significantly different from condition 1 (P , 0:05).
322–460 ms
462–640 ms
76
J. Yang, Y. Wang / Neuroscience Letters 326 (2002) 73–76
(matched) condition [14], and was larger over the right than over the left hemisphere. Sensitivity to stimulus probability change is a definite characteristic of N2b. N2pc is a negative-going voltage deflection that is typically observed 200– 300 ms after the onset of a visual search array, and it is largest over areas of visual cortex in the hemisphere contralateral to the location of an attended object within the search array [3,20]. N2pc was generally evoked by physical difference or incongruence between stimuli. It is sensitive to the differences in discrimination difficulty between tasks. N270 was different from N2b and N2pc. N270 can be evoked not only by physical feature and spatial discrepancy, but also by the conflict of mental mismatching. Furthermore, N270 is not affected by changing stimulus probability [1]. In our study, no asymmetry was observed in N270. N400 is a component originally observed when subjects read sentences that ended with a semantically incongruous word and it was also elicited by contextual word pairs [7,8]. N400 was not followed by LPC and it had a centroparietal maximum, these characteristics are different from those of N270, and N270 is much faster than N400. The ERP pattern for attention to spatial location is a P1 enhancement followed by an N1 enhancement [10]. No P1 enhancement was found in our results, but we observed the enhancement of N150 (N1). The enhancement of N150 may represent the activity in the dorsal stream, produced from the striate cortex to the parietal lobe and encoding spatial aspects of visual information [9]. Due to the insertion of the N270 component, LPC in condition 2 was delayed, which contributes to the significant mean amplitude difference in the time window from 322 to 460 ms. SNW was more positive at posterior areas in the location discrepancy condition. It is found that when spatial information was maintained in working memory, SNW activity rapidly rose at the recording sites overlying posterior parietal and occipital cortical areas [12]. SNW might be related to some extent with the revaluation of behavioral response in location discrimination. In conclusion, the negative component N270 was recorded on the posterior scalp in the spatial location discrepancy task. Considering present and previous results, it appears that there are several specialized brain areas involved in the generation of N270 in different tasks. Moreover, it appears that distinctive areas responsible for N270 generation are not only restricted to the ventral streams, but also to the dorsal streams. The authors would like to thank Professor S.A. Hillyard for his valuable comments. This research was partly supported by Beijing Natural Science Foundation (7002021). [1] Cui, L.L., Wang, Y.P., Kong, J., Wang, H.J., Tian, S.J. and Wang, D.Q., The effects of probabilities on event-related potential N270, J. Brain Nerv. Dis. (Shijiazhuang China), 8 (2000) 275–278.
[2] Cui, L.L., Wang, Y.P., Wang, H.J., Tian, S.J. and Kong, J., Human brain sub-systems for discrimination of visual shapes, NeuroReport, 11 (2000) 2415–2418. [3] Eimer, M., The N2pc component as an indicator of attentional selectivity, Electroenceph. clin. Neurophysiol., 99 (1996) 225–234. [4] Gimenez-Amaya, J.M., Functional anatomy of the cerebral cortex implicated in visual processing, Rev. Neurol., 30 (2000) 656–662. [5] Itti, L. and Koch, C., Computational modeling of visual attention, Nat. Rev. Neurosci., 2 (2001) 145–218. [6] Kong, J., Wang, Y., Zhang, W., Wang, H., Wei, H., Shang, H., Yang, X. and Zhuang, D., Event-related brain potentials elicited by a number discrimination task, NeuroReport, 11 (2000) 1195–1197. [7] Kuperman, S., Porjesz, B., Arndt, S., Begleiter, H., Cizadlo, T., O’Connor, S. and Rohrbaugh, J., Multi-center N400 ERP consistency using a primed and unprimed word paradigm, Electroenceph. clin. Neurophysiol., 94 (1995) 462–470. [8] Kutas, M. and Hillyard, S.A., Reading senseless sentences: brain potentials reflect semantic incongruity, Science, 207 (1980) 203–205. [9] Mangun, G.R., Neural mechanisms of visual selective attention, Psychophysiology, 32 (1995) 4–18. [10] Mangun, G.R. and Hillyard, S.A., Spatial gradients of visual attention: behavioral and electrophysiological evidence, Electroenceph. clin. Neurophysiol., 70 (1988) 417–428. [11] Martin-loeches, M., Hinojosa, J.A. and Rubia, F.J., Insights from event-related potentials