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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>The Current and Future Role of Visual Question Answering in eXplainable Artificial Intelligence</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Marta Caro-Martínez</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Anjana Wijekoon</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Belén Díaz-Agudo</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Juan A. Recio-García</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Department of Software Engineering and Artificial Intelligence, Universidad Complutense de Madrid</institution>
          ,
          <country country="ES">Spain</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>School of Computing, Robert Gordon University</institution>
          ,
          <addr-line>Aberdeen, Scotland</addr-line>
        </aff>
      </contrib-group>
      <abstract>
        <p>Over the last few years, we have seen how the interest of the computer science research community on eXplainable Artificial Intelligence has grown in leaps and bounds. The reason behind this rise is the use of Artificial Intelligence in many daily life tasks, and the consequent necessity of people to understand the intelligent systems' behaviour. Computer vision-related tasks are not an exception, for example, Visual Question Answering tasks. The Artificial Intelligence models that carry out this specific task make an efort to answer questions about what we can watch in a particular image. In this work, we review the existing work about eXplainable Artificial Intelligence on Visual Question Answering which is a problem on which there is still much work to be done. Moreover, we open the discussion about the challenges to overcome regarding this topic, like the future role of Visual Question Answering to address eXplainable Artificial Intelligence issues or dificulties.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;eXplainable Artificial Intelligence</kwd>
        <kwd>XAI</kwd>
        <kwd>Visual Question Answering</kwd>
        <kwd>VQA</kwd>
        <kwd>Natural Language Processing</kwd>
        <kwd>NLP</kwd>
        <kwd>Computer Vision</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Artificial Intelligence (AI) has become an integral part of human life due to the high volume of
research targeted towards helping people perform many complex tasks. For example, there is a
huge interest in making machines observe, understand and perform multiple tasks with images,
i.e. machine vision. Machine vision-related tasks have multiple useful applications in many
domains, like detecting breast cancer, detecting manufacturing industrial defects, or helping
disabled people [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. Furthermore, AI research has extended to reasoning with multiple modalities
including images. One of these and the focus of this paper is Visual Question Answering (VQA),
which involves reasoning with computer vision and natural language [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. AI models for VQA
try to answer questions about the content of a specific image (an example is shown in Figure 1).
Moreover, VQA shares the common challenge with other AI tasks that it lacks explainability,
which afects the users’ trust and the system’s performance as a consequence.
      </p>
      <p>
        In recent years, eXplainable Artificial Intelligence (XAI) is one of the most popular research
ifelds on AI [
        <xref ref-type="bibr" rid="ref3 ref4">3, 4</xref>
        ]. This popularity has risen due to the increment of AI systems applications
in daily life, and especially in critical domains like healthcare, security, or industry. Another
reason is the increasing complexity of AI algorithms and methodologies. For instance, previous
approaches such as rule-based systems and decision trees [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ] were simple and importantly
interpretable [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. However, the increasing complexity of more recent gradient-based models
and algorithms, commonly referred to as black boxes, renders them non-interpretable for
end-users [
        <xref ref-type="bibr" rid="ref3 ref6">3, 6</xref>
        ].
      </p>
      <p>
        In the literature, VQA has been achieved using both knowledge-light [
        <xref ref-type="bibr" rid="ref7 ref8">7, 8</xref>
        ] and
knowledgeintensive methods [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]. In this paper, we explore the explainability of both approaches due to
the necessity of including XAI in VQA to increase users’ trust on these approaches. While
knowledge-intensive approaches may seem interpretable, it is worth exploring due to the
increasing demand for explainability and the lack of existing review in this research area.
Accordingly, this paper will study and review the existing work on applying XAI techniques to
make VQA more explainable. Additionally, we want to depict challenges and future work lines
that are going to be necessary to develop in the following years. Specifically, we will explore
the future work on XAI applied to explain VQA and also the challenges in XAI research that
can be addressed using VQA techniques.
      </p>
      <p>The rest of the paper is organised as follows. Section 2 presents the literature review
methodology followed by a review of literature in Visual Question Answering (Section 3). Section 4
presents the existing literature that explored explainability in the context of VQA and we
conclude with Section 5 which discusses open challenges and the utility of VQA in XAI. Finally,
we end the paper getting some conclusions in Section 6.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Literature Review Methodology</title>
      <p>To study the literature related to VQA and VQA with explanations we have performed a
structured search considering diferent terms and dates. We used the Google Scholar 1 database.</p>
      <p>The first set of searches were a way to introduce ourselves in the topic and in the VQA
algorithms. Once we discovered there were two main types of VQA algorithms
(knowledgelight and knowledge-intensive), we started the search for the rest of the terms (related to
transformers especially). In the following sections, divided mainly according to knowledge-light
and knowledge-intensive classification, we describe and discuss the works selected from the
search.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Visual Question Answering</title>
      <p>
        Visual Question Answering is a task that emerged from the necessity of answering questions
about an image or video. For example, VQA is utilised when helping the visually impaired to
understand the content of a photo [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. VQA as an AI task is complex (compared to other tasks
like classification or regression) and requires contributions from two key domains: computer
vision and language modelling [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. It difers from other computer vision tasks in that we do not
know the question to answer until run time. In VQA, we can discuss diferent types of questions
regarding the knowledge that we need to access to answer them [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. According to literature,
we have identified the following types of questions in VQA:
• Object detection. For example, “Are there dogs in the picture?”.
• Fine-grained recognition. For example, “What type of dog breed appears in the picture?”.
• Action or activity detection and recognition. For example, “Is the dog eating?”.
• Additional knowledge-based reasoning. For example, “Is the dog breed the favourite dog
breed of Queen Elizabeth II?”.
