Visual Attention to Text and Pictorial Food Labels: An Eye Tracking Experiment
Phase: NA
Conditions: Health Behavior
Sponsor: University of North Carolina, Chapel Hill

Complete Title: Visual Attention to Text and Pictorial Food Labels: An Eye Tracking 
Experiment  
Short Title: Visual Attention to Text and Pictorial Food Labels: An Eye Tracking Experiment 
Protocol Date: 6/24/2024 
NCT #:  NCT05958888 
 
Study Principal Investigator:  
Marissa G. Hall 
University of North Carolina 
email: mghall@unc.edu 
  
 
 
  
 
 

Protocol Synopsis  
 
Study Title 
Visual Attention to Text and Pictorial Food Labels: An Eye Tracking 
Experiment 
Funder 
National Heart, Lung, and Blood Institute (NHLBI) 
Clinical Phase 
NA 
Study Rationale 
• Adults in the US consume excessive sodium, added sugars, and 
saturated fats, leading to high rates of hypertension, type 2 
diabetes, and heart disease.  
• Structural factors like targeted marketing of unhealthy foods, 
price barriers, and low use of Nutrition Facts labels contribute to 
worse dietary outcomes among Latino populations. 
• Front-of-package (FOP) food labels, especially "high-in" labels 
(e.g., "High in sugar"), are a promising policy solution to reduce 
purchase of unhealthy foods.  
• Visual elements like icons and graphics in FOP labels may be 
more effective for Latino and limited English proficiency 
populations by improving noticeability and comprehension. 
• However, it’s unknown how different types of FOP labels affect 
visual attention, message effectiveness, and understandability 
among Latino and limited English proficiency populations.  
Study 
Objective(s) 
The primary objective of this study is to examine attention elicited by 
different types of FOP sodium labels (i.e., FOP sodium label types) 
among adults identifying as Hispanic or Latino/a/é (hereinafter Latino).  
 
Primary  
• To evaluate whether intervention FOP sodium labels elicit higher 
dwell time on the FOP sodium label than control messages.  
 
Secondary 
• To evaluate whether intervention FOP sodium labels elicit higher 
levels of 3 secondary outcomes (fixation count on the FOP 
sodium label, self-reported attention to the FOP sodium label, and 
perceived message effectiveness of the FOP sodium label), 
compared to the control. 
• To evaluate whether (1) self-reported attention to the FOP sodium 
label, (2) perceived message effectiveness of the FOP sodium 
label, and (3) how understandable the FOP sodium label was 
differs by label type. 
Study Design 
 
Within-participants randomized experiment.  
Subject 
Population 
key criteria for 
and Exclusion: 
Inclusion Criteria 
1. Age 18 and older 
2. Self-identifies as Hispanic or Latino 
Exclusion Criteria 

3. Less than 18 years old 
4. Does not identify as Hispanic or Latino 
5. Has one of the following conditions: (Wears bifocals, glaucoma, 
permanently dilated pupils, eye implants [artificial lenses, not 
contact lenses], less than 2 eyes, or blindness) 
Number of 
Subjects  
~60 
Study Duration 
Each subject’s participation will last approximately 30 minutes. 
The enrollment period is expected to last ~4 months. 
Study Phases 
  
There are two phases: 
(1) Screening: screening for eligibility and obtaining consent and  
(2) Intervention: study intervention/experimental treatment. 
Efficacy 
Evaluations 
The primary outcome is the amount of time spent looking at the FOP 
sodium label (i.e., dwell time). This outcome will be measured using eye 
tracking technology. The secondary eye tracking outcomes are 1) number 
of times looking at the FOP sodium label (i.e., fixation count), 2) time to 
first fixation on the FOP sodium label, and 3) dwell time on “natural” 
claim.   
 
Other secondary outcomes include: 1) self-reported attention to the FOP 
sodium label, assessed with 1 item for each label type adapted from 
Nonnemaker et al. 2010, 2) perceived message effectiveness of the FOP 
sodium label, assess with 3 items for each label type, adapted from Baig 
et al. 2019, and 3) how understandable the FOP sodium label was, 
assessed with 1 item for each label type, adapted from Brewer et al. 2019. 
Response options for all measures will range from 1 (low values) to 5 
(high values).   
Statistical and 
Analytic Plan 
We will evaluate the impact of FOP sodium label types on primary and 
secondary outcomes using separate mixed effects linear regression 
models for each outcome, accounting for repeated measures. 
Primary outcome 
• We will run a mixed effects linear regression model, regressing 
dwell time on an indicator variable for FOP sodium label type. 
The control label will serve as the reference group, and the 
intercept will be treated as random. 
 
Secondary outcomes 
• We will use pairwise comparisons to compare predicted means for 
the three intervention FOP sodium label types. The same 
modeling approach will be applied to secondary outcomes. We 
will correct for multiple tests using the Benjamini-Hochberg 
method, treating each outcome as a family of tests and controlling 
the false discovery rate at 0.05. 

Data and Safety 
Monitoring Plan 
• The principal investigators are responsible for data quality 
management and ongoing assessment of safety.   
 
