Niki Efthymiou 2026-07-30T16:52:44+00:00
  • Τel: 210772-2420, 2964

  • nefthymiou@central.ntua.gr
  • Office: 2.2.19, Old ECE Building

Biography

Niki Efthymiou holds a Ph.D. in Electrical and Computer Engineering from the National Technical University of Athens (NTUA, 2023), specializing in Automated Perception and Learning Systems for Human Activity Recognition. She is currently affiliated with the Athena Research Center and maintains connections with the NTUA School of Electrical and Computer Engineering, where she contributes to European and national projects and is involved in supervising Master’s theses. Her core research interest centers on developing novel automated systems for perceiving and modeling complex human behavior, leveraging advanced Machine Learning and Computer Vision across two complementary domains.

Specializing in Child-Robot Interaction, her work focuses on designing intelligent perception systems for social robots in therapeutic and edutainment. This research explores robust, multi-modal sensing capabilities (action/gesture recognition), scaling systems from integrated multi-camera setups to lightweight solutions for open environments. Complementing this visual expertise, her interests in Digital Phenotyping utilize smart wearable biometric data to extract stable digital profiles. A critical focus is applying advanced ML and statistical models for the early detection and prevention of relapses in individuals with psychiatric disorders, framed as a high-stakes anomaly detection challenge.

Her academic foundation also includes an M.Sc. in Computational Mechanics (NTUA) and a Diploma/M.Eng. in Applied Mathematical and Physical Sciences (NTUA).

Teaching & Courses

Publications

2025

Garyfalli V, Kalisperakis E, Smyrnis A, Lazaridi M, Karantinos T, Mantas A, Filntisis P P, Efthymiou N, Zlatintsi A, Maragos P, N Smyrnis

Smartwatch-Derived Digital Phenotypes Relate to Psychopathology Dimensions in Patients With Psychotic Spectrum Disorders: Longitudinal Observational Study Journal Article

JMIR Ment Health, 12 , pp. e75774, 2025.

BibTeX | Links: [PDF]

2024

A Zlatintsi, P P Filntisis, N Efthymiou, C Garoufis, G Retsinas, T Sounapoglou, I Maglogiannis, P Tsanakas, N Smyrnis, P Maragos

Person Identification and Relapse Detection from Continuous Recordings of Biosignals Challenge: Overview and Results Journal Article

IEEE Open Journal of Signal Processing, 2024.

BibTeX | Links: [PDF]

N Efthymiou, G Retsinas, P P Filntisis, P Maragos

Augmenting Transformer Autoencoders with Phenotype Classification for Robust Detection of Psychotic Relapses Conference

Proc. IEEE Int’l Conference on Acoustics, Speech, and Signal Processing (ICASSP 2024), Seoul, Korea, 2024.

BibTeX | Links: [PDF]

2023

G Retsinas, N Efthymiou, D Anagnostopoulou, P Maragos

Mushroom Detection and Three Dimensional Pose Estimation from Multi-View Point Clouds Journal Article

Sensors, 23 (7), pp. 3576, 2023.

BibTeX | Links: [PDF]

E Kalisperakis, T Karantinos, M Lazaridi, V Garyfalli, P P Filntisis, A Zlatintsi, N Efthymiou, A Mantas, L Mantonakis, T Mougiakos, I Maglogiannis, P Tsanakas, P Maragos, N Smyrnis

Smartwatch digital phenotypes predict positive and negative symptom variation in a longitudinal monitoring study of patients with psychotic disorders Journal Article

Frontiers in Psychiatry, 14 , 2023.

BibTeX | Links: [PDF]

E Fekas, A Zlatintsi, P P Filntisis, C Garoufis, N Efthymiou, P Maragos

Relapse Prediction from Long-Term Wearable Data using Self-Supervised Learning and Survival Analysis Conference

Proc. 48th Int'l Conf. on Acoustics, Speech, and Signal Processing (ICASSP-2023), Rhodes Island, 2023.

