# Investigating the influence of affinity on the gaze behavior of individuals with Autism Spectrum Disorder (ASD) based on their unique autistic traits

Julie Fournier, Pauline Mann, Emma Bucher, Elise Etchamendy, Giorgia Tiscini, Meriem Outtas, Lu Zhang, Myriam Chérel

<figure><img src="image_1.png" /></figure>

## ► To cite this version:

Julie Fournier, Pauline Mann, Emma Bucher, Elise Etchamendy, Giorgia Tiscini, et al. Investigating the influence of affinity on the gaze behavior of individuals with Autism Spectrum Disorder (ASD) based on their unique autistic traits. Displays, 2026, 91, pp.103228. 10.1016/j.displa.2025.103228. hal-05372715

HAL Id: hal-05372715

https://hal.science/hal-05372715v1

Submitted on 13 Jan 2026

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

# Investigating the influence of affinity on the gaze behavior of individuals with Autism Spectrum Disorder (ASD) based on their unique autistic traits☆

Julie Fournier<sup>a,*</sup>, Pauline Mann<sup>b</sup>, Emma Bucher<sup>b</sup>, Elise Etchamendy<sup>b</sup>, Giorgia Tiscini<sup>b</sup>, Meriem Outtas<sup>a</sup>, Lu Zhang<sup>a</sup>, Myriam Chérel<sup>b</sup>

## ARTICLE INFO

**Keywords:**

Autism Spectrum Disorders

Affinity

Eye movements

Eye tracking

Visual attention

## ABSTRACT

Autism spectrum is very wide, but autistic people share some traits such as social or language impairments. Another common characteristic is a strong passion, called an affinity, which can be anything from a movie character to a topic like history, or even a specific object. Numerous testimonies attest to the support provided by affinities for autistic individuals, offering a reassuring space in a sometimes frightening world. Clinical psychologists consider affinities as keys that can unlock language and learning for people with ASD. However, objective evidence of this role is still lacking. In this study, we used eye-tracking technology to explore the visual attention patterns of autistic individuals when presented with their affinity compared to neutral stimuli. We recruited 52 autistic participants and showed them 38 images: 10 featuring their affinity and 28 neutral ones, while recording their eye movements. Eye-tracking data provided crucial insights into how visual attention is modulated by affinities. Our results reveal significant variability in visual engagement depending on the specific autistic traits and affinities of the participants. Some showed heightened visual engagement with affinity images, while others withdrew their gaze. Some exhibited a mixed response, with both increased engagement and gaze withdrawal, and a few showed no difference between the two sets of images. These findings highlight the complex relationship between visual attention and affinities in autistic individuals, highlighting the potential of eye-tracking as a tool for understanding and leveraging these affinities in therapeutic and educational settings.

## 1. Introduction

Autism spectrum disorders (ASD) are a specific condition that affects the way people perceive their environment, their body and, in general, the language. It can cause social issues, anxiety, language impairment, etc. This affects one birth in 54 [1], which represents several tens of millions of people around the world. Whatever the etiology of autism, whether genetic or neurodevelopmental [2], the psychodynamic approach in which we participate is more focused on understanding the specific functioning of the “autistic mind” [3]. The utilization of the spectrum reference is therefore a powerful illustration of its diversity, necessitating a multidimensional understanding. This approach highlights the need to consider the uniqueness of each autism expressed in

the three criteria corresponding to the solutions autistic individuals tend to implement.

a) A hold alienation with retention of objects, in the absence of drive objects (which are rejected because they are too aggressive and invasive) [4]: For individuals with autism, this lack of demarcation between internal, external, high, low spaces, and their bodies, often leads to a sense of invasion and anxiety. This is experienced through intrusive gazes, hypersensitivity to noise, and overwhelming physical contact. In order to protect themselves from this invasion, they reject the drive objects (vocal, oral, anal, scopic) which are perceived as aggressive and invasive for themselves. Consequently, they exhibit

<footnote><sup>a</sup> Univ Rennes, INSA Rennes, CNRS, IETR - UMR 6164, 20 avenue des buttes de Coesmes, CS 70839. 35700 Rennes, France</footnote>

<footnote><sup>b</sup> Univ Rennes 2, RPpsy, France</footnote>

<footnote>* This paper was recommended for publication by Prof Guangtao Zhai.</footnote>

<footnote>* Corresponding author at: Univ Rennes, INSA Rennes, CNRS, IETR - UMR 6164, France.
E-mail address: julie.fournier@irisa.fr (J. Fournier).</footnote>
a tendency toward immutability, avoidance of others, and a withdrawal into oneself, which may lead them into profound solitude [5].

b) A return of the enjoyment<fnref n="1" /> on the border [6]: to protect themselves against both internal and external invasions ASD individuals create a border between them and the surrounding world. We could think of this border as a kind of skin on the body that marks a difference between themselves and the environment. By electing an affinity, a specific interest, a particular object that emphasizes individuals' strengths and talents, the subject constructs a customized border, capable of demarcating between themselves and the world. This out-of-body object, or “affinity,” allows the overwhelming enjoyment to be located outside the body, in a border that mediates it, by introducing a gap between the subject and others.

c) An operation of connection on a double or on an object [7]: we understand the affinity as an operation of connection on a double or on an object that facilitates the expansion of knowledge concerning a specific interest and all its intricacies. The double is specifically at play when the subject integrates the dynamics of an object or a living being to compensate for their own. Relying on a double, whether animal or human, allows autistic individuals to humanize themselves further, as they may complain about their difficulty in feeling alive [8]. When this border unfolds and becomes more complex, it enables them to better interact with their environment.

## 1.1. Affinity therapy

In recent years, affinity therapy has been developed in the USA, initially with parents, and subsequently by American and French researchers. This therapeutic approach aims to facilitate the development of these three core functions in individuals with autism, leading to enhance receptiveness to the world and language. The affinity therapy was first described in 2014 by Ron Suskind, a famous journalist, in his book “Life animated: a story of sidekicks, heroes and autism” [9] awarded with Pullitzer price. He tells the story of his son Owen, who lost his ability to speak at the age of 3. He was diagnosed with a regressive autism, and his only interest was in watching Disney classics over and over again. Contrary to what specialists recommended, he decided to foster his son's passion, and one day Owen repeated a character's line. Gradually, he became able to talk to his family again, first using lines from his favorite films, and then using his own words. Now Owen works in a cinema and writes his own animated script. Thanks to this first testimony, other people with autism told the great support their affinity is to them, and psychologists have begun to delve into the matter opting to work with what has often been labeled as an obsession, rather than attempting to eliminate it. Another study in France brings together evidence from clinical work on this question [10]. To them, this “affinity” can play the role of the autistic border and can also be considered as double able to open up the ASD individual to the surrounding world (see Fig. 1-1).

## 1.2. Objective of the research

Psychologists empirically observe the benefit of this therapy centered on the affinity, however no objective study demonstrates that it has a real impact on people with ASD. The aim of this paper is to examine the significance of affinity in the attention given by people with autism. Understanding how individuals with ASD visually engage with their affinities can provide valuable insights into their cognitive and

emotional processes [11]. Visual behavior, reflected in gaze patterns that allow us to access visual attention, serves to better appreciate how these individuals perceive and interact with their environment. By studying these behaviors in the context of their affinities, we can gain a deeper understanding of the ways in which these interests influence their perception and interaction with the world. Visual attention, the process by which individuals selectively focus on certain aspects of their environment while ignoring others [12], plays a crucial role in this context.

Visual attention serves as a window into the mind [13], revealing what captures an individual's focus and how they process visual information. For individuals with ASD, affinities often represent areas of high interest and engagement, which can influence their visual attention in distinctive ways. Eye tracking technology offers a precise and non-intrusive method to study visual attention. By tracking the movement of the eyes, researchers can gather detailed data on where and for how long individuals look at specific stimuli [14]. This technology provides invaluable insights into the cognitive processes underlying visual attention and engagement. In the context of ASD, eye tracking allows us to observe how affinities influence visual attention in real-time, offering a unique opportunity into the perceptual and attentional strategies employed by individuals with ASD.