 

Introduction 
The primary objective of this study is to examine attention elicited by different types of 
front-of-package (FOP) sodium labels (i.e., FOP sodium label types) among adults identifying as 
Hispanic or Latino.  
 
Study Protocol 
Participants will complete a randomized experiment programmed using Tobii Lab Pro 
software and Qualtrics. After providing informed consent, participants will view images of cans 
of soup with 4 different labels (a text-only sodium label, an icon and text sodium label, a 
pictorial and text sodium label, and a control barcode label). Participants will view each label in 
a random order. An eye tracker will be used to measure amount of time spent looking at the 
front-of-package sodium label (i.e., dwell time) (primary outcome) and secondary outcomes: 
number of times looking at the front-of-package sodium label (i.e., fixation count), time to first 
fixation on the front-of-package sodium label, and dwell time on “Natural” claim. After viewing 
all labels, participants will use Qualtrics to rate each label for the remainder of secondary 
outcomes: self-reported attention to front-of-package sodium label, perceived message 
effectiveness of front-of-package sodium label, and understandability of front-of-package 
sodium label. 
 
Statistical Considerations 
General Principles  
We will use a two-sided critical alpha of 0.05 to conduct all statistical tests. We will use 
complete case analysis to handle any missing data in analyses of the primary and secondary 
outcomes.  
 
Primary Outcome 
Primary outcome: Amount of time spent looking at the FOP sodium label (i.e., dwell time). This 
outcome will be measured using eye tracking technology.  
Hypothesis 1. We predict that each of the three intervention FOP sodium label types will 
elicit higher dwell time on the FOP sodium label compared to the control. We predict that 
the pictorial FOP sodium label will elicit higher amounts of dwell time than the icon 
label, the icon label will elicit higher amounts than the text-only label, and the pictorial 
label will elicit higher amounts than the text-only label.   
 
Secondary Outcomes 
Eye tracking secondary outcomes: 1) number of times looking at the FOP sodium label (i.e., 
fixation count), 2) time to first fixation on the FOP sodium label, and 3) dwell time on “natural” 
claim.   
 
Hypothesis 2. We predict that each of the three intervention FOP sodium label types will 
elicit higher levels of the 3 secondary eye-tracking outcomes (fixation count on the FOP 
sodium label, self-reported attention to the FOP sodium label, and perceived message 
effectiveness of the FOP sodium label), compared to the control. We predict that the 
pictorial FOP sodium label will elicit higher amounts of these outcomes than the icon 
label, the icon label will elicit higher amounts than the text-only label, and the pictorial 
label will elicit higher amounts than the text-only label.   

 
Other secondary outcomes: 1) self-reported attention to the FOP sodium label, assessed with 1 
item for each label type adapted from Nonnemaker et al. 2010, 2) perceived message 
effectiveness of the FOP sodium label, assess with 3 items for each label type, adapted from Baig 
et al. 2019, and 3) how understandable the FOP sodium label was, assessed with 1 item for each 
label type, adapted from Brewer et al. 2019. Response options for all measures will range from 1 
(low values) to 5 (high values).   
 
Hypothesis 3. We predict that each of the three intervention FOP sodium label types will 
elicit lower levels of two outcomes (time to first fixation on the FOP sodium label and 
dwell time on the “natural” claim), compared to the control. We predict that the pictorial 
FOP sodium label will elicit lower amounts of these outcomes than the icon label, the 
icon label will lower amounts than the text-only label, and the pictorial label will elicit 
lower amounts than the text-only label.  
 
Statistical Methods 
We will assess the impact of FOP sodium label type on the primary and secondary outcomes 
using mixed effects linear regression models to account for repeated measures. We will use 
separate models for each outcome. 
 
1. Analyses of the primary outcome: 
a. We will run a mixed effects linear regression model, regressing dwell time on an 
indicator variable for FOP sodium label type. The control label will be the 
reference group. The model will treat the intercept as random. We will use 
pairwise comparisons to compare predicted means for the three intervention FOP 
sodium label types to each other.  
 
2. Analyses of the secondary outcomes: 
a. We will use the same modeling approach used in the primary outcome to examine 
the impact of FOP sodium label type on secondary outcomes.  
 
For analyses of primary and secondary outcomes, will use the Benjamini-Hochberg method to 
correct for multiple tests. These analyses will treat each outcome as a family of tests, correcting 
for the six tests within each outcome and controlling the false discovery rate at 0.05.  
 
 
Sample Size Needs 
Respondents will be approximately 60 US adults ages 18+ who identify as Latino. We powered 
the study to detect an effect size of d=0.27 or larger, assuming 4 repeated measures, 80% power, 
a correlation among repeated measures of 0.60, and a nonsphericity correction of 1. This effect 
size is conservative given that our recent meta-analysis found a large effect size for the impact of 
pictorial (vs. text) warnings on dwell time (d=1.74) in eye tracking studies.   
 
Exclusions and Outliers 
We do not expect any outliers on survey measures because the Likert-style response options are 
constrained. We do not plan to exclude outliers for eye tracking outcomes, as is typical for eye 
tracking studies.