Current Biology 18, 668–671, May 6, 2008 ª2008 Elsevier Ltd All rights reserved

DOI 10.1016/j.cub.2008.03.059

ReportGaze Following in Human Infants
Depends on Communicative Signals
Atsushi Senju1,* and Gergely Csibra1
1School of Psychology
Birkbeck, University of London
Malet Street
London WC1E 7HX
United Kingdom

Summary
Humans are extremely sensitive to ostensive signals, like eye
contact or having their name called, that indicate someone’s
communicative intention toward them [1–3]. Infants also pay
attention to these signals [4–6], but it is unknown whether
they appreciate their significance in the initiation of communicative acts. In two experiments, we employed video presentation of an actor turning toward one of two objects andrecorded infants’ gaze-following behavior [7–13] with eyetracking techniques [11, 12]. We found that 6-month-old
infants followed the adult’s gaze (a potential communicative-referential signal) toward an object only when such an
act is preceded by ostensive cues such as direct gaze (experiment 1) and infant-directed speech (experiment 2). Sucha link between the presence of ostensive signals and gaze following suggests that this behavior serves a functional role inassisting infants to effectively respond to referential communication directed to them. Whereas gaze following in many
nonhuman species supports social information gathering[14–18], in humans it initially appears to reflect the expectation of a more active, communicative role from the information source.
Results
In two experiments, 6-month-old infants watched simple actions on a computer screen while their gaze direction was continuously recorded by an eye tracker. Each trial started with themodel looking down to a table and ended with the model shifting her gaze toward one of two colorful toys placed to hereither side (Figures 1A and 1F). The crucial variable that separated the experimental conditions was what happened between these phases, and in particular, whether any ostensive
communicative cues preceded the gaze shift. We measured
whether infants (1) followed the model’s gaze immediately after her head turn and (2) made more eye movements toward, or(3) fixated longer to, the gazed object. Difference scores were
calculated for each measurement and tested against chancelevel as well as compared between conditions.
In experiment 1, infants in the eye contact (EC) condition
watched the model looking up toward the viewer and raising
her eyebrows slightly before turning to one of the objects(Figure 1B). Eye contact and eyebrow raise are ostensive signals that indicate the model’s intention to initiate communicative interaction with the viewer. In this situation, infants weremore likely to look to the same object than to the other one*Correspondence: a.senju@bbk.ac.uk

immediately after the model’s head turn [t(9) = 4.11, p = .003]
and made more eye movements toward the gazed object
than toward the opposite one [t(9) = 4.52, p = .001]. This result
replicates the earlier finding that infants at this age follow
others’ gaze on a computer screen when the objects are close
to the models [12].
Another group of infants was assigned to the no eye contact(NEC) condition, in which we removed the ostensive signal
from the stimulus. Thus, instead of the model making eye contact with the viewer, a colorful moving cartoon image wasoverlaid on her head for the same duration as the eye contact
in EC condition in order to attract infants’ attention to theensuing head turn (Figure 1C). In this condition, the difference
scores did not differ from zero in any measurements (allts < .82, all ps > .31), indicating no tendency to follow themodel’s gaze in the absence of eye contact. Group comparisons revealed that infants in the EC condition were more likely
to follow the model’s gaze [t(18) = 2.74, p = .013] and mademore frequent looks toward the gazed object [t(18) = 2.17, p =.043] than infants in NEC condition (Figure 2A). In sum, a periodof ostensive eye contact did, whereas a nonostensive attention-directing stimulus did not, elicit gaze following in 6 montholds. Note that the direct gaze and the moving cartoon image
equally captured infants’ attention to the model’s face: Infants
looked longer to the face during the eye-contact or movingcartoon-image (average duration per trial: 1.61 s for EC condition and 1.54 s for NEC condition) conditions than during thebaseline phase [average duration per trial: 1.05 s for EC condition and 1.09 s for NEC condition; F(1,18) = 51.08, p < .001],
although looking duration across experimental conditions
did not differ from one another (all Fs < .51, all ps > .48).
Eye contact is not the only ostensive stimulus and is not the
only one that infants are sensitive to. Adults tend to talk to infants with a specific intonation pattern, called infant-directedspeech, which in most situations would inform a baby thathe or she is being addressed. Infants, and even naive newborns, have been shown to preferentially orient toward thesource of this stimulus [6] and respond to it similarly as they
do to eye contact. If gaze following depends on the presenceof ostensive cues in young infants, rather than being tuned
to the specific stimulus of direct gaze that produces eye contact, infant-directed speech should also be sufficient to elicit
gaze following.
In experiment 2, new groups of infants observed exactly thesame visual stimuli as we used in the NEC condition of experiment 1, but we added a female voice saying ‘‘hello’’ at the onset of moving cartoon image. Half of the infants heard thegreeting in infant-directed speech (IDS), characterized bya wide range of pitch variation (Figure 1D). Infants in this condition were more likely to look to the gazed direction immediately after the model’s shift of gaze [t(9) = 3.00, p = .015] andmade more eye movements toward [t(9) = 3.37, p = .008],
and fixated longer at [t(9) = 3.61, p = .006], the gazed object
than the opposite direction. Thus, just like eye contact,a word uttered in infant-directed fashion before the headturn was sufficient to elicit gaze following in infants.
To check whether the infant-directed intonation or the
speech stimulus itself made infant follow the gaze of theGaze Following Depends on Communicative Signals
669