This technology has been widely used to investigate social impairments in autism [15]. Eye-tracking studies involving ASD people usually focus hypothesis able to explain their social difficulties. They have shown that it is hard for people with autism to recognize actions [16] and emotions [17,18], as they pay more attention to details. Another explanation for these problems is that autistic people seem to have a narrower field of view [19]. A study also explores their visual preferences among a set of stimuli displayed simultaneously and found that they look more easily at objects than at social stimuli [20]. Other studies focus more on how to help people with autism to live with less anxiety, and more autonomously, for example with service dogs [21].

All of these studies used eye-tracking techniques to investigate the attention of autistic people and provide a body of evidence on how they interact with their environment. We thus decided to use similar protocol for our research and get insights on the attention of autistic subjects toward their affinity. In a previous study, we have shown that there is no difference in visual behavior in the general population depending on whether we look at a center of interest or not [22]. We have also tried to detect a particular gaze behavior common to all autistic people when they are looking at their affinity, but the results are not conclusive [23]. We have thus decided to continue the research by adding new autistic subjects and rethinking our analysis method. Rather than looking for a single behavior, we tried to measure the influence of several criteria in the subjects' expression of autism on their reaction to affinity. It has indeed been proved that autistic people with poorer communication skills also demonstrate higher difficulties in face processing [24]. In addition, high-level and low-level functioning autisms seem to have various effects on visuospatial cueing [25]. Some autistic traits may influence the visual behavior toward the affinity.

The paper is organized as follow: first, we will detail our experimental protocol and the analysis steps we have followed; we will then explain our results before concluding this paper.

# 2. Material & method

## 2.1. Experimental protocol

### 2.1.1. Recruitment of subjects

With a team of psychologists and computer scientists, we have visited and engaged with four distinct institutions, each specialized in accommodating individuals with autism. At each facility, we dedicated a month to meticulously replicate our established protocol divided in 2 steps. Initially, we observed and participated in their daily routines for a two-week period, aiming to become familiar with all the residents. We

<footnote n="1">¹ “Enjoyment” is a concept introduced by Lacan in the lesson of the 5th march 1958 of his seminary “The formations of the unconscious” (1958–1959). This concept highlights the complex and paradoxical nature of pleasure, which can be overwhelming and disruptive rather than solely gratifying. This phenomenon is often observed in strong act repetitions.</footnote>
<figure><img src="image_5.png" /><figcaption>Fig. 1–1. The relationship scheme between ASD people and the affinity.</figcaption></figure>

engaged in various activities with them, focusing on identifying those who meet all the 3 criteria detailed in introduction and thus were eligible to participate in the experiment. Those 3 criteria were used by the psychologists to establish the ASD diagnosis.

Once we identified the autistic participants, our next step was to discern their affinities. While some individuals readily expressed their interests during activities, we anticipated that others might find it more challenging, particularly when interacting with the unfamiliar individuals we were. We needed time to recognize the “pseudopods” [26] they were extending to us and to understand how to respond, just as they needed time to adjust to our presence. The caregiver team was always of great support, as they held valuable information about the specificities of each subject. For individuals that seem to have more than one affinity, we selected the one they share the most with others.

In a second step, we conducted the eye tracking experiment properly. For 2 weeks, we welcomed the subjects in a dedicated room where we set up our experimental equipment. We proposed 2 different activities: the first one consisted in offering them a digital activity while the second was the experiment itself. The purpose of this activity was to establish a relationship through a digital object, which often carries a dimension of their affinity. This allowed us to bond more easily and gain a better understanding of how they used this object as a solution. We provided access to 2 computers and 2 tablets and let them free to use the devices as they pleased or to seek guidance on new applications they wanted to learn. The subjects usually come first to benefit from the digital activity and become familiar with the environment and material, and then come back another day for the proper experiment. Not all residents of the institutions were diagnosed with ASD. Nevertheless, everyone was free to participate and benefit from this digital activity and even from the experiment if they wanted to. The idea was to be as inclusive as possible; we simply did not retain their data for our study.

However, for some other ASD patients it was impossible to come and ask for this digital activity, as it is quite impossible for them to get together. For these specific subjects, we have come in their environment with a tablet, using it to watch educative videos for example, and let them come to us and take the tablet. Once this first meeting occurred, the positive energy of the moment made it possible for them to come to the experiment room and take part to the eye tracking test. This approach over a long period allowed us to create a link with them, and even to identify affinities for 2 subjects. Of course, we did not force anyone to take part in either the digital activity or the experiment. Some subjects for whom we had identified an affinity categorically refused to come and take part in the experiment or preferred to leave before the end. Consequently, we opted not to include them in the final sample.

For some other subjects, the experiment was impossible due to the nature of their affinity. As we need to display it on a screen, we could only select subjects whose affinity has a visual representation. If it only involves other senses: auditory, tactile or even gustatory, we could not include them in them in this study. However, this is not a major bias,

since the modality seems to have a reduced impact on the attention of autistic people [27].

In total, 52 autistic subjects took part to the experiment. The details are described in Table 1.

For some of the subjects, coming to the experiment may have induced anxiety, as it involves social interaction and demands. This is partly the reason why some of them felt the need to be accompanied by a familiar person. Sometimes, one of the psychologists of the project manages to make the experience less frightening, and her presence is enough, but for others it is more complicated. For these, a caregiver came with them. This caregiver could be their favorite special needs educator, a psychologist from the institution, or its director. Whatever the case, it provided a reassuring presence they can turn to and talk to at any time.

### 2.1.2. Eye tracking protocol

The eye tracking protocol is a free viewing task: we show 38 images to each subject with no particular instruction while we record the gaze position with an eye tracker. The images are projected on screen for 4 sec, and a grey screen appears for 2 sec between 2 images. This grey screen has 2 goals: the first one is to allow the eyes to rest before the next image because the brightness of the screen can cause eye strain; and the second one is to minimize the impact of the previous image on the gaze attention on the next one. Based on this methodology, the experiment lasts 3 min 46 sec, which may not seem like much, but in reality is long enough for an autistic audience.

For autistic people, it is indeed sometimes difficult to stay quietly seated in front of a screen, looking at images they didn't choose. We had to consider this when we developed our protocol, and even with a particular attention given to the experiment duration, it was impossible for 5 subjects to finish it. They have stood up and left the room before the end, so we did not retain their data for the analysis and they do not appear in Table 1. One of them explained that the screen strained his eyes, others that it was too long for them and others just stood up and walked on the room and finally left it. They were equally distributed along the autism spectrum as 2 of them have very strong difficulties, 2 others are much more autonomous and the last one is in the middle, so

<table><caption>**Table 1**

Statistics about the participants to the experiment.</caption><thead><tr><th>Institution</th><th>Number of subjects</th><th>Mean age</th><th>[Male; Female]</th><th>Type of care</th></tr></thead><tbody><tr><td>1</td><td>15</td><td>16,1 ± 3,2</td><td>[13;2]</td><td>Day care</td></tr><tr><td>2</td><td>16</td><td>36,25 ±<br>10,25</td><td>[12;4]</td><td>Full time care</td></tr><tr><td>3</td><td>13</td><td>11,15 ±<br>3,53</td><td>[12;1]</td><td>Day and full<br>time care</td></tr><tr><td>4</td><td>8</td><td>15,62 ±<br>5,78</td><td>[6;2]</td><td>Day and full<br>time care</td></tr></tbody></table>
that their exclusion does not affect the representativity of our popula-
tion. Nevertheless, we are talking about a small minority of subjects, and
we have done our best to make the experience as fun and fluid as
possible, so that we can acquire data on as wide a range of subjects as
possible.

Another tricky aspect of this experiment was the calibration phase of
the eye tracker required before the proper recording. An eye tracker
emits infrared light towards the eyes, and then a camera captures the
reflection of this light on the cornea and the retina. By analyzing the
position and movement of these reflections, the eye tracker can deter-
mine where the person is looking. However, the morphology of the eye is
unique for each person, so the device needs to be calibrated to make a
precise link between the position of the reflection and the actual position
of the gaze on the screen. This calibration process involves the subject to
focus on specific points on the screen or in the environment while the
eye tracker records how their eyes respond. Usually, it uses 5 or 9
different point locations for the calibration followed by 4 additional
ones to validate it. However, the request we made for them to fix their
gaze on a point can be challenging. Indeed, this task represents a form of
social interaction, requiring visual engagement, which individuals with
autism typically tend to avoid; consequently, some preferred to avert
their gaze from the screen. In this setting, although visual engagement is
facilitated by the computer's neutral intermediary, difficulty persists for
some. Thus, we had to find strategies to capture their attention. We then
sought to make this request in the most implicit way, by conveying it
through an animated gif featuring a minion (from the animated movie
Despicable Me), jumping onto the screen accompanied by a sound effect.
Nevertheless, even with this fun way of calibrating the device, it was
very difficult to complete this step correctly for most of the subjects.
Therefore, we decided to reduce the number of calibration points,
keeping only 2 of them but we kept the 4 validation points to ensure
quality. It is indeed possible to reduce the number of calibration points
without decreasing the accuracy if the targets are well placed [28].
Combining these 2 strategies, and with encouragement it has become
possible to correctly calibrate the eye tracker for most of the subjects.
For those for whom this approach was not successful, we did not retain
the data for further analysis.

