| Interpreting and improving natural-language processing (in machines) with natural language-processing (in the brain)
M. Toneva and L. Wehbe
Neural network models for NLP are typically implemented without the explicit encoding of language rules and yet they are able to break one performance record after another. Despite much work, it is still unclear what the representations learned by these networks correspond to. We propose here a novel approach for interpreting neural networks that relies on the only processing system we have that does understand language: the human brain. We use brain imaging recordings of subjects reading complex natural text to interpret word and sequence embeddings from 4 recent NLP models - ELMo, USE, BERT and Transformer-XL. We study how their representations differ across layer depth, context length, and attention type. Our results reveal differences in the context-related representations across these models. Further, in the transformer models, we find an interaction between layer depth and context length, and between layer depth and attention type. We finally use the insights from the attention experiments to alter BERT: we remove the learned attention at shallow layers, and show that this manipulation improves performance on a wide range of syntactic tasks. Cognitive neuroscientists have already begun using NLP networks to study the brain, and this work closes the loop to allow the interaction between NLP and cognitive neuroscience to be a true cross-pollination.
| Investigating Task Effects on Brain Activity During Stimulus Presentation in MEG
M. Toneva*, O.Stretcu*, B. Poczos, and T. Mitchell
Human Brain Mapping, 2019
Recorded brain activity of subjects who perceive the same stimulus (e.g. a word) while performing different semantic tasks (e.g. identifying whether the word belongs to a particular category) has been shown to differ across tasks. However, it is not well understood how precisely the task contributes to this brain activity. In the current work, we propose multiple hypotheses of how possible interactions between the task and stimulus semantics can be related to the observed brain activity. We test these hypotheses by designing machine learning models to represent each hypothesis, training them to predict the recorded brain activity, and comparing their performance. We investigate a magnetoencephalography (MEG) dataset, where subjects were tasked to answer 20 yes/no questions (e.g. `Is it manmade?') about concrete nouns and their line drawings. Each question-stimulus pair is presented only once. Here we consider each question as a different task. We show that incorporating task semantics improves the prediction of single-trial MEG data by an average of 10% across subjects.
| An Empirical Study of Example Forgetting during Deep Neural Network Learning
M. Toneva*, A. Sordoni*, R. Tachet des Combes*, A. Trischler, Y. Bengio, and G. Gordon
[abs] [pdf] [code] [open review]
Inspired by the phenomenon of catastrophic forgetting, we investigate the learning dynamics of neural networks as they train on single classification tasks. Our goal is to understand whether a related phenomenon occurs when data does not undergo a clear distributional shift. We define a ``forgetting event'' to have occurred when an individual training example transitions from being classified correctly to incorrectly over the course of learning. Across several benchmark data sets, we find that: (i) certain examples are forgotten with high frequency, and some not at all; (ii) a data set's (un)forgettable examples generalize across neural architectures; and (iii) based on forgetting dynamics, a significant fraction of examples can be omitted from the training data set while still maintaining state-of-the-art generalization performance.
| Word Length Processing in Left Lateraloccipital through Region-to-Region Connectivity: an MEG Study
M. Toneva and T. Mitchell
Human Brain Mapping, 2018
A previous MEG study found that many features of stimuli can be decoded around the same time but at different places in the brain, posing the question of how information processing is coordinated between brain regions. Previous approaches to this question are of two types. The first uses a classifier or regression to uncover the relative timings of feature decodability in different brain regions. While addressing when and where information is processed, this approach does not specify how information is coordinated. The second type estimates when the connectivity between regions changes. While this approach assumes that information is coordinated by communication, it does not directly relate to the information content. We aim to more directly relate processing of information content to connectivity. We examine whether, during presentation of a word stimulus, the length of the word relates to how strongly the region that best encodes word length - left lateraloccipital cortex (LOC) - connects to other regions, at different times. For this purpose, we analyze MEG data from an experiment in which 9 subjects were presented 60 concrete nouns along with their line drawings. Our results suggest that the region that is best at encoding a perceptual stimulus feature - word length - has a connectivity network in which the connection strengths vary with the value of the feature. Furthermore, we observe this relationship prior to the peak information decodability in any region. One hypothesis is that information necessary for the processing of the feature is communicated to the seed region by varying connection strengths. Further analysis for a stimulus feature with a later decodability peak, such as a semantic feature, would add to the current results.
