Continuing the Syuzhet Discussion

March 7, 2015February 11, 2016 annieswafford Syuzhet, Uncategorized Digital Humanities, distant reading, sentiment analysis, signal processing, Syuzhet package, text analysis, visualizations

[Update: Matthew Jockers posted a response to this critique yesterday. Rather than contribute to what he calls a “blogging frenzy,” and in the absence of a comments field on his blog, I will make a few points here:

1) It is clear that the Syuzhet package needs more peer review and rigorous testing — designed to confirm or refute hypotheses — before it will be possible to make valid claims about archetypal plot structures. I have attempted to model that testing and review here.

2) Matt seems to misunderstand my critique. I am not arguing about whether or not Portrait of the Artist represents a “man in a hole” plot shape; I’m pointing out that any Syuzhet plot shape can easily be the result of low-pass filter artifacts instead of a reflection of the computed sentiment (itself hard to analyze at the single word or sentence level), and that they therefore cannot yet be said to reliably reflect the emotional trajectories of novels.]

[This is a continuation of an ongoing dialogue about the Syuzhet package and literary text-mining. If you want to know the full history, check out Eileen Clancy’s Storify on the subject.]

[Update: The code that generates the graphs for this blog post is now available at https://github.com/jswafford/syuzhet-samples.]

A few weeks ago, Matthew Jockers published Syuzhet, an interesting package for the programming language R that uses sentiment analysis, together with a low-pass filter, to uncover one of “six, or possibly seven, archetypal plot shapes” (also known as foundation shapes) in any novel. Earlier this week, I posted a response, documenting some potential issues with the package, including problems with the sentence splitter, inaccuracies in the sentiment analysis algorithms, and ringing artifacts in the foundation shapes. A few days ago, Jockers responded; his newest blog post claims that while some of these problems do exist, they are limited to “one sentence here or one sentence there” and that in aggregate, the sentiment analysis succeeds. Jockers cites the apparent similarities in the emotional trajectories and foundation shapes produced with several different sentiment analysis algorithms on the same text as proof that Syuzhet is “good enough” that we can draw meaningful conclusions based on its foundation shapes.

This blog post investigates this claim, and draws two conclusions:

We can’t learn much from foundation shapes, because they don’t always reflect the emotional valence of novels; in extreme cases, Syuzhet’s foundation shapes can be virtually unrelated to the estimated sentiments of their novels.
We cannot truly evaluate whether the sentiment analysis methods are “good enough” without benchmarks to define success.

Foundation Shapes

In his recent blog post, Jockers presents the emotional valences for Portrait of the Artist generated by Syuzhet’s four different sentiment analysis algorithms (left-hand graph), and the resulting foundation shapes (right-hand graph):

Although there are noticeable similarities between the four emotional valences in the graph on the left, they also have some significant differences, such as at x=8 where the Stanford line reaches its maximum while the Afinn and NRC lines drop downwards. And yet, these differences disappear in the foundation shapes on the right: all four curves reach their maximum around the 80% mark.

Jockers believes that these similar foundation shapes indicate that Syuzhet works, and that, despite the unreliability of the sentiment analysis, Syuzhet can still find the “latent emotional trajectory that represents the general sense of the novel’s plot.” I worried, though, that some of these similarities may be more due to ringing artifacts (which I discussed in my last post) than due to actual agreement between the different sentiment analysis methods.

Fortunately, there’s an easy way to test this: we can manually change the emotional valence for Portrait of the Artist and see if the foundation shape changes accordingly. For example, we can take the sentiment estimated by the bing method and simply set the valence for the final third of the novel to 0 (neutral sentiment): this is the equivalent of keeping the first two thirds of Portrait of the Artist the same, but changing the final third of the novel to consist of exclusively emotionless words. We would expect that the foundation shape would flatten out to 0 during the final third to reflect this change. Here’s what happens:

Surprisingly, the foundation shape is nearly identical: this suggests that the rise in the final third of the foundation shape is indeed a ringing artifact and not a result of an increase in positive emotion in the text.

In fact, we can take this even further: the foundation shape remains the same even if we make all but the middle twenty sentences of Portrait of the Artist neutral, leaving less than 0.5% of the novel unchanged:

These observations cast Jockers’s comparison of the sentiment analyzers in a new light. Their similar foundation shapes do not validate Syuzhet’s sentiment analysis algorithm; they merely demonstrate that Syuzhet’s foundation shapes can make dissimilar curves similar.

