Yu et al.
Journal of Physiological Anthropology(2023) 42:8
https://doi.org/10.1186/s40101-023-00325-4

ORIGINAL ARTICLE

Journal of
Physiological Anthropology

Open Access

Effects of fearful face presentation timeand observer’s eye movement on the gaze cue
effectChuntai Yu1, Keita Ishibashi2 and Koichi Iwanaga2*   

Abstract
Background There are many conflicting findings on the gaze cueing effect (GCE) of emotional facial expressions.
This study aimed to investigate whether an averted gaze, accompanied by a fearful expression of different durations,
could enhance attentional orientation, as measured by a participant’s eye movements.
Methods Twelve participants (3 females) completed the gaze cue task, reacting to a target location after observing
changes in the gaze and expression of a face illustrated on a computer screen. Meanwhile, participants’ eye movements were monitored by electrooculography. The GCE was calculated by reaction time as an indicator of attention
shift.
Results The analysis of the overall data did not find a significant effect of fearful facial expressions on the GCE. However, analysis of trial data that excluded a participant’s eye movement data showed that brief (0, 100 ms) presentationof the fearful facial expression enhanced the GCE compared to that during a neutral facial expression, although when
the presentation time of the fearful expression was increased to 200 or 400 ms, the GCE of the fearful expression wasat the same level as when model showed a neutral expression.
Conclusions The results suggest that the attention-enhancing effect of gaze cues induced by rapidly presented fearful expressions occurs only when the effect of eye movement trials is excluded. This effect may be mediated by reflexively neural circuits in the amygdala that process threatening stimuli. However, as the expression duration increased,
the fearful expression’s attention-enhancing effect decreased. We suggest that future studies on the emotion modulation of GCE should consider the negative effects of participants’ saccades and blinks on the experimental results.
Keywords Gaze cueing effect, Fear facial expression, Spatial attention, Electrooculography, Amygdala
Background
Humans are regarded as social animals, and facial information is a social cue necessary for smooth interindividual communication. Facial information such as facial*Correspondence:
Koichi Iwanaga
iwanaga@faculty.chiba-u.jp
1
Graduate School of Science and Engineering, Chiba University, 1‑33
Yayoi‑Cho, Inage‑Ku, Chiba 263‑8522, Japan
2
Design Research Institute, Chiba University, 1‑33 Yayoi‑Cho, Inage‑Ku,
Chiba 263‑8522, Japan

expressions and gaze directions can effectively convey
the expresser’s mental state, such as interest, intention,and emotion, to other individuals [1]. Humans have thehighest proportion of exposed white sclera among primates, making their eyes structurally suitable for eye gazecommunication [2, 3]. As a result, humans are more sensitive to another person’s gaze direction, which conveys
information about important events in the environment.
By reading and interpreting gaze direction, the observer
detects and adjusts spatial attention accordingly [4].
Numerous studies [5–10] have verified a reflexive reaction, called the gaze cueing effect (GCE), that orients© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
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Yu et al. Journal of Physiological Anthropology(2023) 42:8

one’s attention to the direction of another person’s gaze.
The GCE is generally considered to promote the sharing
of attention between two people on the same object (joint
attention), which is a crucial ability to promote interindividual social interaction.
Friesen et al. [6] modified the Posner task into the gazecueing task, which examined whether participants shifted
their attention to gaze the direction. In this task, a facial
stimulus (gaze cue) that looks to the left or right was firstpresented as a cue in the center of a screen, and a target was presented on either the same side (congruent) or
opposite side (incongruent) of the gaze cue. Participants
responded to the target position by pressing a button toindicate which side of the screen the target was on, andthe reaction time and correct answer rate were recorded.
Participants generally detected targets faster when thetarget was congruent rather than incongruent with thegaze cue. The difference in reaction time between incongruent and congruent trials reflected the magnitude ofgaze-evoked attentional orientation as the GCE.
Understanding emotional facial expressions is anotherimportant skill in guiding social interactions [11].
Humans appear to share neural circuits for processing gaze and facial expressions, and studies have shownthat the brain regions for processing gaze direction andaffective perception information are highly correlated
and interact during activation [12, 13]. Fearful and angry
facial expressions are considered threat-related, andprevious studies have reported involuntary processingof threatening information [14, 15]. The combinationof fearful expression and gaze may signal a direction of
threat in the environment, resulting in humans shifting
their concentration of attention more rapidly to adapt toa dangerous situation.
However, Hietanen and Leppänen [16] conducted aseries of experiments and reported that facial expressions (neutral, happy, angry, fearful) did not affect the
GCE. Mathews et al. [17] reported that fearful expressions had a significantly larger GCE than neutral expressions only in the individuals with high anxiety level. Theyinterpreted this as anxious people being more sensitive to
information about potential threats.
In subsequent studies [18–20], a non-anxious group
and a general group also reported that facial expression
affected the GCE, contradicting previous findings. Graham et al. [18] conducted experiments using dynamic
stimuli presentation methods ranging from neutral toemotional gazes (e.g., fear, disgust, pleasure). They foundthat the reaction time was shorter for emotional gazes
than for neutral ones and that the magnitude of the GCE
was greater in response to emotional expressions than toneutral ones. Lassalle and Itier [19, 20] considered theeffect of the presentation order of gaze and facial stimuli.