The images presented to subjects were divided into 2 different sets: the neutral one and the affinity one. The neutral dataset is composed of 28 images expected to be as neutral as possible. These images represent scenes that do not evoke strong emotions or reactions, as they are typically ordinary, such as landscapes, interior design, or scenes with low meaning. The goal is to provide a panel of what they encounter in their everyday life regardless of age or personal experience. You can see some of the neutral images in Fig. 2-1. They were viewed by all the subjects, which made it difficult to find images that don't represent someone's affinity.

The second set of images is the affinity dataset. Unlike neutral ones, the affinity images are individually tailored to each subject based on their affinity. As a result, each image is only seen by one subject. We chose these images according to the information provided by the caregivers, and what the subjects agreed to show us about their affinities to be as precise as possible. For example, we took pictures of the tractor of one of the institutions, or the gate of another, or the crafts or artwork done by some of the subjects. A panel of affinity images is presented in Fig. 2-2.

About the organization of the images, we chose to display 3 neutral
images, followed by 1 affinity image, then 2 more neutral images, before

showing another affinity one and so on until the end. The idea is to have
an equal distribution of images all along the experiment duration. On
the one hand, this allows us to reproduce real-life conditions where they
are more exposed to everyday stimuli than to their affinity, which is
important to get results usable for caregivers, and on the other hand, it
allows us to reduce the emotional charge that may be associated with
their affinity. It happened frequently that the arousal due to visualiza-
tion of affinity images causes physical movements such as contact with
the screen or eye tracker, which can be dangerous for the experimental
equipment. This protocol is the same as the one described in [23].

In addition to the eye tracking data, we also recorded the depth
between the subjects and the screen during the experiment. It has been
previously noticed that individuals with ASD find it difficult to remain
seated quietly during the entire duration of the experiment, indeed most
of them move. At times, the observed movements are stereotyped,
serving as a means to reduce the arousal. Usually, those repetitive
movements occurred in reaction to the stimuli presented on the screen.
Some subjects did hand-flapping (stereotyped movements) as their af-
finity appeared, some pointed at the images, or brought their nose so
close to the screen that the eye tracker could no longer detect their gaze.
Those movements are clues about the attention paid by the subjects and
can also shed light on a lack of eye tracking data. We have therefore
recorded them using a Kinect camera as videos of greyscale depth maps.
These videos are not precise enough to identify the subjects, but they are
sufficient to detect the variations in their position.

We used an eye tracker Tobii Pro X3-120 eye tracker having a sam-
pling rate of 120 Hz. The stimuli were displayed on a Dell Ultrasharp 27
USB-C Hub Monitor, which is a 27" ultra HD screen. In the different
institutions, we couldn't benefit from height adjustable chairs, so that
the subjects sat on simple chairs and the eye tracker was mounted on a
base with adjustable orientation positioned just below the screen. The
subjects sat between 60 and 80 cm from the screen to maximize visual
comfort, and gaze tracking. We could not reproduce the same room
illumination in all the institutions, however we set up the eye tracker to
have the best possible conditions. The depth was recorded using a Kinect
for Xbox One, which has an optimal precision between 1 and 2 m [29].
We have thus positioned it above and slightly behind the screen. To
synchronize the gaze and depth recordings, we used the clock of the
control computer. You can see the details of the experimental material in
Fig. 2–3.

## 2.2. Data analysis

2.2.1. *Collected data pre-processing*

The recorded data first need to be preprocessed before the statistical
analysis. This pre-processing has 2 main goals: the first one is to make
eye position and depth data analyzable and interpretable, while the
second one is to remove all the data that are not reliable. The method-
ology is explained in the next subsections.

2.2.1.1. *Eye tracking data pre-processing.* The eye tracker records the gaze position, but this information cannot tell us anything about the subjects’ visual attention without translating it into visual movements. The first step of the pre-processing was therefore to make the difference between these 3 eye movements fixations, saccades and blinks. The blinks are easy to detect because the eyelids cover the eyes, making them undetectable for a short time. Then, there are several methods for differentiating between fixations and saccades[30]. We used the default

<figure><img src="image_6.png" /><figcaption>Fig. 2–1. Examples of neutral images showed to all the subjects.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Fig. 2-2. Examples of affinity images. Each image has been selected for one particular subject.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 2-3. Diagram of experimental set-up. (a) The Kinect camera; (b) The presentation screen; (c) The Tobii Pro X3-120 eye tracker; (d) the control computer.</figcaption></figure>

method of the Tobii Pro software algorithm [31], which is a velocity threshold technic. As the gaze position is recorded at a precise moment, it is possible, in measuring the distance between 2 gaze points, to deduce a speed. Using a threshold of 20°.s⁻¹, fixations are points with a speed below this threshold and saccades are the others. To reinforce the reliability of this distinction, there is also a minimum threshold of 60 ms on the duration of fixations.

Another pre-processing step we undertook was to exclude the first projected image from the analysis. Despite the specific calibration strategy employed, this stage remained a bit tricky. It was difficult to get them to watch the calibration point, so we attempted to induce their attention by making little noises or pointing at the screen. This was necessary to get a calibration as precise as possible. However, it has an impact on the natural visual attention deployed in the very beginning of the experiment. Usually, the subjects don't maintain constant eye contact with the screen, their gaze drifts around the room so that it is not always well tracked. Nevertheless, with our encouragement, they gaze at the screen much more during the calibration, and by extension, during the presentation of the first image. This introduces a bias in the deployed visual attention. As we are interested in the subjects' spontaneous visual engagement, we have decided to exclude this first image from our study.

2.2.1.2. *Depth data pre-processing.* The recorded depth videos are greyscale videos. We cannot know the precise distance between the subject and the screen. All that we know is that darker greyscales are for shorter distances. This is not a problem, as we are interested in the body movements, which means the variations in grey levels. However, the subjects are not the only ones in the Kinect's field; it also records the content of the room. Moreover, some subjects move a lot during the experiment sometimes even stand and sit again, and they are rarely alone in front of the screen, their favorite caregiver or one of the psychologists of the project sit next to them. The first step was thus to identify the subject on each depth frame. To do so, we used a simple segmentation pipeline:

1. First, we clustered each frame into 4 different grey levels using the k-means algorithm. The darker one contains the screen; the second one

is for the subject and his supporting partner; and the 2 last ones are for the background.

2. Then we binarize the frame, keeping only the second grey level. We then apply morphological opening to separate the subject from his surroundings, and we decompose the result into connected components.

3. On the first frame, as we asked the subject to sit in front of the screen, we know that he is positioned laterally in the middle, and in the lower third of the Kinect field of view. We thus keep only the connected component which barycenter is the closest to this point on the first frame. On the next ones, we keep the connected component which barycenter is the closest to the barycenter of the final mask of the previous frame.

4. Finally, we apply a morphological closing to remove potential holes and get the final mask.

This workflow is summarized in Fig. 2-4.

For videos where it is particularly difficult to make the difference between the subject and his partner, we used a mask to ignore the pixels that are too far to the right or left of the frame. The depth variations were then computed on the final masks only.

### 2.2.2. Statistical analysis

A previous study [23] showed that the gaze behavior of ASD people facing their affinity can be different, however this difference is not the same for all subjects. We have thus decided to explore what these differences can be, and how they are expressed according to the specific characteristics of each individual.

2.2.2.1. *Subjects clustering.* The first step to analyze all the data was then to group the subjects based on criteria we believed might influence their relationship to affinity. We established with psychologists 7 different criteria within which we divided all the subjects into 2 to 4 groups.

