In self-raced reading experiments, participants read stimuli (e.g., words, sentences, or paragraphs). It is called self-paced because participants control the timing of how each part of the sentence stimulus is displayed.
Don't worry, you don't need to program the experimental procedure yourself. We (or specifically, Hal Tily, now at Nuance Technology) have programmed a web-based self-paced reading app. This app, CrowdExp-SPR will display your stimuli, randomize their presentation, create a Latin Square Design (we'll learn more about what this later), record reading times and more. More about that ... now.
Here is an example of what participants will see when they take your experiment (this particular display is specific to CrowdExp-SPR). For the participants, the stimulus sentence will advance word-by-word with each press of the SPACE button.
CrowdExp-SPR will record the times between button presses. Those are the reading times that we will analyze to test our predictions.
This particular type of self-paced reading is called moving-window word-by-word self-paced reading. The moving-window part refers to the fact that only one word is shown at each time and that pressing SPACE both advances to the next word and also hides the previous word. This particular type of self-paced reading also employs an uninformative mask: alternative versions of self-paced reading might show the word boundaries in the mask (e.g., "- --- --- ----- -- --- -----.").
Notice also the progress bar at the top of the page, telling participants how many more sentences they still have to read before the experiment is over.
One challenge whenever experimenters want to measure how fast we can do something (like how fast we can read) is that participants might get carried away. For example, someone might just keep pressing the SPACE bar as fast as they can. That will lead to maximally fast reading times and make it impossible to detect any effects on those reading times.
So, to prevent this problem, we want to make sure that participants in our experiment actually read and understand the sentences we show them. This is achieved by comprehension questions. By default, CrowdExp-SPR will ask one yes/no comprehension questions after each stimulus. For the example stimulus given above, we might ask the following question:
CrowdExp-SPR will record both the answer (yes/no)—and thus its accuracy (correct/incorrect)—and the reaction time it took to answer the question.
CrowdExp-SPR will return word-by-word reading times, as well as the reaction time and accuracy of the comprehension question for each sentence. The word-by-word reading times will be your primary outcome variable.
That is, your experiment will use reading times to test the predictions of theories about language processing. Any effect that leads to changes in processing speed, and thus word-by-word reading times, can in theory be detected in the self-paced reading paradigm. For example, it typically takes between 150-450msecs to read a word (and press the SPACE key). Words will be read more or less quickly, depending on their length, frequency, etc., or because they are surprising in context.
Beyond the reading times, some hypotheses also make predictions about the answer reaction time or accuracy. But even if we don't directly test predictions about these alternative outcome variables, answer accuracy is standardly used in order to exclude participants who did not read the sentences carefully. For example, a common exclusion criterion is to exclude from the analysis all data from any participant who did not answer at least 85% of the questions correctly. We will discuss more about exclusions in the Analysis section.
Now that you have a bit of an idea of the procedure we will be employing, it's time to learn more about the structure of experiments and important constraints on the stimuli materials.