RTFM: G ENERALISING TO N OVEL E NVIRONMENT D YNAMICS VIA R EADING
A BSTRACT
Obtaining policies that can generalise to new environments in reinforcement learning is challenging.
In this work, we demonstrate that language understanding via a reading policy learner is a promising vehicle for generalisation to new environments.
We propose a grounded policy learning problem, Read to Fight Monsters (RTFM), in which the agent must jointly reason over a language goal, relevant dynamics described in a document, and environment observations.
We procedurally generate environment dynamics and corresponding language descriptions of the dynamics, such that agents must read to understand new environment dynamics instead of memorising any particular information.
In addition, we propose txt 2 π , a model that captures three-way interactions between the goal, document, and observations.
On RTFM, txt 2 π generalises to new environments with dynamics not seen during training via reading.
Furthermore, our model outperforms baselines such as FiLM and language-conditioned CNNs on RTFM.
Through curriculum learning, txt 2 π produces policies that excel on complex RTFM tasks requiring several reasoning and coreference steps.
I NTRODUCTION
Reinforcement learning (RL) has been successful in a variety of areas such as continuous control (Lillicrap et al., 2015),
dialogue systems (Li et al., 2016) and game-playing (Mnih et al., 2013).
However, RL adoption in real-world problems is limited due to poor sample efﬁciency and failure to generalise to environments even slightly different from those seen during training.
We explore language-conditioned policy learning where agents use machine reading to discover strategies required to solve a task, thereby leveraging language as a means to generalise to new environments.
Prior work on language grounding and language-based RL (see Luketina et al.
for a recent survey) are limited to scenarios in which language speciﬁes the goal for some ﬁxed environment dynamics (Branavan et al., 2011; Hermann et al., 2017; Bahdanau et al., 2019;
Fried et al., 2018;
Co-Reyes et al., 2019), or the dynamics of the environment vary and are presented in language for some ﬁxed goal (Branavan et al., 2012).
In practice, changes to goals and to environment dynamics tend to occur simultaneously—given some goal, we need to ﬁnd and interpret relevant information to understand how to achieve the goal.
That is, the agent should account for variations in both by selectively reading, thereby generalising to environments with dynamics not seen during training.
Our contributions are two-fold.
First, we propose a grounded policy learning problem that we call Read to Fight Monsters (RTFM).
In RTFM, the agent must jointly reason over a language goal, a document that speciﬁes environment dynamics, and environment observations.
In particular, it must identify relevant information in the document to shape its policy and accomplish the goal.
To necessitate reading comprehension, we expose the agent to ever changing environment dynamics and corresponding language descriptions such that it cannot avoid reading by memorising any particular environment dynamics.
We procedurally generate environment dynamics and natural language templated descriptions of dynamics and goals to produced a combinatorially large number of environment dynamics to train and evaluate RTFM.
Second, we propose txt 2 π to model the joint reasoning problem in RTFM.
We show that txt 2 π generalises to goals and environment dynamics not seen during training, and outperforms previous language-conditioned models such as language-conditioned CNNs and FiLM (Perez et al., 2018;
Bahdanau et al., 2019) both in terms of sample efﬁciency and ﬁnal win-rate on RTFM.
Through curriculum learning where we adapt txt 2 π trained on simpler tasks to more complex tasks, we obtain agents that generalise to tasks with natural language documents that require ﬁve hops of reasoning between the goal, document, and environment observations.
Our qualitative analyses show that txt 2 π attends to parts of the document relevant to the goal and environment observations, and that the resulting agents exhibit complex behaviour such as retrieving correct items, engaging correct enemies after acquiring correct items, and avoiding incorrect enemies.
Finally, we highlight the complexity of RTFM in scaling to longer documents, richer dynamics, and natural language variations.
We show that signiﬁcant improvement in language-grounded policy learning is needed to solve these problems in the future.
R ELATED W ORK
Language-conditioned policy learning.
A growing body of research is learning policies that follow imperative instructions.