**Type of affinity:** An affinity can be anything. This means it can be an object or a person from the real world, as well as a fictional character. Our experimental protocol requires to project images of the subjects' affinities onto a screen. For subjects who elected an affinity which is already digital, its representation onscreen is closest to the real object
<figure><img src="image_9.png" /><figcaption>Fig. 2-4. Flowchart of the subject's segmentation process.</figcaption></figure>

than those who have an affinity in the real world. This may affect the potential gaze involvement differently. The two groups for those criteria are thus: Numerical affinity (24 subjects), and Non numerical affinity (28 subjects).

**Age:** The people's age affects the way they look at their environment [32]. In addition to that, the affinity is not a simple passion; it builds up gradually over several years. For the youngest subjects, this work is usually at its very beginning while for oldest one it is much more developed. Besides, youngest subjects have often less patience, which may have an impact on their visual attention toward their affinity. On the other hand, older subjects grew up at a time when knowledge about autism, and particularly about affinities, was much less taken into consideration. Therefore, they had fewer opportunities to develop their affinity, and this may affect their reaction toward it. We have defined 4 different groups for this criterion: 6-12 years old (10 subjects), 13-18 years old (16 subjects), 19-25 years old (12 subjects), and 26 years old and more (14 subjects).

**Establishment of a border:** For autistic subjects the border is made of an object or a person, real or fictive of their choosing, where they locate what might invade their own body, such as gaze or voice. This

border serves not only to establish a boundary between themselves and the surrounding world, but also to enable mediation with others. Depending on how this border is developed, he/she will have more or less difficulties with interactions. When the border is less developed, he/she can feel invaded by his/her environment, whether it is a person or even something that generates too strong an emotion. We have divided here the subjects into 3 groups: Border widening (20 subjects), Outline of a border (17 subjects) and Precarious border (15 subjects).

**Return of enjoyment to the body:** Whatever the elaboration of the autistic border, it happens that the person feels invaded. In this case, the excess emotion flows back into the body, sometimes expressing itself with a certain aggressiveness. Some of them hit those around them to release this emotional overload, as a protection. By targeting the other person, they seek to alleviate this excessive presence or demand. For other ASD persons, the return of the enjoyment may express itself in the form of self-mutilation. The invasion is such that they try to extract it from their own body, which is a sign of great anxiety. Finally, for some autistic people this return of enjoyment is undirected. They seem less invaded because they do not need to target others or themselves for protection. The 3 groups we have created are thus Hetero-aggressive (22 subjects), Self-mutilation (12 subjects), and Undirected (18 subjects).

**Affinity as a living double:** Some autistic persons elect an affinity that is or seems to be alive. It can be an animal, a real person, or a fictional character. This type of affinity enables the person to establish a connection with their object, facilitating the integration of double's dynamics through imitation. This mimicry makes it easier for them to express themselves and connect with those around them, even if it is by copying. They embody the behaviors and/or words of these doubles, in order to compensate for their own motor [33] and speech difficulties. The 2 groups for this are Yes (30 subjects) and No (22 subjects).

**Access to speech:** During our research, we observed that subjects with access to speech also have a more elaborate and better-defined affinity. The ability to speak enables them to exchange and share this affinity, improving their social interactions. Nevertheless, the opposite is as relevant. Access to speech and the development of affinity contributes to the mutual complexification of one another. For this criterion the 2 groups are Yes (24 subjects) and No (28 subjects).

**Use of a partner:** In most cases, a caregiver, or at least a psychologist of the project accompanied the subjects for the experiment. This preferred partner provided a reassuring presence for this unusual activity. However, not all subjects got the same use of their partner. Some exchanged a look, a word, or a gesture, while others did not involve this help at all, either because they were not capable of it, or because they did not need it. The way subjects use their partner tell us about the strength of their autistic border. We have defined the two groups Yes (35 subjects) and No (17 subjects) for this criteria.

A summary of the statistics for all the groups is visible in Table 2.

We calculated the correlation between the subjects assigned to each criterion in order to assess their relevance. We have defined the correlation between the two groups A and B as:

$$Corr(A, B) = \frac{\#(A \cap B)}{\#(A \cup B)}$$

The results are presented in the matrix Fig. 2-5.

You can see in this matrix that the strongest correlation is for the border widening and the ability to speak criteria (0.69). We have mentioned earlier that the efficiency of the autistic border plays a major role in the subject's ability to open up to others, this high correlation supports this hypothesis. There is also a relatively high correlation between Numerical affinity and Affinity as a living double and between Non numerical affinity and No identification to affinity groups (0.57 and 0.53 respectively). Here again, this is consistent with the clinical hypotheses formulated. Numerical affinities are often movies' characters that are easy to identify with, while not numerical ones are more centered on objects and activities. There is another relevant correlation
<table><caption>**Table 2**
Statistics about the subjects in each group.</caption><thead><tr><th>Criteria</th><th>Group</th><th>Number of subjects</th><th>Mean age</th><th>[Male; Female]</th></tr></thead><tbody><tr><td rowspan="2">Type of affinity</td><td>Numerical</td><td>24</td><td>17.25 ± 9.46</td><td>[21;3]</td></tr><tr><td>Not numerical</td><td>28</td><td>24.18 ± 13.61</td><td>[22;6]</td></tr><tr><td rowspan="4">Age</td><td>6–12</td><td>10</td><td>8.40 ± 1.17</td><td>[9;1]</td></tr><tr><td>13–18</td><td>16</td><td>14.43 ± 1.63</td><td>[15;1]</td></tr><tr><td>19–25</td><td>12</td><td>20.08 ± 1.98</td><td>[8;4]</td></tr><tr><td>26+</td><td>14</td><td>38.21 ± 9.38</td><td>[11;3]</td></tr><tr><td rowspan="4">Establishment of a border</td><td>Border widening</td><td>20</td><td>20.95 ± 9.59</td><td>[17;3]</td></tr><tr><td>Outline of a border</td><td>17</td><td>21.82 ± 14.52</td><td>[15;2]</td></tr><tr><td>Precarious border</td><td>15</td><td>20.07 ± 13.49</td><td>[11;4]</td></tr><tr><td>Return of enjoyment to the body</td><td>Hetero-aggressive</td><td>22</td><td>19.50 ± 11.69</td><td>[19;3]</td></tr><tr><td rowspan="3">Affinity as a living double</td><td>Self-mutilation</td><td>12</td><td>27.25 ± 13.80</td><td>[8;4]</td></tr><tr><td>Undirected</td><td>18</td><td>18.61 ± 11.10</td><td>[16;2]</td></tr><tr><td>Yes</td><td>30</td><td>17.83 ± 9.11</td><td>[24;6]</td></tr><tr><td rowspan="2">Access to speech</td><td>No</td><td>22</td><td>25.27 ± 14.76</td><td>[19;3]</td></tr><tr><td>Yes</td><td>24</td><td>19.46 ± 9.56</td><td>[20;4]</td></tr><tr><td rowspan="2">Use of a partner</td><td>No</td><td>28</td><td>22.29 ± 14.24</td><td>[23;5]</td></tr><tr><td>Yes</td><td>35</td><td>19.66 ± 10.69</td><td>[30;5]</td></tr><tr><td></td><td>No</td><td>17</td><td>23.71 ± 15.02</td><td>[13;4]</td></tr></tbody></table>

of 0,51 between Use of a partner and Numerical Affinity. This might support the hypothesis that using digital devices can enhance openness to the world and social connection, as those subjects also seem to be more into interaction when their affinity is numerical.

The other correlation values are all quite small, which means that the groups are relatively disjoint. They are thus well designed to study the impact of each criterion on the visual behavior of subjects depending on whether they are looking at their affinity or not.

### 2.2.2.2. Metrics.
Our goal is to detect potential variations in the gaze attention that the subjects deploy toward stimuli. To do so, we used common eye tracking metrics:

* Tracking ratio: it is the ratio of time during which the subject's gaze is properly tracked. It is usually used as a quality of eye tracking recording metric, however, in the case of an autistic audience, it is also indicative of visual attention [34]. It is indeed frequent that subjects decide to look away from the screen. It leads to poor tracking ratios even if the eye tracker had no problem to detect their gaze. However, this is still an indicator of quality, thus we decided not to consider stimuli with a tracking ratio lower than 50 % (simple thresholding) so that the other metrics remain meaningful (see Table 3 for the details of filtered stimuli).