This is not to say that the values at the ends never matter; as another experiment, I artificially raised the emotional valence of the opening and closing two-hundred sentences of Portrait of the Artist (about 8% of the novel), leaving the rest unchanged. This is the equivalent of changing the text of Portrait of the Artist so the opening and closing are extremely happy:

Interestingly, the new foundation shape (blue) now shows the midpoint of the novel as less negative than the area around it, even though it is still the most negative portion of the story (since we only changed the very beginning and end). This is a classic ringing artifact: the foundation shape can’t reflect the emotional heights at both ends of the story without altering the middle because the correct shape cannot be approximated by low-frequency sinusoids.

Since we’ve now seen several foundation shapes that don’t reflect the emotional valences that generated them, it’s reasonable to wonder just how dissimilar two graphs could be while still maintaining the same foundation shape. I asked Daniel Lepage (a professional programmer with a degree in mathematics) how we might find such graphs. He pointed out that Syuzhet computes foundation shapes by discarding all but the lowest terms of the Fourier transform. This means that stories where much of the emotional valence is determined by higher terms can have wildly different valences, yet still share a foundation shape. To test this, he created multiple signals—graphs of the emotional valences of hypothetical texts—that share the foundation shape of Portrait of the Artist (according to Syuzhet):

These sample signals clearly have very little in common with each other or with Portrait of the Artist, and yet they all produce completely identical foundation shapes, so a foundation shape may be entirely unlike the emotional trajectory of its novel.

The fourth example signal is particularly interesting: practically all of the variation is determined by the higher Fourier terms. This means that by making nearly-invisible low-frequency changes to the original valence, we can completely alter its foundation shape:

Obviously, this is a worst-case scenario: it is unlikely that a real book would perform quite so badly. Nonetheless, this proves that we cannot assume that Syuzhet’s foundation shapes reliably reflect the emotional trajectories of their novels.

Sentiment Analysis

Of course, the quality of the foundation shapes is a moot point unless we trust the underlying sentiment analysis. Jockers and I essentially agree on the worth of sentiment analysis as applied to novels: in his words, “Frankly, I don’t think any of the current sentiment detection methods are especially reliable.” All approaches—from the lexicon-based approaches to the more advanced Stanford parser—have difficulty with anything that doesn’t sound like a tweet or product review, which is not surprising. He and I have both shown a number of examples in which sentiment analysis fails to produce the emotional valence that a human would assign—such as “Well, it’s like a potato”—which suggests that modern sentiment analysis may not be up to the task of handling the emotional complexities of novels.

Although the Stanford parser does boast 80-85% accuracy, it was trained and tested on movie reviews, which do not generally have the same degrees of ambiguity and nuance as novels. The other three analysis methods Syuzhet provides are all based on word-counting; a cursory examination of modern sentiment analysis literature indicates that this hasn’t been the state of the art for quite some time. Even Bing Liu, creator of the Bing lexicon (Syuzhet’s default lexicon), states on his website that “although necessary, having an opinion lexicon is far from sufficient for accurate sentiment analysis.”[1]

Ultimately, however, this debate is skirting the real issue, which Lisa Rhody raised in a comment on my last blog post. She asked how “sentence-level errors in detecting sentiment present problems in the aggregate” and wondered “how these errors might build on themselves to continue to cause concern at scale.” In other words, is sentiment analysis really, as Jockers says, “good enough”?

The short answer is: we can’t tell.

Sentiment analysis experts deal with this problem by assembling corpora of human-annotated documents, such as manually-evaluated tweets or movie reviews (which are “annotated” by how many stars the viewer gave the movie). They can use this data both to train and to test their algorithms, measuring how frequently the machine provides the same response as an “average” human.

For novels, we have no such corpus with which to test a sentiment analyzer, and so our evaluations are pure guesswork: we hope that phrases like “not good” and “like a potato” don’t happen too often; we hope that sarcasm and satire are infrequent enough; we hope that errors in sentence-splitting won’t affect our results; but ultimately we cannot confirm it either way.

This is not to say that the project is doomed: we could approach this problem using the same strategies mentioned above. For example, we could ask scholars to mark the emotional valence of many novels sentence by sentence (or paragraph by paragraph, perhaps) using some crowdsourcing tool, and use this to create benchmarks showing us exactly how people evaluate emotional trajectories, on average.[2] Then, as different packages emerge that purport to analyze the emotional valence of novels, we could actually compare them with a large corpus of human-annotated texts.