The granularity of instructions vary from high-level instructions for application control (Branavan, 2012) and games (Hermann et al., 2017; Bahdanau et al., 2019) to step-by-step navigation (Fried et al., 2018).
In contrast to learning policies for imperative instructions, Branavan et al.
(2011; 2012); Narasimhan et al.
(2018) infer a policy for a ﬁxed goal using features extracted from high level strategy descriptions and general information about domain dynamics.
Unlike prior work, we study the combination of imperative instructions and descriptions of dynamics.
Furthermore, we require that the agent learn to ﬁlter out irrelevant information to focus on dynamics relevant to accomplishing the goal.
Language grounding.
Language grounding refers to interpreting language in a non-linguistic context.
Examples of such context include images (Barnard & Forsyth, 2001), games (Chen & Mooney, 2008;
Wang et al., 2016), robot control (Kollar et al., 2010; Tellex et al., 2011), and navigation (Anderson et al., 2018).
We study language grounding in interactive games similar to Branavan (2012);
Hermann et al.
(2017) or Co-Reyes et al.
(2019), where executable semantics are not provided and the agent must learn through experience.
Unlike prior work, we require grounding between an underspeciﬁed goal, a document of environment dynamics, and world observations.
In addition, we focus on generalisation to not only new goal descriptions but new environments dynamics.
R EAD TO F IGHT M ONSTERS
We consider a scenario where the agent must jointly reason over a language goal , relevant environment dynamics speciﬁed in a text document, and environment observations .
In reading the document, the agent should identify relevant information key to solving the goal in the environment.
A successful agent needs to perform this language grounding to generalise to new environments with dynamics not seen during training.
To study generalisation via reading, the environment dynamics must differ every episode such that the agent cannot avoid reading by memorising a limited set of dynamics.
Consequently, we procedurally generate a large number of unique environment dynamics (e.g. effective(blessed items, poison monsters) ), along with language descriptions of environment dynamics (e.g. blessed items are effective against poison monsters) and goals (e.g. Defeat the order of the forest).
We couple a large, customisable ontology inspired by rogue-like games such as NetHack or
Diablo, with natural language templates to create a combinatorially rich set of environment dynamics to learn from and evaluate on.
In RTFM, the agent is given a document of environment dynamics, observations of the environment, and an underspeciﬁed goal instruction.
Figure 1 illustrates an instance of the game.
Concretely, we design a set of dynamics that consists of monsters (e.g. wolf, goblin), teams (e.g. Order of the Forest), element types (e.g. ﬁre, poison), item modiﬁers (e.g. fanatical, arcane), and items (e.g. sword, hammer).
When the player is in the same cell with a monster or weapon, the player picks up the item or engages in combat with the monster.
The player can possess one item at a time, and drops existing
[Figure]
Doc:
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Defeat
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ig h t n in [Figure] o n [Figure]
ter [Figure] a r e wea k a g a [Figure]
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ter (cid:213)s [Figure] n d S o ld ie r (cid:213)s w ea p o n
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a r e d e f ea t e d [Figure] y fa n at ica l
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h imm e ri n g wea p o n s. weapons if they pick up a new weapon.
A monster moves towards the player with 60% probability, and otherwise moves randomly.
The dynamics, the agent’s inventory, and the underspeciﬁed goal are rendered as text.
The game world is rendered as a matrix of text in which each cell describes the entity occupying the cell.
We use human-written templates for stating which monsters belong to which team, which modiﬁers are effective against which element, and which team the agent should defeat (see appendix H for details on collection and G for a list of entities in the game).
In order to achieve the goal, the agent must cross-reference relevant information in the document and as well as in the observations.
During every episode, we subsample a set of groups, monsters, modiﬁers, and elements to use.
We randomly generate group assignments of which monsters belong to which team and which modiﬁer is effective against which element.
A document that consists of randomly ordered statements corresponding to this group assignment is presented to the agent.
We sample one element, one team, and a monster from that team (e.g. “ﬁre goblin” from “Order of the forest”) to be the target monster.
