REVIEW 3 major objections 6 minor 52 references
Learning Sign Language Representation using CNN LSTM, 3DCNN, CNN RNN LSTM and CCN TD
T0 review · 3 major / 6 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read A 3DCNN that learns spatial and temporal features directly from video outperforms the three other compared architectures on both a new Trinidad and Tobago Sign Language dataset (91%) and American Sign Language (83%).
desk verdict The paper's central 3DCNN-best claim is undermined by a likely frame-level train/test split that leaks the same videos into both sides, and the new-sign test confirms poor generalization. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing mechanism is the three-dimensional convolutional layer, which slides learnable 3D filters across a volume made by stacking video frames, so the same operation captures both spatial structure in each frame and motion across frames. The paper contrasts this with two-frame CNN-plus-recurrent designs (CNN-LSTM and CNN-RNN-LSTM) and a time-distributed wrapper that applies a 2D CNN independently to each timestamp. The 3DCNN's direct spatiotemporal feature learning is what the paper credits for the higher accuracy and faster prediction on newly submitted signs.
What would settle it
A concrete check: record a larger TTSL test set with multiple signers, different backgrounds, and varied lighting, then re-run the four architectures; if 3DCNN's margin over CNN-LSTM and CNN-TD shrinks or reverses on those held-out videos, the paper's central ranking is an artifact of the single-signer dataset rather than a property of the models.
Extended reading notes
Core claim
On the paper's own terms, the discovery is a comparative ranking: when the same ten-word, ten-to-twenty-videos-per-word dataset (six ASL signs, four TTSL signs) is run through four architectures under shared preprocessing, loss, and optimizer settings, the 3DCNN is the best classifier. Its classification reports show 91% accuracy on the TTSL subset and 83% on the ASL subset, with the highest recall among all models; it also used the least RAM and GPU during training and made correct predictions on three of four new TTSL signs in a saved-model webcam simulation, whereas the runner-up CNN-TD recognized only one. The paper therefore claims that 3DCNN's ability to learn spatiotemporal features directly from stacked video frames makes it the best available base for a sign-language learning and assessment application, at least for these datasets.
Load-bearing premise
The load-bearing assumption is that 10 to 20 videos per sign, all produced by one signer in one setting, represent the sign well enough that accuracy differences among models on this dataset will survive contact with real learners and new environments.
Editorial extensions
If this is right
- A 3DCNN-based sign-language tuition application can translate a learner's recorded sign and give a correctness grade within seconds; in the paper's simulation, the 3DCNN returned predictions on new webcam signs in 3 to 10 seconds after the first run.
- The same training pipeline extends to a sign language for which no prior recognition dataset exists, since the authors built and used a new TTSL dataset from scratch.
- For small sign datasets, two-stage CNN-plus-recurrent designs can be worse than a single spatiotemporal model; CNN-RNN-LSTM underperformed because its setup was too complex for the data.
- Time-distributed CNN is a viable competitor on the held-out TTSL split (87.5% recall) but fails to generalize to newly recorded signs, so model choice should be validated on fresh captures rather than only on the test split.
- Resource use matters for deployment: 3DCNN had the highest parameter count but the lowest RAM and GPU usage during training, making it practical for a classroom-app use case.
Reading between the lines
- If 3DCNN's advantage holds on a larger multi-signer corpus, the same architecture could serve as a generic starting point for other under-resourced sign languages in the Caribbean, with fine-tuning on a small local vocabulary.
- The finding that CNN-TD scored well on the split but failed on new signs suggests that single-signer accuracy may be inflated by background and clothing cues; a controlled experiment that removes the signer from the frame, for example by training on pose keypoints instead of raw pixels, would test whether the models are learning the sign or the person.
- The paper's grading idea could be tested directly against human raters: compare the model's per-sign certainty score with a teacher's pass or fail judgment on the same videos to calibrate the certainty output as a usable grade.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper compares four neural architectures (CNN-LSTM, 3DCNN, CNN-RNN-LSTM, and CNN-TD) on a self-captured dataset of 162 videos covering 10 signs from American Sign Language and Trinidad and Tobago Sign Language. The central claim is that 3DCNN is the best-performing model, with 91% accuracy on the TTSL subset and 83% on the ASL subset. The paper also reports a small 'new sign' webcam evaluation in which 3DCNN correctly identified 3 of 4 TTSL signs while CNN-TD identified only Doubles, and concludes that 3DCNN is the most suitable basis for a sign-language tuition system.
