Introduction

The overall goal of this project is to build a word recognizer for American Sign Language video sequences, demonstrating the power of probabalistic models. In particular, this project employs hidden Markov models (HMM's) to analyze a series of measurements taken from videos of American Sign Language (ASL) collected for research (see the RWTH-BOSTON-104 Database). In this video, the right-hand x and y locations are plotted as the speaker signs the sentence. ASLR demo

The raw data, train, and test sets are pre-defined. You will derive a variety of feature sets (explored in Part 1), as well as implement three different model selection criterion to determine the optimal number of hidden states for each word model (explored in Part 2). Finally, in Part 3 you will implement the recognizer and compare the effects the different combinations of feature sets and model selection criteria.

At the end of each Part, complete the submission cells with implementations, answer all questions, and pass the unit tests. Then submit the completed notebook for review!

PART 1: Data

Features Tutorial

Load the initial database

A data handler designed for this database is provided in the student codebase as the AslDb class in the asl_data module. This handler creates the initial pandas dataframe from the corpus of data included in the data directory as well as dictionaries suitable for extracting data in a format friendly to the hmmlearn library. We'll use those to create models in Part 2.

To start, let's set up the initial database and select an example set of features for the training set. At the end of Part 1, you will create additional feature sets for experimentation.

In [62]:
%load_ext autoreload
%autoreload 2
The autoreload extension is already loaded. To reload it, use:
  %reload_ext autoreload
In [63]:
import numpy as np
import pandas as pd
from asl_data import AslDb

asl = AslDb()  # initializes the database
asl.df.head()  # displays the first five rows of the asl database, indexed by video and frame
Out[63]:
left-x left-y right-x right-y nose-x nose-y speaker
video frame
98 0 149 181 170 175 161 62 woman-1
1 149 181 170 175 161 62 woman-1
2 149 181 170 175 161 62 woman-1
3 149 181 170 175 161 62 woman-1
4 149 181 170 175 161 62 woman-1
In [64]:
asl.df.ix[98, 1]  # look at the data available for an individual frame
Out[64]:
left-x         149
left-y         181
right-x        170
right-y        175
nose-x         161
nose-y          62
speaker    woman-1
Name: (98, 1), dtype: object

The frame represented by video 98, frame 1 is shown here: Video 98

Feature selection for training the model

The objective of feature selection when training a model is to choose the most relevant variables while keeping the model as simple as possible, thus reducing training time. We can use the raw features already provided or derive our own and add columns to the pandas dataframe asl.df for selection. As an example, in the next cell a feature named 'grnd-ry' is added. This feature is the difference between the right-hand y value and the nose y value, which serves as the "ground" right y value.

In [65]:
asl.df['grnd-ry'] = asl.df['right-y'] - asl.df['nose-y']
asl.df.head()  # the new feature 'grnd-ry' is now in the frames dictionary
Out[65]:
left-x left-y right-x right-y nose-x nose-y speaker grnd-ry
video frame
98 0 149 181 170 175 161 62 woman-1 113
1 149 181 170 175 161 62 woman-1 113
2 149 181 170 175 161 62 woman-1 113
3 149 181 170 175 161 62 woman-1 113
4 149 181 170 175 161 62 woman-1 113
Try it!
In [66]:
from asl_utils import test_features_tryit
# TODO add df columns for 'grnd-rx', 'grnd-ly', 'grnd-lx' representing
# differences between hand and nose locations

asl.df['grnd-ly'] = asl.df['left-y'] - asl.df['nose-y']
asl.df['grnd-lx'] = asl.df['left-x'] - asl.df['nose-x']
asl.df['grnd-rx'] = asl.df['right-x'] - asl.df['nose-x']

# test the code
test_features_tryit(asl)
asl.df sample
left-x left-y right-x right-y nose-x nose-y speaker grnd-ry grnd-ly grnd-lx grnd-rx
video frame
98 0 149 181 170 175 161 62 woman-1 113 119 -12 9
1 149 181 170 175 161 62 woman-1 113 119 -12 9
2 149 181 170 175 161 62 woman-1 113 119 -12 9
3 149 181 170 175 161 62 woman-1 113 119 -12 9
4 149 181 170 175 161 62 woman-1 113 119 -12 9
Out[66]:
Correct!
In [67]:
# collect the features into a list
features_ground = ['grnd-rx', 'grnd-ry', 'grnd-lx', 'grnd-ly']
# show a single set of features for a given (video, frame) tuple
[asl.df.ix[98, 1][v] for v in features_ground]
Out[67]:
[9, 113, -12, 119]
Build the training set

Now that we have a feature list defined, we can pass that list to the build_training method to collect the features for all the words in the training set. Each word in the training set has multiple examples from various videos. Below we can see the unique words that have been loaded into the training set:

In [68]:
training = asl.build_training(features_ground)
print("Training words: {}".format(training.words))
Training words: ['JOHN', 'WRITE', 'HOMEWORK', 'IX-1P', 'SEE', 'YESTERDAY', 'IX', 'LOVE', 'MARY', 'CAN', 'GO', 'GO1', 'FUTURE', 'GO2', 'PARTY', 'FUTURE1', 'HIT', 'BLAME', 'FRED', 'FISH', 'WONT', 'EAT', 'BUT', 'CHICKEN', 'VEGETABLE', 'CHINA', 'PEOPLE', 'PREFER', 'BROCCOLI', 'LIKE', 'LEAVE', 'SAY', 'BUY', 'HOUSE', 'KNOW', 'CORN', 'CORN1', 'THINK', 'NOT', 'PAST', 'LIVE', 'CHICAGO', 'CAR', 'SHOULD', 'DECIDE', 'VISIT', 'MOVIE', 'WANT', 'SELL', 'TOMORROW', 'NEXT-WEEK', 'NEW-YORK', 'LAST-WEEK', 'WILL', 'FINISH', 'ANN', 'READ', 'BOOK', 'CHOCOLATE', 'FIND', 'SOMETHING-ONE', 'POSS', 'BROTHER', 'ARRIVE', 'HERE', 'GIVE', 'MAN', 'NEW', 'COAT', 'WOMAN', 'GIVE1', 'HAVE', 'FRANK', 'BREAK-DOWN', 'SEARCH-FOR', 'WHO', 'WHAT', 'LEG', 'FRIEND', 'CANDY', 'BLUE', 'SUE', 'BUY1', 'STOLEN', 'OLD', 'STUDENT', 'VIDEOTAPE', 'BORROW', 'MOTHER', 'POTATO', 'TELL', 'BILL', 'THROW', 'APPLE', 'NAME', 'SHOOT', 'SAY-1P', 'SELF', 'GROUP', 'JANA', 'TOY1', 'MANY', 'TOY', 'ALL', 'BOY', 'TEACHER', 'GIRL', 'BOX', 'GIVE2', 'GIVE3', 'GET', 'PUTASIDE']

The training data in training is an object of class WordsData defined in the asl_data module. in addition to the words list, data can be accessed with the get_all_sequences, get_all_Xlengths, get_word_sequences, and get_word_Xlengths methods. We need the get_word_Xlengths method to train multiple sequences with the hmmlearn library. In the following example, notice that there are two lists; the first is a concatenation of all the sequences(the X portion) and the second is a list of the sequence lengths(the Lengths portion).