      </p>
      <p>• Commonsense reasoning inference. For example, “Does the dog love her humans?”.</p>
      <p>
        There are two key approaches to implementing VQA: knowledge-intensive and
knowledgelight methods. Both approaches typically involve the following steps: 1) object detection in an
image with high accuracy with fine-grained details; 2) language comprehension of the question;
and 3) compilation of the answer utilising the information from steps 1 and 2, and external
knowledge sources (if required) [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. Step 3 might be the most challenging one due to the
complex reasoning we have to carry out. Sometimes we can find that our questions are very
easy to answer considering the objects detected from the image. However, often, we need to
infer knowledge from other knowledge sources to disambiguate the uncertainties between
our question and the objects detected in our image [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. These uncertainties are caused by
open-ended, ambiguous questions that can take multiple answers or ones that require additional
information not available on the image [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Mainly, the knowledge-intensive methods are the
methods that try to overcome this problem (see Section 3.2).
      </p>
      <p>In the following sections, we explore diferent methodologies used to implement VQA in
detail.</p>
      <sec id="sec-3-1">
        <title>3.1. Knowledge-light AI Methods</title>
        <p>The state-of-the-art knowledge-light methods for VQA are vision-language (VL) fusion deep
neural architectures. They are optimised to learn the representations of individual modalities as
well as the alignment between modalities in a fusion architecture.</p>
        <p>
          The alignment is enforced by the multi-modal contrastive loss which is derived from the
theories of Mutual Information and Noise-contrastive Estimation [
          <xref ref-type="bibr" rid="ref13">13</xref>
          ]. The multi-modal
contrastive loss can be calculated in many forms and often uses a combination of the following in
the loss function. Implementation of these losses is also enabled by momentum encoding which
regulates the weight updates in pre-trained encoders [
          <xref ref-type="bibr" rid="ref14">14</xref>
          ].
        </p>
        <p>
          • Inter-modal Alignment forces representations of the matching image, text pairs to be
closer in the feature space while pushing apart the representations of unmatched image,
text pairs [
          <xref ref-type="bibr" rid="ref8">8</xref>
          ].
• Intra-modal Alignment forces the encoders to learn semantic diferences between matched
and unmatched instances of the same modality. For instance, representations of similar
images are forced to be closer while representations of diferent images are pushed
apart [
          <xref ref-type="bibr" rid="ref7">7</xref>
          ].
        </p>
        <p>
          The state-of-the-art VQA models are the ALIGN model trained using contrastive loss [
          <xref ref-type="bibr" rid="ref15">15</xref>
          ],
ALBEF model trained using the inter-modal alignment [
          <xref ref-type="bibr" rid="ref8">8</xref>
          ]; VL model by authors of [
          <xref ref-type="bibr" rid="ref7">7</xref>
          ] trained
using Triple Constrative Loss; VinVL [
          <xref ref-type="bibr" rid="ref16">16</xref>
          ] which integrates improved object detection with VL
modelling. They all follow similar fusion architectures while difering in training objectives,
training data utilised and pre-train/fine-tune tasks.
        </p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Knowledge-intensive AI Methods</title>
        <p>
          In general, we can say that the knowledge-intensive or knowledge-enhanced methods are the
ones that need to use external knowledge, from a diferent knowledge source that it is not the
image, and the question, to get an answer [
          <xref ref-type="bibr" rid="ref12 ref2">12, 2</xref>
          ].
        </p>
        <p>
          Using additional knowledge sources can be remarkable in VQA tasks, because as we have
mentioned previously, not all the questions that we can find are as simple that we can answer
them with only that information. For example, we can have an image where several types of
food appear. We can also have the following question: “How many types of fruits are in the
picture?” (see Figure 1). The algorithm should recognise not only the foods that we have in the
image, but identify and understand which foods are fruits and which ones are not. Then, we
can also say that knowledge-intensive methodologies overcome one of the biggest problems
that deep learning models have since these ones only consider the information that we can
ifnd in the training data and in the query [
          <xref ref-type="bibr" rid="ref12 ref2">2, 12</xref>
          ]. We have to think that training data can scale
but never cover all the possible knowledge present in the world. Therefore, it makes sense
to use other bigger, various, and deeper knowledge sources to complement our training data.
Moreover, deep learning models are limited, they cannot learn all the knowledge. Regarding
this point, knowledge-intensive methods help to enhance the knowledge learnt [
          <xref ref-type="bibr" rid="ref2">2</xref>
          ]. Then it
is reasonable to wonder whether knowledge-intensive methods for VQA are better than deep
learning and whether they are also the future of VQA algorithms.
        </p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Explainability of VQA</title>
      <p>
        It seems in general VQA systems do in fact follow human reasoning: detect objects in the
image and establish the relations between those objects [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. This has been the key to make the
reasoning process of these methods understandable to humans. We categorise such approaches
as: interpretable methods where the VQA is a pipeline of sub-tasks and the outcome of each
step is used to explain the answer; knowledge-light methods that use architectural changes
or optimisation techniques to generate an explanation; and knowledge-intensive methods that
exploit external knowledge sources and reasoning to generate explanations. In the next sections,
we explore these methods.
      </p>
      <sec id="sec-4-1">
        <title>4.1. Interpretable Methods for VQA</title>
        <p>These models are the ones whose execution process is divided into several steps. This way, we
can get intermediate results in every step that can be shown to the users in order to make the
process understandable. That is why these approaches are considered interpretable, although
the methods used in every step are black-boxes, mainly neural networks.</p>
        <p>
          One example approach is the Grounded Visual Question Answering model (GVQA) [
          <xref ref-type="bibr" rid="ref17">17</xref>
          ].