Significance. If the comparative ranking were reliable, the paper would provide a useful empirical data point on a previously unexplored sign language (TTSL) and a reasonable baseline for future work on Caribbean sign languages. The authors are transparent about the small dataset and the same-signer/same-environment limitation, and the new-sign experiment is an honest attempt to probe generalization. However, the load-bearing issue is that the reported accuracies and the resulting ranking rest on an evaluation protocol whose validity is not established: the text in Sections III.C and III.D indicates a frame-level random split, which can leak near-duplicate frames from the same video into both training and test sets. The paper's own Section IV.E then shows poor transfer to a new video, which is consistent with inflated test results. The central claim therefore needs substantial rework before the comparison can be trusted.
major comments (3)
- [III.C and III.D] The data-splitting procedure is described at the frame level, not the video level: Section III.C states that the capture application 'split the videos into frames' and then 'the dataset which is referring to the captured frames was divided by training, validation or testing, with training being 80% and testing and validation 20%', and Section III.D similarly says videos were 'broken up' before frames were extracted and parsed through each model. Because each video is a 35-frame clip, adjacent frames are near-duplicates, so a random frame-level split places frames from the same recording in both training and test sets. This violates the independence assumption and can inflate all reported accuracies, potentially changing the model ranking. The evaluation should be redone with a video-level split (e.g., group frames by source video and assign whole videos to train/validation/test), and the paper should report per-video or per-clip evaluation metrics.
- [IV.E] The new-sign experiment directly undermines the external validity of the reported classification accuracies. The text states that both 3DCNN and CNN-TD had 87.5% recall on the TTSL dataset, yet when tested on a newly recorded webcam video of the same signer in the same environment, CNN-TD correctly identified only 'Doubles' and 3DCNN correctly identified 3 of 4 signs. The authors attribute this to the dataset being 'extremely similar in terms of the signs being completed by the same person in the same environment.' This is evidence that the high test-set accuracies reflect memorization of the recording conditions rather than robust sign recognition. The claim that 3DCNN is the best model for a real-time tuition system therefore needs support from an evaluation that controls for signer and environment, such as leave-one-signer-out or cross-environment testing.
- [IV (all subsections)] The paper reports a single 80/20 train/test split with no repeated runs, no error bars, and no statistical comparison. With roughly 162 videos total, the test set is on the order of tens of videos spread across 10 classes, so per-class support is very small. The reported differences between models (e.g., 91% vs. 87.5% on TTSL) may not be statistically distinguishable. The comparison should be repeated over multiple random splits (with video-level grouping) and reported as mean ± standard deviation, and the authors should state the per-class test support so readers can judge the reliability of the reported precision and recall values.
minor comments (6)
- [Title] The title uses 'CCN TD' while the body consistently refers to 'CNN-TD'; this should be corrected.
- [III.B] There is a typo: 'For 3CDNN processing' should read 'For 3DCNN processing'.
- [IV (Table IV)] The heading 'ACCURACY AND LOSS VALUES INTERPRETION' contains a typo; it should be 'Interpretation'.
- [IV and figures] Figure 6 is a generic illustration of a confusion matrix, but the per-model confusion matrices described in the text are not shown. Either include the actual confusion matrices or point to supplementary material.
- [IV.E and Table XIII] Table XIII is referenced as presenting the new-sign results, but the table is not visible in the manuscript; the table should be included or the results should be described in full in the text.
- [V.Discussion] The discussion cites reference [28] to support the claim that other models outperform CNN-TD on video spatiotemporal datasets, but it does not explain how that prior work relates to the present architectures, hyperparameters, or dataset; please clarify the relevance.