Figure 1. Selected Frames from the Stimuli
Each video started with the baseline phase (A), followed by the attentiongetting phase (B–E) and gazing phase (F). The attention-getting phaseincluded eye contact (EC) or no eye contact (NEC) in experiment 1 and infant-directed speech (IDS) or adult-directed speech (ADS) in experiment 2.
The baseline and the gazing phases were identical across conditions. The
curves on (D) and (E) represent the pitch contour of the speech.

model, we presented another group of infants with the same
stimuli with the exception that the word ‘‘hello’’ was voiced
in a flat adult-directed speech (ADS, Figure 1E). Note that the
speech was produced by the same voice and had the same
duration and volume as in the IDS condition. Nevertheless,none of the difference scores differed from zero in the ADS
condition (all ts < 1.40, all ps > .13). When we compared thetwo conditions in experiment 2 (Figure 2B), we found that infants were more likely to follow the model’s gaze immediately
after her head turn in the IDS than in the ADS condition [t(18) =2.38, p = .028]. Because the visual stimuli were exactly thesame in the two conditions, these results again support our
prediction that infant-directed speech, with the infant as theaddressee, facilitates gaze-following behavior in 6 montholds, whereas adult-directed speech does not (see also
Supplemental Results available online).
We further analyzed whether the effect of the presence ofostensive signals on gaze following was consistent acrossthe two experiments. The difference scores were analyzed
with two-way ANOVAs for experiment (1 or 2) and condition(ostensive or nonostensive) as between-subject factors. The
results revealed that infants were more likely to follow gaze

Figure 2. Measures of Gaze Following
Difference scores were presented for direction of the first face-to-object
saccade after the model’s head turn (First), frequency of face-to-object saccades (Frequency), and duration of object fixation (Duration) in each condition in experiments 1 (A) and 2 (B). The following abbreviations are used: EC,eye contact condition; NEC, no eye contact condition; IDS, infant-directedspeech condition; and ADS, adult-directed speech condition; **p < .01,
*p < .05. Error bars represent standard error.

after ostensive signals than after nonostensive attention getters [F(1,36) = 13.1, p < .001]. Because the main effects of experiment and the interactions did not even approach the levelof statistical significance (all Fs < .70, all ps > .38), we conclude
that the effect of the presence of ostensive signals on gazefollowing was equivalent with eye contact and infant-directedspeech, rather than being specific to the particular visual orauditory features of these stimuli.

