Journal of the Institute for Psychological and Physical Science, Vol. 2, No. 1, 119–124, 2010

Note
1)

ERP-P3 for Pictures Varies in Amplitude According to Stimulus Content
Aki AKAMINE*1), Mitsuro KIDA*2)   This study explored whether the P3 event-related brain potential (ERP) is sensitive to the contents ofpictures presented during a discriminative reaction time (RT) task. In the Stop-cars task, five categories ofpicture (cars, people, electronics, flowers, and landscapes) were presented randomly, with probabilities of .40,
.30, .10, .10, and .10, respectively. Thirty-one participants were asked to respond to every stimulus that was nota car by pressing a button. Another twenty-one participants also engaged in a Stop-figures task, which was
identical to the Stop-cars task except that simple geometric figures replaced the car stimuli. ERPs forequiprobable stimuli (electronics, flowers, and landscapes) were analyzed. Two types of P3s were seen at around
380 ms and 520 ms after stimulus onset. The first component (early P3) featured a parietal maximal and seemed
equivalent to the “classical P3” (P3b). The second component (late P3) was more anteriorly distributed. For bothtasks, the amplitudes of early P3 differed across the stimuli. Additionally, the early P3 elicited by electronics
stimuli was larger during the Stop-figures task than during the Stop-cars task. It is well known that P3 (P3b)amplitudes can vary as a function of stimulus probability during a simple oddball task. However, the present
results suggest that P3 amplitude for complex pictures in a discriminative RT task might be sensitive to stimulus
content rather than probabilities.
Keywords: event-related brain potentials; early P3; late P3; picture content; stimulus probability

Event-related brain potentials (ERPs) are voltage fluctuations that are temporally associated with some physical and/or mental occurrence, and that contain components thatspan a continuum between exogenous and endogenous
potentials (Picton et al., 2000). To date, numerous studies
have examined the relationship between ERP components
and various human cognitive functions.
One of the most extensively investigated ERP components is the P3 (P3b or P300). The P3 component is a large
positive deflection that peaks between 300 and 800 ms after
the occurrence of an attended, task-relevant event. DuncanJohnson and Donchin (1977) used a simple oddball task todemonstrate that P3 amplitudes vary as a function of
stimulus probability. There is therefore a general agreementthat P3 amplitudes are indeed sensitive to the stimulus
probability. On the other hand, a number of studies havereported that the P3s elicited by emotional pictures arelarger than those elicited by neutral pictures (e.g., Akamine& Kida, 2001; Cuthbert, Schupp, Bradley, Birbaumer, &Lang, 2000; Johnston, Miller, & Burleson, 1986). Theselatter studies suggest that P3 amplitudes can also besensitive to the picture content.
Many have noted that the P3 is not a unitary brain
potential, but instead represents a summation of activity
from various widely distributed areas in the brain (e.g.,
Johnson, 1993; Kok, 2001). Several researchers haveidentified various subcomponents of P3 (e.g., Christensen,
Ivkovich, & Drake, 2001; Falkenstein, Hohnsbein, &Hoormann, 1994; Kayser, Bruder, Tenke, Stewart, &Quitkin, 2000). Sugimoto, Nittono and Hori (2007) notethat some studies have consistently shown an enhancementof late positive potential elicited by emotional pictures, andthat these studies may analyze the component consisting of
the P300 and subsequent positive slow wave. In ourprevious study, two types of P3s were elicited using color
pictures presented during discriminative reaction time (RT)tasks (Akamine & Kida, 2004). Here, the early P3 peakedat around 380 ms after stimulus onset over parietal scalp
sites. The late P3 peaked at around 520 ms after stimulus
onset, with a central-parietal scalp distribution. The early*1) Department of Child Care Studies, School of Human Care Studies, Nagoya University of Arts and Sciences*2) Department of Psychology, Faculty of Psychological and Physical Sciences, Aichi Gakuin University
Requests for reprints should be sent to: E-mail: akamine@nuas.ac.jp