into the temporal and hierarchical organization of ventral and dorsal streams of visual systems in selective attention, Psychophysiology, 36 (1999) 721–736. [12] Mecklinger, A. and Pfeifer, E., Event-related potentials reveal topographical and temporal distinct neuronal activation patterns for spatial and object working memory, Brain Res. Cogn. Brain Res., 4 (1996) 211–224. [13] Moscovitch, C., Kapur, S., Kohler, S. and Houle, S., Distinct neural correlates of visual long-term memory for spatial location and object identity: a position emission tomography study in humans, Proc. Natl. Acad. Sci. USA, 92 (1995) 3721–3725. [14] Smid, H.G.O.M., Jakob, A. and Heinze, H.J., An eventrelated brain potential study of visual selective attention to conjunctions of color and shape, Psychophysiology, 36 (1999) 264–279. [15] Smith, M.E. and Halgren, E., Dissociations of recognition memory components following temporal lobe lesions, J. Exp. Psychol. Learn. Mem. Cogn., 15 (1989) 50–60. [16] Tresch, M.C., Sinnamon, H.M. and Seamon, J.G., Double dissociation of spatial and object visual memory: evidence from selective inference in intact human subjects, Neuropsychologia, 31 (1993) 11–219. [17] Ungerleider, L.G. and Mishkin, M., Two cortical visual systems, In D.J. Ingle, M.A. Goodale and J.W. Mansfield (Eds.), Analysis of Visual Behavior, MIT Press, Cambridge, MA, 1982, pp. 549–586. [18] Wang, Y.P., Kong, J., Tang, X.F., Zhuang, D. and Li, S.W., Event-related potential N270 is elicited by mental conflict processing in human brain, Neurosci. Lett., 293 (2000) 17– 20. [19] Wang, H.J., Wang, Y.P., Kong, J., Cui, L.L. and Tian, S.J., Enhancement of conflict processing activity in human brain under task relevant condition, Neurosci. Lett., 298 (2001) 155–158. [20] Woodman, G.F. and Luck, S.J., Electrophysiological measurement of rapid shifts of attention during visual search, Nature, 400 (1999) 867–869.
Event-related potentials elicited by stimulus spatial discrepancy in humans Jing Yang, Yuping Wang* Department of Neurology, Xuanwu Hospital, Capital University of Medical Sciences, Beijing 100053, PR China Received 17 December 2001; accepted 19 February 2002
Abstract Sixteen subjects were instructed to discriminate whether the spatial locations of two visual stimuli presented in sequence were identical and event-related potentials (ERPs) were recorded from their scalps. The first and the second stimuli were presented in the same location in condition 1, but were in different locations in condition 2. ERP components of P100, N150, late positive component (LPC) and slow negative wave (SNW) were recorded in condition 1; in condition 2, N150 was enhanced and N270 was elicited before LPC. N150, N270 and SNW were all mainly distributed bilaterally over P3, P4, Pz, O1, O2, and Oz. N270 represents the brain activity for processing spatial discrepancy. There are several specialized brain areas involved in the generation of the N270. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Event-related potentials; Spatial discrepancy; Conflict; N270; Slow negative wave
Several lines of investigation have led to the proposal that there exist two distinct modes of analysis for visual information in primates and man. One is primarily concerned with the discrimination of contours and figural properties of stimuli and is hypothesized to mediate the identification of details of objects. The other is concerned with orienting towards events in visual space and the processing of information about stimulus location [17]. Cortical areas along the ‘dorsal stream’ (including the posterior parietal cortex) are primarily concerned with spatial localization and directing attention and gaze towards objects of interest in the scene. Cortical areas along the ‘ventral stream’ (including the inferotemporal cortex) are mainly concerned with the recognition and identification of visual stimuli [5]. It has been reported that an event-related potential (ERP) component N270 can be elicited on the human scalp after the onset of the second stimulus (S2) in a stimulus pair when the stimulus features show some discrepancy from the first one (S1) [1,2,6,18,19]. Under those conditions, the attribute information from the S2 conflicts with that encoded in human brain from the S1 which might be modulated mainly in the ventral stream. Therefore, this component was considered to represent the activity of a conflict processing system * Corresponding author. Tel.: 186-10-63013355x2867; fax: 186-10-63042809. E-mail address: [email protected] (Y. Wang).