Circularity Check
No circularity: the paper is an empirical model comparison with no fitted-input relabeling, load-bearing self-citation, or derivation that reduces to its own inputs.
full rationale
This paper is a purely empirical benchmark comparison of four neural architectures (CNN-LSTM, 3DCNN, CNN-RNN-LSTM, and CNN-TD) on a small self-collected ASL/TTSL video-frame dataset. The central claim, that 3DCNN achieves 91% accuracy on TTSL and 83% on ASL and ranks best, is directly supported by classification reports, confusion matrices, and accuracy/loss curves reported in Section IV; it is not derived from any equation that assumes the conclusion. No fitted parameter is relabeled as a prediction: the models are trained on one split and evaluated on a held-out split, and even the 'new sign' experiment in Section IV.E is an additional evaluation rather than a restatement of training data. The paper contains no load-bearing self-citations; all cited prior work is external model or procedure references. The possible frame-level rather than video-level data split noted by the skeptic is a data-leakage and external-validity concern, but it does not make the reported accuracies equivalent to the inputs by construction, so it falls outside the circularity definition used here.
Assumptions & free parameters
free parameters (5)
- Epochs =
15 to 20
- Early stopping patience =
5 or 7
- Sequence length =
35 frames
- Batch size =
Not reported
- Image resolution =
Not reported
assumptions (4)
- standard math Categorical cross-entropy loss with softmax activation is appropriate for this multiclass classification task.
- domain assumption Convolutional and recurrent layers can extract spatiotemporal features from sign language videos.
- domain assumption The 80/20 train/test split yields a test set representative of the class distribution.
- domain assumption The signs are visually distinguishable from the recorded frames alone.
Cite this review
Pith. "Pith review of Learning Sign Language Representation using CNN LSTM, 3DCNN, CNN RNN LSTM and CCN TD." pith.science (2026). https://pith.science/paper/IXX54XGL
@misc{pith2026241218187,
author = {Pith},
title = {Pith review of: Learning Sign Language Representation using CNN LSTM, 3DCNN, CNN RNN LSTM and CCN TD},
year = {2026},
howpublished = {\url{https://pith.science/paper/IXX54XGL}},
note = {Machine review of arXiv:2412.18187}
}
read the original abstract
Existing Sign Language Learning applications focus on the demonstration of the sign in the hope that the student will copy a sign correctly. In these cases, only a teacher can confirm that the sign was completed correctly, by reviewing a video captured manually. Sign Language Translation is a widely explored field in visual recognition. This paper seeks to explore the algorithms that will allow for real-time, video sign translation, and grading of sign language accuracy for new sign language users. This required algorithms capable of recognizing and processing spatial and temporal features. The aim of this paper is to evaluate and identify the best neural network algorithm that can facilitate a sign language tuition system of this nature. Modern popular algorithms including CNN and 3DCNN are compared on a dataset not yet explored, Trinidad and Tobago Sign Language as well as an American Sign Language dataset. The 3DCNN algorithm was found to be the best performing neural network algorithm from these systems with 91% accuracy in the TTSL dataset and 83% accuracy in the ASL dataset.