They use diferent algorithms depending on the type of question that we come across (yes/no
or non yes/no question). They also divide the model’s behaviour process to get the answer in
diferent steps (getting important parts in the image, retrieving concepts from the question,
classifying the type of questions or predicting the answer). So, in every step, the model uses
diferent deep learning algorithms. Nevertheless, the model obtains an output in every step,
that can be shown to the target user, making more transparent the reasoning process carried
out by the model. This transparency makes the model interpretable compared to other models
that take the decision in one shot. Another example is the work by Li et al. [
          <xref ref-type="bibr" rid="ref18">18</xref>
          ]. In this case, the
method divides the process to carry out in three steps: 1) word prediction (a CNN algorithm is
used to solve a classification problem, where an image should be associated with a set of words);
2) sentence generation (where a single-layer LSTM algorithm is applied to get the probability of
having a specific word in a set of words, taking into account the set of words that we got in
step 1; and 3) answer reasoning (the sentence from step 2 and the question are encoded by two
LSTM algorithms to get the answer). Authors claim that the system is interpretable because
users can watch the results obtained in every step, which are the words and the sentences that
describe the image according to the VQA model.
        </p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. Knowledge-intensive Methods for VQA with Explainability</title>
        <p>
          Knowledge-intensive methods for VQA use external knowledge sources to provide explanations.
The process carried out by these systems is divided into steps, separating the representation
from the reasoning. The graph built to represent the knowledge to use to get the answer can be
also used as an explanation itself, or used as the knowledge source for an explanation system.
Therefore, knowledge-intensive methods are able to provide explainability [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ]. Moreover, the
advantages that we pointed out about this type of system in Section 3.2 plus their explainability
make knowledge-intensive methods a strong candidate in future when implementing
explainability for VQA. Next, we describe some examples found in the literature to illustrate these
ideas.
        </p>
        <p>
          The authors of [
          <xref ref-type="bibr" rid="ref20">20</xref>
          ] proposed a post-hoc and model-agnostic approach to provide
counterfactual explanations for VQA. In particular, they want to check “What is the response of the VQA
model if we substitute word X with word Y in question q”. The authors delete words or replace
words in the questions using a knowledge graph (WordNet2) to get the substitute words. They
aim to get these words by looking for synonyms, hypernyms, hyponyms, or siblings in the
graph between the words. The original question and the modified questions together with their
answers (obtained by a specific VQA model) are presented to the user as local explanations.
They also present users with global explanations which is VQA model performance comparison
between when answering the original questions and the modified explanations.
        </p>
        <p>
          VLC-BERT [
          <xref ref-type="bibr" rid="ref21">21</xref>
          ] is VQA model that uses COMET for explaining its answers. COMET
(Commonsense Transformer) is a commonsense reasoning generation transformer model that given
a subject and a relation, it predicts a possible object. An example from the authors is if the
subject is “taking a nap” and the relation is “causes” a possible object is “have energy”. It is
trained and tested on ATOMIC [
          <xref ref-type="bibr" rid="ref22">22</xref>
          ] and ConceptNet knowledge graphs both of which consist
of social commonsense knowledge. Commonsense reasoning extracted from the COMET is
used in VLC-BERT to improve answer generation making it knowledge-intensive.
        </p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Knowledge-light Methods for VQA with Explainability</title>
        <p>
          There are also examples of post-hoc explanation approaches, that are independent of the VQA
reasoning process and utilise an explanation module that generates visual and/or textual
explanations. Most commonly the generative model is a Deep Learning model that annotates the
RoIs in the image. The authors of [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ] introduced a VQA model that includes an LSTM-based
explanation module. It takes the question and the answer as the input and their multinomial
distribution on the important concepts to generate an explanation. The explanation is both textual
and visual: the image RoIs that explain the answer are marked in colours, and a complementary
text explains the reason behind the answer.
        </p>
        <p>
          More recent transformer-based VQA models generate explanations in an ante-hoc manner.
Authors of [
          <xref ref-type="bibr" rid="ref23">23</xref>
          ] proposed the CtF framework that extracts keywords from both input image
and question to filter information from the RoI of the image and question tokens to produce
answers. The semantic reasoning between RoIs and the question keywords is presented as the
explanations. A similar approach to learn from diferent granularity levels for VQA is used by
authors of [
          <xref ref-type="bibr" rid="ref24">24</xref>
          ]. They use Kullback Leibler divergence as the loss to align between two modules
that learn coarse-grained and fine-grained fusion of the image and question. The answers are
explained by visualising the attention on RoIs and question words. The authors of [
          <xref ref-type="bibr" rid="ref25">25</xref>
          ] extend
the CtF framework with an explanation generation module in addition to predicting the answer.
A transformer-based decoder model generates the explanation and it is trained along with the
answer classification task.
        </p>
      </sec>
      <sec id="sec-4-4">
        <title>4.4. Evaluating the Explanations for VQA</title>
        <p>
          Evaluation of explanation quality has improved over the years as much as the implementation
of the explainability into VQA. This is supported by dedicated datasets created for Explainability
in VQA such as VQA-X and VQA-HAT. In addition, some works set out to use a very
wellknown explainer (for example LIME or GradCAM) to generate explanations from the image
and compare those explanations with the one obtained by their own methods [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ].
        </p>
        <p>
          Quantitative evaluation using questionnaires to capture users’ opinions on the explanation
systems is another common approach we encountered in the reviewed literature. We find the
use of questionnaires with Likert scales [
          <xref ref-type="bibr" rid="ref26">26</xref>
          ] that is similar to what we encounter in other XAI
evaluation domains. They can be used to allow users to pick what is preferred explanation
approach (between proposed and a baseline from the literature). Following is a list of existing
evaluation metrics and novel metrics proposed to evaluate the explanations for VQA:
        </p>
        <p>
          BLEU-4 [
          <xref ref-type="bibr" rid="ref27">27</xref>
          ]. It is a well-known standard sentence-comparison metric. In this case to evaluate
textual explanations [
          <xref ref-type="bibr" rid="ref19 ref25">19, 25</xref>
          ]. Originally, it is evaluated to check the performance in machine
translation. METEOR [
          <xref ref-type="bibr" rid="ref28">28</xref>
          ]. It is a metric that aims the same goal than BLEU-4 [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ]. ROUGE-L [
          <xref ref-type="bibr" rid="ref29">29</xref>
          ].