Current Biology Vol 18 No 9670

Discussion
From immediately after birth, human infants are exceptionallysensitive to adults’ ostensive signals such as eye contact [4, 5]
or infant-directed speech [6] that select them as the target ofa simultaneous or subsequent communicative act. They preferentially orient toward the source of these signals, sometimes
responding to them by smiling [19, 20]. The current results
indicate that, at least by 6 months of age, they are also more
likely to follow others’ gaze when such signals are present.
Such an effect cannot be solely explained by attentional factors because nonsocial ‘‘attention getters,’’ which elicited thesame amount of visual orientation to the model’s head, did
not facilitate gaze-following behavior. The current results
also contradict the proposal that young infants reflexively shift
their attention to the same direction as a perceived headmotion, regardless of the communicative context [9, 10, 13].
Instead, our results are consistent with the observation thatyoung infants require strong ostensive cues for gaze following [8] and attentional-gaze cueing [21] and that additional
communication signals, such as pointing and verbalization,
facilitate the response in older infants [7].
Neuroimaging studies have revealed that a network ofbrain regions that include parts of the prefrontal cortex isequally activated for stimuli, such as eye contact and hearing
one’s name, that indicate self-directed communicative intentions [3], and a recent study has demonstrated a similareffect in 4-month-old infants [5]. Interestingly, the prefrontal
cortex also specifically responds to object-referential gaze
when it follows eye contact [22]. Infants have been shown
to more probably detect referential gaze shifts when ostensive signals are present [23] and display prefrontal cortex
activation in response to object-directed gaze shifts that follow eye contact [24]. These findings suggest that the neuralprocesses that enable detecting ostensive signals and interpreting referential gaze shifts partly overlap and that theseprocesses mature early in life. It is not yet known whether
gaze-following behavior relies on these neural processes inhuman infants, but this seems likely in the light of the present
results.
Gaze-following behavior has been demonstrated in a wide
range of animal species, such as nonhuman primates [16–18], goats [14], and ravens [15]. Such behavior has a clear
adaptive significance because it allows the observer to lookat events in the environment that have already caught anotherindividual’s attention. This adaptive benefit does not dependon communication. Thus, the fact that gaze following is tied
to ostensive contexts in human infants suggests that thisbehavior may serve communicative purposes, such as interpreting deictic reference during interactions, in early humandevelopment. Comparative data from other species are not
yet available to evaluate whether this effect is truly human specific. However, the fact that various nonhuman primates readily follow the head orientation of animals depicted on static
pictures (e.g., [25, 26]) and that gaze following is rare in the infant of nonhuman primates (e.g., [27, 28]) suggest that the link
between communication signals and co-orientation wasestablished in human evolution. Just like direct gaze, which
is a threat signal in nonhuman primates [29–31] but gained
a different function during human evolution by indicating theintention to initiate and maintain interactions between parties[1], gaze following may also have been ‘‘exapted’’ for communicative purposes in humans and may not be entirely homologous with similar behaviors displayed by other species.