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In a stimulus presentation sequence in which the expression changed from neutral to fearful after a gaze change,
the fearful expression enhanced the GCE. This sequenceof stimulus cues is considered to have high ecologicalvalidity, meaning it is close to what might happen in a realenvironment. Therefore, by using this stimulus sequence,the enhanced attentional shifts in fearful expressions canbe correctly induced.
One factor that has contributed to the conflicting
results of previous studies is thought to be fearful expression presentation time. In studies of spatial cues, an
important factor called stimulus onset asynchrony (SOA)
which meaning the length of time between a cue stimulus and a target presentation. It has been reported that
SOA affects the GCE. A short SOA (150, 300 ms) produces a robust GCE, while the GCE losses in long SOA
show that an automatic shift of attention characterizes
the GCE [6]. McCrackin and Itier [21] reported that theeffects of fearful facial expressions could occur at a 200ms SOA when a stimulus presentation sequence is used
in which the facial expression changes from neutral tofear after a gaze change; this result supported the theoryof reflexive information processing by the fearful expression. However, Graham et al. [18] argued that 300 ms was
not enough time for the integration of gaze and facial
expression, as no effect of fearful expression was seen on
the GCE in SOA of less than 300 ms.
Gaze direction and fearful expression appear to be integrated in the early period of visual information processing. The presentation time may affect the threat message
formed by the combination of fearful expression andaverted gaze. A short presentation time may be perceived
as to indicate an obvious threat, while a long one may be
judged as ambiguous regarding the presence of a threat.
Therefore, the presentation time of fearful expression
may affect the intensity of the perceived threat and thus
affect the spatial attention shift of gaze direction.
In typical gaze cue tasks, SOA refers to the length oftime from gaze presentation to target presentation.
In a dynamic gaze cueing task testing the effect of the
fearful expression, it is necessary to set the SOA as thetotal presentation time of the gaze cue and the fearfulexpression. However, due to the different experimental
task designs in previous studies, their results cannot bedirectly compared. Therefore, it is necessary to investigate the effect of facial expression presentation time on
the effect of fearful expression rather than simply to consider SOA as a factor.
Moreover, the inconsistency of findings among
the previous studies may be related to differencesamong the participants’ eye movements from experiment to experiment [22, 23]. Bannerman et al. [24]reported that fearful expressions evoked faster andYu et al. Journal of Physiological Anthropology(2023) 42:8

more saccades in participants than neutral expressions. Therefore, the emotional content of a presented
face may induce spontaneous eye movements in participants. Visual exploration in primates depends on
saccadic eye movements that cause alternations of neural suppression and enhancement [25]. Saccades will
inevitably divert spatial attention, affecting the target’s
reaction time and thereby affecting the GCE. Moreover,unlike the manual response, the saccade response will
induce the earlier inhibition of attention shift in thecue direction (inhibition of return) to develop earlier[26]. To the best of our knowledge, however, only one
study has investigated the effect of saccade on emotion
modulation in GCE. McCrackin et al. [27] investigatedthe effect of saccades generated during a gaze cueing
task. In that study, happy expression elicited a greater
GCE than neutral tongue trials when eye movements
were removed but not when they were included. For
the GCE enhancement effect of the fearful expression,
there was no difference in the results from before andafter the eye movement trial was removed. In the present study, while excluding saccades, we also focusedon the effect of eye blinking on the experimental results
because blinks may interrupt visual information input.
In simple terms, eye blinking may affect the perception of the presentation time of the fearful expression,
resulting in a negative influence on experimental data.
McCrackin et al. [27] reported on the proportion of
trials that included saccades but not on the proportion that included blinking. To better discuss the effectof the fearful expression on participants’ spontaneouseye movements, it is necessary to report the number ofblink trials in the experiment and to discuss the effectof blinking on the experimental results.
Electrooculography (EOG) is a physiological measurement of eye movements that records changes in thecornea‒retina potential [28]. Vertical eye movements(blinks) can be measured by placing electrodes on thelids for VEOG (vertical EOG). Meanwhile, horizontal
eye movements (saccades) can be measured by placing
electrodes on the external canthi for HEOG (horizontal EOG). Since the EOG technique can simultaneously
measure horizontal eye movement saccades and verticaleye movement blinks with a high temporal resolution andcan be synchronized with the event signal of the experimental task, we believe that EOG is a suitable measurement of eye movements for investigating the influenceof eye movement occurring during the execution of thegaze cueing task in this study design.
In summary, we conducted an experiment to explore
the effects of fearful expression presentation time and ofa participant’s eye movements on the GCE of fearful andPage 3 of 12

neutral expressions to expand our understanding of theattention-shifting behavior evoked by fearful expressions.

Methods
Participants

The sample size was estimated based on prior studies on
the effects of facial expression (ηp2 = 0.22) and of SOA
on reaction time (ηp2 = 0.86) [21]. A statistical power
analysis using G*Power [29] indicated an optimal sample
size of N = 8 if the effect size ηp2 = 0.2 with α = 0.05 andpower = 0.95.
Twelve university students (3 female) with normal
vision (including corrected-to-normal vision) participated in the experiment. The age of the participants was
25.0 ± 1.7 years (M ± S.D.), and all were right-handed. All
participants gave written informed consent before participating in the experiment. The experimental implementation sequence of this study was approved by the ethics
committee of The Institute of Engineering and Center for
Frontier Medical Engineering of the Graduate School at
Chiba University (Acceptance Number: R2-11).
Stimuli

Two male and two female head models of neutral andfear facial expressions with a straight gaze were generated
by 3D facial model generation software (FaceGen Modeller 3.5, Singular Inversions). The fearful expression was
created using the Facial Action Coding System (FACS)
built in FaceGen Modeller, which specifies a set of Nos.
1, 2, 4, 5, 7, 20, and 25 action units (AUs). All these AUs
were considered characteristics of fearful expression [30,31]. By using 3D model rendering software (Blender,
Blender Foundation), facial images were created with thegaze of each model oriented to the left or right 20° fromthe straight gaze. Each stimulus was trimmed to a size of
12.6° × 20°, showing the region from the top of the headto the upper neck.
The stimuli were presented by a program created by
PsychoPy3.0 on a 24.5-inch LCD monitor (ROG SWIFTPG258Q, 1920 × 1080 pixels, 240 Hz, ASUS) connected
to a Windows 10 computer against a dark gray (64, 64,
64 RGB) background. Participants observed the stimulus at 50 cm from the LCD and responded using a keyboard. A chinrest ensured a fixed distance of 50 cm fromthe computer screen and minimized participants’ head
movements.
Procedure

The experiment included three factors: facial expression,
congruency, and duration of facial expression presentation, including two levels of expression conditions (fearand neutral expressions) and three levels of gaze–target
congruency (congruent, incongruent, and straight gaze).

