1. Variation in Subjective Trust with
Changing Facial Features
William Teng
94396558/Michael D. Nunez
wteng1@uci.edu
Abstract
This study aimed to study trustworthiness through the use of
computer generated human faces as the stimuli in a repeated
measures 2x3x2x2x2x3 factorial design. The stimuli contained both
male and female faces. The subjects were to rate each presented
face on a scale of 1 to 7, with 1 being “most trustworthy” and 7
being “least trustworthy”. After all subsequent trials were
completed; the mean ratings of untrustworthiness were obtained
and thus analyzed through the use of repeated-measures ANOVA
test. The results consistently showed a significant effect of
“expression” on trustworthiness.
1 Introduction
In this experiment, we aimed to identify how a variety of facial features used to
generate computer images of faces related to the subjective judgments of trust in
those faces for human decision-makers.
2 Experiment
2.1 Participants
A total of xx participants completed the experiment.

2. 2.2 Stimuli
Figure 1: A Sample Face Stimulus
A total of 144 faces were generated for the experiment. These were constructed
through exhaustively considering every combination of four binary facial features
(male vs female, large vs small eyes, round vs thin face, and hair up vs hair down),
and two ternary features (smiling, neutral, and frowning expressions, and high,
level, and low gaze). A sample of face stimulus is shown in Figure 1.
2.3 Stimuli
Each participant viewed all 144 faces in a different, randomly chosen order, and
judged their subjective trust of each face on a seven-point scale, ranging from
“completely trustworthy” to “completely untrustworthy”.
3 Results
Figure 2:
Figure 2: This is a plotted graph of mean untrustworthiness for model 1, which
includes measures of “gender” and “hair”. A significant interaction effect was

3. found between the two variables [F (1,47) = 7.756, p = 0.008, r² = 0.1416]. Male
with hair up was significantly less trustworthy than female with hair up and the
inverse for hair down.
In this model consisting of variables “gender” and “hair”, repeated-
measures ANOVA found a significant interaction effect between the two variables
[F (1,47) = 7.756, p = 0.008, r² = 0.1416], indicating that males with hair up were
significantly less trustworthy than females with hair up and the inverse was true for
hair down. No significant main effects were found, however, for “gender” [F (1,47)
= 0.085, p = 0.773] or “hair” [F (1,47) = 0.879, p = 0.353].
Figure 3:
Figure 3: This is a plotted graph for model 2 containing variables of “expression”
and “face”. The variable “expression” yielded a significant main effect with [F
(2,94) = 8.727, p = 0.000]. Contrast revealed that smiling was significantly more
trustworthy than a neutral expression [F (1,47) = 11.695, p = 0.001, r² = 0.1993].
Through repeated-measures ANOVA, no significant main effect was found
for the variable “face” [F (1,47) = 0.363, p = 0.550]. However, “expression” did
yield a significant effect at [F (2,94) = 8.727, p < 0.01]. The interaction between
“face” and “expression” yielded no significant results [F (2,94) = 1.573, p = 0.213].
Further contrast on “expression” revealed that smiling was significantly more
trustworthy than a neutral expression [F (1,47) = 11.695, p = 0.001, r² = 0.1993] but
no significant difference was between frowning and smiling [F (1,47) = .141, p =
0.709].

4. Figure 4:
Figure 4: This figure displays a plotted graph for model 3 containing variables of
“eyes” and “expression”. Once again, “expression” yielded a significant main
effect of [F (2,94) = 8.727, p < 0.01]. A separate contrast yielded that smiling was
significantly more trustworthy than neutral expression [F (1,47) = 11.695, p =
0.001, r² = 0.1993] furthermore, frowning was also found to be more trustworthy
than neutral
A significant main effect was found, utilizing repeated-measures ANOVA,
for the variable “expression” with [F (2,94) = 8.727, p < 0.01]. However, no
significant main effect was found for the variable “eyes” with [F (1,47) = 1.606, p =
0.211]. Furthermore, no interaction effect was found between the two variables [F
(2,94) = 0.020, p = 0.980]. Lastly, contrast for “expression” revealed that there was
a significant difference between frowning and neutral with frowning appearing more
trustworthy than neutral [F (1,47) = 12.537, p = 0.001, r² = 0.2106] smiling was also
found to be more trustworthy than neutral [F (1,47) = 11.695, p = 0.001, r² =
0.1993].
Model 4 included comparisons between variables of “gaze” and “eyes”.
Unfortunately, both measure yielded insignificant results. Measure of “gaze”
showed that there was no significant difference between high, level, or low gazes [F
(2,94) = 1.112, p = 0.333]. “Eyes” also displayed no significant results between
large and small eyes [F (1,47) = 1.606, p = 0.211]. No interaction effect was found
between the two variables either [F (2,94) = 1.763, p = 0.177].
Lastly, model 5 compared variables “gaze” against “gender”. Again, “gaze”
produced insignificant results [F (2,94) = 1.112, p = 0.333]. “Gender” also yielded
no significant results [F (1,47) = 0.085, p = 0.773]. Unfortunately, there was also no
interaction effect between the two variables [F (2,94) = 2.412, p = 0.095].

