Paper:
We propose a novel attention mechanism to enhance Convolutional Neural Networks for fine-grained recognition. The proposed mechanism reuses CNN feature activations to find the most informative parts of the image at different depths with the help of gating mechanisms and without part annotations. Thus, it can be used to augment any layer of a CNN to extract low-and high-level local information to be more discriminative. Differently, from other approaches, the mechanism we propose just needs a single pass through the input and it can be trained end-to-end through SGD. As a consequence, the proposed mechanism is modular, architecture-independent, easy to implement, and faster than iterative approaches. Experiments show that, when augmented with our approach, Wide Residual Networks systematically achieve superior performance on each of five different finegrained recognition datasets: the Adience age and gender recognition benchmark, Caltech-UCSD Birds-200-2011, Stanford Dogs, Stanford Cars, and UEC Food-100, obtaining competitive and state-of-the-art scores.

Review:
The manuscript describes a novel attentional mechanism applied to fine-grained recognition. 
On the positive side, the approach seems to consistently improve the recognition accuracy of the baseline  (a wide residual net). The approach is also consistently tested on the main fine-grained recognition datasets (the Adience age and gender recognition benchmark, Caltech-UCSD Birds-200-2011, Stanford Dogs, Stanford Cars, and UEC Food-100).
On the negative side, the paper could be better written and motivated.
First, some claimed are made about how the proposed approach "enhances most of the desirable properties from previous approaches” (see pp 1-2) but these claims are never backed up. More generally since the paper focuses on attention, other attentional approaches should be used as benchmarks beyond the WRN baseline. If the authors want to claim that the proposed approach is "more robust to deformation and clutter” then they should design an experiment that shows that this is the case. 
Beyond, the approach seems a little ad hoc. No real rationale is provided for the different mechanisms including the gating etc and certainly no experimental validation is provided to demonstrate the need for these mechanisms. More generally, it is not clear from reading the paper specifically what computational limitation of the CNN is being solved by the proposed attentional mechanism. 
Some of the masks shown in Fig 3 seem rather suspicious and prompt this referee to think that the networks are seriously overfitting to the data. For instance, why would attending to a right ear help in gender recognition? 
The proposed extension adds several hyperparameters (for instance the number K of attention heads). Apologies if I missed it but I am not clear how this was optimized for the experiments reported. In general, the paper could be clearer. For instance, it is not clear from either the text or Fig 2 how H goes from XxYxK for the attention head o XxYxN for the output head.
As a final point, I would say that while some of the criticisms could be addressed in a revision, the improvements seem relatively modest. Given that the focus of the paper is already limited to fine-grained recognition, it seems that the paper would be better suited for a computer vision conference.
Minor point: 
"we incorporate the advantages of visual and biological attention mechanisms” not sure this statement makes much sense. Seems like visual and biological are distinct attributes but visual attention can be biological (or not, I guess) and it is not clear how biological the proposed approach is. Certainly no attempt is made by the authors to connect to biology.
"top-down feed-forward attention mechanism” -> it should be just feed-forward attention. Not clear what "top-down feed-forward” attention could be...