Victoria Manousaki

Although existing methods for action anticipation have shown considerably improved performance on the pre- dictability of future events in videos, the way they exploit information related to past actions is constrained by time du- ration and encoding complexity. This paper addresses the task of action anticipation by taking into consideration the history of all executed actions throughout long, procedu- ral activities. A novel approach noted as Visual-Linguistic Modeling of Action History (VLMAH) is proposed that fuses the immediate past in the form of visual features as well as the distant past based on a cost-effective form of linguistic constructs (semantic labels of the nouns, verbs, or actions). Our approach generates accurate near-future action pre- dictions during procedural activities by leveraging informa- tion on the long- and short-term past. Extensive experimen- tal evaluation was conducted on three challenging video datasets containing procedural activities, namely the Mec- cano, the Assembly-101, and the 50Salads. The obtained results validate the importance of incorporating long-term action history for action anticipation and document the sig- nificant improvement of the state-of-the-art Top-1 accuracy performance.

The temporal alignment of two complete action/activity sequences has been the focus of interest in many research works. However, the problem of partially aligning an incomplete sequence to a complete one has not been sufficiently explored. Very effective alignment algo- rithms such as Dynamic Time Warping (DTW) and Soft Dynamic Time Warping (S-DTW) are not capable of handling incomplete sequences. To overcome this limitation the Open-End DTW (OE-DTW) and the Open- Begin-End DTW (OBE-DTW) algorithms were introduced. The OE- DTW has the capability to align sequences with common begin points but unknown ending points, while the OBE-DTW has the ability to align unsegmented sequences. We focus on two new alignment algorithms, namely the Open-End Soft DTW (OE-S-DTW) and the Open-Begin-End Soft DTW (OBE-S-DTW) which combine the partial alignment capabil- ities of OE-DTW and OBE-DTW with those of Soft DTW (S-DTW). Specifically, these algorithms have the segregational capabilities of DTW combined with the soft-minimum operator of the S-DTW algorithm that results in improved, differentiable alignment in the case of continuous, unsegmented actions/activities. The developed algorithms are well-suited tools for addressing the problem of action prediction. By properly match- ing and aligning an on-going, incomplete action/activity sequence to pro- totype, complete ones, we may gain insight in what comes next in the on-going action/activity. The proposed algorithms are evaluated on the MHAD, MHAD101-v/-s, MSR Daily Activities and CAD-120 datasets and are shown to outperform relevant state of the art approaches. Keywords: Segregational Soft Dynamic Time Warping · Temporal Alignment · Action Prediction · Activity Prediction · Duration Prognosis · Graphs

We present a novel approach for the visual prediction of human-object interactions in videos. Rather than forecasting the human and object motion or the future hand-object contact points, we aim at predicting (a) the class of the on-going human-object interaction and (b) the class(es) of the next active object(s) (NAOs), i.e., the object(s) that will be involved in the interaction in the near future as well as the time the interaction will occur. Graph matching relies on the efficient Graph Edit distance (GED) method. The experimental evaluation of the proposed approach was conducted using two well-established video datasets that contain human-object interactions, namely the MSR Daily Activities and the CAD120. High prediction accuracy was obtained for both action prediction and NAO forecasting.

Aligning the execution of complete actions captured in segmented videos has been a problem explored by Dynamic Time Warping (DTW) and Soft Dynamic Time Warping (S-DTW) algorithms. The limitation of these algorithms is that they cannot align unsegmented actions, ie, actions that appear between other actions. This limitation is mitigated by the use of two existing DTW variants, namely the Open-End DTW (OE-DTW) and the Open-Begin-End DTW (OBE-DTW). OE-DTW is designed for aligning actions of known begin point but unknown end point, while OBE-DTW handles continuous, completely unsegmented actions with unknown begin and end points. In this paper, we combine the merits of S-DTW with those of OE-DTW and OBE-DTW. In that direction, we propose two new DTW variants, the Open-End Soft DTW (OE-S-DTW) and the Open-Begin-End Soft DTW (OBE-S-DTW). The superiority of the proposed algorithms lies in the combination of the soft-minimum operator and the relaxation of the boundary constraints of S-DTW, with the segregational capabilities of OE-DTW and OBE-DTW, resulting in better and differentiable action alignment in the case of continuous, unsegmented videos. We evaluate the proposed algorithms on the task of action prediction on standard datasets such as MHAD, MHAD101-v/-s, MSR Daily Activities and CAD-120. Our experimental results show the superiority of the proposed algorithms to existing video alignment methods.