In conclusion, our study demonstrated that beyond (1) the
preference for signals that indicate for infants that they arebeing addressed by someone [4, 5] and (2) their tendency tofollow behaviors (e.g., a head turn) that have potential referential significance [7–10], these two biases are linked together inhuman infants. Such combination of biases could function toallow human infants to benefit from referential communication
directed to them and could be one of the developmental rootsof ostensive-referential communication in humans [32].
Experimental Procedures
Participants
In experiment 1, 20 6.5-month-old infants (ten female, ten male) completed
the study. Their mean age was 197.3 days (range: 180–209 days). Ten infants(five female, five male, mean age: 199.1 days) were assigned for the eye contact (EC) condition, and the other ten infants (five male, five female, mean
age: 195.5 days) were assigned for the no eye contact (NEC) condition. An
additional 12 infants were excluded from the analyses because of inattentiveness (eight infants who had less than three trials with gazing from thehead to one of the objects after the head turn), parental interference (one)or technical error (three).
Another 20 6.5-month-old infants (ten female, ten male) completed experiment 2. Their mean age was 196.1 days (range: 180–211 days). Ten infants(five female, five male, mean age: 192.9 days) were assigned for the experimental condition, and the other ten infants (five male, five female, mean age:
199.3 days) were assigned for the control condition. A further nine infants
were excluded from the analyses because of inattentiveness (eight) andparental interference (one). Informed consent was obtained from a parentof each infant before the study.
Apparatus
A Tobii (Stockholm, Sweden) 1750 Eye Tracker was used to record infants’looking behavior. The eye tracker was integrated with a 17 inch LCD monitor, on which stimuli were displayed with Tobii’s ClearView AVI presentation
software. Infants were seated on a parent’s lap 50 cm from the monitor onwhich the stimuli were presented. A video camera was mounted on top of
the screen, through which the experimenter monitored the infants’ face. A
five-point calibration was administered before the recording (for technicaldetails about the apparatus and the calibration procedure, see [11]).
Stimuli and Procedure
In experiment 1, each stimulus started with a scene with a female model,
seated behind a table, facing down. Two toy objects were placed on the table, one to each side of the model (Figure 1). The videos consisted of threephases. The first one was the baseline phase (Figure 1A), in which the model
remained still for 2 s. This was followed by the attention-getting phase,
which differed between conditions. In the EC condition, a beep sounded
and the model looked up, looked into the camera, and raised her eyebrows.
This phase lasted for 2 s (Figure 1B). In the NEC condition, the model remained still and a colorful moving cartoon image was overlaid on thehead of the model for 2 s (Figure 1C). The third phase was the gazing phase.
In this one, the model turned her head toward one of the two objects (1 s)and fixated the object for a further 5 s (Figure 1E). Note that the model
kept the neutral facial expression and remained silent throughout the whole
sequence. The videos were edited with Final Cut Express software (Apple,
Cupertino, California) in order to control the duration of each phase andoverlay the cartoon images on the face.
Six trials were presented to each infant. The stimulus in each trial contained a unique pair of objects. The direction of the model’s gaze was counterbalanced in ABBABA order. Half of the infants saw a leftward gaze in thefirst trial, and the other half saw a rightward gaze first. Before the start ofeach trial, infants’ attention was drawn to the center of the screen, on which
the model’s face would appear, by colorful cartoon animations and beeping
sounds. When the infant was attending to the screen, the experimenter
pressed the key and started the trial.
In experiment 2, the stimuli and the procedure were the same as in the
NEC condition of experiment 1, except that, instead of a beep, a female
voice saying ‘‘hello’’ was presented at the beginning of attention-getting
phase. The greeting was uttered either in infant-directed speech (IDS condition, Figure 1D) or in adult-directed speech (ADS condition, Figure 1E), differing primarily in pitch and pitch contour. The two versions were recorded

Gaze Following Depends on Communicative Signals
671

from the same person and were edited with Final Cut Express software tomatch the overall amplitude and duration between conditions. The study
was approved by the ethics committee of the School of Psychology,
Birkbeck, University of London.
Data Analysis
After the recording, a gaze-replay movie file showing the exact location ofeach infant’s gaze was exported at 25 frames per second temporal resolution. These data were then analyzed frame by frame for each phase (baseline phase, attention-getting phase, and gazing phase). The principal measurement of gaze following was whether the first eye-movement saccadefrom the head toward an object in the gazing phase (i.e., after the headturn started) went to the object looked at by the model (congruent saccade)or toward the object opposite one (incongruent saccade). Infants needed toelicit such face-to-object saccade in at least three trials to be included in theanalyses. We calculated the standard difference score [9, 13] for each infant
by subtracting the number of trials with incongruent saccade (i) from thenumber of trials with congruent saccade (c) and dividing the result by the total number of trials with face-to-object saccades. In addition, the frequency
of face-to-object saccades and the duration of the fixation to each object
were calculated for both gaze-congruent and gaze-incongruent object ineach trial. Then the difference scores were calculated for these measurements in a similar way to that of the first measure [i.e., d = (c 2 i)/(c + i)].
To examine infants’ attention to the head, we also calculated the durationof looking to the model’s head separately for the baseline, attention-getting,and gazing phases.
Supplemental Data
Additional Results are available at http://www.current-biology.com/cgi/
content/full/18/9/668/DC1/.
Acknowledgments
We thank Coralie Chevallier, Tessa Dekker, Teodora Gliga, Mark Johnson,
Sarah Lloyd-Fox, Evelyne Mercure, Sotaro Shimada, Victoria Southgate,
and Tuomas Teinonen for their help in conducting the experiment and for
discussions. This work was funded by UK Medical Research Council Programme Grant #G9715587, a Pathfinder grant (CALACEI) from the European
Commission, and an Economic and Social Research Council/Medical
Research Council Interdisciplinary Postdoctoral Fellowship.
Received: March 7, 2008
Revised: March 29, 2008
Accepted: March 31, 2008
Published online: April 24, 2008
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