This metric tries to measure the quality of summaries created by machines. However, it is being
used in the evaluation of explanations for VQA [
          <xref ref-type="bibr" rid="ref19 ref25">19, 25</xref>
          ]. CIDEr [
          <xref ref-type="bibr" rid="ref30">30</xref>
          ]. CIDEr is an actual metric
to measure VQA [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ]. It provides a score about the quality of a sentence that describe a specific
image. SPICE [
          <xref ref-type="bibr" rid="ref31">31</xref>
          ]. It aims the same task than CIDEr [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ]. Earth Mover Distance (EMD) [
          <xref ref-type="bibr" rid="ref32">32</xref>
          ].
Although it is originally used to compare histograms, several authors use it to compare the
image regions highlighted in their explanation to image regions highlighted by human judges,
or in annotated images in XAI for VQA datasets [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ]. Rank correlation [
          <xref ref-type="bibr" rid="ref33">33</xref>
          ]. It is a metric to
transform two images in a list of pixels, and compare them. Faithfulness score [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ] that checks
the consistency between the visual explanation vectors obtained with a well-know explainer
from the textual explanation, and the predicted answer from the VQA module. Intersection of
Union between RoIs in the attention mask and the ground truth is used as a measure of visual
explanation accuracy by the authors of [
          <xref ref-type="bibr" rid="ref24">24</xref>
          ]. Failure case Analysis is a manual qualitative process
where the author presented cases where the answer predicted by the VQA model is diferent
from the ground-truth, however, the answer was correct and the explanation was accurate [
          <xref ref-type="bibr" rid="ref34">34</xref>
          ].
        </p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Challenges and Future Work on VQA related to XAI</title>
      <p>
        In this section, we want to explore the role of VQA related to XAI, not only about how we are
going to explain VQA in the future, but how VQA could support XAI methodologies to improve
users’ trust on diferent AI models. VQA can play a key role in explanation comprehension
and past literature on XAI has highlighted the need to personalise explanations to reduce the
cognitive burden on the user [
        <xref ref-type="bibr" rid="ref35">35</xref>
        ]. Tailoring explanations to match the mental model of the
user and the ability to interact with the user to provide clarifications, scrutinise and argue [
        <xref ref-type="bibr" rid="ref36">36</xref>
        ]
are some of the approaches proposed to address personalisation. We find that VQA provides an
opportunity to implement such interactions and improve comprehension and user satisfaction.
The Alipour et al.’s work [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ] introduces a SOTA architecture to solve the problem of VQA.
Using the features from the images to apply a ResNet algorithm, authors obtain attention maps
that point out the important part in the image to get an answer. However, the users can interact
with the image, drawing the parts that they consider the most important. That new knowledge
is included to execute the SOTA architecture, so the prediction is calculated again. As we can
see there are some existing works that include interactivity in their explanations to improve
them according to users’ mental model. However, there is so much work left to do regarding
this topic, for example using VQA to help users to understand the visual outputs generated
by well-known explainers, like LIME, Grad-CAM, or Anchors. These outputs are explanations
itself for AI models and tasks, but they might be confusing for users.
      </p>
      <p>
        Example mock-up of how VQA can be used in post-explanation interactions is depicted in
Figure 2. In this Figure we display an example of possible questions and the answers that could
be obtained with VQA. On the left side, we show visual explanations obtained when applying a
XAI technique (GradCAM, LIME, or Nearest Neighbours) to explain an artificial inteligence task
(for example, image classification or text classification). Then, we treat the explanation to be the
visual component. On the right side, we have examples of possible user questions to ask about
the visual explanations, and the answers to be provided by VQA. The questions can be about the
explanation, and even about the prediction or the visual input itself. A particular methodology
that might be used is the one proposed by Kim et al. [
        <xref ref-type="bibr" rid="ref37">37</xref>
        ], in which they generate explanations
for charts (of any kind) using VQA methods. This type of proposal could be useful to explain
charts obtained with LIME, Anchors, etc. for tabular or text data. Moreover, such VQA model
can be integrated with an existing interactive model that implements interactive-XAI [
        <xref ref-type="bibr" rid="ref36">36</xref>
        ].
There are many challenges in implementing such methods and they vary by the preferred
approach: knowledge-intensive or knowledge-light.
      </p>
      <p>A knowledge-light approach to VQA will find the diversity and complexity of the visual
explanations challenging. As seen in Figure 2, the three explainers generate significantly
diferent explanations. However, the task can be simplified if the VQA model is implemented on
a single data modality (image vs tabular) or a specific explainer (LIME vs GradCAM). Another
key challenge is the lack of data for fine-tuning or training such VQA model. In a
knowledgelight data-driven approach empirical evaluation should indicate how well the pre-training
transfer to question answering of visual explanations, however, much efort is needed to create
datasets that can be used for fine-tuning and training.</p>
      <p>
        Regarding challenges related to knowledge-intensive methods, the largest one might be
compiling a comprehensive database for VQA [
        <xref ref-type="bibr" rid="ref38">38</xref>
        ] that not only helps to increase the performance
of VQA methods but also their explainability. Doing that, we could build extensive graphs
to represent our knowledge and extract from them, more detailed and accurate explanations.
Moreover, this task must be also helpful when we want to apply VQA to explain explanations
generated by well-known explainers. These datasets will also be helpful when evaluating VQA
to explain explanations themselves. However, we could propose to use GPT-3 to generate
explanations from this kind of images. Moreover, there is only a limited amount of state-of-the-art
techniques for knowledge-intensive VQA methods that are explainable. Although some authors
claim that knowledge-intensive methods are transparent and can help users to understand the
reasoning process carried out by the system [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], there is a lack of focused research. Therefore,
more approaches are necessary, especially in evaluating the quality of explainability.