Additionally, we sample one modiﬁer that beats the element and an item to be the item that defeats the target monster (e.g. “fanatical sword”).
Similarly, we sample an element, a team, and a monster from a different team to be the distractor monster (e.g. poison bat), as well as an item that defeats the distractor monster (e.g. arcane hammer).
In order to win the game (e.g. Figure 1), the agent must
1. identify the target team from the goal (e.g. Order of the Forest) 2. identify the monsters that belong to that team (e.g. goblin, jaguar, and ghost) 3.
identify which monster is in the world (e.g. goblin), and its element (e.g. ﬁre) 4.
identify the modiﬁers that are effective against this element (e.g. fanatical, shimmering) 5.
ﬁnd which modiﬁer is present (e.g. fanatical), and the item with the modiﬁer (e.g. sword)
6. pick up the correct item (e.g. fanatical sword) 7.
engage the correct monster in combat (e.g. ﬁre goblin).
If the agent deviates from this trajectory (e.g. does not have correct item before engaging in combat, engages with distractor monster), it cannot defeat the target monster and therefore will lose the game.
The agent receives a reward of +1 if it wins the game and -1 otherwise.
RTFM presents challenges not found in prior work in that it requires a large number of grounding steps in order to solve a task.
In order to perform this grounding, the agent must jointly reason over a language goal and document of dynamics, as well as environment observations.
In addition to the environment, the positions of the target and distractor within the document are randomised—the agent cannot memorise ordering patterns in order to solve the grounding problems, and must instead identify information relevant to the goal and environment at hand.
We split environments into train and eval sets.
No assignments of monster-team-modiﬁer-element are shared between train and eval to test whether the agent is able to generalise to new environments with dynamics not seen during training via reading.
There are more than 2 million train or eval environments without considering the natural language templates, and 200 million otherwise.
With random ordering of templates, the number of unique documents exceeds 15 billion.
M ODEL
We propose the txt 2 π model, which builds representations that capture three-way interactions between the goal, document describing environment dynamics, and environment observations.
We begin with deﬁnition of the Bidirectional Feature-wise Linear Modulation (FiLM 2 ) layer, which forms the core of our model.
4. B IDIRECTIONAL F EATURE - WISE L INEAR M ODULATION (F I LM 2 ) LAYER
[Table]
/qh69LBZBPJSkCnosePHYgq2FNpTNdtKu3WzC7kYoob/AiwdFvPqTvPlv3LY5aOuDgcd7M8zMCxLBtXHdb6ewtr6xuVXcLu3s7u0flA+P2jpOFcMWi0WsOgHVKLjEluFGYCdRSKNA4EMwvp35D0+oNI/lvZkk6Ed0KHnIGTVWal70yxW36s5BVomXkwrkaPTLX71BzNIIpWGCat313MT4GVWGM4HTUi/VmFA2pkPsWipphNrP5odOyZlVBiSMlS1pyFz9PZHRSOtJFNjOiJqRXvZm4n9eNzXhjZ9xmaQGJVssClNBTExmX5MBV8iMmFhCmeL2VsJGVFFmbDYlG4K3/PIqadeq3mW11ryq1N08jiKcwCmcgwfXUIc7aEALGCA8wyu8OY/Oi/PufCxaC04+cwx/4Hz+AGvljKA=</latexit> +
ReLU +
MaxPool output summary
Feature-wise linear modulation (FiLM), which modulates visual inputs using representations of textual instructions, is an effective method for image captioning (Perez et al., 2018) and instruction following (Bahdanau et al., 2019).
In RTFM, the agent must not only ﬁlter concepts in the visual domain using language but ﬁlter concepts in the text domain using visual observations.
To support this, FiLM 2 builds codependent representations of text and visual inputs by further incorporating conditional representations of the text given visual observations.
Figure 2 shows the FiLM 2 layer.
We use upper-case bold letters to denote tensors, lower-case bold letters for vectors, and non-bold letters for scalars.
Exact dimensions of these variables are shown in Table 4 in appendix B. Let x text denote a ﬁxed-length d text -dimensional representation of the text and X vis the representation of visual inputs with height H , width W , and d vis channels.