While Jockers agrees that comparing Syuzhet’s outputs with human-annotated texts “would be a great test,” it’s more than merely useful: it’s absolutely necessary. Without such benchmarks, we have no way to assess the validity of Syuzhet’s sentiment analysis; we can only guess based on the way it handles sample sentences.[3]

All in all, Syuzhet’s lack of benchmarks and inaccurate foundation shapes are cause for concern. It has a long way to go before we can make reliable claims about the number of archetypal plot shapes novels share.

[1] His 2010 paper “Sentiment Analysis and Subjectivity” includes a discussion of the more complicated analyses beyond basic word-counting that are required for state-of-the-art sentiment analysis.

[2] It’s also possible that we’d discover some novels where the individual differences between readers make it impossible to determine a consensus; perhaps there are novels that have no “emotional trajectory” at all?

[3] As we’ve already seen, this leaves much to be desired.

Problems with the Syuzhet Package

March 2, 2015February 11, 2016 annieswafford Syuzhet, Uncategorized Digital Humanities, distant reading, literary studies, novels, Portrait of the Artist As a Young Man, programming, R, sentiment analysis, signal processing, Syuzhet package, text mining

I’ve been watching the developments with Matthew Jockers’s Syuzhet package and blog posts with interest over the last few months. I’m always excited to try new tools that I can bring into both the classroom and my own research. For those of you who are just now hearing about it, Syuzhet is a package for extracting and plotting the “emotional trajectory” of a novel.

The Syuzhet algorithm works as follows: First, you take the novel and split it up into sentences. Then, you use sentiment analysis to assign a positive or negative number to each sentence indicating how positive the sentence is. For example, “I’m happy” and “I like this” would have positive numbers, while “This is terrible” and “Everything is awful” would get negative numbers. Finally, you smooth out these numbers to get what Jockers calls the “foundation shape” of the novel, a smooth graph of how emotion rises and falls over the course of the novel’s plot.

This is an interesting idea, and I installed the package to try it out, but I’ve encountered several substantial problems along the way that challenge Jockers’s conclusion that he has discovered “six, or possibly seven, archetypal plot shapes” common to novels. I communicated privately with him about some of these issues last month, and I hope these problems will be addressed in the next version of the package. Until then, users should be aware that the package does not work as advertised.

I’ll proceed step-by-step through the process of using the package, explaining the problems at each step.

1. Splitting Sentences

The first step of the algorithm is to split the text into sentences using Syuzhet’s “get_sentences” function. I tried running this on Charles Dickens’s Bleak House, and immediately ran into trouble: in many places, especially around dialogue, Syuzhet incorrectly interpreted multiple sentences as being just one sentence. This seemed to be particularly common around quotation marks. For example, here’s one “sentence” from the middle of Chapter III, according to Syuzhet:[1]

Mrs. Rachael, I needn’t inform you who were acquainted with the late Miss Barbary’s affairs, that her means die with her and that this young lady, now her aunt is dead–”

“My aunt, sir!”

“It is really of no use carrying on a deception when no object is to be gained by it,” said Mr. Kenge smoothly, “Aunt in fact, though not in law.

As you can imagine, these grouping errors are likely to cause problems for works with extensive dialogue (such as most novels and short stories).[2]

2. Assigning Value to Words

The second step is to compute the emotional valence of each sentence, a problem known as sentiment analysis. The Syuzhet package provides four options for sentiment analysis: “Bing”, “AFINN”, “NRC”, and “Stanford”; “Bing” is the default, and is what Jockers recommends in his documentation.

“Bing,” “AFINN,” and “NRC” are all simple lexicons: each is a list of words with a precomputed positive or negative “score” for each word, and Syuzhet computes the valence of a sentence by simply adding together the scores of every word in it.

This approach has a number of drawbacks:

Since each word is scored in isolation, it can’t process modifiers. This means firstly that intensifiers have no effect, so that adding “very” or “extremely” won’t change the valence, and secondly (and more worryingly) that negations have no effect. Consequently, the sentence “I am not happy today” has exactly the same positive valence as “I am extremely happy today” or just “I’m happy.”
For the same reason, the algorithm can’t take the multiple meanings of words into consideration, so words such as “well” and “like” are often marked as positive, even when they’re used in neutral ways. The “Bing” lexicon, for example, considers the sentence “I am happy” to be less positive than the sentence “Well, it’s like a potato.”[3]
All three lexicons primarily contain contemporary English words, because they were developed for analyzing modern documents like product reviews and tweets. As a result, words of dialect may produce neutral values regardless of their actual emotional valence, and words whose meanings have changed since the Victorian period may have scores that do not at all reflect their use in the text. For example, “noisome,” “odours,” “execrations,” and “sulphurous” are negative words in Portrait of the Artist but are not negative in Bing’s lexicon.
Syuzhet’s particular implementation of this approach only counts a word once for a given sentence even if it’s repeated, so that e.g. “I am happy–so happy–today” has the same valence as “I am happy today.”
These lexicons also do not provide much nuance: Bing and NRC assign every word a value of -1 (negative terms), 0 (neutral terms), or 1 (positive terms). Thus, the two sentences “This is decent” and “This is wonderful!” both have valence 1, even though the second is clearly much more positive.

To demonstrate some of these problems, I composed the following simple paragraph:

I haven’t been sad in a long time.
I am extremely happy today.
It’s a good day.
But suddenly I’m only a little bit happy.
Then I’m not happy at all.
In fact, I am now the least happy person on the planet.
There is no happiness left in me.
Wait, it’s returned!
I don’t feel so bad after all!

According to common sense, we’d expect the sentiment assigned to these sentences to start off fairly high, then decline rapidly from lines 4 to 7, and finally return to neutral (or slightly positive) at the end.

Using the Syuzhet package, we get the following sentiment trajectory:

The emotional trajectory does pretty much exactly the opposite of what we expected. It starts negative, because “I haven’t been sad in a long time” contains only one word with a recognized value, which is “sad.” Then it rises to be at the same level of positivity for the next few lines, because “I am extremely happy today.” and “There is no happiness left in me” are equally positive. At the end, as the narrative turns hopeful again, Syuzhet’s trajectory drops back to negative because it detected the word “bad” in the sentence. [4]

This example showcases a number of the weaknesses of this sentiment analysis strategy on very straightforward text; I expect that these problems will be far worse for novels that contain emotion implied though metaphors or imagery patterns, or use satire and sarcasm (e.g. most works by Jane Austen, Jonathan Swift, Mark Twain, or Oscar Wilde), irony, or an unreliable narrator (e.g. much of postmodern literature).

Essentially, the Syuzhet package creates graphs of word frequency grouped by theme (positive and negative) throughout a text more than it does graphs of emotional valence in a text.

3. Foundation Shapes

The final step of Syuzhet is to turn the emotional trajectory into a Foundation Shape–a simplified graph of the story’s emotional valence that (hopefully) echoes the shape of the plot. But once again, I found some problems. Syuzhet produces the Foundation Shape by putting the emotional trajectory through an ideal low-pass filter, which is designed to eliminate the noise of the trajectory and smooth out its extremes. Ideal low-pass filters work by approximating the function with a fixed number of sinusoidal waves; the smaller the number of sinusoids, the smoother the resulting graph will be.

However, ideal low-pass filters often introduce extra lobes or humps in parts of the graph that aren’t well-approximated by sinusoids. These extra lobes are called ringing artifacts, and will be larger when the number of sinusoids is lower.

Here’s a simple example:

The graph on the left is the original signal, and the graph on the right demonstrates the ringing artifacts caused by a low-pass filter (specifically, by zeroing all but the first five terms of the Fourier transform). The original signal just has one lobe in the middle, but the low-pass filter introduces extra lobes on either side.

By default, Syuzhet uses an even lower cutoff than the example above (keeping only three Fourier terms). Consequently, we should expect to find inaccurate lobes in the resulting foundation shapes. The Portrait of the Artist foundation shape that Jockers presented in his post “Revealing Sentiment and Plot Arcs with the Syuzhet Package” already shows this: [5]

The full trajectory opens with a largely flat stretch and a strong negative spike around x=1100 that then rises back to be neutral by about x=1500. The foundation shape, on the other hand, opens with a rise, and in fact peaks in positivity right around where the original signal peaks in negativity. In other words, the foundation shape for the first part of the book is not merely inaccurate, but in fact exactly opposite the actual shape of the original graph.

This is a pretty serious problem, and it means that until Syuzhet provides filters that don’t cause ringing artifacts, it is likely that most foundation shapes will be inaccurate representations of the stories’ true plot trajectories. Since the foundation shape may in places be the opposite of the emotional trajectory, two foundation shapes may look identical despite having opposing emotional valences. Jockers’s claim that he has derived “the six/seven plot archetypes” of literature from a sample of “41,383 novels” may be due more to ringing artifacts than to an actual similarity between the emotional structures of the analyzed novels.