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Aki AKAMINE, Mitsuro KIDA

P3 would be equivalent to the “classical P3” associatedwith the perceptual stage of processing. The late P3 might
be similar to P-CR (Falkenstein et al., 1994), in that itreflects not the response selection itself but rather aspectsof the cognitive processes that follow the overt reaction(e.g., closure of response selection, or a correctness checkdone after the response is made). However, there are few
studies investigating the subcomponents of P3, as far as weknow. It is not clear whether these components vary
according to stimulus content and/or probabilities in thesame way. The functional characterization of the late P3
remains unclear.
Purpose of the Present Study
To examine whether the amplitudes of early P3 and lateP3 are sensitive to picture content, ERPs for threeequiprobably-presented categories of picture (electronics,
flowers, and landscapes) were recorded. In the present
study, we used a Stop/NoStop task, which is a lesscommonly used discriminative RT task designed by Kida
and Kawano (1996). In this paradigm, the participants are
required not to make a motor response to a particular
stimulus (Stop), but instead to respond to all other stimuli(NoStop). Our previous study (Akamine & Kida, 2004)
showed that more participants produced two distinct
positive peaks between 300 and 600 ms following stimulus
onset during the Stop/NoStop task than during the traditional discriminative RT task (Go/NoGo task).
Two Stop/NoStop task conditions were used in thepresent study: A Stop-cars task and a Stop-figures task. In
both tasks, the same four categories of picture (electronics,
flowers, landscapes, and people) were assigned as NoStop
stimuli. It was assumed that participants could discriminate
more easily the Stop stimuli from the Nostop stimuli in the
Stop-figures task than in the Stop-cars task. Thus, ERPs for
the NoStop stimuli were recorded separately for eachcategory and for each task. However, the ERP elicited by
pictures of people was not analyzed, given that the stimulus
probabilities for these pictures differed from those for theother categories.2)

MethodParticipants
Fifty-two students at Aichi Gakuin University (37 womenand 15 men; mean age = 22.0 years) participated in the
study for pay.
Procedure
Stimuli. Six groups of colored picture were used in thisstudy: Cars, simple geometric figures, electronics, flowers,
landscapes, and people. The car and simple geometricfigure categories each consisted of 20 different images. The
people category included images of eight different ordinary
people (neutral stimuli) and eight different images of people
with some type of skin disease or external injury (negative
emotional stimuli). The remaining three categories (flowers,
electronics, and landscapes) each consisted of five different
pictures.
The stimuli were presented one at a time on a computer
screen positioned approximately 1 m in front of the participants. Each picture subtended a visual angle of 14.0°
horizontally and 10.0° vertically, and was presented with afixed stimulus onset asynchrony of 3,000 ms (500 ms on
and 2,500 ms off).
Discriminative RT tasks. The participants performed
either of two kinds of discriminative RT task. In the
Stop-cars task (N = 31), pictures from the five categories(cars, people, electronics, flowers, and landscapes) were
presented randomly with probabilities of 0.40, 0.30, 0.10,
0.10, and 0.10, respectively. The participants were required
to respond to all pictures except for “cars” (i.e., people,
electronics, flowers, and landscapes) by pressing a button
with the index finger of their right hand.
In the Stop-figures task (N = 21), pictures of simple
geometric figures were used instead of cars but the otherpictures were the same as those used in the Stop-cars task.
The participants’ task was to press a button in response to
all pictures except the geometric figures with the index
finger of their right hand.3)
Each task condition consisted of six blocks of 50 trials
each. Participants were instructed to respond as accurately
and quickly as possible. Fifty practice trials were given
prior to complication of the tasks.
ERP Recording and Data Collection
Electrophysiological data were collected during thediscriminative RT tasks. Electroencephalograms (EEG)
were recorded from four midline sites, Fz, Cz, Pz, and Oz,
referenced to linked earlobes. An electrooculogram (EOG)
was recorded from the electrode located below the righteye. Electrode impedances did not exceed 10 kOhms. The
EEG and EOG were amplified using the San-ei 360 system(time constant 3s, high-pass filter 30Hz). The data, together
with trial information, were stored on a magnetic tape andprocessed offline. All recordings were digitized at 500 Hz.
ERP waveforms were calculated separately for each participant, picture category, and task condition. The period
between 200 ms before and 1,000 ms after the onset of eachstimulus was averaged. The trials in which eye movements