BibTeX | Links: [PDF] [Slides]

G Retsinas, N Efthymiou, P Maragos

Mushroom Segmentation and 3D Pose Estimation From Point Clouds Using Fully Convolutional Geometric Features and Implicit Pose Encoding Conference

Proc. 2023 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 4th Agriculture Vision Workshop, Vancouver, Canada, 2023.

BibTeX | Links: [PDF]

N Efthymiou, G Retsinas, P P Filntisis, A Zlatintsi, E Kalisperakis, V Garyfalli, T Karantinos, M Lazaridi, N Smyrnis, P Maragos

From Digital Phenotype Identification To Detection Of Psychotic Relapses Conference

Proc. IEEE International Conference on Healthcare Informatics, Houston, TX, USA, 2023.

BibTeX | Links: [PDF] [Slides]

D Anagnostopoulou, G Retsinas, N Efthymiou, P P Filntisis, P Maragos

A Realistic Synthetic Mushroom Scenes Dataset Conference

Proc. 2023 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 4th Agriculture Vision Workshop, Vancouver, Canada, 2023.

BibTeX | Links: [PDF] [Poster]

2022

N Efthymiou, P P Filntisis, P Koutras, A Tsiami, J Hadfield, G Potamianos, P Maragos

ChildBot: Multi-robot perception and interaction with children Journal Article

Robotics and Autonomous Systems, 150 , pp. 103975, 2022.

BibTeX | Links: [PDF]

A Zlatintsi, P P Filntisis, C Garoufis, N Efthymiou, P Maragos, A Manychtas, I Maglogiannis, P Tsanakas, T Sounapoglou, E Kalisperakis, T Karantinos, M Lazaridi, V Garyfali, A Mantas, L Mantonakis, N Smyrnis

e-Prevention: Advanced Support System for Monitoring and Relapse Prevention in Patients with Psychotic Disorders Analysing Long-Term Multimodal Data from Wearables and Video Captures Journal Article

Sensors, 22 (19), pp. 7544, 2022.

BibTeX | Links: [PDF]

D Anagnostopoulou, N Efthymiou, C Papailiou, P Maragos

Child Engagement Estimation in Heterogeneous Child-Robot Interactions Using Spatiotemporal Visual Cues Conference

Proc. 2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2022), Kyoto, Japan, 2022.

BibTeX | Links: [PDF]

M Panagiotou, A Zlatintsi, P P Filntisis, A J Roumeliotis, N Efthymiou, P Maragos

A Comparative Study of Autoencoder Architectures for Mental Health Analysis using Wearable Sensors Data Conference

Proc. 30th European Signal Processing Conference (EUSIPCO), Belgrade, Serbia, 2022.

BibTeX | Links: [PDF] [Slides]

C Garoufis, A Zlatintsi, P P Filntisis, N Efthymiou, E Kalisperakis, T Karantinos, V Garyfalli, M Lazaridi, N Smyrnis, P Maragos

Towards Unsupervised Subject-Independent Speech-Based Relapse Detection in Patients with Psychosis using Variational Autoencoders Conference

Proc. 30th European Signal Processing Conference (EUSIPCO), Belgrade, Serbia, 2022.

BibTeX | Links: [PDF] [Slides]

2021

N Efthymiou, P P Filntisis, G Potamianos, P Maragos

Visual Robotic Perception System with Incremental Learning for Child–Robot Interaction Scenarios Journal Article

Technologies, 9 (4), pp. 86, 2021.

BibTeX | Links: [PDF]

P. P. Filntisis, N. Efthymiou, G. Potamianos,, P. Maragos

An Audiovisual Child Emotion Recognition System for Child-Robot Interaction Applications Conference

Proc. 29th European Signal Processing Conference (EUSIPCO 2021), Dublin, Ireland, 2021.

BibTeX | Links: [Slides] [PDF]

C. Garoufis, A. Zlatintsi, P. P. Filntisis, N. Efthymiou, E. Kalisperakis, V. Garyfalli, T. Karantinos, L. Mantonakis, N. Smyrnis, P. Maragos

An Unsupervised Learning Approach for Detecting Relapses from Spontaneous Speech in Patients with Psychosis Conference

Proc. IEEE-EMBS International Conference on Biomedical and Health Informatics (BHI-2021), 2021.