While Syuzhet is a very interesting idea, its implementation suffers from a number of problems, including an unreliable sentence splitter, a sentiment analysis engine incapable of evaluating many sentences, and a foundation shape algorithm that fundamentally distorts the original data. Some of these problems may be fixable–there are certainly smoothing filters that don’t suffer from ringing artifacts[6]–and while I don’t know what the current state of the art in sentence detection is, I imagine algorithms exist that understand quotation marks. The failures of sentiment analysis, though, suggest that Syuzhet’s goals may not be realizable with existing tools. Until the foundation shapes and the problems with the implementation of sentiment analysis are addressed, the Syuzhet package cannot accomplish what it claims to do. I’m looking forward to seeing how these problems are addressed in future versions of the package.

Special Thanks:

I’d like to thank the following people who have consulted with me on sentiment analysis and signal processing and read versions of this blog post.

Daniel Lepage, Senior Software Engineer, Maternity Neighborhood

Rafael Frongillo, Postdoctoral Fellow, Center for Research on Computation and Society, Harvard University

Brian Gawalt, Senior Data Scientist, Elance-oDesk

Sarah Gontarek

[1] The excerpt doesn’t include quotation marks at the beginning and end because both the opening and closing sentences are part of larger passages of dialogue.

[2] This problem was not visible with the sample dataset of Portrait of the Artist, because the Project Gutenburg text uses dashes instead of quotation marks.

[3] This example also shows another problem: longer sentences may be given greater positivity or negativity than their contents warrant, merely because they have greater number of positive or negative words. For instance, “I am extremely happy!” would have a lower positivity ranking than “Well, I’m not really happy; today, I spilled my delicious, glorious coffee on my favorite shirt and it will never be clean again.”

[4] The Stanford algorithm is much more robust: it has more granularity in its categories of emotion and does consider negation. However, it also fails on the sample paragraph above, and it produced multiple “Not a Number” values when we ran it on Bleak House, rendering it unusable.

[5] Other scholars have also been noticing similar problems, as Jonathan Goodwin’s results demonstrate: (https://twitter.com/joncgoodwin/status/563734388484354048/photo/1).

[6] For example, Gaussian filters do not introduce ringing artifacts, though they have their own limitations (http://homepages.inf.ed.ac.uk/rbf/HIPR2/freqfilt.htm).

SUNY New Paltz Funded a Digital Scholarship Center

March 1, 2015 annieswafford Uncategorized Digital Humanities, grant proposals, public higher ed, SUNY New Paltz, Undergraduate Education

I’m happy to report that SUNY New Paltz has funded an interdisciplinary digital scholarship center to be housed in the Sojourner Truth Library! My colleague Melissa Rock (Department of Geography) and I submitted a grant proposal for internal funds, and the President and Provost agreed to fully fund its initial start-up. We’re very excited that the administration has decided to make digital scholarship such a high priority!

We’re still tossing around name ideas–the current leader is Digital Arts, Social Sciences, and Humanities Lab (DASSH Lab, for short)–and we won’t have access to our new space for a few months yet, but we’re working on setting up a temporary home as we gear up for workshops, training sessions for classes, and a speaker series.

Here’s the information about the center:

Faculty members in departments throughout the university, including Geography, English, Education, Anthropology, Computer Science, Biology, and Graphic Design, have expressed great interest in integrating digital technologies into their own research and classroom curricula. However, they lack the expertise, equipment, and access to space necessary to use these technologies effectively; most specialized computer labs are reserved for professors and students in that department, and most other computer labs, in addition to lacking specialized software, are consistently booked with classes. This center will provide the training, equipment, and software, and workshops necessary for faculty from throughout the campus to support teaching and learning with digital technology by creating digital video essays, podcasts, websites, digital archives and editions, and visualizations. This center is vital to ensure that SUNY New Paltz professors are using cutting-edge techniques in their research and pedagogy.

Stay tuned for more information!

Born Digital: From Archives to Maps

December 2, 2014December 3, 2014 annieswafford Talks archives, Digital Humanities, digital humanities talks, distant reading, editions, GIS, network visualizations, topic modeling, visualizations

Below are links to the tools, data, instructions, and examples I mentioned in my talk on building digital humanities projects, given at SUNY New Paltz on December 3rd in the Honors College.