      </p>
      <p>Another line of future research work could be methods that combine transformers-based
architectures with knowledge bases. This could be an opportunity to enhance both proposals and
overcome their weaknesses taking advantage of the strong features of each type of methodology.
Answers for questions that require additional knowledge-based reasoning and commonsense
reasoning inference (see Section 3) could be improved this way.</p>
      <p>Finally, we want to remark that there is not Case-Based Reasoning (CBR) methodologies
applied to VQA or CBR applied to XAI for VQA. Therefore, exploring the role of CBR for this
task could be interesting for the CBR community.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusions</title>
      <p>As with many other AI models, Visual Question Answering (VQA) models requires explanations
for their target users to help them to understand how the model has predicted an answer for
a specific question regarding the content in an image. In this work, we have studied some of
the literature regarding VQA methods in general to comprehend the problem that we need
to explain and the explainability of VQA methods. There are some promising approaches
to implementing explainability into VQA methods, however, they are sparse often specific
to the VQA method. We have found out that there are two key approaches to VQA:
datadriven methods and knowledge-intensive methods. Former VQA methods that performed VQA
as a pipeline of sub-tasks using CNN and RNN methods are considered transparent. More
recent knowledge-light and intensive methods required ante-hoc or post-hoc explainability. In
challenges for the future, we emphasise the possibility of using VQA to answer questions about
explanations generated by well-known explainers. The addition of interactivity can also lead to
enhanced user satisfaction in XAI systems since we can incorporate the user’s mental model,
allow disagreements and discover questions not answered by current XAI methods.</p>
    </sec>
    <sec id="sec-7">
      <title>Acknowledgments</title>
      <p>Supported by the Horizon 2020 Future and Emerging Technologies (FET) programme of the
European Union through the iSee project (CHIST-ERA-19-XAI-008, PCI2020-120720-2).
Funding in Spain by MCIN/AEI/10.13039/501100011033 and in the UK by EPSRC grant number
EP/V061755/1.</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          [1]
          <string-name>
            <given-names>S.</given-names>
            <surname>Shakya</surname>
          </string-name>
          , et al.,
          <article-title>Analysis of artificial intelligence based image classification techniques</article-title>
          ,
          <source>Journal of Innovative Image Processing (JIIP) 2</source>
          (
          <year>2020</year>
          )
          <fpage>44</fpage>
          -
          <lpage>54</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          [2]
          <string-name>
            <given-names>Q.</given-names>
            <surname>Wu</surname>
          </string-name>
          , et al.,
          <article-title>Visual question answering: A survey of methods and datasets</article-title>
          ,
          <source>Computer Vision and Image Understanding</source>
          <volume>163</volume>
          (
          <year>2017</year>
          )
          <fpage>21</fpage>
          -
          <lpage>40</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          [3]
          <string-name>
            <given-names>D.</given-names>
            <surname>Gunning</surname>
          </string-name>
          , D. Aha,
          <article-title>Darpa's explainable artificial intelligence (xai) program</article-title>
          ,
          <source>AI</source>
          magazine
          <volume>40</volume>
          (
          <year>2019</year>
          )
          <fpage>44</fpage>
          -
          <lpage>58</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          [4]
          <string-name>
            <given-names>A. B.</given-names>
            <surname>Arrieta</surname>
          </string-name>
          , et al.,
          <article-title>Explainable artificial intelligence (xai): Concepts, taxonomies, opportunities and challenges toward responsible ai</article-title>
          ,
          <source>Information fusion 58</source>
          (
          <year>2020</year>
          )
          <fpage>82</fpage>
          -
          <lpage>115</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref5">
        <mixed-citation>
          [5]
          <string-name>
            <given-names>C. C.</given-names>
            <surname>Aggarwal</surname>
          </string-name>
          , et al.,
          <source>Recommender systems</source>
          , volume
          <volume>1</volume>
          , Springer,
          <year>2016</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref6">
        <mixed-citation>
          [6]
          <string-name>
            <given-names>Y.</given-names>
            <surname>Zhang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>P.</given-names>
            <surname>Tiňo</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Leonardis</surname>
          </string-name>
          ,
          <string-name>
            <given-names>K.</given-names>
            <surname>Tang</surname>
          </string-name>
          ,
          <article-title>A survey on neural network interpretability</article-title>
          ,
          <source>IEEE Transactions on Emerging Topics in Computational Intelligence</source>
          <volume>5</volume>
          (
          <year>2021</year>
          )
          <fpage>726</fpage>
          -
          <lpage>742</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref7">
        <mixed-citation>
          [7]
          <string-name>
            <given-names>J.</given-names>
            <surname>Yang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Duan</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Tran</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Xu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Chanda</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Chen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Zeng</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Chilimbi</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Huang</surname>
          </string-name>
          ,
          <article-title>Visionlanguage pre-training with triple contrastive learning</article-title>
          ,
          <source>in: Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition</source>
          ,
          <year>2022</year>
          , pp.
          <fpage>15671</fpage>
          -
          <lpage>15680</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref8">
        <mixed-citation>
          [8]
          <string-name>
            <given-names>J.</given-names>
            <surname>Li</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R.</given-names>
            <surname>Selvaraju</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Gotmare</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Joty</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Xiong</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S. C. H.</given-names>
            <surname>Hoi</surname>
          </string-name>
          ,
          <article-title>Align before fuse: Vision and language representation learning with momentum distillation</article-title>
          ,
          <source>Advances in neural information processing systems</source>
          <volume>34</volume>
          (
          <year>2021</year>
          )
          <fpage>9694</fpage>
          -
          <lpage>9705</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref9">
        <mixed-citation>
          [9]
          <string-name>
            <given-names>P.</given-names>
            <surname>Wang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Q.</given-names>
            <surname>Wu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Shen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Dick</surname>
          </string-name>
          ,
          <string-name>
            <surname>A. Van Den Henge</surname>
          </string-name>
          ,
          <article-title>Explicit knowledge-based reasoning for visual question answering</article-title>
          ,
          <source>in: Proceedings of the 26th International Joint Conference on Artificial Intelligence</source>
          ,
          <year>2017</year>
          , pp.