* Fixations number and duration: the fixations are necessary for the brain to process the visual information. They are thus a big clue for the visual attention [17,15,20,16].

* Saccades amplitude: to process the entire visual field, we use saccades to let the eyes have an accurate perception of it. The size of these saccades can then tell us about the interest of subjects for the stimuli. It is computed as follows:

$$ \text{saccade amplitude} = \frac{\sqrt{(x_{\text{end}} - x_{\text{begin}})^2 + (y_{\text{end}} - y_{\text{begin}})^2}}{\text{NPPD}} $$

with $(x_{\text{begin}}, y_{\text{begin}})$ the coordinates of the previous fixation, $(x_{\text{end}}, y_{\text{end}})$ the coordinates of the next one, and NPPD the number of pixels per degree, which can be computed with

$$ \text{NPPD} = \frac{\text{width}_{\text{image}}}{2 * \arctan\left(\frac{0.5 * \text{width}_{\text{screen}}}{d}\right)} $$

where *d* is the distance between the subject and the screen.

In addition to these eye tracking metrics, we also computed the depths variations between the subjects and the screen during the experiment using the depth videos and masks previously extracted. For each frame, we define the depth variation as the difference between the maximum depth reached and the current depth:

$$ \Delta depth(t) = depth_{\text{max}} - depth(t) $$

The depth is represented as the mean grey level of pixels included in the subject's mask. As shorter distances are represented with darker grey levels (smaller values), higher Δdepth values means that the subject is closer to the screen.

These 5 metrics are computed for all the images over all the projection time, but also independently for the 3 thirds (named early, middle and late) of this duration. The goal is to detect the global differences in gaze behavior as well as smaller ones depicting the variations in attention allocation between bottom-up attention (stimuli-driven), top-down attention (task-driven) and a mix of these 2. The early period corresponds in some extent to the bottom-up attention only, the middle period to the top-down attention while the late periods implies mixed attention.

### 2.2.2.3. Detection of significant differences.
We have compared the values of the previously defined metrics on the neutral stimuli and on the affinity ones for all the created groups of subjects. We have used the Mann-Whitney test [35] to detect the significant differences between the 2 sets of stimuli. According to the D'Agostino test, the distributions of our metrics are not normal. As we cannot assume a specific distribution of values, the non-parametric Mann-Whitney U test is the best suited to test whether the type of stimuli has an influence on visual engagement or not [36]. We set the significance threshold to $p = 0.05$.

## 3. Results

The results of the statistical analysis on all the groups are presented in Table 4.

The results are not all significant for all the groups, however, we got significant results for all the criteria. The only metric, which is never significant over the entire stimuli observation duration, is the depth between the subject and the screen. This probably means that the variations in position when looking at affinity images are not consistent for the subjects of a same group, whatever the criteria considered. Now, we can zoom more precisely on the results for each criterion.

**Type of affinity:** Subjects with a numerical affinity show significantly shorter fixations and longer saccades on affinity images. The combination of these 2 results mean that their eyes move faster from one fixation point to the next one and that these points are further apart on affinity stimuli. This is a clue for a higher attention for these images. For subjects with a non-numerical affinity, there is no significant result
<figure><img src="image_10.png" /><figcaption>Fig. 2–5. Correlation matrix between all the criteria. A lighter colour indicates a weaker correlation, and the redder the colour, the stronger the correlation. Black lines separate the different categories.</figcaption></figure>

<table><caption>**Table 3**
Details of the filtered/conserved stimuli.</caption><thead><tr><th rowspan="2">Institution</th><th colspan="2">Filtered stimuli</th><th colspan="2">Conserved stimuli</th><th rowspan="2">Proportion of filtering</th></tr><tr><th>Neutral</th><th>Affinity</th><th>Neutral</th><th>Affinity</th></tr></thead><tbody><tr><td>1</td><td>246</td><td>93</td><td>159</td><td>57</td><td>61.41 %</td></tr><tr><td>2</td><td>373</td><td>133</td><td>84</td><td>35</td><td>80.96 %</td></tr><tr><td>3</td><td>292</td><td>102</td><td>59</td><td>27</td><td>82.08 %</td></tr><tr><td>4</td><td>268</td><td>73</td><td>20</td><td>7</td><td>92.66 %</td></tr></tbody></table>

except for the saccade amplitude that are longer on the middle period of the observations duration (see Table 5). However in the absence of any other significant result, the outcome on the middle period is too weak to conclude anything about the effect of the affinity on the attention.

**Age:** For the youngest subjects (6–12 years old), no significant result appears for any metric. They are probably too young to have a fairly well-developed affinity to modify their attention when they face it. For 13–18 years old subjects, the eyes are less well tracked, the fixations are

fewer and shorter, and the saccades are longer on affinity images, which is paradoxical. The combination of a lower tracking ratio, and fewer and shorter saccades would be a sign of a withdrawal of the gaze, whereas the combination of shorter fixations and longer saccades shows a greater exploration of the affinity images. This paradox can be explained by an affinity that becomes stronger as the subjects get older, while it is still difficult for them to accept the request and to share their affinity. It generates thus a higher attention and at the same time an anxiety, which expresses with a gaze withdrawal. As the subjects get older (19–25), the results become more consistent as the fixations are shorter and the saccades longer on affinities. They deploy a stronger attention for these stimuli. Finally, for older subjects, there is no significant result over the entire observation duration, however the depth is significant on late period (see Table 6).

As the result for the depth is almost significant for the entire observation duration, as well as for the three periods separately, we can conclude that the subjects stand closer to the screen when their affinity is displayed. This also is a clue of a higher attention as they decide to move closer to the screen, probably to get physically closer to their
<caption>**Table 4**</caption>

Results of the experiment on all the metrics. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. **Bold** values indicate significant results.