BibTeX | Links: [PDF] [Poster]

Dafni Anagnostopoulou, Niki Efthymiou, Christina Papailiou, Petros Maragos

Engagement Estimation During Child Robot Interaction Using DeepConvolutional Networks Focusing on ASD Children Conference

Proc. IEEE Int'l Conf. Robotics and Automation (ICRA-2021), Xi'an, 2021.

BibTeX | Links: [PDF] [Video] [Slides]

2020

P. P. Filntisis, N. Efthymiou, G. Potamianos, P. Maragos

Emotion Understanding in Videos Through Body, Context, and Visual-Semantic Embedding Loss Conference

Proc. 16th European Computer Vision Conference Workshops (ECCVW) - Workshop on Bodily Expressed Emotion Understanding, 2020.

BibTeX | Links: [PDF] [Code]

I. Maglogiannis, A. Zlatintsi, A. Menychtas, D. Papadimatos, P.P. Filntisis, N. Efthymiou, G. Retsinas, P. Tsanakas,, P. Maragos

An intelligent cloud-based platform for effective monitoring of patients with psychotic disorders Conference

Int’l Conf. on Artificial Intelligence Applications and Innovation (AIAI-2020), Halkidiki, Greece, 2020.

BibTeX | Links: [PDF]

G Retsinas, P P Filntisis, N Efthymiou, E Theodosis, A Zlatintsi, P Maragos

Person Identification Using Deep Convolutional Neural Networks on Short-Term Signals from Wearable Sensors Conference

ICASSP 2020 - 2020 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2020.

BibTeX | Links: [PDF]

2019

P P Filntisis, N Efthymiou, P Koutras, G Potamianos, P Maragos

Fusing Body Posture With Facial Expressions for Joint Recognition of Affect in Child–Robot Interaction Journal Article

IEEE Robotics and Automation Letters (with IROS option), 4 (4), pp. 4011-4018, 2019.

Abstract | BibTeX | Links: [PDF]

2018

N. Efthymiou, P. Koutras, P. ~P. Filntisis, G. Potamianos, P. Maragos

MULTI-VIEW FUSION FOR ACTION RECOGNITION IN CHILD-ROBOT INTERACTION Conference

Proc. IEEE Int'l Conf. on Image Processing, Athens, Greece, 2018.

Abstract | BibTeX | Links: [PDF]

A Tsiami, P Koutras, Niki Efthymiou, P P Filntisis, G Potamianos, P Maragos

Multi3: Multi-sensory Perception System for Multi-modal Child Interaction with Multiple Robots Conference

IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, 2018.

Abstract | BibTeX | Links: [PDF]

A Tsiami, P P Filntisis, N Efthymiou, P Koutras, G Potamianos, P Maragos

FAR-FIELD AUDIO-VISUAL SCENE PERCEPTION OF MULTI-PARTY HUMAN-ROBOT INTERACTION FOR CHILDREN AND ADULTS Conference

Proc. IEEE Int'l Conf. Acous., Speech, and Signal Processing (ICASSP), Calgary, Canada, 2018.

Abstract | BibTeX | Links: [PDF]

Jack Hadfield, Petros Koutras, Niki Efthymiou, Gerasimos Potamianos, Costas S Tzafestas, Petros Maragos

Object assembly guidance in child-robot interaction using RGB-D based 3d tracking Conference

2018 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), IEEE 2018.

BibTeX | Links: [PDF]

2017

A Zlatintsi, P Koutras, G Evangelopoulos, N Malandrakis, N Efthymiou, K Pastra, A Potamianos, P Maragos

COGNIMUSE: a multimodal video database annotated with saliency, events, semantics and emotion with application to summarization Journal Article

EURASIP Journal on Image and Video Processing, 54 , pp. 1–24, 2017.

Abstract | BibTeX | Links: [PDF]

2015

A Zlatintsi, P Koutras, N Efthymiou, P Maragos, A Potamianos, K Pastra

Quality Evaluation of Computational Models for Movie Summarization Conference

Costa Navarino, Messinia, Greece, 2015.

Abstract | BibTeX | Links: [PDF]