Recent research in Visual Question Answering (VQA) has revealed state-of-the-art models to be inconsistent in their understanding of the world  they answer seemingly difficult questions requiring reasoning correctly but get simpler associated sub-questions wrong. These sub-questions pertain to lower level visual concepts in the image that models ideally should understand to be able to answer the reasoning question correctly. To address this, we first present a gradient-based interpretability approach to determine the questions most strongly correlated with the reasoning question on an image, and use this to evaluate VQA models on their ability to identify the relevant sub-questions needed to answer a reasoning question. Next, we propose a contrastive gradient learning based approach called Sub-question Oriented Tuning (SOrT) which encourages models to rank relevant sub-questions higher than irrelevant questions for an < image, reasoning-question > pair. We show that SOrT improves model consistency by up to 6.5% points over existing approaches, while also improving visual grounding and robustness to rephrasings of questions. Current visual question answering (VQA) models struggle with consistency. They often correctly answer complex reasoning questions, i.e, those requiring common sense knowledge and logic on top of perceptual capabilities, but fail on associated low-level perception questions, i.e., those directly related to the visual content in the image. For e.g., in Fig 1, models answer the reasoning question Was this taken in the daytime? correctly, but fail on the associated perception question Is the sky bright? indicating that the models likely answered the reasoning question correctly for the wrong reason(s). In this work, we explore the usefulness of leveraging information about sub-questions , i.e., low-level perception questions relevant to a reasoning question, and irrelevant questions , i.e., any other questions about the image unrelated to the reasoning question, to improve consistency in VQA. Selvaraju et al. (2020) have studied this problem and introduced the VQA-Introspect dataset that draws a distinction between higher-level reasoning questions and lower-level perception sub-questions. We augment this dataset with additional perception questions from the VQAv2 dataset such that each < image, reasoning question > pair contains a set of relevant perception questions, which we refer to as sub-questions (e.g.,Is the sky bright? in Fig 1) and irrelevant perception questions, which we refer to as irrelevant questions (e.g., Is the train moving? in Fig 1) throughout this paper. We use Gradient-based Class Activation Mapping (Grad-CAM) vectors (Selvaraju et al., 2019a)  a faithful function of the model's parameters, question, answer and image  to propose an interpretability technique that determines the questions most strongly correlated with a reasoning question for a model. This is measured by ranking questions based on the cosine similarity of their Grad-CAM vectors with that of the reasoning question. We find that top-performing VQA models often rank irrelevant questions higher than relevant questions. Motivated by this, we introduce a new approach based on contrastive gradient learning to fine-tune a VQA model by enforcing relevant sub-questions to be ranked higher than irrelevant questions while answering a reasoning question. This is achieved by forcing the cosine similarity of the reasoning question's Grad-CAM vector with that of a sub-question to be higher than with that of an irrelevant question . We find that our approach improves the model's consistency, defined as the frequency with which the model correctly answers a sub-question given that it correctly answers the reasoning question. proach on visual grounding by comparing Grad-CAM heatmaps with human attention maps collected in the VQA-HAT dataset (Das et al., 2016). We find that our approach of enforcing this language-based alignment through better ranking of sub-questions also improves visual grounding. We also demonstrate that training VQA models by aligning Grad-CAM vectors helps in improving robustness to rephrasings of questions, as evaluated on the VQA-Rephrasings dataset (Shah et al., 2019). Visual Question Answering . The VQA task (Agrawal et al., 2015) requires answering a freeform natural language question about visual content in an image. Previous work has shown that models often do well on the task by exploiting language and dataset biases (Agrawal et al., 2017; Zhang et al., 2015; Ramakrishnan et al., 2018; Guo et al., 2019; Manjunatha et al., 2018). In order to evaluate the consistency of models, Selvaraju et al. (2020) collected a new dataset, VQA-Introspect, with human explanations via sub-questions and answers for reasoning questions in the VQA dataset. Model