Question: Can your method be applied to other generative ZSL models?
Evidence: In this subsection, we discuss our main experimental results. As we observe that the results are heavily influenced by hyper-parameter tuning strategy, our main goal throughout our experiments is the validation of the proposed sample probing idea by integrating it into strong generative GZSL baselines, and then comparing results using the same tuning methodology. Using this principle, we present two main types of analysis: (i) the evaluation of the proposed approach using ESZSL as the probe model in combination with a number of generative GZSL models, and (ii) the evaluation of alternative closed-form probe models within our framework.
Generative GZSL models with sample probing. To evaluate the sample probing approach as a general technique to improve generative model training, we integrate it to four recent generative GZSL approaches: conditional Wasserstein GAN (cWGAN), LisGAN, TF-VAEGAN and FREE. We additionally report results for the variant of TF-VAEGAN with the fine-tuned representations (TF-VAEGAN-FT), as it is the only one among them with reported fine-tuning results.
For the cWGAN, we follow the implementation details described in Sariyildiz & Cinbis (2019), and tune hyper-parameters using our policy. For LisGAN, TF-VAEGAN and FREE models, we use the official repositories shared by their respective authors. We use the version of TF-VAEGAN without feedback loop, for simplicity, as the model yields excellent performance with and without feedback loop. In all models (except cWGAN), we only re-tune the number of training iterations of the original models using our hyper-parameter tuning policy, to make the re-Table: Evaluation of sample probing with multiple generative GZSL models on four benchmark datasets. Each row pair shows the effect of adding sample probing to a particular generative GZSL model, using ESZSL as the closed-form probe model. We use the same hyper-parameter optimization policy in all cases to make results comparable. sults comparable, as it is unclear how the original values were obtained. We keep all remaining hyper-parameters unchanged to remain as close as possible to the original implementations.
The results over the four benchmark datasets are presented in Table. In terms of the h-scores, we observe improvements in 17 out of 19 cases, at varying degrees (up to 4.6 points ). Only in two cases we observe a slight degradation (maximum of 0.2 points) in performance. Overall, these improvements over already strong and state-of-the-art (or competitive) baselines validate the effectiveness of the proposed sample probing approach, suggesting that it is a valid method towards end-to-end learning of generative GZSL models directly optimized for synthetic train data generation purposes.
Sample probing with alternative closed-form models. We now evaluate our approach with different closed-form probe models, specifically ESZSL, Sem2Vis and Vis2Sem, as described in Section 3.3. For these experiments, we use the TF-VAEGAN as the base generative model.
The results with four configurations over four benchmark datasets are presented in Table. First of all, in terms of h-scores, we observe considerable performance variations across the probe models and datasets: Sem2Vis performs the best on CUB (+0.9 over the baseline), ESZSL provides a clear gain on FLO (+4.6) and a relative improvement on AWA (+0.3), and Vis2Sem improves the most on SUN (+1.8). These results suggest that sample probe alternatives have their own advantages and disadvantages, and their performances can be data dependent. Therefore, in a practical application, probe model options can be incorporated into the model selection process. More in-depth understanding of closed-form model characteristics for sample probing purposes, and the formulation and evaluation of other probe models can be important future work directions. Overall, the fact that we observe equivalent (2) or better (9) h-scores in 11 out of 12 sample probing experiments indicates the versatility of the approach in terms of compatibility with various closed-form probe models.
Comparison to other generative GZSL approaches. Performance comparisons across independent experiment results can be misleading due to differences in formulation-agnostic implementation and model selection details. Nevertheless, an overall comparison can be found in Appendix A. and probe-validation classes, respectively. We observe that using either one during the evaluation of the sample probing ZSL model, brings its own characteristic results (Table). On all datasets, using zsl-loss increases the seen accuracy while using gzsl-loss increases the unseen accuracy. We choose among these two options using our same hyper-parameter tuning policy, on the validation set. Effect of sample probing loss weight. Figure shows the validation and test set h-score values as a function of sample probing loss weight. In the test set results, we observe an overall increasing performance trend with larger loss weights, up to the weight 6, highlighting the contribution of sample probing. The optimal weight with respect to the validation and the test sets, however, differs. This observation is an example for the difficulty of tuning the ZSL model based on validation set. We set the loss weight to 5 following our hyper-parameter tuning policy, which yields almost 0.5 lower than the maximum test-set score observed for this single hyper-parameter.
Quantitative analysis of sample quality. We quantitatively evaluate the sample quality using Fréchet (Wasserstein-2) distance, which is also used in the FID metric for evaluating GAN models. In Table, we provide a comparison for TF-VAEGAN and our approach for respective mean per-class Fréchet distances between real and synthetic samples (200 synthetic samples per class) of unseen classes on three datasets. The results show that sample probing helps generator to generate more realistic samples compared to TF-VAEGAN. We further investigate the qualitative analysis of the sample quality via t-SNE visualizations in Appendix B.
Table 1: Evaluation of sample probing with multiple generative GZSL models on four bench_x0002_mark datasets. Each row pair shows the effect of adding sample probing to a particular generative GZSL model, using ESZSL as the closed-form probe model. We use the same hyper-parameter optimization policy in all cases to make results comparable. We observe h-score improvements at varying degrees in 17 out of 19 model, feature & dataset variations.
Answer: Many thanks for this suggestion. In the revised manuscript, we now evaluate the proposed approach using two additional closed-form ZSL models as the probe models, and report the results in the newly added Table 2. As discussed in Section 4.1, we observe improvements via sample probing in 11 out of 12 cases, which supports the general applicability of the method.