In [69]:
training.get_word_Xlengths('CHOCOLATE')
Out[69]:
(array([[-11,  48,   7, 120],
        [-11,  48,   8, 109],
        [ -8,  49,  11,  98],
        [ -7,  50,   7,  87],
        [ -4,  54,   7,  77],
        [ -4,  54,   6,  69],
        [ -4,  54,   6,  69],
        [-13,  52,   6,  69],
        [-13,  52,   6,  69],
        [ -8,  51,   6,  69],
        [ -8,  51,   6,  69],
        [ -8,  51,   6,  69],
        [ -8,  51,   6,  69],
        [ -8,  51,   6,  69],
        [-10,  59,   7,  71],
        [-15,  64,   9,  77],
        [-17,  75,  13,  81],
        [ -4,  48,  -4, 113],
        [ -2,  53,  -4, 113],
        [ -4,  55,   2,  98],
        [ -4,  58,   2,  98],
        [ -1,  59,   2,  89],
        [ -1,  59,  -1,  84],
        [ -1,  59,  -1,  84],
        [ -7,  63,  -1,  84],
        [ -7,  63,  -1,  84],
        [ -7,  63,   3,  83],
        [ -7,  63,   3,  83],
        [ -7,  63,   3,  83],
        [ -7,  63,   3,  83],
        [ -7,  63,   3,  83],
        [ -7,  63,   3,  83],
        [ -7,  63,   3,  83],
        [ -4,  70,   3,  83],
        [ -4,  70,   3,  83],
        [ -2,  73,   5,  90],
        [ -3,  79,  -4,  96],
        [-15,  98,  13, 135],
        [ -6,  93,  12, 128],
        [ -2,  89,  14, 118],
        [  5,  90,  10, 108],
        [  4,  86,   7, 105],
        [  4,  86,   7, 105],
        [  4,  86,  13, 100],
        [ -3,  82,  14,  96],
        [ -3,  82,  14,  96],
        [  6,  89,  16, 100],
        [  6,  89,  16, 100],
        [  7,  85,  17, 111]], dtype=int64), [17, 20, 12])
More feature sets

So far we have a simple feature set that is enough to get started modeling. However, we might get better results if we manipulate the raw values a bit more, so we will go ahead and set up some other options now for experimentation later. For example, we could normalize each speaker's range of motion with grouped statistics using Pandas stats functions and pandas groupby. Below is an example for finding the means of all speaker subgroups.

In [70]:
df_means = asl.df.groupby('speaker').mean()
df_means
Out[70]:
left-x left-y right-x right-y nose-x nose-y grnd-ry grnd-ly grnd-lx grnd-rx
speaker
man-1 206.248203 218.679449 155.464350 150.371031 175.031756 61.642600 88.728430 157.036848 31.216447 -19.567406
woman-1 164.661438 161.271242 151.017865 117.332462 162.655120 57.245098 60.087364 104.026144 2.006318 -11.637255
woman-2 183.214509 176.527232 156.866295 119.835714 170.318973 58.022098 61.813616 118.505134 12.895536 -13.452679

To select a mean that matches by speaker, use the pandas map method:

In [71]:
asl.df['left-x-mean'] = asl.df['speaker'].map(df_means['left-x'])
asl.df.head()
Out[71]:
left-x left-y right-x right-y nose-x nose-y speaker grnd-ry grnd-ly grnd-lx grnd-rx left-x-mean
video frame
98 0 149 181 170 175 161 62 woman-1 113 119 -12 9 164.661438
1 149 181 170 175 161 62 woman-1 113 119 -12 9 164.661438
2 149 181 170 175 161 62 woman-1 113 119 -12 9 164.661438
3 149 181 170 175 161 62 woman-1 113 119 -12 9 164.661438
4 149 181 170 175 161 62 woman-1 113 119 -12 9 164.661438
Try it!
In [72]:
from asl_utils import test_std_tryit
# TODO Create a dataframe named `df_std` with standard deviations grouped
# by speaker
df_std = asl.df.groupby("speaker").std()

# test the code
test_std_tryit(df_std)
df_std
left-x left-y right-x right-y nose-x nose-y grnd-ry grnd-ly grnd-lx grnd-rx left-x-mean
speaker
man-1 15.154425 36.328485 18.901917 54.902340 6.654573 5.520045 53.487999 36.572749 15.080360 20.269032 0.0
woman-1 17.573442 26.594521 16.459943 34.667787 3.549392 3.538330 33.972660 27.117393 17.328941 16.764706 0.0
woman-2 15.388711 28.825025 14.890288 39.649111 4.099760 3.416167 39.128572 29.320655 15.050938 16.191324 0.0
Out[72]:
Correct!

Features Implementation Submission

Implement four feature sets and answer the question that follows.

  • normalized Cartesian coordinates

    • use mean and standard deviation statistics and the standard score equation to account for speakers with different heights and arm length
  • polar coordinates

    • calculate polar coordinates with Cartesian to polar equations
    • use the np.arctan2 function and swap the x and y axes to move the $0$ to $2\pi$ discontinuity to 12 o'clock instead of 3 o'clock; in other words, the normal break in radians value from $0$ to $2\pi$ occurs directly to the left of the speaker's nose, which may be in the signing area and interfere with results. By swapping the x and y axes, that discontinuity move to directly above the speaker's head, an area not generally used in signing.
  • delta difference

    • as described in Thad's lecture, use the difference in values between one frame and the next frames as features
    • pandas diff method and fillna method will be helpful for this one
  • custom features