Yu et al. Journal of Physiological Anthropology(2023) 42:8

In addition, four durations of facial expression presentation (0, 100, 200, and 400 ms) were set. Because thestraight gaze condition was set as a pseudo-condition, it
was excluded from the analysis. Participants completed apractice block and five experimental blocks. Participants
completed 24 trials in the practice block (one trial foreach experimental condition). Each experimental blockcontained 8 repetitions for the left and right gaze directions and 4 repetitions for the straight gaze direction.
As a result, there were 128 trials in each of the 16 conditions (2 expressions × 2 gaze – target congruency × 4
durations of facial expression presentation) and 32 trials
in the straight gaze condition (2 expressions × 4 durationsof facial expression presentation) for each experimental block, lasting about 8 min. Participants were allowed
to take proper rest periods between blocks. Thus, participants completed the experiment in approximately
60 min.
Each trial began with a central fixation point prompted
at a random time of 900 ~ 1000 ms, in which a neutral
expression facial image with a straight gaze was presented for 500 ms. After each neutral presentation, a gazecue consisting of an image of a face with a left, straight,
or right gaze was presented within 100 ms to present a
perception of a gaze shift. Second, as emotional cues, thefacial expression either remained neutral or changed tofear and was presented for 0, 100, 200, or 400 ms. Finally,
the asterisk target (2.5° × 2.5°) appeared on the left or
right side of the facial stimulus. The target would randomly appear either left or right of the face. Participants
were instructed to respond to the location of the target(left or right) as quickly and accurately as possible bypressing the “left arrow” or “right arrow” key with theirright index finger and middle finger. Participants werealso asked to keep their eyes fixed on a certain fixation

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cross during the completion of the experiment. Each participant’s reaction time (RT) was recorded (see Fig. 1).
The gaze direction was either congruent with the target
location (looking toward the location where the target
would later appear) or incongruent with it (looking in the
opposite direction). Left and right gaze trials were averaged within the two gaze-congruency conditions.
The period from the start of the fixation point to theend of the participant’s response was considered as one
trial, and the subsequent trial was started after a blankpicture was presented for 1000 ms. Participants were
informed that they must maintain their focus on the fixation point until a blank frame appeared.
EOG measurements and data classification criteria

EOG was recorded to measure the participant’s eye
movements at a sampling rate of 1000 Hz and visualized in real-time using biological signal analysis software(AcqKnowledge 4.1, Biopac Systems) Two electrodes
were placed on the left and right temples (horizontal eye
movement detection), two were placed above and below
the right eye (vertical eye movement detection), and areference electrode was placed on the forehead.
Before the experiment began, each participant was
instructed to maintain a fixed gaze at the fixation point,
and baseline EOG was recorded in both the horizontal
and vertical directions for 5 s. During the duration of theexperimental stimulus between the Fixation frame andthe Target frame (see Fig. 1), if the maximum amplitudein the horizontal or vertical EOG was greater than the
maximum amplitude in the baseline, it was considereda saccade (horizontal) or a blink (vertical) trial, whereas
if the maximum amplitude in the horizontal or vertical
EOG was not greater than that in the baseline, it wasconsidered a non-eye-movement trial. We synchronized

Fig. 1 Sequence of experimental stimuli. This diagram shows only one example of facial and target conditions (fearful-congruent condition)

Yu et al. Journal of Physiological Anthropology(2023) 42:8

these classification markers to the reaction time data
before data analysis.
Statistical analysis

Statistical analyses were conducted using SPSS Statistics(Chicago, IL, USA). The correct RTs were analyzed separately for all trials, including both eye movement trials
and non-eye movement trials, by using a repeated measures analysis of variance (ANOVA) with within-subject
factors of facial expression (neutral and fear), congruency(congruent and incongruent), and facial expression presentation time (0, 100, 200, and 400 ms).
We also performed an ANOVA on the GCE, which
was calculated as the difference between incongruent
and congruent RTs (RTincongruent − RTcongruent) using
facial expression and facial expression presentation time
as within-subject factors.
Statistical significance was accepted at the 5% level(p < 0.05). The Greenhouse‒Geisser correction wasapplied where sphericity was violated.

Results
Table 1 shows the exclusion rates resulting from eachparticipant’s eye movement, error response, and deviation of RT. Trials in which an incorrect response wasmade (mean = 0.7%, SD = 0.6%) and those in which
the participant’s mean RT was above or below 3 SDs(mean = 3.1%, SD = 1.7%) were removed before themean for each condition was calculated. Because weaimed to investigate the influence of a participants’ eyePage 5 of 12

movement on the experimental results, we compared
the analyses of data including and excluding eye movement trials.
Analysis of all trials including eye movement trials

A 2 (facial expression: “neutral”; “fear”) × 2 (congruency: congruent; incongruent) × 4 (facial expression
presentation time: 0, 100, 200, and 400 ms) repeatedmeasures ANOVA was conducted on the mean reaction times of total data including eye movements trials.
The results showed a main effect of congruency (F(1, 11) = 20.57, p < 0.001, ηp2 = 0.65), as participants
responded to gazed-at (congruent) targets were more
quickly than to non-gazed-at (incongruent) targets.
However, there was no main effect of facial expression (F (1, 11) = 1.52, p = 0.244, ηp2 = 0.12) or of facial
expression presentation time (F (3, 33) = 2.05, p = 0.126,
ηp2 = 0.15). No significant interaction was observed
between facial expression and congruency (F (1,11) = 0.01, p = 0.942, ηp2 = 0.004), between congruency
and facial expression presentation time (F (3, 33) = 0.6,
p = 0.62, ηp2 = 0.05), or between facial expression andfacial expression presentation time (F (3, 33) = 1.21,
p = 0.321, ηp2 = 0.10).
Finally, the three-way interaction was not significant (F (3, 33) = 1.41, p = 0.256, ηp2 = 0.11). As the main
effect of and interaction with facial expression did notshow statistical significance, the effect of the fearfulexpression on the GCE was not examined (see Fig. 2).

