Parallel Backpropagation for Shared-Feature Visualization

High-level visual brain regions contain subareas in which neurons appear to respond more strongly to examples of a particular semantic category, like faces or bodies, rather than objects. However, recent work has shown that while this finding holds on average, some out-of-category stimuli also activate neurons in these regions. This may be due to visual features common among the preferred class also being present in other images. Here, we propose a deep-learning-based approach for visualizing these features. For each neuron, we identify relevant visual features driving its selectivity by modelling responses to images based on latent activations of a deep neural network. Given an out-of-category image which strongly activates the neuron, our method first identifies a reference image from the preferred category yielding a similar feature activation pattern. We then backpropagate latent activations of both images to the pixel level, while enhancing the identified shared dimensions and attenuating non-shared features. The procedure highlights image regions containing shared features driving responses of the model neuron. We apply the algorithm to novel recordings from body-selective regions in macaque IT cortex in order to understand why some images of objects excite these neurons. Visualizations reveal object parts which resemble parts of a macaque body, shedding light on neural preference of these objects.

Paper

Similar papers

Peer review

Reviewer aP8u6/10 · confidence 4/52024-07-10

Summary

This paper presents an innovative method for explaining why an IT neuron that is supposed to tune to a particular object class or category would respond to outside-of-category stimuli. The proposed method uses parallel backpropagation to highlight the features in the out-of-category stimuli that are shared by the stimuli in the tuned class. The method helps discover some shared features between highly activating bodies and objects in IT neurons but also fails in other cases.

Strengths

The method is original, innovative, sound, and very clearly presented. It can be useful for IT neurophysiological research to resolve some mysteries in the neural codes in IT.

Weaknesses

The paper focuses on the presentation of the method. The presentation of the scientific results is not very systematic. They are shown as anecdotal illustrations of some success and failure cases. Hence, the scientific insights provided are a bit preliminary, and the significance of the results is perhaps limited. The contribution is solid but perhaps a bit thin.

Questions

Perhaps the usefulness of the method is more general than the authors envisioned. Can the method be applied to neurons in V4 and V1? Can it be used to analyze artificial deep networks to understand "neural codes" in CNN? Also, the assumption of the approach is that neurons are tuned to one single category, but could neurons be tuned to multiple categories or multiple features?

Rating

6

Confidence

4

Soundness

3

Presentation

4

Contribution

3

Limitations

There are no concerns about the limitation issue.

Reviewer 5Zdi10/10 · confidence 3/52024-07-11

Summary

A deep-learning-based approach is proposed in the paper "Parallel Backpropagation for Shared-Feature Visualization" to visualize shared visual features in high-level visual brain regions, which are typically thought to respond selectively to particular categories like bodies or faces. Despite this selectivity, these neurons occasionally respond to stimuli outside of their category, possibly due to shared visual characteristics. By backpropagating activations to the pixel level and enhancing shared features while attenuating non-shared ones, the authors present a strategy for highlighting these shared features using a deep neural network to model neural responses and identify relevant features.

Strengths

The text is very well structured, and the questions and methodology are written in a very clear and detailed manner. This work follows an innovative approach which presents a novel and exciting way to use DL in order to gain insights of single neuron selectivity across the visual hierarchy. The method's steps—which include parallel backpropagation, determining neuron-specific picture similarity, and training a linear readout on top of a CNN—are fully explained. Finally, this work includes an original experimental component that differentiates from a lot of other applications of DL on already existing datasets. A strategy for visualizing shared elements that drive brain reactions to out-of-category stimuli is presented in this research, which shows promise. The method has the potential to further our understanding of how the brain processes visual information, even though there is still room for improvement.

Weaknesses

In this work, the method is heavily dependent on the deep neural network used, and how effectively it can fit the neural data. Fortunately, the cases where the tunning properties are not captured by the model can be identified as mentioned in the end of the results section. The ability to generalize to other categories such as face patches was not tested and remains to be tested. The technique is predicated on the idea that within-category and out-of-category photos share a significant amount of attributes. It is not clear what we expect for the model to do and how useful outcomes are going to be in situations where there is little overlap. Finally, while the single neuron tuning specificity is the main topic of this work, it remains to be seen how a similar approach but with population representations compares.

Questions

Subsequent research ought to concentrate on enhancing the underlying models and attribution methods as well as verifying the approach in various scenarios such as with different categories and in a closed-loop manner. The authors already acknowledge these directions.

Rating

10

Confidence

3

Soundness

4

Presentation

4

Contribution

4

Limitations

The authors have a limitation section that addresses their work's assumptions.