    • These are your own design; combine techniques used above or come up with something else entirely. We look forward to seeing what you come up with! Some ideas to get you started:
In [73]:
# TODO add features for normalized by speaker values of left, right, x, y
# Name these 'norm-rx', 'norm-ry', 'norm-lx', and 'norm-ly'
# using Z-score scaling (X-Xmean)/Xstd


def normalize(df, label):
    numerator = df[label] - df['speaker'].map(df.groupby("speaker").mean()[label])
    denominator = df['speaker'].map(df.groupby("speaker").std()[label])

    return numerator / denominator


asl.df['norm-rx'] = normalize(asl.df, 'right-x')
asl.df['norm-ry'] = normalize(asl.df, 'right-y')
asl.df['norm-lx'] = normalize(asl.df, 'left-x')
asl.df['norm-ly'] = normalize(asl.df, 'left-y')
features_norm = ['norm-rx', 'norm-ry', 'norm-lx', 'norm-ly']
In [74]:
# TODO add features for polar coordinate values where the nose is the origin
# Name these 'polar-rr', 'polar-rtheta', 'polar-lr', and 'polar-ltheta'
# Note that 'polar-rr' and 'polar-rtheta' refer to the radius and angle


def cart2polar(x_series, y_series):
    r = np.sqrt(x_series**2 + y_series**2)
    theta = np.arctan2(x_series, y_series)

    return r, theta


asl.df['polar-rr'], asl.df['polar-rtheta'] = cart2polar(
    asl.df['grnd-rx'], asl.df['grnd-ry'])
asl.df['polar-lr'], asl.df['polar-ltheta'] = cart2polar(
    asl.df['grnd-lx'], asl.df['grnd-ly'])

features_polar = ['polar-rr', 'polar-rtheta', 'polar-lr', 'polar-ltheta']
In [75]:
# TODO add features for left, right, x, y differences by one time step, i.e. the "delta" values discussed in the lecture
# Name these 'delta-rx', 'delta-ry', 'delta-lx', and 'delta-ly'
asl.df['delta-rx'] = asl.df['right-x'].diff()
asl.df['delta-lx'] = asl.df['left-x'].diff()
asl.df['delta-ry'] = asl.df['right-y'].diff()
asl.df['delta-ly'] = asl.df['left-y'].diff()

beg_idx = [(vid, frame) for vid, frame in asl.df.index.tolist() if frame == 0]
asl.df.loc[beg_idx, ['delta-rx', 'delta-lx', 'delta-ry', 'delta-ly']] = 0

features_delta = ['delta-rx', 'delta-ry', 'delta-lx', 'delta-ly']
In [178]:
# TODO add features of your own design, which may be a combination of the above or something else
# Name these whatever you would like
asl.df['delta-norm-rx'] = normalize(asl.df, 'delta-rx')
asl.df['delta-norm-ry'] = normalize(asl.df, 'delta-ry')
asl.df['delta-norm-lx'] = normalize(asl.df, 'delta-lx')
asl.df['delta-norm-ly'] = normalize(asl.df, 'delta-ly')
# TODO define a list named 'features_custom' for building the training set
features_custom = ['delta-norm-rx', 'delta-norm-ry', 'delta-norm-lx', 'delta-norm-ly']
In [182]:
features_all = [features_delta, features_ground, features_norm, features_polar, features_custom]
features_all = sum(features_all, [])
features_all
Out[182]:
['delta-rx',
 'delta-ry',
 'delta-lx',
 'delta-ly',
 'grnd-rx',
 'grnd-ry',
 'grnd-lx',
 'grnd-ly',
 'norm-rx',
 'norm-ry',
 'norm-lx',
 'norm-ly',
 'polar-rr',
 'polar-rtheta',
 'polar-lr',
 'polar-ltheta',
 'delta-norm-rx',
 'delta-norm-ry',
 'delta-norm-lx',
 'delta-norm-ly']

Question 1: What custom features did you choose for the features_custom set and why?

Answer 1:

I chose delta-norm features which is obtained by standardizing delta features. By standardizing, I mean

$$ z = \frac{X - \mu}{\sigma} $$

Why did I choose these features?

  • Each person has a different body shape(arm width, height, etc.) Hence, it can result in significantly different signals
  • It also keeps numbers small such that it makes the prediction easier because predicting the range of -1 ~ 1 is easier than predicting -100 ~ 100.

Features Unit Testing

Run the following unit tests as a sanity check on the defined "ground", "norm", "polar", and 'delta" feature sets. The test simply looks for some valid values but is not exhaustive. However, the project should not be submitted if these tests don't pass.

In [77]:
import unittest

# import numpy as np


class TestFeatures(unittest.TestCase):
    def test_features_ground(self):
        sample = (asl.df.ix[98, 1][features_ground]).tolist()
        self.assertEqual(sample, [9, 113, -12, 119])

    def test_features_norm(self):
        sample = (asl.df.ix[98, 1][features_norm]).tolist()
        np.testing.assert_almost_equal(sample, [1.153, 1.663, -0.891, 0.742],
                                       3)

    def test_features_polar(self):
        sample = (asl.df.ix[98, 1][features_polar]).tolist()
        np.testing.assert_almost_equal(sample,
                                       [113.3578, 0.0794, 119.603, -0.1005], 3)

    def test_features_delta(self):
        sample = (asl.df.ix[98, 0][features_delta]).tolist()
        self.assertEqual(sample, [0, 0, 0, 0])
        sample = (asl.df.ix[98, 18][features_delta]).tolist()
        self.assertTrue(sample in [[-16, -5, -2, 4], [-14, -9, 0, 0]],
                        "Sample value found was {}".format(sample))


suite = unittest.TestLoader().loadTestsFromModule(TestFeatures())
unittest.TextTestRunner().run(suite)
....
----------------------------------------------------------------------
Ran 4 tests in 0.005s

OK
Out[77]:
<unittest.runner.TextTestResult run=4 errors=0 failures=0>

PART 2: Model Selection

Model Selection Tutorial

The objective of Model Selection is to tune the number of states for each word HMM prior to testing on unseen data. In this section you will explore three methods:

  • Log likelihood using cross-validation folds (CV)
  • Bayesian Information Criterion (BIC)
  • Discriminative Information Criterion (DIC)
Train a single word

Now that we have built a training set with sequence data, we can "train" models for each word. As a simple starting example, we train a single word using Gaussian hidden Markov models (HMM). By using the fit method during training, the Baum-Welch Expectation-Maximization (EM) algorithm is invoked iteratively to find the best estimate for the model for the number of hidden states specified from a group of sample seequences. For this example, we assume the correct number of hidden states is 3, but that is just a guess. How do we know what the "best" number of states for training is? We will need to find some model selection technique to choose the best parameter.