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ERP-P3 and Contents of Picturesor blinks occurred and those trials that involved an incorrect
response or no response were excluded from the averaging
of ERPs. The averaged ERPs were aligned to a 200-ms
prestimulus baseline. The following analyses were
performed on the data of 51 participants; the data of one
individual (a woman) who participated in the Stop-figures
task had to be excluded from analysis due to excessive
eye-blink artifacts.
ERPs showed the N1, P2 and N2 early components.
These were followed by two large positive deflections witha latency range of 300–600ms after stimulus onset; thesecomponents were identified as early P3 and late P3 seenaround 380 ms and 500 ms after stimulus onset, respectively. However, all ERPs did not clearly exhibit two
positive peaks. For this reason, the early P3 amplitude wasdesignated as the mean amplitude of the waveform over a
40-ms period between 360 and 400 ms. Similarly, the late
P3 amplitude was designated as the mean amplitude of the
waveform over a 40-ms period between 500 and 540 ms.
The data at Oz had to be removed due to indistinct
waveforms obtained from many of the participants.
Therefore, analyses were performed only on data collectedfrom the Fz, Cz and Pz sites.4)

Results
Behavioral Data
Table 1 presents the mean error rates and RT for eachstimulus, in each task. Although the Stop stimuli induced
more errors than did the NoStop stimuli, participants overall
made relatively few errors.

The RT data were submitted to a two-way mixed analysis
of variance (ANOVA) with the factors of task (Stop-cars
task and Stop-figures task) and stimulus (electronics,
flowers, and landscapes). Both main effects of task andNoStop stimulus were significant, F (1, 49) = 9.53, p< .01;
F (2, 98) = 104.02, p< .001, respectively. A significant task× stimulus interaction was also obtained, F (2, 98) = 34.26,
p< .001. The simple main effects of task were significant
for the electronics and landscapes, F (2, 98) = 26.66, p<.001; F (2, 98) = 4.82, p< .05, respectively, but not for theflowers. Both RTs for the electronics and for the landscapes
were longer in the Stop-cars task than in the Stop-figurestask. In addition, the simple main effects of stimulus weresignificant for each task, F (3, 98) = 128.10, p< .001 in the
Stop-cars task; F (3, 98) = 9.93, p< .001 in the Stop-figurestask. Multiple comparison tests revealed that the RTs for the
Stop-cars task were shortest for the flowers, followed by
the landscapes and then the electronics. Furthermore, theRTs for the Stop-figures task were longer for the electronics
than for both the flowers and landscapes, HSD (3, 98) =14.36, p < .05.
ERP Data
Figure 1 shows grand-mean waveforms elicited by the
NoStop stimuli for three categories (electronics, flowers,
and landscapes) in each task. Table 2 presents the mean
amplitudes of early P3 and late P3 at each electrode in eachtask.
Early P3. The early P3 was maximal at the Pz site. The
early P3 amplitude data at the Pz site were submitted to a
two-way ANOVA, as was done for the RT data. Although

Table 1: Mean Error Rates and Reaction Times
Stop stimuli

NoStop stimuli
NeutralpeopleNegative
peopleElectronics

Flowers

Landscapes

Error rate (%)
Stop-cars task
M
SD

5.19
3.51

0.50
2.38

0.36
1.27

0.54
2.41

0.32
1.30

0.54
1.91

M
SD

3.13
2.62

0.11
0.48

0.11
0.48

0.17
0.73

0.33
1.45

0.50
1.59

M
SD

—
—

384.9
36.2

406.5
38.6

448.9
30.6

383.9
39.0

400.4
40.6

M
SD

—
—

366.3
56.5

365.2
52.8

382.6
53.0

363.8
53.4

372.2
52.1

Stop-figures task

Reaction time (ms)Stop-cars task

Stop-figures task

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Aki AKAMINE, Mitsuro KIDA

Figure 1: Grand mean ERP waveforms elicited by NoStop stimuli.

the main effect of task was not significant, the main effectof stimulus and the interaction between task and stimulus
were both significant, F (2, 98) = 35.53, p < .001, and F (2,98) = 18.16, p < .001, respectively. The simple main effectof task was significant for the electronics stimuli, F (2, 98)= 10.73, p< .001. The electronics stimuli elicited a larger
early P3 in the Stop-cars task than in the Stop-figures task.
However, there were no significant task differences in earlyP3 amplitude elicited by the flowers or the landscapes. In
addition, the simple main effects of stimulus were significant for each task, F (3, 98) = 40.73, p< .001 in the
Stop-cars task; F (3, 98) = 12.95, p< .001 in the Stopfigures task. Multiple comparison tests revealed that theearly P3 amplitudes in the Stop-cars task were largest for
the flowers, followed by the landscapes and then theelectronics. In the Stop-figures task, the early P3 amplitudes
yielded by the flowers and landscapes were both larger thanthose elicited by the electronics, HSD (3, 98) = 2.67, p <.05.
Late P3. The late P3 had a central-parietal scalp distribution. The amplitude data at the Cz site were also
submitted to a two-way ANOVA.
The main effect of stimulus was significant, F (2, 98) =16.72, p < .001, although the main effect of task and theinteraction between task and stimulus were not significant.

