With self-paced reading, for one word we get one result (one number telling us how long the person needed to read that word).
Will the results also work that way when we do eye-tracking, or will the results be more complicated? Think about what you saw in the
previous task when you watched videos of how people's eyes move. Can you think of any situations where it will be complicated to
determine how long a person took to read a word? Can you think of any situations where we will not get one result for one word
(e.g., situations where we will get more than one number for one word, or situations where we will get less than one number for one
word)?
Imagine I am doing an eye-tracking experiment and I want to see how long people take to read each word in the following sentence:
- The key to the cabinets are sitting on the table.
Specifically, I want to know how long people take to read "cabinets".
Now let's imagine I record people's eyes moving while they read the sentence, and I observe the following pattern:
This picture tells us that the eye movements followed the following pattern:
- First, the person looked at (made a fixation on) the word the.
- Next, they moved their eyes (made a saccade) and then looked at the word to.
- Next, they looked at the beginning of the word cabinets.
- Then, they moved their eyes, but not to another word --- they just looked at another spot on the same word cabinets.
- Then, their eyes jumped back, and looked at the word key!
- Then, they jumped forward and looked at cabinets again.
- Next, they jumped forward and looked at the phrase are sitting.
- Next, they looked at on.
- Next, they looked at table.
- Next, their eyes jumped back again, and they looked at cabinets again!
- Last, then again moved their eyes within the same word -- looking at another spot on the word cabinets.
So they made eleven fixations at different places in this sentence. For each of these fixations, the eye-tracker will also have
recorded how long the fixation was (e.g., how long they spent looking at "cabinets" during fixation #3, etc.), but let's not worry
about that yet.
If you wanted to know how long people spent to read the word "cabinets", what would
you do? If we were doing self-paced reading we would have just one number; but with eye-tracking, they looked at this
word five different times. Which of these fixations might you pay attention to if
you're trying to calculate how long people spent reading the word?
As usual, there's no right or wrong answer, but I want you to think about this problem and I want to see what solution you think might
be best.
Let's think again about the example from the previous question. Here is a picture of the data pattern again; after the picture I have
also shown the same data pattern as a table, in case you have trouble viewing the picture.
1 |
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2 |
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3 |
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4 |
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5 |
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6 |
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7 |
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11 |
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The key |
to the |
cabinets |
are sitting |
on the |
table. |
As we discussed in the previous question, there are a lot of possible ways we could measure how long people took to read cabinets, because they looked at it five different times.
Among people who do research on eye-tracking, there are several common ways we can measure how long people took to read a word. Here
are some of them:
- First fixation duration: Measure how long was the first fixation on the word. In this example, that is fixation
#3.
- First pass duration (also called gaze duration): Add up all the fixations from the first time
the person looked at this word, until the first time they looked at anything else. In other words, how much time did they spend
looking at the word until they looked away. In this example, that means we'd add up fixation #3 plus fixation #4; fixation #5
is when they looked away from the word, so we wouldn't include it.
- Go-past time (also called regression path duration): Add up all fixations, on this word
or any other words, from the first time the person looked at this word, until
the first time they looked at a later word. In other words, this is how much time they needed from the first time they looked
at this word until they were able to go past this word. In this example, that means we'd add up fixations #3, #4, #5, and #6;
the first time they went past the word cabinets was fixation #7, so we wouldn't include that. Crucially, we still
count fixation #5, even though it's not looking at the word cabinets; maybe the time they were looking back at
previous words is still time they were using to try to understand the word cabinets and figure out how it fits into
the sentence!
- Total time: Add up all the fixations on this word. In this example, that means we'd add up fixations #3, #4, #6,
#10, and #11.
Which of these measures do you think would be most useful? Or, do you think different measures would be useful for different things?
If so, what do you think would be the important differences between them? For example, what do you think one measure (such as total
time) might tell us that is different from what another measure (such as first pass time) might tell us?