In [78]:
import warnings
from hmmlearn.hmm import GaussianHMM


def train_a_word(word, num_hidden_states, features):
    warnings.filterwarnings("ignore", category=DeprecationWarning)

    training = asl.build_training(features)
    X, lengths = training.get_word_Xlengths(word)
    model = GaussianHMM(n_components=num_hidden_states,
                        n_iter=1000).fit(X, lengths)
    logL = model.score(X, lengths)
    return model, logL


demoword = 'BOOK'
model, logL = train_a_word(demoword, 3, features_ground)
print("Number of states trained in model for {} is {}".format(
    demoword, model.n_components))
print("logL = {}".format(logL))
Number of states trained in model for BOOK is 3
logL = -2331.1138127433196

The HMM model has been trained and information can be pulled from the model, including means and variances for each feature and hidden state. The log likelihood for any individual sample or group of samples can also be calculated with the score method.

In [79]:
def show_model_stats(word, model):
    print("Number of states trained in model for {} is {}".format(
        word, model.n_components))

    variance = np.array([np.diag(model.covars_[i])
                         for i in range(model.n_components)])

    for i in range(model.n_components):  # for each hidden state
        print("hidden state #{}".format(i))
        print("mean = ", model.means_[i])
        print("variance = ", variance[i])
        print()


show_model_stats(demoword, model)
Number of states trained in model for BOOK is 3
hidden state #0
mean =  [ -3.46504869  50.66686933  14.02391587  52.04731066]
variance =  [ 49.12346305  43.04799144  39.35109609  47.24195772]

hidden state #1
mean =  [ -11.45300909   94.109178     19.03512475  102.2030162 ]
variance =  [  77.403668    203.35441965   26.68898447  156.12444034]

hidden state #2
mean =  [ -1.12415027  69.44164191  17.02866283  77.7231196 ]
variance =  [ 19.70434594  16.83041492  30.51552305  11.03678246]

Try it!

Experiment by changing the feature set, word, and/or num_hidden_states values in the next cell to see changes in values.

In [80]:
my_testword = 'CHOCOLATE'

# Experiment here with different parameters
model, logL = train_a_word(my_testword, 3, features_ground)

show_model_stats(my_testword, model)
print("logL = {}".format(logL))
Number of states trained in model for CHOCOLATE is 3
hidden state #0
mean =  [ -9.30211403  55.32333876   6.92259936  71.24057775]
variance =  [ 16.16920957  46.50917372   3.81388185  15.79446427]

hidden state #1
mean =  [   0.58333333   87.91666667   12.75        108.5       ]
variance =  [  39.41055556   18.74388889    9.855       144.4175    ]

hidden state #2
mean =  [ -5.40587658  60.1652424    2.32479599  91.3095432 ]
variance =  [   7.95073876   64.13103127   13.68077479  129.5912395 ]

logL = -601.3291470028638
Visualize the hidden states

We can plot the means and variances for each state and feature. Try varying the number of states trained for the HMM model and examine the variances. Are there some models that are "better" than others? How can you tell? We would like to hear what you think in the classroom online.

In [81]:
%matplotlib inline
In [82]:
import math
from matplotlib import (cm, pyplot as plt, mlab)


def visualize(word, model):
    """ visualize the input model for a particular word """

    variance = np.array([np.diag(model.covars_[i])
                         for i in range(model.n_components)])
    figures = []

    for parm_idx in range(len(model.means_[0])):

        xmin = int(min(model.means_[:, parm_idx]) - max(variance[:, parm_idx]))
        xmax = int(max(model.means_[:, parm_idx]) + max(variance[:, parm_idx]))

        fig, axs = plt.subplots(model.n_components, sharex=True, sharey=False)
        colours = cm.rainbow(np.linspace(0, 1, model.n_components))

        for i, (ax, colour) in enumerate(zip(axs, colours)):
            x = np.linspace(xmin, xmax, 100)
            mu = model.means_[i, parm_idx]
            sigma = math.sqrt(np.diag(model.covars_[i])[parm_idx])
            ax.plot(x, mlab.normpdf(x, mu, sigma), c=colour)
            ax.set_title(
                "{} feature {} hidden state #{}".format(word, parm_idx, i))
            ax.grid(True)

        figures.append(plt)

    for p in figures:
        p.show()


visualize(my_testword, model)
ModelSelector class

Review the SelectorModel class from the codebase found in the my_model_selectors.py module. It is designed to be a strategy pattern for choosing different model selectors. For the project submission in this section, subclass SelectorModel to implement the following model selectors. In other words, you will write your own classes/functions in the my_model_selectors.py module and run them from this notebook:

  • SelectorCV: Log likelihood with CV
  • SelectorBIC: BIC
  • SelectorDIC: DIC

You will train each word in the training set with a range of values for the number of hidden states, and then score these alternatives with the model selector, choosing the "best" according to each strategy. The simple case of training with a constant value for n_components can be called using the provided SelectorConstant subclass as follow:

In [83]:
from my_model_selectors import SelectorConstant

# Experiment here with different feature sets defined in part 1
training = asl.build_training(features_ground)

word = 'VEGETABLE'  # Experiment here with different words

model = SelectorConstant(training.get_all_sequences(),
                         training.get_all_Xlengths(),
                         word, n_constant=3).select()

print("Number of states trained in model for {} is {}".format(
    word, model.n_components))
Number of states trained in model for VEGETABLE is 3
Cross-validation folds

If we simply score the model with the Log Likelihood calculated from the feature sequences it has been trained on, we should expect that more complex models will have higher likelihoods. However, that doesn't tell us which would have a better likelihood score on unseen data. The model will likely be overfit as complexity is added. To estimate which topology model is better using only the training data, we can compare scores using cross-validation. One technique for cross-validation is to break the training set into "folds" and rotate which fold is left out of training. The "left out" fold scored. This gives us a proxy method of finding the best model to use on "unseen data". In the following example, a set of word sequences is broken into three folds using the scikit-learn Kfold class object. When you implement SelectorCV, you will use this technique.

In [84]:
from sklearn.model_selection import KFold
from asl_utils import combine_sequences

# Experiment here with different feature sets
training = asl.build_training(features_ground)

word = 'VEGETABLE'  # Experiment here with different words
word_sequences = training.get_word_sequences(word)
split_method = KFold()

for cv_train_idx, cv_test_idx in split_method.split(word_sequences):
    print("Train fold indices:{} Test fold indices:{}".format(
        cv_train_idx, cv_test_idx))  # view indices of the folds
    X, y = combine_sequences(cv_train_idx, word_sequences)
Train fold indices:[2 3 4 5] Test fold indices:[0 1]
Train fold indices:[0 1 4 5] Test fold indices:[2 3]
Train fold indices:[0 1 2 3] Test fold indices:[4 5]

Tip: In order to run hmmlearn training using the X,lengths tuples on the new folds, subsets must be combined based on the indices given for the folds. A helper utility has been provided in the asl_utils module named combine_sequences for this purpose.