[2,6,18]. In this study, subjects were asked to make a spatial discrimination and we attempted to examine whether such a wave can also be evoked by spatial discrepancy which is processed in the dorsal stream. Sixteen right-handed adults (eight males and eight females), aged 24–38 years, served as paid subjects. None of them had any history of neurologic or psychiatric diseases. All participants had reached university education level and had normal or corrected to normal vision. Visual stimuli were presented on a monitor, 100 cm in front of the subjects. The computer screen was carefully positioned so that the stimuli (presented green-on-black) occurred on the subject’s horizontal straight-ahead line of sight. A stimulus system (STIM, Neurosoft, Inc. Sterling, USA) was employed for controlling the presentation of the stimuli. S1 and S2 in a stimulus pair were green rotundities flashing 300 ms in sequence and separated by an interval of 500 ms. The interval between the end of the previous S2 and the onset of the following S1 was 5 s. The stimulus located randomly in one of five positions relative to the central fixation point: central; left-top; right-top; left-bottom; and right-bottom (1.48 lateral to the vertical meridian, and 1.48 above or below the horizontal meridian). Each stimulus subtended a visual angle of 1.78 (diameter). The stimulus pairs were divided into two conditions: in condition 1, S2 matched S1 in position; in condition 2, S2 was different from S1 in position.
0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 2) 00 20 4- 5
74
J. Yang, Y. Wang / Neuroscience Letters 326 (2002) 73–76
Subjects were seated in a dimly lit, electrically shielded and sound attenuated chamber, with response buttons under their left and right hands. They were required to discriminate whether the position of S2 was identical to S1 or not. After the onset of S2, subjects pressed the left button of the pushpad as fast and accurately as possible when S2 matched S1, and pressed the right button when S2 showed some difference from S1 in position. Hands used for response were counterbalanced in the first and the second half of the test in each subject. Following ten practice trials, the 160 stimulus trials were presented. The electroencephalogram (EEG) was recorded from 20 scalp electrodes (Fz, Cz, Pz, Oz, FP1, F3, F7, C3, T3, P3, T5, O1, FP2, F4, F8, C4, T4, P4, T6, O2) according to the International 10–20 System. The linked earlobes were used as reference. Vertical and horizontal electro-oculograms (EOGs) were recorded by electrodes situated above and below the left eye, and on the outer canthi of both eyes, respectively. Electrode impedances were kept below 5 kV. EEG was amplified with a bandpass of 0.05–100 Hz, sampled at 500 Hz and stored on a hard disk for off-line analysis. ERPs were averaged for each condition separately.