Table 1 Data exclusion rates resulting from eye movement, error response, and deviation of RT
Data exclusion rates (%)
Participant

Blink eye movement

Total eye movement

Error response

Deviation of RT
above or below
3 SDs

1

7.7

12.0

1.0

2.3

2

4.0

4.3

0.1

1.8

3

22.8

27.5

0.0

5.3

4

9.8

12.4

0.6

6.7

5

13.1

15.0

0.3

3.1

6

4.8

7.0

1.4

1.3

7

11.5

13.5

0.1

1.5

8

16.7

18.0

1.0

1.4

9

7.0

9.5

0.6

4.4

10

10.7

13.6

0.3

2.3

11

10.1

10.4

1.8

3.5

12

1.4

2.3

0.6

3.1

Mean (SD)

10.0 (5.8)

12.1 (6.6)

0.7 (0.6)

3.1 (1.7)

Values show the percentages of 800 trials (160 trials × 5 blocks) that were excludedYu et al. Journal of Physiological Anthropology(2023) 42:8

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Fig. 2 Mean reaction time (RT) for each facial expression presentation time and fear (left) and neutral (right) expressions for all trial data. Error bars
indicate standard errors of the mean

Analysis of trials excluding eye movement trials

As described above, a three-way repeated measures
ANOVA was conducted on mean reaction times,
excluding the data of eye movement trials.
Congruency had a significant main effect (F (1,11) = 68.14, p < 0.001, ηp2 = 0.86), the same as when theanalysis of eye movements was included, but reflectsthat the effects were stronger when eye movement
data were excluded. Facial expression presentation
time (F (1.55, 17.06) = 3.82, p = 0.051, ηp2 = 0.26) hada significant main effect. Although the main effect offacial expressions (F (1, 11) = 0.13, p = 0.728, ηp2 = 0.01)
was not well established, significant interactions wereobserved between facial expression and congruency(F(1, 11) = 9.60, p = 0.01, ηp2 = 0.46), congruency andfacial expression presentation time(F (3, 33) = 14.48,
p = 0.001, ηp2 = 0.57), and facial expression and facial
expression presentation time(F (3, 33) = 4.08, p = 0.014,
ηp2 = 0.27). Finally, the three-way interaction was significant (F (3, 33) = 3.05, p = 0.026, ηp2 = 0.24). These interaction results showed that the effect of facial expression
was modulated by facial expression presentation timeand congruency (see Fig. 3).

Since a significant three-way interaction was foundbetween facial expression, congruency, and facial
expression presentation time, we conducted ANOVAs on the congruent and incongruent trials separately. Results showed that for RT in congruent
trails, facial expressions had a certain trend toward
a significant main effect (F (1, 11) = 3.50, p = 0.088,
ηp2 = 0.24). No significant main effect of facial expression presentation time was found (F (1.78, 19.62) = 2.26,
p = 0.135, ηp2 = 0.17), but the interaction between
facial expression and facial expression presentation
time approached the borderline of significance (F (3,33) = 2.64, p = 0.076, ηp2 = 0.19). Next, we conducteda simple main effect analysis for each factor. The Bonferroni correction (two-tailed) was applied to tests ofstatistical significance of post-hoc comparison, andthe significance level was set at 0.008. Simple main
effect analysis of facial expression showed shorter
RTs for fearful than for neutral trials when the fearful expression was prompted 100 ms or 200 ms before
the target (100 ms condition: 321.1 ms vs 329.1 ms,
F (1, 11) = 8.83, p = 0.013, ηp2 = 0.44; 200 ms condition: 318.3 ms vs 323.7 ms, F (1, 11) = 5.80, p = 0.035,
ηp2 = 0.35). The simple main effect of facial expression

Fig. 3 Mean reaction time (RT) for each facial expression presentation time and fear (left) and neutral (right) expressions when the eye movement
trials data were excluded. Error bars indicate standard errors of the meanYu et al. Journal of Physiological Anthropology(2023) 42:8

presentation time was also significant in the fearful expression condition (F (3, 33) = 7.80, p = 0.002,
ηp2 = 0.41). A further multiple comparison reflectedthat the RT was longer for the 0 ms condition than for
the 100 or 200 ms condition (ps < 0.005), and RT for the
200 ms condition was shorter for the 400 ms condition(p < 0.005). For RT in incongruent trials, there was asignificant main effect of facial expression presentation
time (F (1.64, 18) = 7.91, p = 0.005, ηp2 = 0.42) and significant interaction between facial expression and facial
expression presentation time (F (3, 33) = 5.50, p = 0.007,
ηp2 = 0.33), but the main effect of facial expression was
not observed (F (1, 11) = 0.51, p = 0.487, ηp2 = 0.04).
Simple main effect analysis of facial expression showed
longer RTs for fearful than for neutral trials only when
the fearful expression was prompted simultaneouslywith the target (0 ms condition: 344.2 ms vs 334.5 ms,
F (1, 11) = 9.54, p = 0.01, ηp2 = 0.46). The simple main
effect of facial expression presentation time in the fearful expression condition was observed (F (3, 33) = 11.84,
p = 0.001, ηp2 = 0.52), reflecting that the RT was longer
for the 0 ms and 100 ms conditions than for the 200 ms
or 400 ms condition (ps < 0.005). There was no significant difference between the 0 ms and 100 ms conditions or between the 200 ms and 400 ms conditions.
As congruency interacted with every other factor,
the magnitude of GCE was computed (RTincongruent − RTcongruent) and analyzed by using a 2 (facial
expression) × 4 (facial expression presentation time)
repeated measures ANOVA. When the interaction issignificant, the Bonferroni correction (two-tailed) wasapplied to tests of statistical significance in the post-hoc

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comparison for the simple main effect of facial expression presentation time, and the significance level was
set at 0.008.
First, significant main effects of facial expression (F (1,11) = 9.53, p = 0.01, ηp2 = 0.46) and facial expression presentation time (F (1, 11) = 14.52, p < 0.001, ηp2 = 0.57) were
found. Moreover, their interaction was also significant (F(3, 33) = 3.49, p = 0.05, ηp2 = 0.24). The simple main effectanalysis of facial expression showed that when the fearful expression was prompted simultaneously with or
100 ms before the target, the fearful expression had a significantly greater effect than the neutral expression (0 mscondition: 14.8 ms vs 7.7 ms, F (1, 11) = 21.06, p < 0.001,
ηp2 = 0.66; 100 ms condition: 16.6 ms vs 5.9 ms, F (1,11) = 42.19, p < 0.001, ηp2 = 0.79). The simple main effectof facial expression presentation time was also significant in the fearful expression condition (F (3, 33) = 16.27,
p < 0.001, ηp2 = 0.59), reflecting that the GCE was larger
for the 0, 100, and 200 ms conditions than for the 400 ms(ps < 0.008, see Fig. 4).