Let Conv denote a convolution layer.
Let + and * symbols denote element-wise addition and multiplication operations that broadcast over spatial dimensions.
We ﬁrst modulate visual features using text features:
[Equation]
Unlike FiLM, we additionally modulate text features using visual features:
[Equation]
[Figure]
The output of the FiLMlayer consists of the sum of the modulated features
V , as well as a max-pooled summary s over this sum across spatial dimensions.
[Equation]
4. T HE TXT 2 π MODEL
We model interactions between observations from the environment, goal, and document using FiLM 2 layers.
We ﬁrst encode text inputs using bidirectional LSTMs, then compute summaries using self-attention and conditional summaries using attention.
We concatenate text summaries into text features, which, along with visual features, are processed through consecutive FiLM 2 layers.
In this case of a textual environment, we consider the grid of word embeddings as the visual features for FiLM 2 .
The ﬁnal FiLM 2 output is further processed by MLPs to compute a policy distribution over actions and a baseline for advantage estimation.
Figure 3 shows the txt 2 π model.
Let E obs denote word embeddings corresponding to the observations from the environment, where
E obs
[: , : , i, j ] represents the embeddings corresponding to the l obs -word string that describes the objects in location ( i, j ) in the grid-world.
Let E doc , E inv , and E goal respectively denote the embeddings corresponding to the l doc -word document, the l inv -word inventory, and the l goal -word goal.
We ﬁrst compute a ﬁxed-length summary c goal of the the goal using a bidirectional LSTM (Hochreiter & Schmidhuber, 1997) followed by self-attention (Lee et al.,
[Equation]
Zhong
[Equation]
al., 2018).
[Equation]
We abbreviate self-attention over the goal as c goal = selfattn( H goal ) .
We similarly compute a summary of the inventory as c inv =
selfattn(BiLSTM inv ( E inv )) .
Next, we represent the document encoding conditioned on the goal using dot-product attention (Luong et al., 2015).
[Equation]
We abbreviate attention over the document encoding conditioned on the goal summary as c doc = attend( H doc , c goal ) .
Next, we build the joint representation of the inputs using successive FiLM 2 layers.
At each layer, the visual input to the FiLM 2 layer is the concatenation of the output of the previous layer with positional features.
For each cell, the positional feature X pos consists of the x and y distance from the cell to the agent’s position respectively, normalized by the width and height of the grid-world.
The text input is the concatenation of the goal summary, the inventory summary, the attention over the document given the goal, and the attention over the document given the previous visual summary.
Let [ a ; b ] denote the feature-wise concatenation of a
[Figure] [Figure]
[Table]
of RTFM. The models are trained on one set of dynamics (e.g. training set) and evaluated on another set of dynamics (e g evaluation set “Train” and and b .
For the i th layer, we have
R ( i ) =
[Equation] ( i − 1) ; X pos ] (17)
T ( i ) =
[ c goal ; c inv ; c doc ; attend(BiLSTM vis - doc ( E doc ) , s ( i − 1) )] (18)
V ( i ) , s ( i ) =
FiLM 2(i)
(R (i) , T (i) )
BiLSTM vis - doc ( E doc ) is another encoding of the document similar to H goal , produced using a separate LSTM, such that the document is encoded differently for attention with the visual features and with the goal.
For i = 0 , we concatenate the bag-of-words embeddings of the grid with positional features as the initial visual features V (0) =
[ (cid:80) j E obs ,j ; X pos ] .
We max pool a linear transform of the initial visual features to compute the initial visual summary s (0) =
MaxPool( W ini V (0) + b ini ) .
Let s (last) denote visual summary of the last FiLM 2 layer.
We compute the policy y policy and baseline y baseline as
[Equation]
where MLP policy and MLP baseline are 2-layer multi-layer perceptrons with ReLU activation.
We train using TorchBeast (K ¨ uttler et al., 2019), an implementation of IMPALA (Espeholt et al., 2018).
Please refer to appendix D for details.