<table><caption>**Table 5**</caption><thead><tr><th>Criteria</th><th>Group</th><th>Tracking ratio</th><th>Fixation number</th><th>Fixation duration</th><th>Saccade amplitude</th><th>Depth</th></tr></thead><tbody><tr><td rowspan="2">Type of affinity</td><td>Numerical</td><td>[58.80%;56.03%)<br>p = 0.20</td><td>[9.27;8.31]<br>p = 0.15</td><td>[174.86 ms;126.08 ms]<br>p = 0.008</td><td>[7.22°;8.70°]<br>p = 0.01</td><td>[7.32;7.79]<br>p = 0.82</td></tr><tr><td>Not numerical</td><td>[56.67%;55.88%)<br>p = 0.15</td><td>[8.65;8.05]<br>p = 0.36</td><td>[138.57 ms;119.75 ms]<br>p = 0.15</td><td>[6.82°;7.36°]<br>p = 0.22</td><td>[6.18;6.60]<br>p = 0.60</td></tr><tr><td rowspan="4">Age</td><td>6-12</td><td>[56.17%;55.12%)<br>p = 0.37</td><td>[7.35;7.50]<br>p = 0.88</td><td>[124.27 ms;117.56 ms]<br>p = 0.95</td><td>[8.18°;7.05°]<br>p = 0.38</td><td>[3.79;4.69]<br>p = 0.39</td></tr><tr><td>13-18</td><td>[55.99%;54.16%)<br>p = 0.01</td><td>[8.82;6.29]<br>p = 0.0008</td><td>[146.12 ms;106.26 ms]<br>p = 0.0003</td><td>[6.82°;8.53°]<br>p = 0.04</td><td>[7.61;5.51]<br>p = 0.14</td></tr><tr><td>19-25</td><td>[58.54%;58.11%)<br>p = 0.57</td><td>[10.90;10.33]<br>p = 0.45</td><td>[189.86 ms;143.83 ms]<br>p = 0.17</td><td>[6.97°;8.82°]<br>p = 0.002</td><td>[4.67;5.31]<br>p = 0.59</td></tr><tr><td>26+</td><td>[55.39%;55.03%)<br>p = 0.61</td><td>[6.99;7.24]<br>p = 0.73</td><td>[124.89 ms;110.80 ms]<br>p = 0.97</td><td>[6.61°;6.72°]<br>p = 0.69</td><td>[7.94;10.43]<br>p = 0.06</td></tr><tr><td rowspan="3">Establishment of a border</td><td>Border widening</td><td>[56.63%;56.25%)<br>p = 0.53</td><td>[8.88;8.47]<br>p = 0.41</td><td>[169.03 ms;113.74 ms]<br>p = 0.01</td><td>[7.18°;8.33°]<br>p = 0.04</td><td>[6.14;7.68]<br>p = 0.22</td></tr><tr><td>Outline of a border</td><td>[57.49%;56.35%)<br>p = 0.19</td><td>[9.52;8.24]<br>p = 0.16</td><td>[144.93 ms;126.73 ms]<br>p = 0.45</td><td>[6.63°;7.37°]<br>p = 0.32</td><td>[6.13;5.51]<br>p = 0.79</td></tr><tr><td>Precarious border</td><td>[55.90%;54.65%)<br>p = 0.12</td><td>[8.13;7.32]<br>p = 0.32</td><td>[133.71 ms;114.01 ms]<br>p = 0.22</td><td>[7.05°;7.98°]<br>p = 0.23</td><td>[7.85;7.89]<br>p = 0.92</td></tr><tr><td rowspan="3">Return of enjoyment to the body</td><td>Hetero-aggressive</td><td>[56.21%;56.11%)<br>p = 0.95</td><td>[8.14;7.25]<br>p = 0.26</td><td>[134.61 ms;110.48 ms]<br>p = 0.17</td><td>[7.08°;7.23°]<br>p = 0.94</td><td>[6.51;8.28]<br>p = 0.17</td></tr><tr><td>Self-mutilation</td><td>[56.07%;54.64%)<br>p = 0.03</td><td>[8.24;7.00]<br>p = 0.10</td><td>[134.47 ms;110.39 ms]<br>p = 0.06</td><td>[6.30°;8.19°]<br>p = 0.01</td><td>[6.62;7.45]<br>p = 0.35</td></tr><tr><td>Undirected</td><td>[57.42%;56.90%)<br>p = 0.47</td><td>[9.74;9.81]<br>p = 0.92</td><td>[174.98 ms;141.95 ms]<br>p = 0.45</td><td>[7.31°;8.41°]<br>p = 0.02</td><td>[6.64;4.77]<br>p = 0.10</td></tr><tr><td rowspan="2">Affinity as a living double</td><td>Yes</td><td>[57.18%;56.28%)<br>p = 0.09</td><td>[9.64;8.61]<br>p = 0.05</td><td>[162.64 ms;125.39 ms]<br>p = 0.007</td><td>[7.08°;8.03°]<br>p = 0.04</td><td>[7.02;7.85]<br>p = 0.62</td></tr><tr><td>No</td><td>[55.98%;55.28%)<br>p = 0.33</td><td>[7.70;7.25]<br>p = 0.70</td><td>[137.68 ms;117.22 ms]<br>p = 0.35</td><td>[6.82°;7.92°]<br>p = 0.09</td><td>[6.03;5.86]<br>p = 0.79</td></tr><tr><td rowspan="2">Access to speech</td><td>Yes</td><td>[57.37%;57.01%)<br>p = 0.53</td><td>[9.71;9.21]<br>p = 0.39</td><td>[168.79 ms;128.80 ms]<br>p = 0.04</td><td>[7.04°;8.09°]<br>p = 0.04</td><td>[6.40;7.73]<br>p = 0.31</td></tr><tr><td>No</td><td>[56.01%;54.56%)<br>p = 0.01</td><td>[8.01;6.79]<br>p = 0.05</td><td>[135.88 ms;114.72 ms]<br>p = 0.07</td><td>[6.91°;7.87°]<br>p = 0.12</td><td>[6.74;6.50]<br>p = 0.98</td></tr><tr><td rowspan="2">Use of a partner</td><td>Yes</td><td>[56.58%;55.81%)<br>p = 0.14</td><td>[8.64;7.97]<br>p = 0.17</td><td>[138.22 ms;115.07 ms]<br>p = 0.04</td><td>[6.75°;7.73°]<br>p = 0.01</td><td>[7.74;8.41]<br>p = 0.73</td></tr><tr><td>No</td><td>[56.93%;56.16%)<br>p = 0.24</td><td>[9.27;8.47]<br>p = 0.26</td><td>[174.53 ms;134.30 ms]<br>p = 0.16</td><td>[7.30°;8.39°]<br>p = 0.15</td><td>[4.69;4.72]<br>p = 0.45</td></tr></tbody></table>

Saccade amplitude values for the subjects with a non-numerical affinity over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. **Bold** values indicate significant results.

<table><thead><tr><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>[7.14°;8.13°]<br>p = 0.38</td><td>[6.99°;7.87°]<br>p = 0.04</td><td>[7.10°;7.20°]<br>p = 0.24</td></tr></tbody></table>

affinity. This increased attention is not expressed in the same way depending on the age group but remains relevant once the affinity has had time to develop.

<caption>**Table 6**</caption>

Depth values for the 19 and more years old subjects over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. **Bold** values indicate significant results.

<table><thead><tr><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>[8.27;10.51]<br>p = 0.06</td><td>[7.58;10.09]<br>p = 0.08</td><td>[7.48;10.13]<br>p = 0.04</td></tr></tbody></table>

**Establishment of a border:** Subjects whose autistic border is widening show significantly shorter fixations and longer saccades on affinities. As we have already explained, this means deeper exploration of these stimuli compared to neutral ones, and thus a higher attention. When the border is more elaborated, it allows the subject to develop knowledge, navigate and interact. When the affinity is well defined, it is likely to elicit a greater attention from the subjects. For subjects whose border is just outlined, we detected no significant difference between the two sets of images: the affinity seems to have no influence on the gaze attention. Finally, for subjects with a precarious border, once again we see no significant difference for any metrics for the entire observation duration, however some differences appear when we focus on the three observation periods (see Table 7).

During the early period, the gaze behavior is the same on all the stimuli. Nevertheless, as the observation time increases, differences appear. The saccades become longer on affinity images, and the fixations become first shorter, and then fewer. These are ambiguous results, but as with young subjects, they can be explained by a greater attention to their affinity combined with anxiety generated by the surprise created by the apparition of the affinity image. This anxiety seems to take precedence over interest as the observation time increases. The effectiveness of the autistic border plays a role in the variation in attention that subjects can
<caption>**Table 7**</caption>

Fixations number and duration and saccades amplitude for the subjects with a precarious border over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. Bold values indicate significant results.

<table><thead><tr><th>Metric</th><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>Fixation number</td><td>[2.94;2.67]<br>p = 0.40</td><td>[3.00;2.92]<br>p = 0.82</td><td>[3.32;2.58]<br>p = 0.05</td></tr><tr><td>Fixation duration</td><td>[122.20<br>ms;123.49 ms]<br>p = 0.82</td><td>[149.41<br>ms;101.07 ms]<br>p = 0.007</td><td>[143.18<br>ms;117.45 ms]<br>p = 0.33</td></tr><tr><td>Saccade amplitude</td><td>[7.17°;7.33°]<br>p = 0.90</td><td>[7.39°;7.40°]<br>p = 0.05</td><td>[6.91°;9.20°]<br>p = 0.02</td></tr></tbody></table>

devote to their affinity.

**Return of enjoyment to the body:** For hetero-aggressive subjects we see no discrepancy in the gaze behavior when they look at their affinity. We detected only one significant difference in the number of fixations during the late period of observation (see Table 8). The results are weak, but they show a desire to withdraw the gaze on affinities in line with the difficulty and anxiety generated by the other's request in these subjects. It may be indicative of their difficulty in forming a connection with others.

For subjects who self-harm, we can notice a lower tracking ratio and longer saccades on affinity images. If we zoom on the three periods, we also find significantly shorter fixations on the late period (see Table 9).

Once again, we find this paradoxical gaze behavior, which reflects both a desire to withdraw the gaze and an increased exploration of affinity stimuli, reflecting greater attention. This is surprising, given that we thought these subjects hadn't invested much in their affinity. If this had been the case, we would either have had no significant difference, or a withdrawal of the gaze generated by the anxiety of the request. The longer saccades, and shorter fixations at the end of the observation duration show that, even if there is anxiety, there is also an increased attention toward these stimuli.

Next, for subjects whose return of enjoyment is not directed, the only significant result is longer saccades on affinities. This again reflects increased interest in these stimuli and greater attentional engagement consistent with their ability to manage what may affect them.