Multiple comparison tests involving the stimulus factor
revealed that the late P3s elicited by the electronics andflowers were both larger than that elicited by thelandscapes. However, there were no significant differencesin late P3 amplitude between the electronics and flowers,
HSD (3, 98) = 1.36, p < .05.

Discussion
In the present study, complex color pictures elicited two
different positive waves between 300 and 600 ms after
stimulus onset. While some participants produced two
distinct positive peaks after the N1–P2–N2 complex, others
produced a terraced positive wave (unclear peak) and alarge positive peak between 300 and 600 ms after stimulus
onset. The early P3 appeared over parietal scalp sites ataround 380 ms after stimulus onset. The late P3 peaked ataround 520 ms after stimulus onset, with a central-parietal
scalp distribution. The characteristics of the ERP
waveforms were exactly the same as those noted in ourprevious study (Akamine & Kida, 2004).
Although the color pictures in 3 categories (electronics,
flowers, and landscapes) were presented equiprobably inboth tasks, the early P3 amplitudes differed across thestimuli. Furthermore, the early P3 amplitudes elicited by─ 122 ─

ERP-P3 and Contents of Pictures

Table 2: Mean Amplitudes of Early P3 and Late P3 (μV)

considered that the late P3 might be similar to P–CR
(Falkenstein et al., 1994), and may therefore reflect aspectsof the cognitive processes that follow an overt reaction(e.g., closure of response selection, or a correctness checkafter the response is made). However, the functional significance of the late P3 may be further elucidated in futurestudies.

NoStop stimuli
Electronics

Flowers

Landscapes

M
SD
M
SD
M
SD

3.45
5.19
6.35
6.87
8.38
5.28

6.20
4.77
11.12
7.49
15.41
6.41

2.72
4.67
6.46
6.55
11.09
5.89

Stop-figures task
Fz M
SD
Cz M
SD
Pz M
SD

6.69
4.92
10.27
7.42
14.68
7.64

7.55
4.00
11.02
8.07
15.69
7.98

4.12
4.02
6.18
8.10
11.84
7.88

M
SD
M
SD
M
SD

7.76
6.27
14.07
7.43
16.77
5.70

7.75
4.53
13.65
6.97
14.86
6.05

4.52
5.84
10.98
6.38
14.58
5.40

Stop-figures task
Fz M
SD
Cz M
SD
Pz M
SD

5.84
7.35
10.84
9.43
13.38
6.33

7.84
5.78
11.32
7.91
12.28
6.55

4.51
5.46
8.29
8.10
11.71
6.15

Early P3
Stop-cars task
Fz
Cz
Pz

Late P3
Stop-cars task
Fz
Cz
Pz

Notes
1)

2)

3)

4)

We presented this study at the 49th Annual Meeting of theSociety for Psychophysiological Research in October 2009,at the Berliner Congress Center.
We reported the ERP elicited by the NoStop people stimuli
at the 25th Annual Meeting of the Japanese society forphysiological psychology and psychophysiology in July
2007, at Sapporo Medical University.
We thank Keita Kogura, a graduate of Aichi Gakukin
University, for his help with the experiment (the Stopfigures condition).
We reported the ERP elicited by the Stop cars stimuli andStop figures stimuli in Journal of the Institute for Psychological and Physical Sciences, Vol. 1, pp. 63–69, in 2009.

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the electronics stimuli were different across the two tasks.
The early P3 noted here would have the same functional
characterization as the classical P3 (P3b) associated withthe perceptual stage of processing. Duncan-Johnson andDonchin (1977) demonstrated effects of stimulus probability on the classical P3 using a simple oddball task.
However, the present study suggests that early P3 amplitude
might be more sensitive to picture content than to probabilities, at least in a discriminative RT task that uses complex
color pictures.
The amplitudes of late P3 also differed across the stimuli.
It appears that late P3 amplitude might also be affected by
picture content. The topographical differences between theearly P3 and late P3 found in the present study support the
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─ 124 ─Final version received, January 4, 2010