5. 4 Discussion
This study of trustworthiness utilized computer generated human faces to analyze
the effects that different facial properties have on the appearance of trust. Subjects
were presented with a series of facial stimuli and rate them on a determined
trustworthiness scale. After all trials were completed, the ratings were collected
amongst all participants and mean ratings were obtained.
The results showed that the variable “expression” had a significant main
effect on mean trustworthiness. Further analysis revealed that a neutral facial
expression was often seen as significantly less trustworthy than either frowning or
smiling. The surprising finding with “expression” was that frowning had no
significant effect on trust when compared to smiling. This is interesting because
frowning is socially associated with negativity whereas smiling is to positivity.
Furthermore, an interaction effect was found between “gender” and “hair”. The data
supported that males with their hair up was significantly less trustworthy than
females with hair up. The inverse was true when gender was paired with the hair
down condition.
Unfortunately, further analysis of other variables failed to reveal any
significant main effects or interaction effects of trustworthiness. It is interesting to
note, however, that the interaction between “gender” and “gaze” yielded results that
appeared to be approaching significance. Perhaps an alteration in the experimental
design would help obtain better results. One fault that may have altered the results
of this experiment was the artificiality of the stimuli. Computer generated faces
provided this experiment with a more controlled and objective mean of varying
facial features. However, it may not have contained enough facial details to simulate
a genuine human face for participants to judge. Perhaps providing subjects with
natural, real human faces could help yield more significant results.
Nonetheless, this study provided a good demonstration of people’s
superficial understanding of trust. The fact that gender had an effect on how a
hairstyle promotes trust or distrust implicates the importance of gender roles and
socially constructed rules on our perception. This is interesting because it suggests
that sense of trust is not an innate instinct, which we are all born with, instead it
may be nurtured by social standards and expectations. It is interesting to debate the
issue of nature vs. nurture when it comes to perception and judgment of any given
environment. The complexity of current societies often imply that human action is a
nurtured phenomenon, however, it is difficult to argue that innate primal instincts
have no effect on behavior.
Lastly, this experiment suggested a social aspect to perception of trust.
Based of that implication, it would be interesting to conduct further study, which
includes another variable of ethnicity. Perhaps ethnicity may have a highly
significance in the perception of trustworthiness. It may also be interesting to
conduct this study under different social settings as well. The current study utilized
only students of the University of California, Irvine, which offers limited social
diversity in terms of current status and environment. Using varying age groups or
maybe even participants located in different countries, might provide drastically
different results. Furthermore, perception on facial expressions should also be
further explored. Facial expressions often imply a particular emotion, which could
be a great factor in determining trust. Whether facial expressions differ in meaning
amongst different cultures could further our understanding towards whether trust is
a natural instinct or a nurtured response. There are many possibilities to the extent

6. of research that could be conducted, however, the current study offered a great
glimpse into understand human perception of trust.
References
Vandekerckhove, Joachim (2014). Lecture 3 [PowerPoint slides]. Retrieved from
https://eee.uci.edu/14w/68200/psych112bw/lec3_p112bw.pdf
Vandekerckhove, Joachim (2014). Lecture 4 [PowerPoint slides]. Retrieved from
https://eee.uci.edu/14w/68200/psych112bw/lec4_p112bw.pdf
Vandekerckhove, Joachim (2014). Lecture 5 [PowerPoint slides]. Retrieved from
https://eee.uci.edu/14w/68200/psych112bw/lec5_p112bw.pdf