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Login and Account Creation 
The user begins by arriving at the login screen. We aimed for simplicity in this screen: there is a login and create account tab, each of which contain labeled fields. The create account tab has some features designed towards fast error detection, namely that a message will be displayed if the username is already taken, immediately as the user is typing; likewise if the repeated password doesn't match the original, a message appears when then user finishes typing (as opposed to only making these errors visible once the user clicks the create account button). During user testing, User 2 noticed the immediate detection of the mistyped password, and commented that it was a useful feature. Additionally, the login and create account allow for the keyboard to be used for efficiency; namely the user can tab through the input fields, and the user can press the Enter button as opposed to needing to click on the widget. During testing, Users 1 and 2 both created their accounts by pressing the Enter key instead of clicking the widget, so this feature turned out to be useful.
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Once the user logs in, he is greeted with the main page, which is split into a left sidebar for displaying and managing the study focus and vocabulary, as well as a right half which displays sentences. We chose to have both of these displayed at once, as opposed to haivng the vocabulary management and sentence viewing components in separate tabs, based on the results of the first paper prototyping iteration, where users encountered visibility issues due to having the vocabulary hidden away in a tab, and were generally dissatisfied about having to frequently switch between the two tabs.
Left Sidebar
Study Focus 
The design originally had the study focus as a text-display of the word currently being the focus of all the example sentences. However, due to user complaints about both visibility and navigation control, the study focus display was changed to a drop-down selection, which keeps a history of all the previous study focuses. Additionally, the popped-out drop-down selection also improves information scent.
Sentence Viewing
. We chose buttons for displaying the vocab words, as opposed to underlines, because this appeared to indicate the clickability affordance the best during user testing. Because some users had difficulty going back to previously viewed sentences during paper prototyping (where we initially displayed only one sentence at a time), we instead made it such that all previously fetched sentences would be displayed in a scrollable list. However, during computer testing, users complained about how once they had fetched a sentence, it wasn't possible to remove it from the list of displayed sentences, hence we introduced a Close button to remove it from the list. However, as users in our own independent testing during GR5 were confused as to whether closing a sentence simply removed it from immediate view or prevented it from ever being fetched again, and because the error of accidentally closing a sentence was not easily recoverable, then we introduced a "Closed Sentences" tab where closed sentences could be found and restored.
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