Discussion
Humans can exploit social information such as gazeand facial expressions, enabling each other to communicate and transmit information more efficiently [32,33]. Previous research has debated whether threatening
information expressed by fearful facial expressions canenhance attention shift evoked by gazing at a target, but
no consistent conclusion has been reached [16, 18, 27].
The present study set out to assess the importance of
two factors, facial expression presentation time and participants’ spontaneous eye movements, that affect theFig. 4 Mean gaze cueing effect (i.e., RT difference between congruent and incongruent trials) for each facial expression presentation time among
neutral and fearful expressions when the eye movement trial data were excluded. Error bars indicate standard errors of the mean. Asterisks indicate
p < 0.008 (the threshold after Bonferroni correction)

Yu et al. Journal of Physiological Anthropology(2023) 42:8

enhancement of GCE by a fearful expression. The results
demonstrated that this enhancement of GCE by a fearful expression was found only in the specific condition
where the two main factors were combined (i.e., fearfulexpression under the short presentation time conditionand excluding the results of the spontaneous eye movement trials). In two separate subsections in the “ Discussion” section, we discuss and summarize the effects ofthese two factors on the GCE enhancement of fearfulexpressions and their potential causation.
Facial expression presentation time

Across the present experimental results, we demonstrated that fearful expressions enhance gaze-evokedspatial attention shifts compared to neutral expressions.
This effect is moderated by the presentation time of fearful expressions. However, this attentional enhancement
effect of fearful expressions was found only in the results
after excluding the data from spontaneous eye movement
trials.
When presentations were brief (i.e., 0 and 100 ms), theGCE of the fearful expression was greater than that of
the neutral expression. The greater GCE can be achievedin two ways: by pointing more quickly to the target incongruent conditions, or more slowly to the target inincongruent conditions. The present study showed that,in congruent trials lasting 100 or 200 ms, participants
responded faster to the target when it was preceded bya fearful expression compared to a neutral expression. In
addition, the attentional enhancement effect was more
pronounced for the 100 ms duration than for the 200 ms
duration, suggesting that attention was more rapidly
directed towards the gaze cue when a fearful expression
was presented. This is consistent with previous findings that fearful expressions speed up the orientation of
spatial attention compared to neutral expressions [21].
In incongruent trials, when the fearful face and the target were presented simultaneously (0 ms condition), theresponse to the target was slower for the fearful expression compared to the neutral expression. This was theunderlying reason for the enhancement of the GCE by
the fearful expression in the 0 ms condition. We consider that findings from previous studies [34, 35] may
explain this result. Carlson and Mujica-Parodi [34] investigated the impact of fearful facial expressions on spatialattention during conscious and unconscious information processing using a dot-probe task. They found that,regardless of conscious awareness, the presentation of
fearful facial threat cues resulted in both faster orientation of attention towards the cued location and slower
disengagement of attention from it. Georgiou et al. [35]suggested that spatial attentional processes may also act

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to delay disengagement from fear-relevant stimuli, eventhough this tendency is stronger among people with highanxiety. The present study adds to previous research bydemonstrating that simultaneously presenting a fearfulexpression and a target impairs participants’ ability todisengage their attention from the gaze-cued side associated with the potential threat. Specifically, the findings
suggest that this effect is more pronounced for fearfulexpressions compared to neutral faces. In summary, theresults of the present study confirm that when the fearful expression and the target were presented simultaneously after the gaze cue, the enhancement effect of GCE
may be due to the difficulty in disengagement of attention from the gaze direction. When the fearful expression lasting for 100 ms, the GCE enhancement may be
due to the faster shift of attention to the eye direction.
However, the RT results for congruent trials in this study
approached, but did not reach, statistical significance,thus limiting the interpretation of the results in the present experiment. This lack of statistical significance could
be due to the relatively small sample size compared toprevious studies, even though a statistical power analysis was performed before the experiment. Moreover, thepresent study did not measure or control for individual
anxiety levels, which may also be a limitation in interpreting the results of this study. Therefore, future studies
should aim to verify the results of this study by increasing
the sample size and controlling individual anxiety levels.
A fearful face with averted gaze is often considered
an indicator of threatening information. For example,
a person looking to the right and expressing fear suggests there may be a danger in that direction. The ability to integrate and understand these cues, interpreted
as an essential survival mechanism, is thought to residein the amygdala, which is part of the limbic system andlocated deep inside the brain’s medial temporal lobe.
The amygdala integrates sensory information andoutputs it to the hypothalamus. In these neural networks, the amygdala plays a vital role in judging thevalue of information to survival [36]. Thus, the amygdala processes and remembers emotional responses(especially fear and anger) and may have pathways forprocessing threat-related signals [37]. In an fMRI study,
Adams et al. [12] showed that expressions related tothreat information, such as fearful expression, could
induce a stronger reaction in the amygdala than theneutral expression and could promote information processing of fearful expression. In addition, previous studies have shown that fear emotion is detected throughthe limbic system; especially, threat information related
to survival will be quickly and automatically processedto get ready for the following action [38, 39].