The averaging epoch was 1700 ms, and the 200 ms before the onset of S1 served as baseline. Trials containing incorrect responses, EOG artifacts or amplifier saturation were excluded from the averages. ERPs for each of the two conditions were averaged over 30 trials. To investigate the neurophysiologic correlates of visual position processing, we compared the amplitude of ERPs in each of the two conditions using a within subject repeated measures of analysis of variance. The reaction time and correct rate (mean ^ SD) were 502.7 ^ 142.7 ms and 98.9 ^ 2.2 for condition 1, and 582.4 ^ 118.4 ms and 98.1 ^ 1.9 for condition 2. There was no difference between the two conditions in correct rate (P . 0:05), while there was a significant difference in reaction time (P , 0:01). In condition 1, ERPs evoked by the S2 consisted of P100, N150, late positive component (LPC) and slow negative wave (SNW). On the other hand, ERPs consisted of P100, N150, N270, LPC and SNW in condition 2 (Fig. 1). In both conditions, P100 and N150 were recorded mainly on the posterior scalp areas. In condition 1, the LPC was recorded broadly on the scalp. In condition 2, the potentials following
Fig. 1. ERPs from stimulus spatial discrimination task. The two vertical dotted lines represent the onset of the S1 and S2. The solid line indicates the discrepancy condition (condition 2) and the dashed line indicates the match condition (condition 1). P100, N150, LPC and SNW were evoked by S2 in condition 1. ERPs evoked by S2 in condition 2 consisted of P100, N150, N270, LPC and SNW.
J. Yang, Y. Wang / Neuroscience Letters 326 (2002) 73–76
the enhanced N150 went continuously to negativity and formed another component named N270. The N270 component was distributed with the most negative amplitude at the central, parietal and occipital regions. Following that component, LPC and SNW were recorded broadly on the scalp. In the first 140 ms following the onset of the S2, the mean amplitude showed no significant difference between the two conditions. P100 components were included in this time segment. In the time window between 142 and 220 ms (N150 was in it), the mean amplitude of condition 2 was significantly more negative than condition 1 at Cz, P3, P4, Pz and O2 (P , 0:05; Table 1). In the interval of 222–320 ms (N270 was in it), the mean amplitudes of condition 2 were more negative than those of condition 1, primarily at C4, Cz, P3, P4, Pz, O1, O2, and Oz. No asymmetry was observed. From 322–460 ms (LPC was in it), the mean amplitudes of condition 2 were more positive than condition 1 at frontal areas (F4, F8, Fp1, Fp2, and Fz). From 462 to 640 ms (SNW was in it), the ERP amplitudes of condition 2 at O1, O2, Oz, P3, P4, Pz and T5 were more positive. No significant difference was found in amplitude between the two conditions after this time window. Previous studies showed that attribute difference between two successively presented stimuli is important for the generation of N270. N270 can be elicited by the conflict of stimulus attributes such as digit value [6], color [1], and shape [2]. N270 can also be evoked by the conflict of mental mismatching such as arithmetic conflict [18]. The results of the present study demonstrate the presence of ERP
75