Interpretability . While prior work has attempted to explain VQA decisions in the visual modality (Selvaraju et al., 2019a,b; Qiao et al., 2017; Liang et al., 2019), the multi-modal task of VQA has a language component which cannot always be explained visually, i.e., visual regions can be insufficient to express underlying concepts (Goyal et al., 2016; Hu et al., 2017). Park et al. (2018) and Wu and Mooney (2019) generate textual justifications through datasets curated with human explanations. Our approach differs by using Grad-CAM vectors which are fully self-contained and faithful to the model, requiring no additional parameters or datasets to interpret its decisions. In recent work on Human-AI collaboration (Bansal et al., 2019, 2021), a key finding is that optimizing solely for model accuracy does not always lead to better overall utility in real-world, high-stakes datasets where AI systems advise humans on making decisions. Instead, improvements on yardsticks related to the trustworthiness of predictions are important steps towards successfully deploying these algorithms. We believe that consistency, the core focus of our work, is an intrinsically important post-hoc explanatory metric and a proxy for common-sense reasoning which could lead to stronger collective performance in such collaborative settings. Aligning network importances . Ross et al. (2017) introduced an approach to train models with input-gradient penalties that led to the generation of faithful explanations and improved generalizability on image classifiers. Selvaraju et al. (2019b) introduced an approach to align visual explanations with regions deemed important by humans, thereby improving visual grounding in VQA models. In followup work, Selvaraju et al. (2020) introduced an approach to align attention maps for the reasoning question and associated perception sub-questions from VQA-Introspect to improve language based grounding. In contrast to attention maps, our work encourages Grad-CAM vectors of a reasoning question to be closer to those of sub-questions and farther away from those of irrelevant questions . Intuitively, this means that we are making the neurons used while answering a reasoning question to be similar to those used while answering a sub-question and dissimilar to those used while answering an irrelevant question . Our experiments show that this alignment improves the model's consistency and visual grounding. Grad-CAM . Grad-CAM, introduced by Selvaraju et al. (2019a), is a technique to obtain visual explanations from any CNN-based deep neural network. In this work, we adopt Grad-CAM to compute the contribution of a neuron at the layer in a VQA model where the vision and language modalities are combined. This is computed by first taking the gradient of the predicted output class score with respect to the neuron activations in the layer. We then point-wise multiply this with the corresponding activations to obtain our Grad-CAM vector. Specifically, if y c denotes the score of the ground-truth output class and A k the activations of layer k of the model, the Grad-CAM vector G ck is computed as follows, G ck = y c A k  A k (1) Unlike Grad-CAM visualizations, these vectors are not visually interpretable as they are not computed on the final convolutional layer of the CNN. Consistency in VQA models . As defined in Selvaraju et al. (2020), the consistency of a VQA model refers to the proportion of sub-questions answered correctly, given that their corresponding reasoning questions were answered correctly. If a model is inconsistent, it is likely relying on incorrect perceptual signals or biases in the dataset to answer questions. Models that are consistent and based on appropriate perceptual signals are more likely to be reliable, interpretable and trustworthy. The key idea behind Sub-question Oriented Tuning (SOrT) is to encourage the neurons most strongly relied on (as assessed by Grad-CAM vectors) while answering a reasoning question (Was this taken in the daytime? in Fig 1) to be similar to those used while answering relevant sub-questions (Is the sky bright?) and dissimilar to those used while answering irrelevant questions (Is the train moving?). This enforces the model to use the same visual and lingustic concepts while making predictions on the reasoning question and the sub-questions . Our loss has the following two components. Contrastive Gradient Loss . With the Grad-CAM vectors of the reasoning question ( GR ) , subquestion ( GS ) and irrelevant question ( GI ) , we formalize our contrastive gradient loss LCG as, LCG = max   0 , cosine-sim( GR , GI ) (cid:122) (cid:125)(cid:124) (cid:123) GR  GI | GR || GI |  GR  GS | GR || GS | (cid:124) (cid:123)(cid:122) (cid:125) cosine-sim( GR , GS )   (2) Binary Cross Entropy Loss . To retain performance of