Yu et al. Journal of Physiological Anthropology(2023) 42:8

Kawashima et al. [40] demonstrated that gaze information is also processed in the amygdala. The detection of gaze direction activates the left amygdala, whichhelps read social signals. Presenting fearful expressions
and averting gaze in a short period of time may induce
rough and rapid information processing in the amygdala, integrating fearful expressions and gaze direction to judge whether there is a threat to survival. As aresult, fearful expression will cause spatial attention to
be distributed more quickly to the gaze direction.
In amygdaloid processing of information about athreatening stimulus, two different neural circuits may
be at work: one for reflexive responses and the other forreflective. By operating in parallel, these circuits can not
only detect the existence of a threat rapidly and roughly
but can also cancel the threat after confirming the safetyof carrying out the most efficient threat response [41].
By adjusting the presentation duration of fearful expressions, Adams et al. [42] found that a short presentationinduced a reflexive response in the amygdala to explicit
threat information, while a long presentation induceda reflective response in the amygdala to an ambiguous
threat. Our results support the hypothesis that when
explicit threat information (such as the fearful expression with a specific direction of gaze in this study) is
prompted for a short time (100 ms), the threat detection
circuit of the amygdala is reflexively activated. The signal
is quickly transmitted to the spatial attention system toguide attention rapidly. This supports the view that the
fearful expression induced an automatic attention shift inprevious studies. Most noteworthy is that, based on the
results of previous studies, the present study is the first to
confirm that the GCE was enhanced when the fearful face
and the target were presented simultaneously, although
no expression effect on congruent RT was found. Future
research may continue to explore the GCE enhancement
effect of fearful expression when the presentation time iswithin 0–100 ms.
However, when the presentation time is longer, but thetarget still does not appear, it may be temporarily considered that there is no threat (or ambiguous threat) inthe environment, the top-down processing of the cortex
affects spatial attention, and the GCE by fearful expression is not enhanced. Such results support the hypothesis of the processing of threatening stimuli: that whenattention shifts to the gaze cue direction and no target
is found, the spatial attention will deviate from the cue
direction to respond to targets appearing in other directions in the environment. Such results could also reflect
human environmental adaptability, as a long-term focus
on a specific direction is detrimental to detecting environmental hazards [43].

Page 9 of 12

In the present study, SOA duration was the time
between the gaze cue and the target appearance. Hence,
the SOA factors in this study were 100, 200, 300, and
500 ms for both fear and neutral expressions. However, the fearful expression occurred for 0, 100, 200,
and 400 ms after the gaze shift (lasting 100 ms), while
the neutral expression was maintained for 0, 100, 200,
and 400 ms. Even though this is a classic experimental
design for investigating emotion modulation in GCE,
the lack of apparent facial motion in neutral expressions
could potentially have affected the results; this may be alimiting aspect of this study. To eliminate this potential
impact in future studies, we expect to create an experimental condition like the ‘neutral tongue’ in McCrackin
et al.’s study [21, 27].
While the present study discussion involves a lot of
speculation about brain circuits that process the gaze of
fearful expressions, obviously, it is not enough to speculate on the neural basis behind the GCE enhancementby the fearful expression based only on the reaction time
data. Therefore, we believe it may be possible to further
confirm the conjecture by introducing neurophysiological methods in future studies.
Spontaneous eye movements

The comparison between total data and eye movement
removal data revealed that a participant’s eye movements
during the experiment affected the detection of the GCE
enhanced by fearful expression.
Similar to the results reported by McCrackin et al., [27]in our study the effect of fearful expression on the GCE
can be clarified by excluding from analysis the data on eye
movements recorded during trials. In contrast, when allof the data were analyzed, no effect of fearful expression
was found. The results of the present study showed thatthe effect of fearful expressions could be detected with asmall sample size (12 participants) if the data affected byeye movements were excluded, even though the effect of
fearful expressions is generally considered to be small. As
we mentioned in the Background section, Graham et al.
[18] argued that a 300-ms cueing time was insufficient
to integrate gaze and facial expressions, as they found noeffect of fearful expressions on the GCE at shorter SOAs.
However, the present study demonstrated that, when thecueing time of fearful expressions was less than 100 ms(i.e., when SOA was less than 200 ms in the present
study), fearful expressions enhanced the GCE. When thecueing time of fearful expressions exceeded 100 ms (i.e.,
when SOA exceeded 200 ms in the present study), theenhancement effect of fearful expressions on the GCE
disappeared, contradicting previous findings. Comparedto the experimental approach of Graham et al. [18], thepresent study required participants to fixate their gazeYu et al. Journal of Physiological Anthropology(2023) 42:8

during the experiment and eliminated experimental datathat had been contaminated by eye movements. Thiselimination of contamination might have contributed
to the detection of the enhanced GCE of fearful expression by brief presentation. Conversely, when data analyses that did not account for the effects of eye movements
were performed, no effect of fear expressions on the GCE
was observed.
There are generally considered to be two types of orientation of visual attention: one is covert visual attention
orientation, which is achieved through internal neurophysiological systems without head or eye movements;
the other is overt visual attention orientation throughbehavioral systems accompanied by head or eye movements [44, 45]. During saccadic eye movements, visual
nerve activity is suppressed [25], and an earlier inhibitionof return for spatial attention shift is developed [26]. Prior
studies have revealed that both overt and covert attention
can induce GCE [46], but studies on the enhancementof GCE by fearful expression have not reached consistent conclusions. In the present study, the participants
were asked to keep their eyes fixed on a certain point
during the completion of the experiment, and to focused
mainly on the effect of covert attention. However, since itis difficult to accurately locate the spatial position of theparticipants’ eye movements during the horizontal eye
movements measured in this study, we cannot discuss theeffect of overt attention of GCE enhancement by fearfulexpression. Therefore, this study focused on the relationship between covert attention and GCE enhancement by
the fearful expression through strict exclusion criteria foreye movement trials. The present results confirm that theenhancement of GCE by fearful expression may be partially achieved by covert attention, which precedes eye
movements and can be deployed simultaneously in multiple places in the environment. This mechanism is also inline with the advantages of threatening stimuli describedabove and is very helpful for efficient visual information
processing and for guiding future eye movements. Nevertheless, the present results do not enable us to discuss
whether the GCE enhancement by fearful expression isdominated by covert attention or the result of the combination of covert and overt attention. This is a limitationof the present study. Future studies need to explore theireffects separately through experimental design.
However, unlike the case in previous studies, mostof the eye movements in this study were caused by eye
blinks (about 82.6% in total eye movements), which havethe potential to temporarily obscure visual information and interrupt the continuity of visual information
input, thus affecting the perceived prompt time [47]. A
blank temporarily interrupts the flow of visual information between the world and the retina. In that instant,