          <fpage>1290</fpage>
          -
          <lpage>1296</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref10">
        <mixed-citation>
          [10]
          <string-name>
            <given-names>S.</given-names>
            <surname>Antol</surname>
          </string-name>
          , et al.,
          <article-title>Vqa: Visual question answering</article-title>
          ,
          <source>in: Proceedings of the IEEE international conference on computer vision</source>
          ,
          <year>2015</year>
          , pp.
          <fpage>2425</fpage>
          -
          <lpage>2433</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref11">
        <mixed-citation>
          [11]
          <string-name>
            <given-names>K.</given-names>
            <surname>Basu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>F.</given-names>
            <surname>Shakerin</surname>
          </string-name>
          , G. Gupta, Aqua:
          <article-title>Asp-based visual question answering</article-title>
          ,
          <source>in: Practical Aspects of Declarative Languages: 22nd International Symposium, PADL</source>
          <year>2020</year>
          ,
          <article-title>New Orleans</article-title>
          , LA, USA, January
          <volume>20</volume>
          -
          <issue>21</issue>
          ,
          <year>2020</year>
          , Proceedings 22, Springer,
          <year>2020</year>
          , pp.
          <fpage>57</fpage>
          -
          <lpage>72</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref12">
        <mixed-citation>
          [12]
          <string-name>
            <given-names>K.</given-names>
            <surname>Marino</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Rastegari</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Farhadi</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R.</given-names>
            <surname>Mottaghi</surname>
          </string-name>
          ,
          <article-title>Ok-vqa: A visual question answering benchmark requiring external knowledge</article-title>
          ,
          <source>in: Proceedings of the IEEE/cvf conference on computer vision and pattern recognition</source>
          ,
          <year>2019</year>
          , pp.
          <fpage>3195</fpage>
          -
          <lpage>3204</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref13">
        <mixed-citation>
          [13]
          <string-name>
            <surname>A.</surname>
          </string-name>
          v. d. Oord,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Li</surname>
          </string-name>
          ,
          <string-name>
            <given-names>O.</given-names>
            <surname>Vinyals</surname>
          </string-name>
          ,
          <article-title>Representation learning with contrastive predictive coding</article-title>
          , arXiv preprint arXiv:
          <year>1807</year>
          .
          <volume>03748</volume>
          (
          <year>2018</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref14">
        <mixed-citation>
          [14]
          <string-name>
            <given-names>K.</given-names>
            <surname>He</surname>
          </string-name>
          ,
          <string-name>
            <given-names>H.</given-names>
            <surname>Fan</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Wu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Xie</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R.</given-names>
            <surname>Girshick</surname>
          </string-name>
          ,
          <article-title>Momentum contrast for unsupervised visual representation learning</article-title>
          ,
          <source>in: Proceedings of the IEEE/CVF conference on computer vision and pattern recognition</source>
          ,
          <year>2020</year>
          , pp.
          <fpage>9729</fpage>
          -
          <lpage>9738</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref15">
        <mixed-citation>
          [15]
          <string-name>
            <given-names>C.</given-names>
            <surname>Jia</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Yang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Xia</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.-T.</given-names>
            <surname>Chen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Z.</given-names>
            <surname>Parekh</surname>
          </string-name>
          ,
          <string-name>
            <given-names>H.</given-names>
            <surname>Pham</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Q.</given-names>
            <surname>Le</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.-H.</given-names>
            <surname>Sung</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Z.</given-names>
            <surname>Li</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Duerig</surname>
          </string-name>
          ,
          <article-title>Scaling up visual and vision-language representation learning with noisy text supervision</article-title>
          ,
          <source>in: International Conference on Machine Learning, PMLR</source>
          ,
          <year>2021</year>
          , pp.
          <fpage>4904</fpage>
          -
          <lpage>4916</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref16">
        <mixed-citation>
          [16]
          <string-name>
            <given-names>P.</given-names>
            <surname>Zhang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>X.</given-names>
            <surname>Li</surname>
          </string-name>
          ,
          <string-name>
            <given-names>X.</given-names>
            <surname>Hu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Yang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Zhang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Wang</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Choi</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Gao</surname>
          </string-name>
          , Vinvl:
          <article-title>Revisiting visual representations in vision-language models</article-title>
          ,
          <source>in: Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition</source>
          ,
          <year>2021</year>
          , pp.
          <fpage>5579</fpage>
          -
          <lpage>5588</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref17">
        <mixed-citation>
          [17]
          <string-name>
            <given-names>A.</given-names>
            <surname>Agrawal</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Batra</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Parikh</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Kembhavi</surname>
          </string-name>
          ,
          <article-title>Don't just assume; look and answer: Overcoming priors for visual question answering</article-title>
          ,
          <source>in: Proceedings of the IEEE conference on computer vision and pattern recognition</source>
          ,
          <year>2018</year>
          , pp.
          <fpage>4971</fpage>
          -
          <lpage>4980</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref18">
        <mixed-citation>
          [18]
          <string-name>
            <given-names>Q.</given-names>
            <surname>Li</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Fu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Yu</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Mei</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Luo</surname>
          </string-name>
          ,
          <string-name>
            <surname>Tell-</surname>
          </string-name>
          and
          <article-title>-answer: Towards explainable visual question answering using attributes and captions</article-title>
          ,
          <source>in: Proceedings of the 2018 Conference on Empirical Methods in Natural Language Processing</source>
          ,
          <year>2018</year>
          , pp.