E XPERIMENTS
We consider variants of RTFM by varying the size of the grid-world ( 6 × 6 vs 10 × 10 ), allowing many-to-one group assignments to make disambiguation more difﬁcult ( group ), allowing dynamic, moving monsters that hunt down the player ( dyna ), and using natural language templated documents ( nl ).
In the absence of many-to-one assignments, the agent does not need to perform steps 3 and 5 in section 3 as there is no need to disambiguate among many assignees, making it easier to identify relevant information.
We compare txt 2 π to the FiLM model by Bahdanau et al.
(2019) and a language-conditioned residual CNN model.
We train on one set of dynamics (e.g. group assignments of monsters and modiﬁers) and evaluated on a held-out set of dynamics.
We also study three variants of txt 2 π .
In no task attn , the document attention conditioned on the goal utterance (equation 16) is removed and the goal instead represented through self-attention and concatenated with the rest of the text features.
In no vis attn , we do not attend over the document given the visual output of the previous layer (equation 18), and the document is instead represented through self-attention.
Transferfrom
Transfer to
[Table]
In no text mod , text modulation using visual features (equation 6) is removed.
Please see appendix C for model details on our model and baselines, and appendix D for training details.
5. C OMPARISON TO BASELINES AND ABLATIONS
We compare txt 2 π to baselines and ablated variants on a simpliﬁed variant of RTFM in which there are one-to-one group assignments (no group ), stationary monsters (no dyna ), and no natural language templated descriptions (no nl ).
Figure 4 shows that compared to baselines and ablated variants, txt 2 π is more sample efﬁcient and converges to higher performance.
Moreover, no ablated variant is able to solve the tasks—it is the combination of ablated features that enables txt 2 π to win consistently.
Qualitatively, the ablated variants converge to locally optimum policies in which the agent often picks up a random item and then attacks the correct monster, resulting in a ∼ 50 % win rate.
Table 1 shows that all models, with the exception of the CNN baseline, generalise to new evaluation environments with dynamics and world conﬁgurations not seen during training, with txt 2 π outperforming FiLM and the CNN model.
We ﬁnd similar results for txt 2 π , its ablated variants, and baselines on a separate, language-based rock-paper-scissors task in which the agent needs to deduce cyclic dependencies (which type beats which other type) through reading in order to acquire the correct item and defeat a monster.
We observe that the performance of reading models transfer from training environments to new environments with unseen types and unseen dependencies.
Compared to ablated variants and baselines, txt 2 π is more sample efﬁcient and achieves higher performance on both training and new environment dynamics.
When transferring to new environments, txt 2 π remains more sample efﬁcient than the other models.
Details on these experiments are found in appendix E.
5. C URRICULUM LEARNING FOR COMPLEX ENVIRONMENTS
[Table]
Due to the long sequence of co-references the agent must perform in order to solve the full RTFM ( 10 × 10 with moving monsters, many-to-one group assignments, and natural language templated documents)
we design a curriculum to facilitate policy learning by starting with simpler variants of RTFM.
We start with the simplest variant (no group , no dyna , no nl ) and then add in an additional dimension of complexity.
We repeatedly add more complexity until we obtain 10 × 10 worlds with moving monsters, many-to-one group assignments and natural language templated descriptions.
The performance across the curriculum is shown in Table g
l a a1 a a3 a y o u
s hou ld u se g rand m a s te rs , s hi m m e rin g ite ms to bea t fire m on s te rs . th e s ha m a n, z o m b ie, gho st m on s te rs a re rebe l en c la ve . po is o nis w ea k aga in st fana tic a l, gl e a m in g. li g h tn in gis d e fea te d b y b le ss e d, mys te riou s. w o lf, ba t, pan the
[Figure]
g l a a1 a a3 a ligh tn in gis de fea te d b y b le ss e d, glea m in g. po is o nis de fea te d b y g ra nd m a s te rs , s o ld ie rs .
c o ldis wea k aga in st a rc an e, m ys te riou s. th e zombie , ghost , wo lf m on s te rs a re s ta r a llian ce . shaman , imp , bata reonthe rebe l en c la ve tea m .
th e goblin , jagua r, pan the r m on s te rs a re o rde r o f th e fo re st . fireisnot goo d aga in st fana tic a l, s h
im m e rin g. p a d
[Figure]
(see Figure 13 in appendix F for training curves of each stage).