Page 10 of 12

visual stimuli from the outside world disappear for 150–
400 ms [48]. As mentioned above, the GCE enhancement by fearful expression is sensitive to the expression’s
presentation time. Therefore, the blinks that occurred
during the stimulus sequence may affect the perceptionof the presentation time of the fearful expression andthus affect the GCE enhancement by the fearful expression. As shown in the removal rate of trials including theeye movements of each participant (Table 1), we foundsome individual differences in the control of eye movements during the experiment. This phenomenon may
be explained by differences in the cognitive resourcesthat participants devote to the experiment. Maffei et al.
[49] reported that participants individually had different
blink rates depending on the difficulty of task execution,
which showed that participants induced low probability of blinking in tasks with high difficulty and a highprobability of blinking in tasks with low difficulty. It wasalso reported that, regardless of the task’s difficulty, eyefatigue increased gradually during a 4 min task, and theblink rate increased accordingly. Considering the influence of such visual fatigue on eye movement, in future
research tasks should be designed for completion within
4 min in one block.

Conclusions
This study found that when a fearful gaze appeared at thesame time as a target or 100 ms before the target, participants focused more intensely on the gaze direction
than when the gaze was neutral. However, as the expression duration increased, the attention-enhancing effect of
the fearful expression attenuated. Such results were seen
only in analyses of data without eye movement. The GCE
enhancement effect of the fearful expression is dominated by a faster response to the target in a short periodof time. Hence, the present results supported that threat
information may automatically orient attention at an
unconscious level. We suggest that in future studies that
explore the influence of facial expressions on the GCE, a
subject’s eye movements during the experiment should
be considered by improving the experimental design oreye movement measurement.
Abbreviations
EOG	Electrooculography
fMRI	Functional magnetic resonance imaging
GCE	Gaze cueing effectRT	Reaction timeSD	Standard deviation
SOA	Stimulus onset asynchrony
Acknowledgements
None.

Yu et al. Journal of Physiological Anthropology(2023) 42:8

Authors’ contributions
All authors made substantial contributions to the conception and design ofthe experiment. CY performed the experiments and analyzed the data. All
authors gave advice regarding the “ Discussion” section and prepared themanuscript. All authors read and approved the final manuscript.
Funding
None.
Availability of data and materials
The datasets used and/or analyzed during the current study are available fromthe corresponding author on reasonable request.

Declarations
Ethics approval and consent to participate
This study was carried out in accordance with the recommendations of the
Ethics Review Committee of Chiba University, with all subjects providing
written informed consent in accordance with the Declaration of Helsinki. The
protocol was approved by the ethics review committee at The Institute ofEngineering and Center for Frontier Medical Engineering of Graduate Schoolat Chiba University (Acceptance Number: R2-11).
Consent for publication
Not applicable.
Competing interest
The authors declare that they have no conflict of interest.
Received: 30 July 2022 Accepted: 12 May 2023

References
1. Kleinke CL. Gaze and eye contact: a research review. Psychol Bull.
1986;100:78–100.
2. Kobayashi H, Kohshima S. Unique morphology of the human eye. Nature.
1997;387(6635):767–8.
3. Kobayashi H, Kohshima S. Unique morphology of the human eye and its
adaptive meaning: comparative studies on external morphology of the
primate eye. J Hum Evol. 2001;40:419–35.
4. Frischen A, Bayliss AP, Tipper SP. Gaze cueing of attention: visual attention,social cognition, and individual differences. Psychol Bull. 2007;133(4):694.
5. Driver J, Davis G, Ricciardelli P, Kidd P, Maxwell E, Baron-Cohen S.
Gaze perception triggers reflexive visuospatial orienting. Vis cogn.
1999;6(5):509–40.
6. Friesen CK, Kingstone A. The eyes have it! Reflexive orienting is triggeredby nonpredictive gaze. Psychon Bull Rev. 1998;5:490–5.
7. Downing P, Dodds CM, Bray D. Why does the gaze of others direct visual
attention? Vis cogn. 2004;11:71–9.
8. Friesen CK, Ristic J, Kingstone A. Attentional effects of counterpredictive
gaze and arrow cues. J Exp Psychol Hum Percept Perform. 2004;30(2):319.
9. Bayliss AP, Di Pellegrino G, Tipper SP. Sex differences in eye gazeand symbolic cueing of attention. Q J Exp Psychol (Hove) Section A.
2005;58(4):631–50.
10. Bayliss AP, Tipper SP. Gaze and arrow cueing of attention reveals individual differences along the autism spectrum as a function of target
context. Br J Psychol. 2005;96(1):95–114.
11. Ekman P, Friesen WV. Constants across cultures in the face and emotion. J
Pers Soc Psychol. 1971;17:124–9.
12. Adams RB Jr, Gordon HL, Baird AA, Ambady N, Kleck RE. Effectsof gaze on amygdala sensitivity to anger and fear faces. Science.
2003;300(5625):1536–1536.
13. Hoffman EA, Haxby JV. Distinct representations of eye gaze and identity
in the distributed human neural system for face perception. Nat Neurosci.
2000;3(1):80–4.
14. De Gelder B. Towards the neurobiology of emotional body language. Nat
Rev Neurosci. 2006;7(3):242–9.