          <fpage>1338</fpage>
          -
          <lpage>1346</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref19">
        <mixed-citation>
          [19]
          <string-name>
            <surname>J. Wu</surname>
            ,
            <given-names>R.</given-names>
          </string-name>
          <string-name>
            <surname>Mooney</surname>
          </string-name>
          ,
          <article-title>Faithful multimodal explanation for visual question answering</article-title>
          ,
          <source>in: Proceedings of the 2019 ACL Workshop BlackboxNLP: Analyzing and Interpreting Neural Networks for NLP</source>
          ,
          <year>2019</year>
          , pp.
          <fpage>103</fpage>
          -
          <lpage>112</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref20">
        <mixed-citation>
          [20]
          <string-name>
            <given-names>T.</given-names>
            <surname>Stoikou</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Lymperaiou</surname>
          </string-name>
          , G. Stamou,
          <article-title>Knowledge-based counterfactual queries for visual question answering</article-title>
          ,
          <source>arXiv preprint arXiv:2303.02601</source>
          (
          <year>2023</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref21">
        <mixed-citation>
          [21]
          <string-name>
            <given-names>S.</given-names>
            <surname>Ravi</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Chinchure</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Sigal</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R.</given-names>
            <surname>Liao</surname>
          </string-name>
          ,
          <string-name>
            <given-names>V.</given-names>
            <surname>Shwartz</surname>
          </string-name>
          , Vlc-bert:
          <article-title>Visual question answering with contextualized commonsense knowledge</article-title>
          ,
          <source>in: Proceedings of the IEEE/CVF Winter Conference on Applications of Computer Vision</source>
          ,
          <year>2023</year>
          , pp.
          <fpage>1155</fpage>
          -
          <lpage>1165</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref22">
        <mixed-citation>
          [22]
          <string-name>
            <given-names>M.</given-names>
            <surname>Sap</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R. Le</given-names>
            <surname>Bras</surname>
          </string-name>
          ,
          <string-name>
            <given-names>E.</given-names>
            <surname>Allaway</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Bhagavatula</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N.</given-names>
            <surname>Lourie</surname>
          </string-name>
          ,
          <string-name>
            <given-names>H.</given-names>
            <surname>Rashkin</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Roof</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N. A.</given-names>
            <surname>Smith</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Y.</given-names>
            <surname>Choi</surname>
          </string-name>
          ,
          <string-name>
            <surname>Atomic:</surname>
          </string-name>
          <article-title>An atlas of machine commonsense for if-then reasoning</article-title>
          ,
          <source>in: Proceedings of the AAAI conference on artificial intelligence</source>
          , volume
          <volume>33</volume>
          ,
          <year>2019</year>
          , pp.
          <fpage>3027</fpage>
          -
          <lpage>3035</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref23">
        <mixed-citation>
          [23]
          <string-name>
            <given-names>B. X.</given-names>
            <surname>Nguyen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Do</surname>
          </string-name>
          ,
          <string-name>
            <given-names>H.</given-names>
            <surname>Tran</surname>
          </string-name>
          ,
          <string-name>
            <given-names>E.</given-names>
            <surname>Tjiputra</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Q. D.</given-names>
            <surname>Tran</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Nguyen</surname>
          </string-name>
          ,
          <article-title>Coarse-to-fine reasoning for visual question answering</article-title>
          ,
          <source>in: Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition</source>
          ,
          <year>2022</year>
          , pp.
          <fpage>4558</fpage>
          -
          <lpage>4566</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref24">
        <mixed-citation>
          [24]
          <string-name>
            <given-names>W.</given-names>
            <surname>Tian</surname>
          </string-name>
          ,
          <string-name>
            <given-names>H.</given-names>
            <surname>Li</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Z.-Q.</given-names>
            <surname>Zhao</surname>
          </string-name>
          ,
          <article-title>Dual capsule attention mask network with mutual learning for visual question answering</article-title>
          ,
          <source>in: Proceedings of the 29th International Conference on Computational Linguistics</source>
          ,
          <year>2022</year>
          , pp.
          <fpage>5678</fpage>
          -
          <lpage>5688</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref25">
        <mixed-citation>
          [25]
          <string-name>
            <given-names>R.</given-names>
            <surname>Vaideeswaran</surname>
          </string-name>
          ,
          <string-name>
            <given-names>F.</given-names>
            <surname>Gao</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Mathur</surname>
          </string-name>
          , G. Thattai,
          <article-title>Towards reasoning-aware explainable vqa</article-title>
          ,
          <source>arXiv preprint arXiv:2211.05190</source>
          (
          <year>2022</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref26">
        <mixed-citation>
          [26]
          <string-name>
            <given-names>K.</given-names>
            <surname>Alipour</surname>
          </string-name>
          , et al.,
          <article-title>A study on multimodal and interactive explanations for visual question answering</article-title>
          , arXiv preprint arXiv:
          <year>2003</year>
          .
          <volume>00431</volume>
          (
          <year>2020</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref27">
        <mixed-citation>
          [27]
          <string-name>
            <given-names>K.</given-names>
            <surname>Papineni</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Roukos</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Ward</surname>
          </string-name>
          , W.-J. Zhu,
          <article-title>Bleu: a method for automatic evaluation of machine translation</article-title>
          ,
          <source>in: Proceedings of the 40th annual meeting of the Association for Computational Linguistics</source>
          ,
          <year>2002</year>
          , pp.