We see that curriculum learning is crucial to making progress on RTFM, and that initial policy training (ﬁrst row of Table 2) with additional complexities in any of the dimensions result in signiﬁcantly worse performance.
We take each of the 5 runs after training through the whole curriculum and evaluate them on dynamics not seen during training.
Table 3 shows variants of the last stage of the curriculum in which the model was trained on 6 × 6 versions of the full RTFM and in which the model was trained on 10 × 10 versions of the full RTFM.
We see that models trained on smaller worlds generalise to bigger worlds.
Despite curriculum learning, however, performance of the ﬁnal model trail that of human players, who can consistently solve RTFM.
This highlights the difﬁculties of the RTFM problem and suggests that there is signiﬁcant room for improvement in developing better language grounded policy learners.
Attention maps.
Figure 5 shows attention conditioned on the goal and on observation summaries produced by intermediate FiLM 2 layers.
Goal-conditioned attention consistently locates the clause that contains the team the agent is supposed to attack.
Intermediate layer attentions focus on regions near modiﬁers and monsters, particularly those that are present in the observations.
These results suggests that attention mechanisms in txt 2 π help identify relevant information in the document.
Analysis of trajectories and failure modes.
We examine trajectories from well-performing policies (80% win rate) as well as poorly-performing policies (50% win rate) on the full RTFM.
We ﬁnd that well-performing policies exhibit a number of consistent behaviours such as identifying the correct item to pick up to ﬁght the target monster, avoiding distractors, and engaging target monsters after acquiring the correct item.
In contrast, the poorly-performing policies occasionally pick up the wrong item, causing the agent to lose when engaging with a monster.
In addition, it occasionally gets stuck in evading monsters indeﬁnitely, causing the agent to lose when the time runs out.
Replays of both policies can be found in GIFs in the supplementary materials 1 .
C ONCLUSION
We proposed RTFM, a grounded policy learning problem in which the agent must jointly reason over a language goal, relevant dynamics speciﬁed in a document, and environment observations.
In order to study RTFM, we procedurally generated a combinatorially large number of environment dynamics such that the model cannot memorise a set of environment dynamics and must instead generalise via reading.
We proposed txt 2 π , a model that captures three-way interactions between the goal, document, and observations, and that generalises to new environments with dynamics not seen during training.
txt 2 π outperforms baselines such as FiLM and language-conditioned CNNs.
Through curriculum learning, txt 2 π performs well on complex RTFM tasks that require several reasoning and coreference steps with natural language templated goals and descriptions of the dynamics.
Our work suggests that language understanding via reading is a promising way to learn policies that generalise to new environments.
Despite curriculum learning, our best models trail performance of human players, suggesting that there is ample room for improvement in grounded policy learning on complex RTFM problems.
In addition to jointly learning policies based on external documentation and language goals, we are interested in exploring how to use supporting evidence in external documentation to reason about plans (Andreas et al., 2018) and induce hierarchical policies (Hu et al., 2019; Jiang et al., 2019). A CKNOWLEDGEMENT
We thank Heinrich K¨uttler and Nantas Nardelli for their help in adapting Torchbeast and the FAIR
London team for their feedback and support.
A P LAYTHROUGH EXAMPLES
These ﬁgures shows key snapshots from a trained policy on randomly sampled environments.
[Figure] [Figure]
agent is cornered by monsters. In 9, the agent is forced to engage in combat and loses.
[Figure]
Fight the monster in the Rebel Enclave.