the model on the base task of answering questions correctly, we add a Binary Cross Entropy Loss term ( LBCE ) that penalizes incorrect answers. Total Loss . Let o R , gt R , o S , gt S , o I and gt I represent the predicted and ground-truth answers for the reasoning, sub-questions and irrelevant questions respectively, and  1 ,  2 ,  3 be tunable hyperparameters. Our total loss L SOrT is, L SOrT = LCG +  1 LBCE ( o R , gt R ) +  2 LBCE ( o S , gt S ) +  3 LBCE ( o I , gt I ) (3) 4 Experiments Dataset. Our dataset pools VQA-Introspect and VQAv2 such that for every reasoning question in VQA-Introspect, we have a set of < sub-question , answer > pairs and a set of < irrelevant question , answer > pairs. The training/val splits contain 54,345/20,256 < image, reasoning question > pairs with an average of 2.58/2.81 sub-questions and 7.63/5.80 irrelevant questions for each pair. Baselines. We compare SOrT against the following baselines: 1) Pythia (Jiang et al., 2018), and 2) SQuINT in which Selvaraju et al. (2020) fine-tuned Pythia with an attention alignment loss to ensure that the model looks at the same regions when answering the reasoning and sub-questions . 1) Mean Precision@1 (MP@1) . Proportion of < image, reasoning question > pairs for which the highest ranked question is a sub-question . 2) Ranking Accuracy . Proportion of < image, reasoning question > pairs whose sub-questions are all ranked above their irrelevant questions . 3) Mean Reciprocal Rank (MRR) . Average value of the highest reciprocal rank of a sub-question among all < image, reasoning question > pairs. Higher is better. 4) Weighted Pairwise Rank (WPR) Loss . For pairs of incorrectly ranked < sub, irrelevant > questions, this computes the differences of their ConsistencyMetrics AccuracyMetrics RankingMetrics Method R (cid:51) S (cid:51)  R (cid:51) S (cid:55)  R (cid:55) S (cid:51)  R (cid:55) S (cid:55)  Consistency%  Reas. similarity scores with the reasoning question. Averaged across all pairs, this computes the extent by which rankings are incorrect. Lower is better. Model Performance. 1) Quadrant Analysis. a . R (cid:51) S (cid:51) The pairs where reasoning and sub-questions are both correctly answered. b . R (cid:51) S (cid:55) The pairs where the reasoning question is correctly answered, while the sub-question is incorrectly answered. c . R (cid:55) S (cid:51) The pairs where the reasoning question is incorrectly answered, while the subquestion is correctly answered. d . R (cid:55) S (cid:55) The pairs where reasoning and sub-questions are both incorrectly answered. 2) Consistency. The frequency with which a model correctly answers a sub-question given that it correctly answers the reasoning question. 3) Reasoning Accuracy . The accuracy on the reasoning split of VQAv2 dataset, and 4) Overall Accuracy . Accuracy on the VQAv2 validation set. We attempt to answer the following questions: Does SOrT help models better identify the perception questions relevant for answering a reasoning question? As described in Sec 3.2, the model ranks perception questions ( sub-questions and irrelevant questions ) associated with an < image, reasoning question > pair according to the cosine similarities of their Grad-CAM vectors with that of the reasoning question. As seen in Table 1, we find that our approach outperforms its baselines on nearly all the ranking metrics. We observe gains of 4-6% points on MP@1 and MRR, and 1.5-2.5% points on Ranking Accuracy. Likewise, the improvement in WPR the soft metric that computes the extent by which rankings are incorrect is a substantial 12% points over Pythia. This confirms that our approach helps better distinguish Figure 2: An example of improvement in consistency between Pythia (top) and SOrT (below) brought about by better sub-question ranking. Does recognizing relevant sub-questions make models more consistent? We find that the improved ranking of sub-questions through SOrT improves consistency by 6.5% points over Pythia, 1.47% points over SQuINT and 0.4% points over an approach that just uses sub-questions while discarding irrelevant questions 1 . As seen in Table 1, the consistency gains are due to significant improvements in the R (cid:51) S (cid:51) and R (cid:51) S (cid:55) quadrants. As seen in Table 1, the consistency gains are due to significant improvements in the R (cid:51) S (cid:51) and R (cid:51) S (cid:55) quadrants. This comes at the expense of a drop in overall accuracy and reasoning accuracy by  1% point, likely due to the active disincentization of memorizing language priors and dataset biases through our contrastive gradient learning approach. Gradient-based explanations have been shown to be more faithful to model decisions compared to attention maps (Selvaraju et al., 2019b). Our results confirm this by showing that aligning Grad-CAM vectors for reasoning and sub-questions makes models more consistent compared to SQuINT, which aligns their attention maps. Fig 2 shows an example of improved consistency using SOrT. The Pythia model answers its sub-question incorrectly. Our approach ranks the relevant subquestion higher than the irrelevant ones and answers it correctly  thus improving consistency. 