| MEG Representational Similarity Analysis Implicates Hierarchical Integration in Sentence Processing
M. Toneva*, N. Rafidi*, D. Schwartz*, S. Jat, and T. Mitchell
Human Brain Mapping, 2018
Multiple hypotheses exist for how the brain constructs sentence meaning. Most fall into two groups based on their assumptions about the processing order of the words within the sentence. The first considers a sequential processing order, while the second uses hierarchical syntactic rules. We test which hypothesis best explains MEG data recorded during reading of sentences with active and passive voice. Under the sequential hypothesis, the voice of a sentence should change its neural signature because word order changes. Under the hierarchical hypothesis, active and passive sentences corresponding to the same proposition should exhibit similar neural signatures. We test how well three language models explain MEG data collected during noun-verb-noun sentence reading. The models we test are bag of words (BoW), sequential word order, and hierarchical. All three models correlate with the MEG data for some timepoints, after verb presentation and briefly post sentence. However, the hierarchical model correlates significantly for more timepoints and is often the best correlated model even if that correlation is not significant. Our analysis shows that a hierarchical model of meaning correlates with neural activity for a longer duration than models which use a bag of words meaning representation or sequential meaning construction. Additionally, just after verb presentation the hierarchical model is the model best correlated with the MEG data. Our method enables the study of language processing hypotheses in the brain at a fine time scale and can be applied to a wide variety of language models.
| Applying artificial vision models to human scene understanding
E. M. Aminoff, M. Toneva, A. Shrivastava, X. Chen, I. Misra, A. Gupta, and M. J. Tarr
Frontiers in Computational Neuroscience, 2015
How do we understand the complex patterns of neural responses that underlie scene understanding? Studies of the network of brain regions held to be scene-selective—the parahippocampal/lingual region (PPA), the retrosplenial complex (RSC), and the occipital place area (TOS)—have typically focused on single visual dimensions (e.g., size), rather than the high-dimensional feature space in which scenes are likely to be neurally represented. Here we leverage well-specified artificial vision systems to explicate a more complex understanding of how scenes are encoded in this functional network. We correlated similarity matrices within three different scene-spaces arising from: (1) BOLD activity in scene-selective brain regions; (2) behavioral measured judgments of visually-perceived scene similarity; and (3) several different computer vision models. These correlations revealed: (1) models that relied on mid- and high-level scene attributes showed the highest correlations with the patterns of neural activity within the scene-selective network; (2) NEIL and SUN—the models that best accounted for the patterns obtained from PPA and TOS—were different from the GIST model that best accounted for the pattern obtained from RSC; (3) The best performing models outperformed behaviorally-measured judgments of scene similarity in accounting for neural data. One computer vision method—NEIL (“Never-Ending-Image-Learner”), which incorporates visual features learned as statistical regularities across web-scale numbers of scenes—showed significant correlations with neural activity in all three scene-selective regions and was one of the two models best able to account for variance in the PPA and TOS. We suggest that these results are a promising first step in explicating more fine-grained models of neural scene understanding, including developing a clearer picture of the division of labor among the components of the functional scene-selective brain network.
|Scene-Space Encoding within the Functional Scene-Selective Network
E. M. Aminoff, M. Toneva, A. Gupta, and M. J. Tarr
Journal of Vision, 2015
High-level visual neuroscience has often focused on how different visual categories are encoded in the brain. For example, we know how the brain responds when viewing scenes as compared to faces or other objects - three regions are consistently engaged: the parahippocampal/lingual region (PPA), the retrosplenial complex (RSC), and the occipital place area/transverse occipital sulcus (TOS). Here we explore the fine-grained responses of these three regions when viewing 100 different scenes. We asked: 1) Can neural signals differentiate the 100 exemplars? 2) Are the PPA, RSC, and TOS strongly activated by the same exemplars and, more generally, are the "scene-spaces" representing how scenes are encoded in these regions similar? In an fMRI study of 100 scenes we found that the scenes eliciting the greatest BOLD signal were largely the same across the PPA, RSC, and TOS. Remarkably, the orderings, from strongest to weakest, of scenes were highly correlated across all three regions (r = .82), but were only moderately correlated with non-scene selective brain regions (r = .30). The high similarity across scene-selective regions suggests that a reliable and distinguishable feature space encodes visual scenes. To better understand the potential feature space, we compared the neural scene-space to scene-spaces defined by either several different computer vision models or behavioral measures of scene similarity. Computer vision models that rely on more complex, mid- to high-level visual features best accounted for the pattern of BOLD signal in scene-selective regions and, interestingly, the better-performing models exceeded the performance of our behavioral measures. These results suggest a division of labor where the representations within the PPA and TOS focus on visual statistical regularities within scenes, whereas the representations within the RSC focus on a more high-level representation of scene category. Moreover, the data suggest the PPA mediates between the processing of the TOS and RSC.