          <fpage>311</fpage>
          -
          <lpage>318</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref28">
        <mixed-citation>
          [28]
          <string-name>
            <given-names>S.</given-names>
            <surname>Banerjee</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Lavie</surname>
          </string-name>
          ,
          <string-name>
            <surname>Meteor:</surname>
          </string-name>
          <article-title>An automatic metric for mt evaluation with improved correlation with human judgments, in: ACL workshop on intrinsic and extrinsic evaluation measures for machine translation</article-title>
          and/or summarization,
          <year>2005</year>
          , pp.
          <fpage>65</fpage>
          -
          <lpage>72</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref29">
        <mixed-citation>
          [29]
          <string-name>
            <surname>C.-Y. Lin</surname>
          </string-name>
          ,
          <article-title>Rouge: A package for automatic evaluation of summaries</article-title>
          , in: Text summarization branches out,
          <year>2004</year>
          , pp.
          <fpage>74</fpage>
          -
          <lpage>81</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref30">
        <mixed-citation>
          [30]
          <string-name>
            <given-names>R.</given-names>
            <surname>Vedantam</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Lawrence Zitnick</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Parikh</surname>
          </string-name>
          , Cider:
          <article-title>Consensus-based image description evaluation</article-title>
          ,
          <source>in: Proceedings of the IEEE conference on computer vision and pattern recognition</source>
          ,
          <year>2015</year>
          , pp.
          <fpage>4566</fpage>
          -
          <lpage>4575</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref31">
        <mixed-citation>
          [31]
          <string-name>
            <given-names>P.</given-names>
            <surname>Anderson</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Fernando</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Johnson</surname>
          </string-name>
          , S. Gould, Spice:
          <article-title>Semantic propositional image caption evaluation, in: Computer Vision-ECCV</article-title>
          <year>2016</year>
          : 14th European Conference, Amsterdam, The Netherlands,
          <source>October 11-14</source>
          ,
          <year>2016</year>
          , Proceedings, Part V 14, Springer,
          <year>2016</year>
          , pp.
          <fpage>382</fpage>
          -
          <lpage>398</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref32">
        <mixed-citation>
          [32]
          <string-name>
            <given-names>O.</given-names>
            <surname>Pele</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Werman</surname>
          </string-name>
          ,
          <article-title>A linear time histogram metric for improved sift matching</article-title>
          ,
          <source>in: Computer Vision-ECCV 2008: 10th European Conference on Computer Vision</source>
          , Marseille, France,
          <source>October 12-18</source>
          ,
          <year>2008</year>
          , Proceedings,
          <source>Part III 10</source>
          , Springer,
          <year>2008</year>
          , pp.
          <fpage>495</fpage>
          -
          <lpage>508</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref33">
        <mixed-citation>
          [33]
          <string-name>
            <surname>A. Das</surname>
            ,
            <given-names>H.</given-names>
          </string-name>
          <string-name>
            <surname>Agrawal</surname>
            ,
            <given-names>L.</given-names>
          </string-name>
          <string-name>
            <surname>Zitnick</surname>
            ,
            <given-names>D.</given-names>
          </string-name>
          <string-name>
            <surname>Parikh</surname>
            ,
            <given-names>D.</given-names>
          </string-name>
          <string-name>
            <surname>Batra</surname>
          </string-name>
          ,
          <article-title>Human attention in visual question answering: Do humans and deep networks look at the same regions?</article-title>
          ,
          <source>Computer Vision and Image Understanding</source>
          <volume>163</volume>
          (
          <year>2017</year>
          )
          <fpage>90</fpage>
          -
          <lpage>100</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref34">
        <mixed-citation>
          [34]
          <string-name>
            <given-names>Y.</given-names>
            <surname>Lin</surname>
          </string-name>
          , et al.,
          <article-title>Revive: Regional visual representation matters in knowledge-based visual question answering</article-title>
          ,
          <source>arXiv preprint arXiv:2206.01201</source>
          (
          <year>2022</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref35">
        <mixed-citation>
          [35]
          <string-name>
            <given-names>Q. V.</given-names>
            <surname>Liao</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Gruen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Miller</surname>
          </string-name>
          ,
          <article-title>Questioning the ai: informing design practices for explainable ai user experiences</article-title>
          ,
          <source>in: Proceedings of the 2020 CHI Conference on Human Factors in Computing Systems</source>
          ,
          <year>2020</year>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>15</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref36">
        <mixed-citation>
          [36]
          <string-name>
            <given-names>P.</given-names>
            <surname>Madumal</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Miller</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Sonenberg</surname>
          </string-name>
          ,
          <string-name>
            <given-names>F.</given-names>
            <surname>Vetere</surname>
          </string-name>
          ,
          <article-title>A grounded interaction protocol for explainable artificial intelligence</article-title>
          ,
          <source>in: Proceedings of the 18th International Conference on Autonomous Agents and MultiAgent Systems</source>
          ,
          <year>2019</year>
          , pp.
          <fpage>1033</fpage>
          -
          <lpage>1041</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref37">
        <mixed-citation>
          [37]
          <string-name>
            <given-names>D. H.</given-names>
            <surname>Kim</surname>
          </string-name>
          , E. Hoque,
          <string-name>
            <given-names>M.</given-names>
            <surname>Agrawala</surname>
          </string-name>
          ,
          <article-title>Answering questions about charts and generating visual explanations</article-title>
          ,
          <source>in: Proceedings of the 2020 CHI conference on human factors in computing systems</source>
          ,
          <year>2020</year>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>13</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref38">
        <mixed-citation>
          [38]
          <string-name>
            <given-names>A.</given-names>
            <surname>Cláudia Akemi Matsuki de Faria</surname>
          </string-name>
          , et al.,
          <article-title>Visual question answering: A survey on techniques and common trends in recent literature</article-title>
          , arXiv e-prints (
          <year>2023</year>
          ) arXiv-
          <fpage>2305</fpage>
          .
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>