Scoring models with other criterion

Scoring model topologies with BIC balances fit and complexity within the training set for each word. In the BIC equation, a penalty term penalizes complexity to avoid overfitting, so that it is not necessary to also use cross-validation in the selection process. There are a number of references on the internet for this criterion. These slides include a formula you may find helpful for your implementation.

The advantages of scoring model topologies with DIC over BIC are presented by Alain Biem in this reference (also found here). DIC scores the discriminant ability of a training set for one word against competing words. Instead of a penalty term for complexity, it provides a penalty if model liklihoods for non-matching words are too similar to model likelihoods for the correct word in the word set.

Model Selection Implementation Submission

Implement SelectorCV, SelectorBIC, and SelectorDIC classes in the my_model_selectors.py module. Run the selectors on the following five words. Then answer the questions about your results.

Tip: The hmmlearn library may not be able to train or score all models. Implement try/except contructs as necessary to eliminate non-viable models from consideration.

In [85]:
words_to_train = ['FISH', 'BOOK', 'VEGETABLE', 'FUTURE', 'JOHN']
import timeit
In [86]:
# TODO: Implement SelectorCV in my_model_selector.py
from my_model_selectors import SelectorCV

# Experiment here with different feature sets defined in part 1
training = asl.build_training(features_ground)
sequences = training.get_all_sequences()
Xlengths = training.get_all_Xlengths()

cv_model_list = []

for word in words_to_train:

    start = timeit.default_timer()
    model = SelectorCV(sequences,
                       Xlengths,
                       word,
                       min_n_components=2,
                       max_n_components=15,
                       random_state=14).select()
    end = timeit.default_timer() - start

    if model is not None:
        print("Training complete for {} with {} states with time {} seconds".
              format(word, model.n_components, end))
        
        cv_model_list.append(model)
        
    else:
        print("Training failed for {}".format(word))
        
Training complete for FISH with 11 states with time 0.23446067998884246 seconds
Training complete for BOOK with 6 states with time 2.337669961998472 seconds
Training complete for VEGETABLE with 2 states with time 0.9285565570171457 seconds
Training complete for FUTURE with 2 states with time 2.1497781430080067 seconds
Training complete for JOHN with 12 states with time 24.004929588001687 seconds
In [87]:
# TODO: Implement SelectorBIC in module my_model_selectors.py
from my_model_selectors import SelectorBIC

# Experiment here with different feature sets defined in part 1
training = asl.build_training(features_ground)
sequences = training.get_all_sequences()
Xlengths = training.get_all_Xlengths()


bic_model_list = []

for word in words_to_train:
    start = timeit.default_timer()

    model = SelectorBIC(sequences,
                        Xlengths,
                        word,
                        min_n_components=2,
                        max_n_components=15,
                        random_state=14, verbose=False).select()

    end = timeit.default_timer() - start

    if model is not None:
        print("Training complete for {} with {} states with time {} seconds".format(
            word, model.n_components, end))
        
        bic_model_list.append(model)

    else:
        print("Training failed for {}".format(word))
Training complete for FISH with 5 states with time 0.1925643530266825 seconds
Training complete for BOOK with 8 states with time 1.1851199230004568 seconds
Training complete for VEGETABLE with 9 states with time 0.39815885000280105 seconds
Training complete for FUTURE with 9 states with time 1.2749047129764222 seconds
Training complete for JOHN with 13 states with time 12.217969883000478 seconds
In [88]:
# TODO: Implement SelectorDIC in module my_model_selectors.py
from my_model_selectors import SelectorDIC

# Experiment here with different feature sets defined in part 1
training = asl.build_training(features_ground)
sequences = training.get_all_sequences()
Xlengths = training.get_all_Xlengths()

dic_model_list = []

for word in words_to_train:
    start = timeit.default_timer()
    model = SelectorDIC(sequences,
                        Xlengths,
                        word,
                        min_n_components=2,
                        max_n_components=15,
                        random_state=14).select()

    end = timeit.default_timer() - start

    if model is not None:
        print("Training complete for {} with {} states with time {} seconds".format(
            word, model.n_components, end))
        
        dic_model_list.append(model)

    else:
        print("Training failed for {}".format(word))
Training complete for FISH with 3 states with time 0.4397394340194296 seconds
Training complete for BOOK with 15 states with time 2.3636560129816644 seconds
Training complete for VEGETABLE with 15 states with time 1.5425242250203155 seconds
Training complete for FUTURE with 15 states with time 2.397094385989476 seconds
Training complete for JOHN with 15 states with time 13.0246704040037 seconds
In [92]:
from io import StringIO
In [105]:
table = StringIO("""Type,Word,States,Seconds
CV,FISH,11,0.23446068
CV,BOOK,6,2.337669962
CV,VEGETABLE,2,0.928556557
CV,FUTURE,2,2.149778143
CV,JOHN,12,24.004929588
BIC,FISH,5,0.192564353
BIC,BOOK,8,1.185119923
BIC,VEGETABLE,9,0.39815885
BIC,FUTURE,9,1.274904713
BIC,JOHN,13,12.217969883
DIC,FISH,3,0.439739434
DIC,BOOK,15,2.363656013
DIC,VEGETABLE,15,1.542524225
DIC,FUTURE,15,2.397094386
DIC,JOHN,15,13.024670404
""")
df = pd.read_csv(table, sep=",")
df = df.groupby("Type").mean()[['Seconds', "States"]]

df.plot(kind='bar', grid=True);

Question 2: Compare and contrast the possible advantages and disadvantages of the various model selectors implemented.

Answer 2:

Type Pros Cons
BIC Fast and good perforamce by utilizing a penalty term As the number of features increases, it's difficult to find a right answer
CV The least number of states implies it's probably generalized well or at least not overfitting Slow because of cross validations
DIC Its performance is likely to be better than BIC because of high number of parameters Too many hidden states implies possible overfitting and more complex model

Model Selector Unit Testing

Run the following unit tests as a sanity check on the implemented model selectors. The test simply looks for valid interfaces but is not exhaustive. However, the project should not be submitted if these tests don't pass.

In [61]:
from asl_test_model_selectors import TestSelectors
suite = unittest.TestLoader().loadTestsFromModule(TestSelectors())
unittest.TextTestRunner().run(suite)
....
----------------------------------------------------------------------
Ran 4 tests in 28.669s

OK
Out[61]:
<unittest.runner.TextTestResult run=4 errors=0 failures=0>

PART 3: Recognizer

The objective of this section is to "put it all together". Using the four feature sets created and the three model selectors, you will experiment with the models and present your results. Instead of training only five specific words as in the previous section, train the entire set with a feature set and model selector strategy.