Reviewer 7NES8/10 · confidence 4/52024-07-17

Summary

The paper shows that a hypothesis for the brain (category-selective neurons are actually selective to generic lower-level features that are present in those categories, not necessarily features specific to those categories) can be reproduced and visualized in a ResNet trained to predict neural activity. If I understand correctly, it is capable of generating hypothetical pairs of images with similar features (as in A.1.1). One could then test if an actual neuron responds similarly to the pair as the model predicts. Or find a real neuron, record, then based on responses, use the model to get a stream of stimuli that should elicit similar responses (because of similar low-level features) and show it to the real neuron to see if it responds as we expect.

Strengths

This is a clear and straightforward method that contributes to tools available for analyzing what drives individual units in regression-to-neural-data deep learning models. Comprehensive and clear background/related work; very clear writing overall and description of methods on high and low levels. I got an intuition pretty quickly for what the method was even before the equations.

Weaknesses

The results are interesting and intriguing to look at (Figure 4), however at the end of the day it comes across as a bit anecdotal as opposed to giving us insight into general principles of shape or object representation. This is not a strong criticism though - I accept it is a good starting point, and still a worthwhile contribution. Also, I note that all the objects are presented on blank backgrounds. I wonder how things would change when the objects or bodies are presented in their natural context within a visual scene? other comments: 111: Maybe this is standard terminology I'm not familiar with, but "readout vector" confused me at first because it makes it sound like it's logits or something? But it's just the weights from the latent representation to a single output unit. Line 131 more clearly calls it "learned weight vector" 145: should be a_2=f(x_2)? It would be interesting to see more mathematical/geometric analysis of the shared features (beyond stubby vs spiky) in the future, e.g. joints at a specific angle, combinations of contours in a certain way, etc.

Questions

see above

Rating

8

Confidence

4

Soundness

4

Presentation

4

Contribution

4

Limitations

see above

Reviewer yQac5/10 · confidence 4/52024-07-17

Summary

The authors proposed a deep learning based method to visualize shared features in neurons that are selective to specific categories, such as faces or bodies, when they respond to out-of-category stimuli. The method identifies visual features driving the selectivity of neurons by modeling responses to images based on latent activations of a deep neural network. The paper highlights the application of this method to body-selective regions in the macaque IT cortex, demonstrating that neurons encode overlapping visual features for bodies and objects. This approach provides insights into why certain non-body objects activate body-selective neurons and offers a more fine-grained understanding of neural responses.

Strengths

The paper is well-structured, with a clear abstract, introduction, methodology, and results sections. While the proposed method is based on well-established deep learning techniques, specifically leveraging latent activations of a deep neural network to model neuron responses, the application to novel recordings from body-selective regions in macaque IT cortex demonstrates its practical utility and empirical soundness. I think the primary contribution lies in providing a tool that allows for a more fine-grained investigation of neuron responses in visual neuroscience. By revealing why certain non-body objects activate body-selective neurons, the paper contributes valuable insights to the understanding of neural selectivity and visual processing.

Weaknesses

The paper primarily applies existing deep learning techniques rather than introducing new machine learning algorithms or models. This might be seen as a limitation for those expecting significant advancements in machine learning methods, especially readers from NeurIPS.

Questions

Can The authors clarify the novel contributions of the proposed method in comparison to existing visualization techniques? How does the approach provide unique insights that are not achievable with current methods? How generalizable is the method to other types of neurons or different brain regions beyond body-selective areas in the macaque IT cortex? Can the proposed approach be adapted to study other semantic categories or species? What are the broader implications of these findings for the field of visual neuroscience? We knew from previous studies that out-of-category stimuli can also activate neurons coding for in-category features.

Rating

5

Confidence

4

Soundness

3

Presentation

3

Contribution

2

Limitations

The authors have addressed the limitations.

Reviewer 5Zdi2024-08-09

I would like to thank the authors for the response to my comments.

Reviewer yQac2024-08-12

Thanks for the response

I went through the answers from the authors and am happy with them. However, I am still concerning about the techenical novelty after going through the paper again. I will keep my score.

Authorsrebuttal2024-08-13

Thank you for your review and comments. After re-assessing the ARRIVAL guidelines, we have made the following changes: 1. We included the animals' body weight in the subsection on Animals and husbandry (A.2). 2. We had previously (anonymously) specified the ethics committes which had reviewed the experiments (A.2); however, we were missing the specific protocol number. We now include it in the text. 3. We moved the ethics statement, including the relevant committees, from the appendix to the experiments section (Section 4: Neural data collection) to make it more prominent. If we have missed relevant information, we would be grateful for additional comments.

Reviewer aP8u2024-08-13

Responses to Authors' rebuttal

I would like to thank authors' interesting discussion on the questions I raised. I do think this is a valuable contribution.

Program Chairsdecision2024-09-25

Decision

Accept (spotlight)

© 2026 NYSGPT2525 LLC