1 These numbers are averaged values from 10-fold cross validation runs on the val split. Does our approach also help with syntactic consistency as tested on rephrased questions? To test whether our approach of aligning Grad-CAM vectors also helps with making models consistent to rephrasings of questions, we use the VQA-Rephrasings dataset introduced in Shah et al. (2019), split into appropriate train / val / test splits containing 85,042 / 24,297 / 12,148 pairs of rephrased questions. We follow the same training protocols outlined earlier for each of our baselines, and retrain Pythia with the additional data. On the held-out test split of this dataset, we observe improvements in consistency 80.73 (SOrT) v/s 79.98 (SQuINT) v/s 79.51 (Pythia). Interestingly, we observe a minor improvement in accuracy as well 66.52 (SOrT) v/s 65.45 (SQuINT) v/s 66.38 (Pythia). This confirms the effectiveness of our approach for both semantic and syntactic consistency. Does enforcing language-based alignment lead to better visual grounding? To evaluate this, we compute visual grounding through Grad-CAM applied on the final convolutional layer. We then compute the correlation of Grad-CAM heatmaps with the validation split of the VQA-Human ATtenion (VQA-HAT) dataset (Das et al., 2016), comprising 4,122 attention maps. This dataset contains human-annotated ground truth' attention maps which indicate the regions humans chose to look at while answering questions about images in the VQAv1 dataset. The proposed method to compare human and model-based attention maps in this work was to rank their pixels according to their spatial attention, and then compute the correlation between these two ranked lists. for Pythia and 0 . 060  0 . 008 for SQuINT. These statistically significant improvements indicate that enforcing language-based alignment during training improves visual grounding on an unseen dataset. A qualitative example that demonstrates the supe-rior visual grounding of SOrT compared to its baselines is shown in Fig 3. For the question Is the baby using the computer? and its corresponding answer Yes , we see that the Grad-CAM heatmap generated by SOrT is closest to that of the human attention map. It is also the only heatmap in this example that actually points to the fingers of the child, which is the essential visual component for answering the question. In this work, we seek to improve consistency in VQA. We first develop language-based interpretability metrics to measure the relevance of a lower-level perception question while answering a higher-level reasoning question. Evaluating state-of-the-art VQA models on these metrics reveals that models often rank irrelevant questions higher than relevant ones. We present SOrT (Sub-question Oriented Tuning), a contrastive gradient learning based approach for teaching VQA models to distinguish between relevant and irrelevant perceptual concepts while answering a reasoning question. SOrT aligns Grad-CAM vectors of reasoning questions with those of sub-questions , while distancing them from those of irrelevant questions . We demonstrate SOrT's effectiveness on datasets that test for semantic as well as syntactic consistency without major changes to accuracy, while also improving visual grounding. The Georgia Tech effort was supported in part by NSF, AFRL, DARPA, ONR YIPs, ARO PECASE, Amazon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the U.S. Government, or any sponsor. The key ethical considerations for this work relate to fairness. Although not ubiquitous in application today, the progress of research in VQA necessitates work in the direction of transparency so as to build trust among users before these systems are widely deployed in the real world. Prior work in this domain has revealed VQA models to exploit visual and language based priors in the datasets they are trained on (Das et al., 2016; Agrawal et al., 2017; Zhang et al., 2015; Ramakrishnan et al., 2018; Guo et al., 2019; Manjunatha et al., 2018). Such models tend to compound the biases prevalent in these datasets, and could have detrimental effects on fairness. Our work could better explain these biases by identifying the most relevant perceptual concepts used by the model while answering reasoning questions. In addition, by improving consistency and visual grounding in VQA systems, our work contributes to mitigating some of these biases.
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