Recognizer Tutorial

Train the full training set

The following example trains the entire set with the example features_ground and SelectorConstant features and model selector. Use this pattern for you experimentation and final submission cells.

In [112]:
# autoreload for automatically reloading changes made in my_model_selectors and my_recognizer
%load_ext autoreload
%autoreload 2

from my_model_selectors import SelectorConstant

def train_all_words(features, model_selector):
    training = asl.build_training(features)  # Experiment here with different feature sets defined in part 1
    sequences = training.get_all_sequences()
    Xlengths = training.get_all_Xlengths()
    model_dict = {}
    for word in training.words:
        model = model_selector(sequences, Xlengths, word, 
                        n_constant=3).select()
        model_dict[word]=model
    return model_dict

models = train_all_words(features_ground, SelectorConstant)
print("Number of word models returned = {}".format(len(models)))
The autoreload extension is already loaded. To reload it, use:
  %reload_ext autoreload
Number of word models returned = 112
Load the test set

The build_test method in ASLdb is similar to the build_training method already presented, but there are a few differences:

  • the object is type SinglesData
  • the internal dictionary keys are the index of the test word rather than the word itself
  • the getter methods are get_all_sequences, get_all_Xlengths, get_item_sequences and get_item_Xlengths
In [113]:
test_set = asl.build_test(features_ground)
print("Number of test set items: {}".format(test_set.num_items))
print("Number of test set sentences: {}".format(len(test_set.sentences_index)))
Number of test set items: 178
Number of test set sentences: 40

Recognizer Implementation Submission

For the final project submission, students must implement a recognizer following guidance in the my_recognizer.py module. Experiment with the four feature sets and the three model selection methods (that's 12 possible combinations). You can add and remove cells for experimentation or run the recognizers locally in some other way during your experiments, but retain the results for your discussion. For submission, you will provide code cells of only three interesting combinations for your discussion (see questions below). At least one of these should produce a word error rate of less than 60%, i.e. WER < 0.60 .

Tip: The hmmlearn library may not be able to train or score all models. Implement try/except contructs as necessary to eliminate non-viable models from consideration.

In [202]:
# TODO implement the recognize method in my_recognizer
from my_recognizer import recognize
from asl_utils import show_errors
from itertools import combinations
from tqdm import tqdm
In [200]:
def get_WER(guesses, test_set):
    """ Get WER """
    S = 0
    N = len(test_set.wordlist)
    num_test_words = len(test_set.wordlist)
        
    for word_id in range(num_test_words):
        if guesses[word_id] != test_set.wordlist[word_id]:
            S += 1
    
    return S / N

def run_train(feat, selector):
    
    models = train_all_words(feat, selector)
    test_set = asl.build_test(feat)
    
    probabilities, guesses = recognize(models, test_set)
    
    return get_WER(guesses, test_set)
In [201]:
features_list = [
    "features_ground",
    "features_delta",
    "features_all",
    "features_custom",
    "features_ground",
    "features_norm",
    "features_polar"    
]
model_selector_list = ["SelectorCV", "SelectorDIC", "SelectorBIC"]
In [205]:
result_list = []

for features in tqdm(features_list):
    for model_selector in model_selector_list:
        score = run_train(eval(features), eval(model_selector))
        
        result = (features, model_selector, score)        
        result_list.append(result)
  0%|          | 0/7 [00:00<?, ?it/s]
100%|██████████| 7/7 [25:51<00:00, 217.23s/it]
In [221]:
result_frame = pd.DataFrame(sorted(result_list, key=lambda x: x[-1]), columns=["feature", "selector", "WER"])
result_frame.head()
Out[221]:
feature selector WER
0 features_all SelectorBIC 0.438202
1 features_all SelectorDIC 0.494382
2 features_all SelectorCV 0.516854
3 features_ground SelectorCV 0.528090
4 features_ground SelectorCV 0.528090
In [222]:
# TODO Choose a feature set and model selector
features = features_all # change as needed
model_selector = SelectorBIC # change as needed

# TODO Recognize the test set and display the result with the show_errors method
models = train_all_words(features, model_selector)
test_set = asl.build_test(features)
probabilities, guesses = recognize(models, test_set)
show_errors(guesses, test_set)
**** WER = 0.43820224719101125
Total correct: 100 out of 178
Video  Recognized                                                    Correct
=====================================================================================================
    2: JOHN WRITE *ARRIVE                                            JOHN WRITE HOMEWORK
    7: JOHN *PEOPLE GO CAN                                           JOHN CAN GO CAN
   12: JOHN CAN *WHAT CAN                                            JOHN CAN GO CAN
   21: JOHN *ARRIVE *JOHN *JOHN *CAR *CAR *FUTURE *MARY              JOHN FISH WONT EAT BUT CAN EAT CHICKEN
   25: JOHN LIKE *LOVE IX IX                                         JOHN LIKE IX IX IX
   28: JOHN LIKE IX *LIKE IX                                         JOHN LIKE IX IX IX
   30: JOHN LIKE *MARY IX IX                                         JOHN LIKE IX IX IX
   36: MARY *JOHN *IX IX *MARY *MARY                                 MARY VEGETABLE KNOW IX LIKE CORN1
   40: JOHN IX *CORN MARY *MARY                                      JOHN IX THINK MARY LOVE
   43: JOHN *JOHN BUY HOUSE                                          JOHN MUST BUY HOUSE
   50: *SOMETHING-ONE JOHN BUY CAR *JOHN                             FUTURE JOHN BUY CAR SHOULD
   54: JOHN *FUTURE *FUTURE BUY HOUSE                                JOHN SHOULD NOT BUY HOUSE
   57: JOHN *JOHN *IX MARY                                           JOHN DECIDE VISIT MARY
   67: JOHN FUTURE *MARY BUY HOUSE                                   JOHN FUTURE NOT BUY HOUSE
   71: JOHN *FUTURE VISIT MARY                                       JOHN WILL VISIT MARY
   74: *IX *MARY *MARY MARY                                          JOHN NOT VISIT MARY
   77: *JOHN BLAME MARY                                              ANN BLAME MARY
   84: *JOHN *JOHN *JOHN BOOK                                        IX-1P FIND SOMETHING-ONE BOOK
   89: *FUTURE IX *IX *IX IX NEW COAT                                JOHN IX GIVE MAN IX NEW COAT
   90: JOHN *IX IX *IX *MARY BOOK                                    JOHN GIVE IX SOMETHING-ONE WOMAN BOOK
   92: JOHN *IX IX *WOMAN WOMAN BOOK                                 JOHN GIVE IX SOMETHING-ONE WOMAN BOOK
  100: POSS NEW CAR BREAK-DOWN                                       POSS NEW CAR BREAK-DOWN
  105: JOHN *SEE                                                     JOHN LEG
  107: JOHN *IX *JOHN *MARY *MARY                                    JOHN POSS FRIEND HAVE CANDY
  108: *JOHN ARRIVE                                                  WOMAN ARRIVE
  113: IX CAR *IX *JOHN *BOX                                         IX CAR BLUE SUE BUY
  119: *MARY *BUY1 IX CAR *IX                                        SUE BUY IX CAR BLUE
  122: JOHN *GIVE1 BOOK                                              JOHN READ BOOK
  139: JOHN *BUY1 WHAT *GIVE1 BOOK                                   JOHN BUY WHAT YESTERDAY BOOK
  142: JOHN BUY YESTERDAY WHAT BOOK                                  JOHN BUY YESTERDAY WHAT BOOK
  158: LOVE JOHN WHO                                                 LOVE JOHN WHO
  167: JOHN IX *IX LOVE MARY                                         JOHN IX SAY LOVE MARY
  171: JOHN *JOHN BLAME                                              JOHN MARY BLAME
  174: *JOHN *GIVE1 GIVE1 *IX *BLAME                                 PEOPLE GROUP GIVE1 JANA TOY
  181: JOHN *BOX                                                     JOHN ARRIVE
  184: *IX *IX *GIVE1 TEACHER APPLE                                  ALL BOY GIVE TEACHER APPLE
  189: JOHN *IX *JOHN BOX                                            JOHN GIVE GIRL BOX
  193: JOHN *IX *IX BOX                                              JOHN GIVE GIRL BOX
  199: *JOHN *ARRIVE *JOHN                                           LIKE CHOCOLATE WHO
  201: JOHN *MAN *IX *WOMAN BUY HOUSE                                JOHN TELL MARY IX-1P BUY HOUSE
In [223]:
# TODO Choose a feature set and model selector
features = features_all # change as needed
model_selector = SelectorDIC # change as needed