**Affinity as a living double:** Subjects who elected an affinity that can be considered as a living double show significantly shorter and fewer fixations as well as longer saccades on affinity images. We assumed that identification with affinity would lead to greater attention for these stimuli, and this is confirmed here. However, there also appears to be a withdrawal of gaze from affinities: the tracking ratio is almost significantly lower and there are fewer fixations. This is probably due to the anxiety generated by the apparition of the affinity because a living double does not necessarily imply an efficient border, capable of withstanding the weight of demand and social interaction. For subjects whose affinity does not allow to connect to, there is no discrepancy between the two sets of images, except in the saccade amplitude of the middle period (see Table 10). It would be a sign of greater attention, nevertheless this is not enough to conclude that affinity has an influence on the visual attention deployed for those subjects.

**Access to speech:** Subjects who are able to speak exhibit shorter fixations and longer saccades on affinities. They deploy an increased

<caption>**Table 8**</caption>

Fixations number values for hetero-aggressive subjects over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. Bold values indicate significant results.

<table><caption>**Table 9**</caption><thead><tr><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>[3.19;2.62]<br>p = 0.07</td><td>[2.96;3.24]<br>p = 0.41</td><td>[3.46;2.78]<br>p = 0.04</td></tr></tbody></table>

Fixations duration values for subjects who harm themselves over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. Bold values indicate significant results.

<table><caption>**Table 10**</caption><thead><tr><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>[126.38 ms;108.15 ms]<br>p = 0.32</td><td>[133.87 ms;108.10 ms]<br>p = 0.31</td><td>[156.99 ms;110.14 ms]<br>p = 0.03</td></tr></tbody></table>

Saccade amplitude values for the subjects with an affinity which they can not connect to, over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. Bold values indicate significant results.

<table><thead><tr><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>[6.68°;8.55°]<br>p = 0.14</td><td>[7.28°;9.06°]<br>p = 0.02</td><td>[6.81°;7.29°]<br>p = 0.19</td></tr></tbody></table>

attention toward these stimuli as they explore them more precisely, indicating a higher level of engagement with their autistic object. A well-defined affinity is likely to facilitate access to speech, as it serves as a border providing protection, regulation, and mediation; thus, reducing the need for withdrawal behavior. On the contrary, subjects who hold back speech show a lower tracking ratio and fewer fixations, which expresses a withdrawal of gaze on affinity images, and probably an anxiety when it arises without them having chosen it. There is still a sign of a greater desire to explore affinities with longer saccades on the middle period (see Table 11), but it is too weak to draw any conclusions.

**Use of a partner:** The results show that subjects who use the support provided by the presence of a caregiver, whether through an exchange of looks, words or physical contacts, have longer saccades and shorter fixations on affinity images. In other words, they pay more attention to these stimuli. On the contrary, there is no significant difference detected for subjects who do not use the presence of their partner. They neither engage more their gaze, nor withdraw it. This would confirm that the role of affinity is enhanced when shared with others. If this is not the case, then it becomes a stimulus like any other in terms of attention.

The ability for the subjects to engage in address, instead of withdrawing their gaze from the screen and isolating themselves, leads us to suppose the efficiency of the boundary in these individuals.

A summary of the results can be seen in Table 12.

## 4. Conclusion

The role and importance of affinity in autistic subjects has been widely described by patients and psychologists, but without any quantitative measurement of its real impact. We have conducted an eye tracking experiment over 52 autistic patients to detect potential changes in visual behavior and attention, depending on whether they were confronted with neutral or affinity stimuli. We have shown them 28 neutral images and 10 affinity images, while recording their body position and gaze location. Previous study showed that there is not one unique behavior when the affinity arises; the reaction is always very specific to one individual. We have thus tried to detect specific behaviors

<caption>**Table 11**</caption>

Saccade amplitude values for the subjects who cannot speak over the three periods of observation duration. The values represent [mean value on neutral images;mean value on affinity images], and the p value of the Mann-Whitney test. Bold values indicate significant results.

<table><thead><tr><th>Early</th><th>Middle</th><th>Late</th></tr></thead><tbody><tr><td>[6.68°;8.55°]<br>p = 0.14</td><td>[7.28°;9.06°]<br>p = 0.02</td><td>[6.81°;7.29°]<br>p = 0.19</td></tr></tbody></table>
<table><caption>**Table 12**
Summary of the effects of the affinity images on the different groups of subjects.</caption><thead><tr><th></th><th></th><th colspan="2">Higher attention</th></tr><tr><th>Anxiety</th><th>Yes</th><th>Yes</th><th>No</th></tr></thead><tbody><tr><td></td><td>Yes</td><td>Return of enjoyment as self-mutilation<br>13-18 years old<br>Precarious border<br>Affinity as a living double</td><td>Unability to speak</td></tr><tr><td></td><td>No</td><td>Undirected return of enjoyment<br>Access to speech<br>19-25 years old<br>Numerical affinity<br>Border widening<br>Use of the partner</td><td>Hetero-aggressive<br>Not numerical affinity<br>6-12, and more than 26 years old<br>No identification to affinity<br>Outline of a border<br>No use of the partner</td></tr></tbody></table>

linked with some criteria about the autistic features, or the affinity nature.

The gaze behavior varies a lot on the 7 defined criteria, ranging from no difference in visual behavior to paradoxical differences combining an increase in attention and a withdrawal of the gaze. In fact, subjects show two main reactions of varying intensity. On the one hand, we observe heightened visual attention showing a greater exploration of affinity images resulting in longer saccades and shorter fixations. On the other hand, anxiety generated by the unchosen intrusion of the affinity en-genders withdrawal of the subjects reflected in a less well tracked gaze and lower fixations. It seems that the subjects for whom we don't observe superior visual attention on affinity images are also those who have the most difficulty in interactions, or for whom the link to affinity is the weakest. We can also observe that subjects who experience anxiety when affinity appears are often already more withdrawn: they are capable of interacting but choose not to do so. This experiment shows the great variability in the link between autistic individuals and their affinity, as well as the invaluable help that the investigation of visual attention and eye tracking can bring to the study of this link. Another insight from our analysis is that when the results are significant only on a portion of the observation duration, it is always in the middle and/or late periods corresponding to the top-down and mixed attention, meaning that it comes from the subject himself.

Finally, each subject is included in several groups whose reactions may differ. That is what makes everyone's reaction unique. The experiment tends to demonstrate the importance for caregivers to consider the specific characteristics of each individual, in order to adapt and support this very subjective solution accordingly. This approach could result in softer educational strategies and supportive interventions.

## 5. Limitations and Perspectives

Although we paid particular attention to the design of the experimental protocol, some limitations remain. As we explained, the affinity and its usage are always very specific for each autistic people. The constraint of using tools without any contact with the subject forces us to use a screen, which prevents us from reproducing the exact use that the subjects have of their affinity. This induces a bias, as an image of the affinity is not the affinity itself, as it doesn't convey its dynamic nature. Thus, the reaction toward this image and the real affinity may differ. A solution would be to use eye-tracking glasses, however none of the subjects agreed to wear them. It would be interesting to reproduce this experiment with autistic subjects who would be comfortable using such glasses or to use videos of affinities, which would make the experiment longer requiring a different population.

Another limitation lies in the number of subjects included in each group, which is sometimes small which can reduce the statistical power of tests. Despite our study involves one of the most important autistic population for such topic, it would be interesting to reproduce this protocol with a larger sample.

## Funding

This work was supported by the Labex Cominlabs (ANR-10-LABX-07-01).

### Consent to participate

All the institutions, the subjects and their family were properly informed about the experiment and their right to stop at any moment.

### Consent for publication

All the institutions, the subjects and their family were properly informed that this work would be published, but that this publication would fully respect their anonymity. All the co-authors accept this work to be published.

### Ethics approval

This project received the approval of the ethic comity of the University of Rennes 2 (ref 2023-008)

## Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Myriam Cherel, Lu Zhang report financial support was provided by CominLabs. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Data availability

According to the contracts signed with the various institutions, the data collected as part of this study will remain strictly confidential.

## References

[1] M. Maenner, K. Shaw, J. Baio, A. Washington, M. Patrick, M. DiRienzo, P. Dietz, Prevalence of Autism Spectrum Disorder among Children Aged 8 Years — Autism and Developmental Disabilities monitoring Network, 11 Sites, United States, 2016, Morb. Mortal. Wkly Rep. (2020), https://doi.org/10.15585/mmwr.ss6904a1.