effects related to the conflict processing on spatial discriminating tasks. The characteristic of N270 in the spatial discrepancy task can be summarized. First, the N270 in spatial discrimination tasks was found showing its main peaks in the 220–320 ms period, therefore presenting a timing similar to that of the N270 for color (about 242–336 ms), although slightly earlier. Second, the N270 in this study is recorded at the central, parietal and occipital regions, while the N270 in previous studies was distributed widely on the scalp [1,2,6]. Numerous studies have shown that the visual system involves different cortical pathways in the perception of object (ventral visual pathway) and spatial (dorsal visual pathway) information [16,17]. The notion of separable working memory systems for object forms and spatial locations was also confirmed by recent neuroimaging studies [13,15]. Some reports support a temporal advantage of the dorsal stream relative to the ventral stream [11]. An earlier peak amplitude of N270 might indicate that spatial discrepancy analyses in the dorsal stream were completed earlier than feature discrepancy analyses in the ventral stream. The ventral stream in relation with the temporal lobe is responsible for the processing and storage of the information about discernment of objects; and the dorsal stream in relation with the parietal lobe is concerned with the analysis of the locations of objects, and their movements in space [4]. This is in accordance with our finding that N270 distribution in spatial discrepancy differed from that elicited by stimulus attribute conflict. N2b was usually elicited in a stimulus feature relevant
Table 1 The mean amplitude of ERP in spatial discrimination tasks a Time window
142–220 ms
Sites
Condition 1
Condition 2
Condition 1
Condition 2
Condition 1
Condition 2
Condition 1
Condition 2
Fp1 Fp2 F3 F4 Fz C3 C4 Cz P3 P4 Pz O1 O2 Oz F7 F8 T3 T4 T5 T6
3.0 ^ 5.5 3.3 ^ 5.0 21.1 ^ 5.9 22.4 ^ 6.1 21.7 ^ 5.6 22.7 ^ 5.4 23.6 ^ 4.4 22.7 ^ 6.4 23.7 ^ 5.6 24.4 ^ 5.2 22.2 ^ 5.8 24.5 ^ 4.9 24.1 ^ 5.0 24.2 ^ 5.2 0.8 ^ 5.9 20.4 ^ 4.0 22.6 ^ 5.3 23.2 ^ 3.7 27.1 ^ 5.5 27.1 ^ 4.4
2.4 ^ 5.0 2.6 ^ 4.8 21.1 ^ 6.3 23 ^ 6.3 23.1 ^ 7.1 23.3 ^ 6.1 25.2 ^ 5.5 25.5 ^ 7.9 b 25.8 ^ 6.8 b 27.0 ^ 6.5 b 25.9 ^ 7.3 b 26.1 ^ 6.1 26.0 ^ 5.7 b 25.6 ^ 5.5 0.7 ^ 5.3 0.1 ^ 3.6 21.8 ^ 4.5 23.3 ^ 4.1 27.6 ^ 6.3 28.5 ^ 6.1
5.2 ^ 6.1 5.6 ^ 6.0 3.7 ^ 5.6 3.6 ^ 5.4 4.1 ^ 6.2 3.3 ^ 4.5 3.2 ^ 4.1 4.1 ^ 5.8 5.1 ^ 4.6 4.4 ^ 5.3 6.4 ^ 5.7 3.3 ^ 5.4 3.6 ^ 5.6 3.2 ^ 5.3 2.7 ^ 5.5 2.1 ^ 3.4 0.7 ^ 4.3 0.6 ^ 2.5 0.1 ^ 4.5 0 ^ 4.3
5.1 ^ 6.2 5.4 ^ 5.6 2.9 ^ 6.1 2.8 ^ 6.3 2.1 ^ 7.1 1.3 ^ 6.1 0.6 ^ 5.9 b 0.6 ^ 8.1 b 1.6 ^ 7.4 b 0.8 ^ 7.6 b 1.4 ^ 8.2 b 1.2 ^ 7.4 b 1.0 ^ 7.2 b 0.9 ^ 6.8 b 2.6 ^ 5.4 2.6 ^ 3.9 0.1 ^ 4.3 20.2 ^ 4.0 21.2 ^ 6.4 21.3 ^ 6.5
20.2 ^ 4.8 1.1 ^ 5.0 20.3 ^ 5.1 0.7 ^ 3.9 21.3 ^ 4.1 0.7 ^ 3.7 1.8 ^ 3.2 20.7 ^ 4.6 3.7 ^ 3.5 3.0 ^ 3.8 4.3 ^ 4.3 2.8 ^ 3.2 3.0 ^ 4.0 2.7 ^ 3.5 0.1 ^ 4.7 1.3 ^ 2.5 0.4 ^ 3.4 1.7 ^ 2.0 0.9 ^ 3.5 0.6 ^ 3.3
2.1 ^ 4.8 b 3.6 ^ 5.2 b 1.8 ^ 3.5 3.2 ^ 4.6 b 0.7 ^ 5.1 b 1.5 ^ 3.7 2.8 ^ 5.0 20.3 ^ 6.2 4.1 ^ 6.0 3.7 ^ 6.9 4.5 ^ 7.1 3.0 ^ 6.4 2.8 ^ 6.6 2.8 ^ 6.3 1.4 ^ 3.3 3.7 ^ 3.0 b 1.2 ^ 2.4 2.7 ^ 3.0 1.2 ^ 5.1 1.3 ^ 5.2
20.5 ^ 3.0 21.0 ^ 3.4 21.3 ^ 2.9 21.9 ^ 3.8 23.1 ^ 3.3 21.0 ^ 2.9 21.5 ^ 3.0 22.6 ^ 4.0 20.4 ^ 3.9 21.4 ^ 3.4 20.3 ^ 3.5 20.6 ^ 3.1 20.8 ^ 3.7 20.8 ^ 3.8 20.3 ^ 3.1 20.7 ^ 2.8 21.1 ^ 2.8 21.3 ^ 2.4 21.6 ^ 3.6 21.9 ^ 3.0