# TODO Recognize the test set and display the result with the show_errors method
models = train_all_words(features, model_selector)
test_set = asl.build_test(features)
probabilities, guesses = recognize(models, test_set)
show_errors(guesses, test_set)
**** WER = 0.4943820224719101
Total correct: 90 out of 178
Video  Recognized                                                    Correct
=====================================================================================================
    2: JOHN *ARRIVE *ARRIVE                                          JOHN WRITE HOMEWORK
    7: JOHN CAN *IX CAN                                              JOHN CAN GO CAN
   12: JOHN CAN *WHAT CAN                                            JOHN CAN GO CAN
   21: JOHN *JOHN *JOHN *JOHN *CAR *CAR *FUTURE *MARY                JOHN FISH WONT EAT BUT CAN EAT CHICKEN
   25: JOHN *JOHN *LOVE IX *JOHN                                     JOHN LIKE IX IX IX
   28: JOHN *MARY IX *JOHN IX                                        JOHN LIKE IX IX IX
   30: JOHN *MARY *MARY IX IX                                        JOHN LIKE IX IX IX
   36: MARY *JOHN *IX IX *MARY *MARY                                 MARY VEGETABLE KNOW IX LIKE CORN1
   40: JOHN IX *CORN MARY *MARY                                      JOHN IX THINK MARY LOVE
   43: JOHN *JOHN BUY HOUSE                                          JOHN MUST BUY HOUSE
   50: *JOHN JOHN BUY CAR *JOHN                                      FUTURE JOHN BUY CAR SHOULD
   54: JOHN *FUTURE *MARY BUY HOUSE                                  JOHN SHOULD NOT BUY HOUSE
   57: JOHN *JOHN *IX MARY                                           JOHN DECIDE VISIT MARY
   67: JOHN FUTURE *MARY BUY HOUSE                                   JOHN FUTURE NOT BUY HOUSE
   71: JOHN *FUTURE VISIT MARY                                       JOHN WILL VISIT MARY
   74: *IX *MARY *MARY MARY                                          JOHN NOT VISIT MARY
   77: *JOHN BLAME MARY                                              ANN BLAME MARY
   84: *JOHN *JOHN *JOHN BOOK                                        IX-1P FIND SOMETHING-ONE BOOK
   89: *MARY IX *IX *IX IX *ARRIVE *ARRIVE                           JOHN IX GIVE MAN IX NEW COAT
   90: JOHN *IX IX *IX *MARY BOOK                                    JOHN GIVE IX SOMETHING-ONE WOMAN BOOK
   92: JOHN *IX IX *IX *JOHN BOOK                                    JOHN GIVE IX SOMETHING-ONE WOMAN BOOK
  100: *IX NEW CAR BREAK-DOWN                                        POSS NEW CAR BREAK-DOWN
  105: JOHN *POSS                                                    JOHN LEG
  107: JOHN *IX *JOHN *MARY *MARY                                    JOHN POSS FRIEND HAVE CANDY
  108: *JOHN ARRIVE                                                  WOMAN ARRIVE
  113: IX CAR *IX *JOHN *JOHN                                        IX CAR BLUE SUE BUY
  119: *MARY *BUY1 IX *JOHN *IX                                      SUE BUY IX CAR BLUE
  122: JOHN *GIVE1 BOOK                                              JOHN READ BOOK
  139: JOHN *ARRIVE WHAT *JOHN BOOK                                  JOHN BUY WHAT YESTERDAY BOOK
  142: JOHN BUY YESTERDAY WHAT BOOK                                  JOHN BUY YESTERDAY WHAT BOOK
  158: LOVE JOHN WHO                                                 LOVE JOHN WHO
  167: JOHN IX *IX LOVE MARY                                         JOHN IX SAY LOVE MARY
  171: JOHN *JOHN BLAME                                              JOHN MARY BLAME
  174: *JOHN *GIVE1 GIVE1 *IX *JOHN                                  PEOPLE GROUP GIVE1 JANA TOY
  181: JOHN *JOHN                                                    JOHN ARRIVE
  184: *IX BOY *GIVE1 TEACHER *IX                                    ALL BOY GIVE TEACHER APPLE
  189: JOHN *MARY *JOHN BOX                                          JOHN GIVE GIRL BOX
  193: JOHN *IX *IX BOX                                              JOHN GIVE GIRL BOX
  199: *JOHN *ARRIVE *JOHN                                           LIKE CHOCOLATE WHO
  201: JOHN *MAN *IX *JOHN BUY HOUSE                                 JOHN TELL MARY IX-1P BUY HOUSE
In [224]:
# TODO Choose a feature set and model selector
features = features_all # change as needed
model_selector = SelectorCV # change as needed