[Figure] [Figure]
[Figure]
in g wea p o n s a r e goo d aga in st li g h t n in g m o n s t e r s . P o is o n m o n s te r a r e d e fea t ed by b le
ss e d a n d f a n at ica l ite m s. Get a r ca n e a n d G r a n d m a s ter (cid:213)s w ea p o n s t o s la y (cid:222) r e m o n s t e r s. Shaman , p a n t h e r, a n d z
[Figure]
m b ie a r e S t a r A lli a n ce . Goblin
[Figure]
r,
[Figure]
G o a l :
11 and 13, the agent obtains “soldier’s knife” while evading monsters.
In 14, the agent defeats the target and wins.
B V ARIABLE DIMENSIONS
Let x text ∈ R d text denote a ﬁxed-length d text -dimensional representation of the text and X vis ∈ R d vis × H × W denote the representation of visual inputs with
Variable
Symbol
Dimension d text -dim text representation
[Equation]
d vis -dim visual representation with height H , width W , d vis channels
[Equation]
Environment observations embeddings
[Equation]
[Table]
word string that describes the objects in location ( i, j ) in the grid-world
[Equation]
[Table]
[Equation]
[Table]
[Equation]
[Table]
C M ODEL DETAILS C. TXT 2 π
Hyperparameters.
The txt 2 π used in our experiments consists of 5 consecutive FiLM 2 layers, each with 3x3 convolutions and padding and stride sizes of 1.
The txt 2 π layers have channels of 16, 32, 64, 64, and 64, with residual connections from the 3rd layer to the 5th layer.
The Goal-doc
LSTM (see Figure 3) shares weight with the Goal LSTM.
The Inventory and Goal LSTMs have a hidden dimension of size 10, whereas the Vis-doc LSTM has a dimension of 100.
We use a word embedding dimension of 30.
C. CNN
[Figure]
Like txt 2 π , the CNN baseline consists of 5 layers of convolutions with channels of 16, 32, 64, 64, and 64.
There are residual connections from the 3rd layer to the 5th layer.
The input to each layer consists of the output of the previous layer, concatenated with positional features.
The input to the network is the concatenation of the observations V (0) and text representations.
The text representations consist of self-attention over bidirectional LSTM-encoded goal, document, and inventory.
These attention outputs are replicated over the dimensions of the grid and concatenated feature-wise with the observation embeddings in each cell.
Figure 8 illustrates the CNN baseline.
C. F I LM BASELINE
The FiLM baseline encodes text in the same fashion as the CNN model.
However, instead of using convolutional layers, each layer is a FiLM layer from Bahdanau et al.
Note that in our case, the language representation is a self-attention over the LSTM states instead of a concatenation of terminal LSTM states.
D T RAINING PROCEDURE
We train using an implementation of IMPALA (Espeholt et al., 2018).
In particular, we use 20 actors and a batch size of 24.
When unrolling actors, we use a maximum unroll length of 80 frames.
Each episode lasts for a maximum of 1000 frames.
We optimise using RMSProp (Tieleman & Hinton, 2012) with a learning rate of 0.005, which is annealed linearly for 100 million frames.
We set α = 0 .
99 and (cid:15) = 0 .
During training, we apply a small negative reward for each time step of − 0 .
02 and a discount factor of 0.99 to facilitate convergence.
We additionally include a entropy cost to encourage exploration.
Let y policy denote the policy.
The entropy loss is calculated as
[Equation]
In addition to policy gradient, we add in the entropy loss with a weight of 0.005 and the baseline loss with a weight of 0.5.
The baseline loss is computed as the root mean square of the advantages (Espeholt et al., 2018).
When tuning models, we perform a grid search using the training environments to select hyperparameters for each model.
We train 5 runs for each conﬁguration in order to report the mean and standard deviation.
When transferring, we transfer each of the 5 runs to the new task and once again report the mean and standard deviation.
[Table]
unseen
[Table]
permutation
[Table]
n  n
[Table]
edge
[Table] [Table]
[Table]
n new edge
[Table]
nodes
[Table]
y
[Figure]
E R OCK - PAPER - SCISSORS
[Figure]
In addition to the main RTFM tasks, we also study a simpler formulation called Rock-paper-scissors that has a ﬁxed goal.