Figures
Reference graph
Works this paper leans on
-
[1]
Ahmed, M.A., Zaidan, B.B., Zaidan, A.A., Salih, M.M. and Lakulu, M.M.B., 2018. A review on systems -based sensory gloves for sign language recognition state of the art between 2007 and 2017. Sensors, 18(7), p.2208
work page 2018
-
[2]
Al-Hammadi, M., Muhammad, G., Abdul, W., Alsulaiman, M. and Hossain, M.S., 2019. Hand gesture recognition using 3D-CNN model. IEEE Consumer Electronics Magazine, 9(1), pp.95-101
work page 2019
-
[3]
Al-Hammadi, M., Muhammad, G., Abdul, W., Alsulaiman, M., Bencherif, M.A. and Mekhtiche, M.A., 2020. Hand gesture recognition for sign language using 3DCNN. IEEE Access, 8, pp.79491-79509
work page 2020
- [4]
-
[5]
Anantha Rao, G., Kishore, P.V.V., Sastry, A.S.C.S., Anil Kumar, D. and Kiran Kumar, E., 2018. Selfie continuous sign language recognition with neural network classifier. In Proceedings of 2nd International Conference on Micro -Electronics, Electromagnetics and Telecommunications (pp. 31-40). Springer, Singapore
work page 2018
-
[6]
Biswas, S., Islam, M.J., Huang, Y. and Rajan, H., 2019, May. Boa meets python: a boa dataset of data science software in python language. In 2019 IEEE/ACM 16th International Conference on Mining Software Repositories (MSR) (pp. 577-581). IEEE
work page 2019
-
[7]
Bragg, D., Caselli, N., Gallagher, J.W., Goldberg, M., Oka, C.J. and Thies, W., 2021, May. ASL Sea Battle: Gamifying Sign Language Data Collection. In Proceedings of the 2021 CHI conference on human factors in computing systems (pp. 1-13)
work page 2021
-
[8]
Braithwaite, B., 2020. Ideologies of linguistic research on small sign languages in the global South: A Caribbean perspective. Language & Communication, 74, pp.182-194
work page 2020
Show all 52 references
-
[9]
and Lamb, A., 2011
Braithwaite, B., Drayton, K.A. and Lamb, A., 2011. The history of deaf language and education in Trinidad and Tobago since 1943. History in Action, 2(1), pp.12-17
2011
-
[10]
and Ferreira, R., 2021, May
Canesche, M., Bragança, L., Neto, O.P.V., Nacif, J.A. and Ferreira, R., 2021, May. Google colab cad4u: Hands -on cloud laboratories for digital design. In 2021 IEEE International Symposium on Circuits and Systems (ISCAS) (pp. 1-5). IEEE
2021
-
[11]
and Chen, W., 2018, November
Chang, Z., Zhang, Y. and Chen, W., 2018, November. Effective adam-optimized LSTM neural network for electricity price forecasting. In 2018 IEEE 9th international conference on software engineering and service science (ICSESS) (pp. 245-248). IEEE
2018
-
[12]
and Zhang, H., 2018
Chen, M., He, X., Yang, J. and Zhang, H., 2018. 3 -D convolutional recurrent neural networks with attention model for speech emotion recognition. IEEE Signal Processing Letters, 25(10), pp.1440-1444
2018
-
[13]
and Lee, B.G., 2018
Chong, T.W. and Lee, B.G., 2018. American sign language recognition using leap motion controller with machine learning approach. Sensors, 18(10), p.3554
2018
-
[14]
and Darrell, T., 2015
Donahue, J., Anne Hendricks, L., Guadarrama, S., Rohrbach, M., Venugopalan, S., Saenko, K. and Darrell, T., 2015. Long -term recurrent convolutional networks for visual recognition and description. In Proceedings of the IEEE conference on computer vision and pattern recognitio...
2015
-
[15]
and Zaim, A.H., 2019
Elmasry, W., Akbulut, A. and Zaim, A.H., 2019. Empirical study on multiclass classification ‐ based network intrusion detection. Computational Intelligence, 35(4), pp.919-954
2019
-
[16]
and Hellinckx, P.,
Elmaz, F., Eyckerman, R., Casteels, W., Latré, S. and Hellinckx, P.,
-
[17]
and Alazab, M., 2021
Gadekallu, T.R., Rajput, D.S., Reddy, M., Lakshmanna, K., Bhattacharya, S., Singh, S., Jolfaei, A. and Alazab, M., 2021. A novel PCA–whale optimization -based deep neural network model for classification of tomato plant diseases using GPU. Journal of Real - Time Image Processi...
2021
-
[18]
and Khehra, B.S., 2022
Gill, H.S. and Khehra, B.S., 2022. An integrated approach using CNN-RNN-LSTM for classification of fruit images. Materials Today: Proceedings, 51, pp.591-595
2022
-
[19]
and Kweon, I.S., 2021, December
Ham, S., Park, K., Jang, Y., Oh, Y., Yun, S., Yoon, S., Kim, C.J., Park, H.M. and Kweon, I.S., 2021, December. KSL -Guide: A Large- scale Korean Sign Language Dataset Including Interrogative Sentences for Guiding the Deaf and Hard -of-Hearing. In 2021 16th IEEE International C...