0.2 ^ 3.0 0.7 ^ 4.7 20.4 ^ 3.0 20.3 ^ 2.9 22.2 ^ 4.3 0.5 ^ 3.3 0.3 ^ 2.6 21.0 ^ 5.5 2.8 ^ 4.2 b 1.5 ^ 3.8 b 3.3 ^ 4.8 b 2.0 ^ 3.6 b 1.3 ^ 3.9 b 1.7 ^ 4.0 b 20.1 ^ 1.9 0.8 ^ 1.9 0.3 ^ 1.5 0.4 ^ 1.6 0.6 ^ 3.6 b 20.4 ^ 3.4
a b
222–320 ms
Mean amplitude ^ SD (mV). Significantly different from condition 1 (P , 0:05).
322–460 ms
462–640 ms
76
J. Yang, Y. Wang / Neuroscience Letters 326 (2002) 73–76
(matched) condition [14], and was larger over the right than over the left hemisphere. Sensitivity to stimulus probability change is a definite characteristic of N2b. N2pc is a negative-going voltage deflection that is typically observed 200– 300 ms after the onset of a visual search array, and it is largest over areas of visual cortex in the hemisphere contralateral to the location of an attended object within the search array [3,20]. N2pc was generally evoked by physical difference or incongruence between stimuli. It is sensitive to the differences in discrimination difficulty between tasks. N270 was different from N2b and N2pc. N270 can be evoked not only by physical feature and spatial discrepancy, but also by the conflict of mental mismatching. Furthermore, N270 is not affected by changing stimulus probability [1]. In our study, no asymmetry was observed in N270. N400 is a component originally observed when subjects read sentences that ended with a semantically incongruous word and it was also elicited by contextual word pairs [7,8]. N400 was not followed by LPC and it had a centroparietal maximum, these characteristics are different from those of N270, and N270 is much faster than N400. The ERP pattern for attention to spatial location is a P1 enhancement followed by an N1 enhancement [10]. No P1 enhancement was found in our results, but we observed the enhancement of N150 (N1). The enhancement of N150 may represent the activity in the dorsal stream, produced from the striate cortex to the parietal lobe and encoding spatial aspects of visual information [9]. Due to the insertion of the N270 component, LPC in condition 2 was delayed, which contributes to the significant mean amplitude difference in the time window from 322 to 460 ms. SNW was more positive at posterior areas in the location discrepancy condition. It is found that when spatial information was maintained in working memory, SNW activity rapidly rose at the recording sites overlying posterior parietal and occipital cortical areas [12]. SNW might be related to some extent with the revaluation of behavioral response in location discrimination. In conclusion, the negative component N270 was recorded on the posterior scalp in the spatial location discrepancy task. Considering present and previous results, it appears that there are several specialized brain areas involved in the generation of N270 in different tasks. Moreover, it appears that distinctive areas responsible for N270 generation are not only restricted to the ventral streams, but also to the dorsal streams. The authors would like to thank Professor S.A. Hillyard for his valuable comments. This research was partly supported by Beijing Natural Science Foundation (7002021). [1] Cui, L.L., Wang, Y.P., Kong, J., Wang, H.J., Tian, S.J. and Wang, D.Q., The effects of probabilities on event-related potential N270, J. Brain Nerv. Dis. (Shijiazhuang China), 8 (2000) 275–278.