Action prediction is defined as the inference of an action label while the action is still ongoing. Such a capability is extremely useful for early response and further action planning. In this paper, we consider the problem of action prediction in scenarios involving humans interacting with objects. We formulate an approach that builds time series representations of the performance of the humans and the objects. Such a representation of an ongoing action is then compared to prototype actions. This is achieved by a Dynamic Time Warping (DTW)-based time series alignment framework which identifies the best match between the ongoing action and the prototype ones. Our approach is evaluated quantitatively on three standard benchmark datasets. Our experimental results reveal the importance of the fusion of human- and object-centered action representations in the accuracy of action prediction. Moreover, we demonstrate that the proposed approach achieves significantly higher action prediction accuracy compared to competitive methods.

Eye movements during text reading can provide insights about reading disorders. We developed the DysLexML, a screening tool for developmental dyslexia, based on various ML algorithms that analyze gaze points recorded via eyetracking during silent reading of children. We comparatively evaluated its performance using measurements collected from two systematic field studies with 221 participants in total. This work presents DysLexML and its performance. It identifies the features with prominent predictive power and performs dimensionality reduction. Specifically, it achieves its best performance using linear SVM, with an accuracy of 97% and 84% respectively, using a small feature set. We show that DysLexML is also robust in the presence of noise. These encouraging results set the basis for developing screening tools in less controlled, larger-scale environments, with inexpensive eye-trackers, potentially reaching a larger population for early intervention. Unlike other related studies, DysLexML achieves the aforementioned performance by employing only a small number of selected features, that have been identified with prominent predictive power. Finally, we developed a new data augmentation/substitution technique based on GANs for generating synthetic data similar to the original distributions.

Eye movements during text reading can provide insights about reading disorders. Via eye-trackers, we can measure when, where and how eyes move with relation to the words they read. Machine Learning (ML) algorithms can decode this information and provide differential analysis. This work developed DysLexML, a screening tool for developmental dyslexia that applies various ML algorithms to analyze fixation points recorded via eye-tracking during silent reading of children. It comparatively evaluated its performance using measurements collected in a systematic field study with 69 native Greek speakers, children, 32 of which were diagnosed as dyslexic by the official governmental agency for diagnosing learning and reading difficulties in Greece. We examined a large set of features based on statistical properties of fixations and saccadic movements and identified the ones with prominent predictive power, performing dimensionality reduction. Specifically, DysLexML achieves its best performance using linear SVM, with an a accuracy of 97 %, with a small feature set, namely saccade length, number of short forward movements, and number of multiply fixated words. Furthermore, we analyzed the impact of noise on the fixation positions and showed that DysLexML is accurate and robust in the presence of noise. These encouraging results set the basis for developing screening tools in less controlled, larger-scale environments, with inexpensive eye-trackers, potentially reaching a larger population for early intervention.

The Bags of Visual Words (BoVWs) framework has been applied successfully to several computer vision tasks. In this work we are particularly interested on its application to the problem of action recognition/classification. The key design decisions for a method that follows the BoVWs framework are (a) the visual features to be employed,(b) the size of the codebook to be used for representing a certain action and (c) the classifier applied to the developed representation to solve the classification task. We perform several experiments to investigate a variety of options regarding all the aforementioned design parameters. We also propose a new feature type and we suggest a method that determines automatically the size of the codebook. The experimental results show that our proposals produce results that are competitive to the outcomes of state of the art methods.