2021
-
[20]
and Phung Ngoc, T., 2021
Huu, P.N. and Phung Ngoc, T., 2021. Hand Gesture Recognition Algorithm Using SVM and HOG Model for Control of Robotic System. Journal of Robotics, 2021
2021
-
[21]
and Kanagachidambaresan, G.R., 2021
Imambi, S., Prakash, K.B. and Kanagachidambaresan, G.R., 2021. PyTorch. In Programming with TensorFlow (pp. 87 -104). Springer, Cham
2021
-
[22]
and Gupta, P., 2021
Jaiswal, S. and Gupta, P., 2021. A review on american sign language character recognition. In Rising Threats in Expert Applications and Solutions (pp. 275-280). Springer, Singapore
2021
-
[23]
and Ginsburg, B., 2021, June
Jia, F., Majumdar, S. and Ginsburg, B., 2021, June. Marblenet: Deep 1d time -channel separable convolutional neural network for voice activity detection. In ICASSP 2021 -2021 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) (pp. 6818-6822). IEEE
2021
-
[24]
and Xie, Y., 2018
Jiang, X., Pang, Y., Li, X., Pan, J. and Xie, Y., 2018. Deep neural networks with elastic rectified linear units for object recognition. Neurocomputing, 275, pp.1132-1139
2018
-
[25]
and Koller, O., 2018
Joze, H.R.V. and Koller, O., 2018. Ms -asl: A large-scale data set and benchmark for understanding american sign language. arXiv preprint arXiv:1812.01053
2018 arXiv
-
[26]
and Burrows, M., 2021
Kaufman, S., Phothilimthana, P., Zhou, Y., Mendis, C., Roy, S., Sabne, A. and Burrows, M., 2021. A learned performance model for tensor processing units. Proceedings of Machine Learning and Systems, 3, pp.387-400
2021
-
[27]
and Cho, C., 2019
Ko, S.K., Kim, C.J., Jung, H. and Cho, C., 2019. Neural sign language translation based on human keypoint estimation. Applied Sciences, 9(13), p.2683
2019
-
[28]
and Fu, Z., 2020
Kong, Z., Zhang, C., Lv, H., Xiong, F. and Fu, Z., 2020. Multimodal feature extraction and fusion deep neural networks for short-term load forecasting. IEEE Access, 8, pp.185373-185383
2020
-
[29]
and Rui, Y., 2018
Li, D., Yao, T., Duan, L.Y., Mei, T. and Rui, Y., 2018. Unified spatio-temporal attention networks for action recognition in videos. IEEE Transactions on Multimedia, 21(2), pp.416-428
2018
-
[30]
and Yun, U., 2021
Lin, J.C.W., Shao, Y., Djenouri, Y. and Yun, U., 2021. ASRNN: a recurrent neural network with an attention model for sequence labeling. Knowledge-Based Systems, 212, p.106548
2021
-
[31]
Understanding and working with Keras
Manaswi, N.K., 2018. Understanding and working with Keras. In Deep Learning with Applications Using Python (pp. 31 -43). Apress, Berkeley, CA
2018
-
[32]
and Han, D.S., 2020, February
Mutegeki, R. and Han, D.S., 2020, February. A CNN -LSTM approach to human activity recognition. In 2020 International Conference on Artificial Intelligence in Information and Communication (ICAIIC) (pp. 362-366). IEEE
2020
-
[33]
and Zhang, L., 2018
Qiao, H., Wang, T., Wang, P., Qiao, S. and Zhang, L., 2018. A time - distributed spatiotemporal feature learning method for machine health monitoring with multi-sensor time series. Sensors, 18(9), p.2932
2018
-
[34]
and Gelly, S.,
Sajjadi, M.S., Bachem, O., Lucic, M., Bousquet, O. and Gelly, S.,
-
[35]
and Woo, W.C., 2015
Shi, X., Chen, Z., Wang, H., Yeung, D.Y., Wong, W.K. and Woo, W.C., 2015. Convolutional LSTM network: A machine learning approach for precipitation nowcasting. Advances in neural information processing systems, 28
2015
-
[36]
and Bird, J., 2018
Spiegel, S., Mueller, F., Weismann, D. and Bird, J., 2018. Cost - sensitive learning for predictive maintenance. arXiv preprint arXiv:1809.10979
2018 arXiv
-
[37]
and Khapra, M., 2020, October