# TODO Recognize the test set and display the result with the show_errors method
models = train_all_words(features, model_selector)
test_set = asl.build_test(features)
probabilities, guesses = recognize(models, test_set)
show_errors(guesses, test_set)
**** WER = 0.5168539325842697
Total correct: 86 out of 178
Video  Recognized                                                    Correct
=====================================================================================================
    2: JOHN *BOOK *ARRIVE                                            JOHN WRITE HOMEWORK
    7: JOHN *PEOPLE *HAVE *HAVE                                      JOHN CAN GO CAN
   12: JOHN CAN *GO1 CAN                                             JOHN CAN GO CAN
   21: JOHN *VIDEOTAPE *VISIT *MARY *CAR *CAR *FUTURE *MARY          JOHN FISH WONT EAT BUT CAN EAT CHICKEN
   25: JOHN *MARY *MARY *JOHN IX                                     JOHN LIKE IX IX IX
   28: JOHN *MARY IX *JOHN IX                                        JOHN LIKE IX IX IX
   30: JOHN LIKE *MARY *MARY *MARY                                   JOHN LIKE IX IX IX
   36: MARY *JOHN *IX *GIVE *MARY *MARY                              MARY VEGETABLE KNOW IX LIKE CORN1
   40: JOHN *MARY *CORN MARY *MARY                                   JOHN IX THINK MARY LOVE
   43: JOHN *FUTURE BUY HOUSE                                        JOHN MUST BUY HOUSE
   50: *JOHN *FRANK BUY CAR *JOHN                                    FUTURE JOHN BUY CAR SHOULD
   54: JOHN SHOULD *MARY BUY HOUSE                                   JOHN SHOULD NOT BUY HOUSE
   57: *MARY *JOHN *IX MARY                                          JOHN DECIDE VISIT MARY
   67: JOHN FUTURE *MARY BUY HOUSE                                   JOHN FUTURE NOT BUY HOUSE
   71: JOHN *FUTURE *BLAME MARY                                      JOHN WILL VISIT MARY
   74: *MARY *MARY *MARY MARY                                        JOHN NOT VISIT MARY
   77: *JOHN BLAME MARY                                              ANN BLAME MARY
   84: *JOHN *ARRIVE *FUTURE BOOK                                    IX-1P FIND SOMETHING-ONE BOOK
   89: *MARY IX *IX *IX IX NEW COAT                                  JOHN IX GIVE MAN IX NEW COAT
   90: JOHN *IX IX *ALL *MARY BOOK                                   JOHN GIVE IX SOMETHING-ONE WOMAN BOOK
   92: JOHN *IX IX *IX *IX BOOK                                      JOHN GIVE IX SOMETHING-ONE WOMAN BOOK
  100: *IX NEW CAR BREAK-DOWN                                        POSS NEW CAR BREAK-DOWN
  105: JOHN *WHO                                                     JOHN LEG
  107: JOHN *JOHN *HAVE *MARY *JOHN                                  JOHN POSS FRIEND HAVE CANDY
  108: *MARY ARRIVE                                                  WOMAN ARRIVE
  113: *JOHN CAR BLUE *JOHN *ARRIVE                                  IX CAR BLUE SUE BUY
  119: *PREFER *BUY1 IX CAR *JOHN                                    SUE BUY IX CAR BLUE
  122: JOHN *HOUSE BOOK                                              JOHN READ BOOK
  139: JOHN *BUY1 WHAT YESTERDAY BOOK                                JOHN BUY WHAT YESTERDAY BOOK
  142: JOHN BUY YESTERDAY WHAT BOOK                                  JOHN BUY YESTERDAY WHAT BOOK
  158: LOVE *MARY WHO                                                LOVE JOHN WHO
  167: JOHN *SOMETHING-ONE *MARY LOVE MARY                           JOHN IX SAY LOVE MARY
  171: *MARY *JOHN BLAME                                             JOHN MARY BLAME
  174: *GIVE1 *GIVE1 GIVE1 *JOHN *CAN                                PEOPLE GROUP GIVE1 JANA TOY
  181: JOHN ARRIVE                                                   JOHN ARRIVE
  184: *IX BOY *GIVE1 TEACHER APPLE                                  ALL BOY GIVE TEACHER APPLE
  189: JOHN *JOHN *JOHN *ARRIVE                                      JOHN GIVE GIRL BOX
  193: JOHN *SOMETHING-ONE *IX BOX                                   JOHN GIVE GIRL BOX
  199: *JOHN CHOCOLATE *MARY                                         LIKE CHOCOLATE WHO
  201: JOHN *SHOULD *IX *IX BUY HOUSE                                JOHN TELL MARY IX-1P BUY HOUSE

Question 3: Summarize the error results from three combinations of features and model selectors. What was the "best" combination and why? What additional information might we use to improve our WER? For more insight on improving WER, take a look at the introduction to Part 4.

Answer 3:

For the best performance,

I have to use every features including my custom features and SelectorBIC. The reason for such high performance is the standardization of features because each person has different body shapes hence different signals.

However, the best score is still low and I believe it can improve further by standardizing every other features which I didn't because of the time limit.

Recognizer Unit Tests

Run the following unit tests as a sanity check on the defined recognizer. The test simply looks for some valid values but is not exhaustive. However, the project should not be submitted if these tests don't pass.

In [176]:
from asl_test_recognizer import TestRecognize
suite = unittest.TestLoader().loadTestsFromModule(TestRecognize())
unittest.TextTestRunner().run(suite)
..
----------------------------------------------------------------------
Ran 2 tests in 16.490s

OK
Out[176]:
<unittest.runner.TextTestResult run=2 errors=0 failures=0>

PART 4: (OPTIONAL) Improve the WER with Language Models

We've squeezed just about as much as we can out of the model and still only get about 50% of the words right! Surely we can do better than that. Probability to the rescue again in the form of statistical language models (SLM). The basic idea is that each word has some probability of occurrence within the set, and some probability that it is adjacent to specific other words. We can use that additional information to make better choices.

Additional reading and resources
Optional challenge

The recognizer you implemented in Part 3 is equivalent to a "0-gram" SLM. Improve the WER with the SLM data provided with the data set in the link above using "1-gram", "2-gram", and/or "3-gram" statistics. The probabilities data you've already calculated will be useful and can be turned into a pandas DataFrame if desired (see next cell).
Good luck! Share your results with the class!

In [ ]:
# create a DataFrame of log likelihoods for the test word items
df_probs = pd.DataFrame(data=probabilities)
df_probs.head()