[2] Cui, L.L., Wang, Y.P., Wang, H.J., Tian, S.J. and Kong, J., Human brain sub-systems for discrimination of visual shapes, NeuroReport, 11 (2000) 2415–2418. [3] Eimer, M., The N2pc component as an indicator of attentional selectivity, Electroenceph. clin. Neurophysiol., 99 (1996) 225–234. [4] Gimenez-Amaya, J.M., Functional anatomy of the cerebral cortex implicated in visual processing, Rev. Neurol., 30 (2000) 656–662. [5] Itti, L. and Koch, C., Computational modeling of visual attention, Nat. Rev. Neurosci., 2 (2001) 145–218. [6] Kong, J., Wang, Y., Zhang, W., Wang, H., Wei, H., Shang, H., Yang, X. and Zhuang, D., Event-related brain potentials elicited by a number discrimination task, NeuroReport, 11 (2000) 1195–1197. [7] Kuperman, S., Porjesz, B., Arndt, S., Begleiter, H., Cizadlo, T., O’Connor, S. and Rohrbaugh, J., Multi-center N400 ERP consistency using a primed and unprimed word paradigm, Electroenceph. clin. Neurophysiol., 94 (1995) 462–470. [8] Kutas, M. and Hillyard, S.A., Reading senseless sentences: brain potentials reflect semantic incongruity, Science, 207 (1980) 203–205. [9] Mangun, G.R., Neural mechanisms of visual selective attention, Psychophysiology, 32 (1995) 4–18. [10] Mangun, G.R. and Hillyard, S.A., Spatial gradients of visual attention: behavioral and electrophysiological evidence, Electroenceph. clin. Neurophysiol., 70 (1988) 417–428. [11] Martin-loeches, M., Hinojosa, J.A. and Rubia, F.J., Insights from event-related potentials into the temporal and hierarchical organization of ventral and dorsal streams of visual systems in selective attention, Psychophysiology, 36 (1999) 721–736. [12] Mecklinger, A. and Pfeifer, E., Event-related potentials reveal topographical and temporal distinct neuronal activation patterns for spatial and object working memory, Brain Res. Cogn. Brain Res., 4 (1996) 211–224. [13] Moscovitch, C., Kapur, S., Kohler, S. and Houle, S., Distinct neural correlates of visual long-term memory for spatial location and object identity: a position emission tomography study in humans, Proc. Natl. Acad. Sci. USA, 92 (1995) 3721–3725. [14] Smid, H.G.O.M., Jakob, A. and Heinze, H.J., An eventrelated brain potential study of visual selective attention to conjunctions of color and shape, Psychophysiology, 36 (1999) 264–279. [15] Smith, M.E. and Halgren, E., Dissociations of recognition memory components following temporal lobe lesions, J. Exp. Psychol. Learn. Mem. Cogn., 15 (1989) 50–60. [16] Tresch, M.C., Sinnamon, H.M. and Seamon, J.G., Double dissociation of spatial and object visual memory: evidence from selective inference in intact human subjects, Neuropsychologia, 31 (1993) 11–219. [17] Ungerleider, L.G. and Mishkin, M., Two cortical visual systems, In D.J. Ingle, M.A. Goodale and J.W. Mansfield (Eds.), Analysis of Visual Behavior, MIT Press, Cambridge, MA, 1982, pp. 549–586. [18] Wang, Y.P., Kong, J., Tang, X.F., Zhuang, D. and Li, S.W., Event-related potential N270 is elicited by mental conflict processing in human brain, Neurosci. Lett., 293 (2000) 17– 20. [19] Wang, H.J., Wang, Y.P., Kong, J., Cui, L.L. and Tian, S.J., Enhancement of conflict processing activity in human brain under task relevant condition, Neurosci. Lett., 298 (2001) 155–158. [20] Woodman, G.F. and Luck, S.J., Electrophysiological measurement of rapid shifts of attention during visual search, Nature, 400 (1999) 867–869.