[2] World Health Organization. (2015). The ICD-10 classification of mental and behavioural disorders.

[3] Laurent, É. (2015). Affinités électives de l'autistic mind. Dans M. Chérel Perrin, Affinity therapy: nouvelles recherches sur l'autisme (pp. 117-27). Rennes: PUR.

[4] Maleval, J.-C. (2021). *La différence autistique*. Vincennes: Presses universitaires de Vincennes.

[5] L. Kanner, M. Rosenberg, Autistic disturbances of affective contact, Neuropsychiatrie De L'enfance Et De L'adolescence(38) (1990) 65-84.

[6] Laurent, E. (1992). *Lecture critique II. L'autisme et la psychanalyse*. (Vol. Série de la Découverte Freudienne, 8). Toulouse: Presses Uni-versitaires du Mirail.

[7] J.-C. Maleval, *L'autiste, son double et ses objets*, Presses Universitaires De Rennes. (2009).

[8] Williams, D. (1992). *Nobody Nowhere: The Extraordinary Autobiography of an Autistic Girl*. (F. Gérard, Trad.) Doubleday.

[9] Suskind, R. (2014). *Life animated, a story of sidekicks, heroes and autism*. Life, Animated : A Story of Sidekicks, Heroes, and Autism.

[10] Perrin-Chérel, M. (2015). *Affinity Therapy*. Éditions Presses Universitaires de Rennes.

[11] C.L. Caldwell-Harris, C.J. Jordan, Systemizing and special interests: Characterizing the continuum from neurotypical to autism spectrum disorder. (Elsevier, éd.),
Learn. Individ. Differ. 29 (2014) 98–105, https://doi.org/10.1016/j.lindif.2013.10.005.

[12] K.K. Evans, T.S. Horowitz, P. Howe, R. Pedersini, E. Reijnen, Y. Pinto, J.M. Wolfe, Visual attention. (W. O. Library, éd.), Wiley Interdiscip. Rev. Cogn. Sci. 2 (5) (2011) 503–514, https://doi.org/10.1002/wcs.127.

[13] J.F. Rauthmann, C.T. Seubert, P. Sachse, M.R. Furtner, Eyes as windows to the soul: Gazing behavior is related to personality. (Elsevier, éd.), J. Res. Pers. 46 (2) (2012) 147–156, https://doi.org/10.1016/j.jrp.2011.12.010.

[14] B.T. Carter, S.G. Luke, Best practices in eye tracking research. (Elsevier, éd.), Int. J. Psychophysiol. 155 (2020) 49–62, https://doi.org/10.1016/j.ijpsycho.2020.05.010.

[15] C. Ames, S. Fletcher-Watson, A review of methods in the study of attention in autism, Dev. Rev. 52–73 (2010), https://doi.org/10.1016/j.dr.2009.12.003.

[16] M. Sotoodeh, H. Taheri-Torbati, N. Hadjikhani, A. Lassalle, Preserved action recognition in children with autism spectrum disorders: evidence from an EEG and eye-tracking study, Psychophysiology (2021), https://doi.org/10.1111/psyp.13740.

[17] Z. Akhtar, T. Guha, Computational Analysis of Gaze Behavior in Autism during Interaction with Virtual Agents, in: ICASSP 2019–2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2019, https://doi.org/10.1109/ICASSP.2019.8682943.

[18] Q. Su, F. Chen, H. Li, N. Yan, L. Wang, Multimodal Emotion perception in Children with Autism Spectrum Disorder by Eye Tracking Study, IEEE-EMBS Conference on Biomedical Engineering and Sciences (IECBES) (2018), https://doi.org/10.1109/IECBES.2018.8626642.

[19] Song, Y., Hakoda, Y., Sanefuji, W., & Cheng, C. (2015). Can They See It? The Functional Field of View Is Narrower in Individuals with Autism Spectrum Disorder. *PLOS ONE*. Doi: 10.1371/journal.pone.0133237.

[20] N. Sasson, L. Turner-Brown, T. Holtzclaw, K. Lam, J. Bodfish, Children with autism demonstrate circumscribed attention during passive viewing of complex social and nonsocial picture arrays, Autism Res. 31–42 (2008), https://doi.org/10.1002/aur.4.

[21] M. Toutain, N. Dollion, L. Henry, M. Grandgeorge, How do Children and Adolescents with ASD look at animals? A Scoping Review. Children 211 (2024) https://doi.org/10.3390/children11020211.

[22] J. Fournier, M. Outtas, Q. Wang, E. Etchamendy, M. Chérel, L. Zhang, Does personal interests affect visual attention-an eye tracking study, in: 10th European Workshop on Visual Information Processing (EUVIP). IEEE, 2022, https://doi.org/10.1109/EUVIP53989.2022.9922683.

[23] Fournier, J., Etchamendy, E., Chérel, M., Outtas, M., & Zhang, L. (2023). The impact of the affinity on ASD people visual engagement. *Proceedings of the 20th International Conference on Content-based Multimedia Indexing* (pp. 28-33). ACM. Doi: 10.1145/3617233.3617236.

[24] English, M. C., Maybery, M. T., & Visser, T. A. (2024, 05 16). Autistic traits specific to communication ability are associated with performance on a Mooney face detection task. (Springer, Ed.) *Attention, Perception, & Psychophysics*, 1-13. Doi: 10.3758/s13414-024-02902-w.

[25] M. Heo, M.C. English, M.T. Maybery, T.A. Visser, 04 01). Visuospatial cueing differences as a function of autistic traits. (Springer, éd.) *Attention, Percept. Psychophys*. 86 (2024) 1342–1359, https://doi.org/10.3758/s13414-024-02871-0.

[26] L. Kanner, Autistic disturbances of affective contact, Nervous Child 2 (3) (1943) 217–250.

[27] D. Poole, E. Miles, E. Gowen, E. Poliakoff, 04 30). Shifting attention between modalities: Revisiting the modality-shift effect in autism. (Springer, éd.) attention, Percept. Psychophys. 83 (2021) 2498–2509, https://doi.org/10.3758/s13414-021-02302-4.

[28] K. Harezlak, P. Kasprowski, M. Stasch, Towards accurate eye tracker calibration—methods and procedures, Procedia Comput. Sci. 1073–1081 (2014), https://doi.org/10.1016/j.procs.2014.08.194.

[29] T. Dutta, Evaluation of the Kinect™ sensor for 3-D kinematic measurement in the workplace, Appl. Ergon. 645–649 (2012), https://doi.org/10.1016/j.apergo.2011.09.011.

[30] Salvucci, D., & Goldberg, J. (2000). Identifying fixations and saccades in eye-tracking protocols. *Proceedings of the 2000 symposium on Eye tracking research & applications* (pp. 71–78). ACM. Doi: 10.1145/355017.355028.

[31] Understanding Tobii Pro Lab's eye tracking metrics. (2023, 06 19). Récupéré sur Tobii Connect: https://connect.tobii.com/s/article/understanding-tobii-pro-lab-eye-tracking-metrics?language=en_US.

[32] Le Meur, O., Coutrot Antoine, Liu, Z., Rämä, P., Le Roch, A., & Helo, A. (2017). Your gaze betrays your age. *Le Meur, O., Coutrot, A., Liu, Z., Rämä, P., Le Roch, A., & Helo, A. (2017, August). Your gaze betrays your age. In 2017 25th European Signal Processing Conference (EUSIPCO) (pp. 1892-1896). IEEE. doi:10.23919/EUSIPCO.2017.8081538.

[33] K. Fournier, C. Hass, S. Naik, N. Lodha, J. Caurbaugh, Motor coordination in autism spectrum disorders: a synthesis and meta-analysis, J. Autism Dev. Disord. 40 (2010) 1227–1240, https://doi.org/10.1007/s10803-010-0981-3.

[34] N. Sasson, J. Elison, Eye Tracking Young Children with Autism, J. Vis. Exp. JoVE (61) (2012) 3675.

[35] H. Mann, D. Whitney, On a test of whether one of two random variables is stochastically larger than the other. (I. o. Statistics, éd.), Ann. Math. Stat. 18 (1) (1947) 50–60.

[36] P. McKnight, J. Najab, Mann-Whitney U Test, The Corsini Encyclopedia of Psychology (2010), https://doi.org/10.1002/9780470479216.corpsy0524.