In Rock-paper-scissors, the agent must interpret a document that describes the environment dynamics in order to solve the task.
Given an set of characters (e.g. a-z), we sample 3 characters and set up a rock-paper-scissors-like dependency graph between the characters (e.g. “a beats b, b beats c, c beats a”).
We then spawn a monster in the world with a randomly assigned type (e.g. “b goblin”), as well as an item corresponding to each type (e.g. “a”, “b”, and “c”).
The attributes of the agent, monster, and items are set up such that the player must obtain the correct item and then engage the monster in order to win.
Any other sequence of actions (e.g. engaging the monster without the correct weapon) results in a loss.
The winning policy should then be to ﬁrst identify the type of monster present, then cross-reference the document to ﬁnd which item defeats that type, then pick up the item, and ﬁnally engage the monster in combat.
Figure 9 shows an instance of Rock-paper-scissors.
Reading models generalise to new environments.
We split environment dynamics by permuting 3-character dependency graphs from an alphabet, which we randomly split into training and held-out sets.
This corresponds to the “permutations” setting in Table 5.
[Figure] [Figure]
We train models on the 10 × 10 worlds from the training set and evaluate them on both seen and not seen during training.
The left of Figure 10 shows the performance of models on worlds of varying sizes with training environment dynamics.
In this case, the dynamics (e.g. dependency graphs) were seen during training.
For 9 × 9 and 11 × 11 worlds, the world conﬁguration not seen during training.
For 10 × 10 worlds, there is a 5% chance that the initial frame was seen during training.
2 Figure 10 shows the performance on held-out environments not seen during training.
We see that all models generalise to environments not seen during training, both when the world conﬁguration is not seen (left) and when the environment dynamics are not seen (right).
Reading models generalise to new concepts.
In addition to splitting via permutations, we devise two additional ways of splitting environment dynamics by introducing new edges and nodes into the held-out set.
Table 5 shows the three different settings.
For each, we study the transfer behaviour of models on new environments.
Figure 11 shows the learning curve when training a model on the held-out environments directly and when transferring the model trained on train environments to held-out environments.
We observe that all models are signiﬁcantly more sample-efﬁcient when transferring from training environments, despite the introduction of new edges and new nodes.
txt 2 π is more sample-efﬁcient and learns better policies.
In Figure 10, we see that the FiLM model outperforms the CNN model on both training environment dynamics and held-out environment dynamics.
txt 2 π further outperforms FiLM, and does so more consistently in that the ﬁnal performance has less variance.
This behaviour is also observed in the in Figure 11.
When training on the held-out set without transferring, txt 2 π is more sample efﬁcient than FiLM and the CNN model, and achieves higher win-rate.
When transferring to the held-out set, txt 2 π remains more sample efﬁcient than the other models.
F C URRICULUM LEARNING TRAINING CURVES
[Figure]
G E NTITIES AND MODIFIERS
Below is a list of entities and modiﬁers contained in RTFM:
Monsters: wolf, jaguar, panther, goblin, bat, imp, shaman, ghost, zombie
Weapons: sword, axe, morningstar, polearm, knife, katana, cutlass, spear
Elements: cold, ﬁre, lightning, poison
Modiﬁers: Grandmaster’s, blessed, shimmering, gleaming, fanatical, mysterious, Soldier’s, arcane
Teams: Star Alliance, Order of the Forest, Rebel Enclave
H L ANGUAGE TEMPLATES
We collect human-written natural language templates for the goal and the dynamics.
The goal statements in RTFM describe which team the agent should defeat.
We collect 12 language templates for goal statements.
The document of environment dynamics consists of two types of statements.
The ﬁrst type describes which monsters are assigned to with team.
The second type describes which modiﬁers, which describe items, are effective against which element types, which are associated with monsters.
We collection 10 language templates for each type of statements.
The entire document is composed from statements, which are randomly shufﬂed.
We randomly sample a template for each statement, which we ﬁll with the monsters and team for the ﬁrst type and modiﬁers and element for the second type.