|Towards a model for mid-level feature representation of scenes
M. Toneva, E. M. Aminoff, A. Gupta, and M. Tarr
Oral presentation. WIML NIPS workshop, 2014
Never Ending Image Learner (NEIL) is a semi-supervised learning algorithm that continuously pulls images from the web and learns relationships among them. NEIL has classified over 400,000 images into 917 scene categories using 84 dimensions - termed “attributes”. These attributes roughly correspond to mid-level visual features whose differential combinations define a large scene space. As such, NEIL’s small set of attributes offers a candidate model for the psychological and neural representation of scenes. To investigate this, we tested for significant similarities between the structure of scene space defined by NEIL and the structure of scene space defined by patterns of human BOLD responses as measured by fMRI. The specific scenes in our study were selected by reducing the number of attributes to the 39 that best accounted for variance in NEIL’s scene-attribute co-classification scores. Fifty scene categories were then selected such that each category scored highly on a different set of at most 3 of the 39 attributes. We then selected the two most representative images of the corresponding high-scoring attributes from each scene category, resulting in a total of 100 stimuli used. Canonical correlation analyses (CCA) was used to test the relationship between measured BOLD patterns within the functionally-defined parahippocampal region and NEIL’s representation of each stimulus as a vector containing stimulus-attribute co-classification scores on the 39 attributes. CCA revealed significant similarity between the local structures of the fMRI data and the NEIL representations for all participants. In contrast, neither the entire set of 84 attributes nor 39 randomly-chosen attributes produced significant results using this CCA method. Overall, our results indicate that subsets of the attributes learned by NEIL are effective in accounting for variation in the neural encoding of scenes – as such they represent a first pass compositional model of mid-level features for scene representation.
| An Exploration of Social Grouping: Effects of Behavioral Mimicry, Appearance, and Eye Gaze
A. Nawroj, M. Toneva, H. Admoni, and B. Scassellati
Oral presentation. In proceedings of the 36th Annual Conference of the Cognitive Science Society (Cogsci 2014)
People naturally and easily establish social groupings based on appearance, behavior, and other nonverbal signals. However, psychologists have yet to understand how these varied signals interact. For example, which factor has the strongest effect on establishing social groups? What happens when two of the factors conflict? Part of the difficulty of answering these questions is that people are unique and stochastic stimuli. To address this problem, we use robots as a visually simple and precisely controllable platform for examining the relative in- fluence of social grouping features. We examine how behavioral mimicry, similarity of appearance, and direction of gaze influence peoples’ perception of which group a robot belongs to. Experimental data shows that behavioral mimicry has the most dominant influence on social grouping, though this influence is modulated by appearance. Non-mutual gaze was found to be a weak modulator of the perception of grouping. These results provide insight into the phenomenon of social grouping, and suggest areas for future exploration.
| The Physical Presence of a Robot Tutor Increases Cognitive Learning Gains
D. Leyzberg, S. Spaulding, M. Toneva, and B. Scassellati
Poster. In Proceedings of the 34th Annual Conference of the Cognitive Science Society (Cogsci 2012)
We present the results of a 100 participant study on the role
of a robot's physical presence in a robot tutoring task. Participants
were asked to solve a set of puzzles while being provided
occasional gameplay advice by a robot tutor. Each participant
was assigned one of five conditions: (1) no advice,
(2) robot providing randomized advice, (3) voice of the robot
providing personalized advice, (4) video representation of the
robot providing personalized advice, or (5) physically-present
robot providing personalized advice. We assess the tutor's effectiveness
by the time it takes participants to complete the
puzzles. Participants in the robot providing personalized advice
group solved most puzzles faster on average and improved
their same-puzzle solving time significantly more than participants
in any other group. Our study is the first to assess the
effect of the physical presence of a robot in an automated tutoring
interaction. We conclude that physical embodiment can
produce measurable learning gains.
|Robot gaze does not reflexively cue human attention
H. Admoni, C. Bank, J. Tan, M. Toneva, and B. Scassellati
Poster. In Proceedings of the 33rd Annual Conference of the Cognitive Science Society (Cogsci 2011)
Joint visual attention is a critical aspect of typical human interactions.
Psychophysics experiments indicate that people exhibit
strong reflexive attention shifts in the direction of another
person's gaze, but not in the direction of non-social cues such
as arrows. In this experiment, we ask whether robot gaze elicits
the same reflexive cueing effect as human gaze. We consider
two robots, Zeno and Keepon, to establish whether differences
in cueing depend on level of robot anthropomorphism. Using
psychophysics methods for measuring attention by analyzing
time to identification of a visual probe, we compare attention
shifts elicited by five directional stimuli: a photograph of
a human face, a line drawing of a human face, Zeno's gaze,
Keepon's gaze and an arrow. Results indicate that all stimuli
convey directional information, but that robots fail to elicit attentional
cueing effects that are evoked by non-robot stimuli,
regardless of robot anthropomorphism.