Page 11 of 12

15. Frijda NH. The emotions. Cambridge: Cambridge University Press; 1986.
16. Hietanen JK, Leppänen JM. Does facial expression affect attention
orienting by gaze direction cues? J Exp Psychol Hum Percept Perform.
2003;29(6):1228.
17. Mathews A, Fox E, Yiend J, Calder A. The face of fear: effects of eye gazeand emotion on visual attention. Vis cogn. 2003;10(7):823–35.
18. Graham R, Kelland Friesen C, Fichtenholtz HM, LaBar KS. Modulationof reflexive orienting to gaze direction by facial expressions. Vis cogn.
2010;18(3):331–68.
19. Lassalle A, Itier RJ. Fearful, surprised, happy, and angry facial expressions
modulate gaze-oriented attention: behavioral and ERP evidence. Soc
Neurosci. 2013;8(6):583–600.
20. Lassalle A, Itier RJ. Emotional modulation of attention orienting by gazevaries with dynamic cue sequence. Vis cogn. 2015;23(6):720–35.
21. McCrackin SD, Itier RJ. Both fearful and happy expressions interact withgaze direction by 200 ms SOA to speed attention orienting. Vis cogn.
2018;26(4):231–52.
22. Ricciardelli P, Bricolo E, Aglioti SM, Chelazzi L. My eyes want to lookwhere your eyes are looking: Exploring the tendency to imitate anotherindividual’s gaze. NeuroReport. 2012;13(17):2259–64.
23. Kuhn G, Kingstone A. Look away! Eyes and arrows engage oculomotor
responses automatically. Atten Percept Psychophys. 2009;71(2):314–27.
24. Bannerman RL, Hibbard PB, Chalmers K, Sahraie A. Saccadic latency ismodulated by emotional content of spatially filtered face stimuli. Emotion. 2012;12(6):1384.
25. Hoffman KL, Dragan MC, Leonard TK, Micheli C, Montefusco-Siegmund
R, Valiante TA. Saccades during visual exploration align hippocampal 3–8
Hz rhythms in human and non-human primates. Front Syst Neurosci.
2013;7:43.
26. Briand KA, Larrison AL, Sereno AB. Inhibition of return in manual and saccadic response systems. Percept Psychophys. 2000;62(8):1512–24.
27. McCrackin SD, Soomal SK, Patel P, Itier RJ. Spontaneous eye-movements
in neutral and emotional gaze-cuing: An eye-tracking investigation.
Heliyon. 2019;5(4):e01583.
28. Creel DJ. The electrooculogram. Handb Clin Neurol. 2019;160:495–9.
29. Faul F, Erdfelder E, Lang A, Buchner A. G*Power 3: a flexible statisticalpower analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods. 2007;39:175–91.
30. Roesch EB, Tamarit L, Reveret L, Grandjean D, Sander D, Scherer KR. FACSGen: A tool to synthesize emotional facial expressions through systematic
manipulation of facial action units. J Nonverbal Behav. 2011;35(1):1–16.
31. Rosenberg EL, Ekman P, (Eds.). What the face reveals: basic and appliedstudies of spontaneous expression using the Facial Action Coding System(FACS). New York: Oxford University Press; 2020.
32. Chen Z, McCrackin SD, Morgan A, Itier RJ. The gaze cueing effect and its
enhancement by facial expressions are impacted by task demands: directcomparison of target localization and discrimination tasks. Front Psychol.
2021;12:696.
33. Argyle M, Cook M, Cramer D. Gaze and mutual gaze. Br J Psychiatry.
1994;165(6):848–50.
34. Carlson JM, Mujica-Parodi LR. Facilitated attentional orienting anddelayed disengagement to conscious and nonconscious fearful faces. J
Nonverbal Behav. 2015;39(1):69–77.
35. Georgiou G, Bleakley C, Hayward J, Russo R, Dutton K, Eltiti S, Fox E. Focusing on fear: Attentional disengagement from emotional faces. Vis cogn.
2005;12(1):145–58.
36. LeDoux J. The amygdala. Curr Biol. 2007;17(20):R868–74.
37. Tabbert K, Stark R, Kirsch P, Vaitl D. Hemodynamic responses of theamygdala, the orbitofrontal cortex and the visual cortex during a fear
conditioning paradigm. Int J Psychophysiol. 2005;57(1):15–23.
38. Öhman A. Face the beast and fear the face: animal and social fears as
prototypes for evolutionary analyses of emotion. Psychophysiology.
1986;23(2):123–45.
39. Öhman A. The role of the amygdala in human fear: automatic detectionof threat. Psychoneuroendocrinology. 2005;30(10):953–8.
40. Kawashima R, Sugiura M, Kato T, Nakamura A, Hatano K, Ito K, et al. The
human amygdala plays an important role in gaze monitoring: A PET
study. Brain. 1999;122(4):779–83.
41. Forgas JP, Williams KD, Von Hippel W, Kipling WD, (Eds.). Social judgments:
Implicit and explicit processes (Vol. 5). New York: Cambridge University
Press; 2003.

Yu et al. Journal of Physiological Anthropology(2023) 42:8

Page 12 of 12

42. Adams RB Jr, Franklin RG Jr, Kveraga K, Ambady N, Kleck RE, Whalen PJ,
Hadjikhani N, Nelson AJ. Amygdala responses to averted vs direct gazefear vary as a function of presentation speed. Soc Cogn Affect Neurosci.
2012;7(5):568–77.
43. Itti L, Koch C. Computational modelling of visual attention. Nat Rev
Neurosci. 2001;2:194–203.
44. Petersen SE, Posner MI. The attention system of the human brain: 20 years
after. Annu Rev Neurosci. 2012;35:73.
45. Henderson JM. Human gaze control during real-world scene perception.
Trends Cogn Sci. 2003;7(11):498–504.
46. Friesen CK, Kingstone A. Covert and overt orienting to gaze direction
cues and the effects of fixation offset. NeuroReport. 2003;14(3):489–93.
47. Baumstimler Y, Parrot J. Stimulus generalization and spontaneous blinking in man involved in a voluntary activity. J Exp Psychol. 1971;88:95–102.
48. VanderWerf F, Brassinga P, Reits D, Aramideh M, Ongerboer de Visser B.
Eyelid movements: behavioral studies of blinking in humans under different stimulus conditions. J Neurophysiol. 200389:2784–2796.
49. Maffei A, Angrilli A. Spontaneous eye blink rate: an index of dopaminergic component of sustained attention and fatigue. Int J Psychophysiol.
2018;123:58–63.

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