Sridhar, A., Ganesan, R.G., Kumar, P. and Khapra, M., 2020, October. Include: A large scale dataset for indian sign language recognition. In Proceedings of the 28th ACM international conference on multimedia (pp. 1366-1375)
2020
-
[38]
and Visumathi, J., 2020
Suresh, A.J. and Visumathi, J., 2020. Inception ResNet deep transfer learning model for human action recognition using LSTM. Materials Today: Proceedings
2020
-
[39]
and Paluri, M., 2015
Tran, D., Bourdev, L., Fergus, R., Torresani, L. and Paluri, M., 2015. Learning spatiotemporal features with 3d convolutional networks. In Proceedings of the IEEE international conference on computer vision (pp. 4489-4497)
2015
-
[40]
and Dulf, E.H., 2022
Tulbure, A.A., Tulbure, A.A. and Dulf, E.H., 2022. A review on modern defect detection models using DCNNs –Deep convolutional neural networks. Journal of Advanced Research, 35, pp.33-48
2022
-
[41]
and Nápoles, G., 2020
Van Houdt, G., Mosquera, C. and Nápoles, G., 2020. A review on the long short-term memory model. Artificial Intelligence Review, 53(8), pp.5929-5955
2020
-
[42]
and Langari, R., 2018
Wahid, M.F., Tafreshi, R., Al -Sowaidi, M. and Langari, R., 2018. Subject-independent hand gesture recognition using normalization and machine learning algorithms. Journal of computational science, 27, pp.69-76
2018
-
[43]
and Wu, J., 2018
Wang, L., Xu, Y., Cheng, J., Xia, H., Yin, J. and Wu, J., 2018. Human action recognition by learning spatio -temporal features with deep neural networks. IEEE access, 6, pp.17913-17922
2018
-
[44]
and Hua, C., 2021, October
Wang, N., Zhu, G., Zhang, L., Shen, P., Li, H. and Hua, C., 2021, October. Spatio -Temporal Interaction Graph Parsing Networks for Human-Object Interaction Recognition. In Proceedings of the 29th ACM International Conference on Multimedia (pp. 4985-4993)
2021
-
[45]
and Anderson, J., 2022
Wang, Q., Ihme, M., Chen, Y.F. and Anderson, J., 2022. A tensorflow simulation framework for scientific computing of fluid flows on tensor processing units. Computer Physics Communications, p.108292
2022
-
[46]
and Wang, H., 2020
Xia, K., Huang, J. and Wang, H., 2020. LSTM -CNN architecture for human activity recognition. IEEE Access, 8, pp.56855-56866
2020
-
[47]
and Shami, A., 2020
Yang, L. and Shami, A., 2020. On hyperparameter optimization of machine learning algorithms: Theory and practice. Neurocomputing, 415, pp.295-316
2020
-
[48]
On the confusion matrix in credit scoring and its analytical properties
Zeng, G., 2020. On the confusion matrix in credit scoring and its analytical properties. Communications in Statistics -Theory and Methods, 49(9), pp.2080-2093
2020
-
[49]
and Zhang, L., 2018, July
Zhang, Y., Chen, Y., Cheung, S.C., Xiong, Y. and Zhang, L., 2018, July. An empirical study on TensorFlow program bugs. In Proceedings of the 27th ACM SIGSOFT International Symposium on Software Testing and Analysis (pp. 129-140)
2018
-
[2018]
Advances in Neural Information Processing Systems, 31
Assessing generative models via precision and recall. Advances in Neural Information Processing Systems, 31
-
[2020]
Neural Computing and Applications, 32(1), pp.279-293
Improved inception -residual convolutional neural network for object recognition. Neural Computing and Applications, 32(1), pp.279-293
-
[2021]
Building and Environment, 206, p.108327
CNN -LSTM architecture for predictive indoor temperature modeling. Building and Environment, 206, p.108327
Reviewed August 11, 2026 · model on record in the stance chip above.
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