eye tracking reading study

[Michiel Spape]

Hi,
Here's my take:
- given that E-Prime uses, I think, a font with constant letter symbol size (I forgot the official name, but the point is that an I takes as much space as a W - as in the font you're probably reading this), it is not that difficult to line them up, as you say. Say, one letter is 12 pixels (you can test that by trial and error), then the word WORDS is 60 pixels. If I want to have two AOIs for the words TWO WORDS, then, as per your second possible way to do this, I'd just show that as one slideText on the slide and make two AOIs. Given that our screen is 640x480 by default (or whatever you have), the we print the TWO WORDS as one slideText in the centre. TWO WORDS is 60 + 48 (TWO plus space makes 4x12=48 pixels) = 108 pixels and should therefore be positioned LEFT at 266 to RIGHT at 374* (LEFT: 320 (screen width centre) - 54 (i.e. 108 / 2) = 266 and RIGHT: 320 + 54 = 374). Thus, your left AIO, if you align it left, can be placed at 266, and should be 36 pixels (since the space shouldn't be included). The AIO right should be aligned right, and can be placed at 374.
Depending on your knowledge of E-Prime (and you'd need some to get Tobii to work properly in E-Prime), that shouldn't be too hard to programme, but let me know if you need help.

- You could also do away with all the AOIs as programmed by the Tobii team and just look at the fixation position on the fly - that is, just take the fix.position, calculate distance to each word and figure out which is the likely candidate. I have some script for that, if you're interested.

- Alternatively, have you thought about just NOT lining up the words? That is, if you have a slide with 3 states, state 1 with one word, 2 with two words, 3 with three words, and put words on slide 2, for instance, at 35% and 65%, then this will be a LOT easier. I can see the point that it doesn't look right, but I think there's plenty that can be said for this experimentally:
1. you probably want to control for word length anyway
2. you probably want to control for saccade length anyway
3. Accurate as Tobii *can* be, I've often found I wanted my AOIs quite a bit larger so that things are accurately detected.

- Finally, I've later come to realise it is a lot easier to just don't do much with Tobii in E-Prime and analyse the "gazedata" separately (in matlab). That is, it's pretty easy to find out later on what word people were fixating (at least, roughly), given that you at least save their positions on the screen. 

Best,
Mich


* obviously, this would make the region one pixel too large, but I'm not compensating for that to simplify matters.



Michiel Spapé
Research Fellow
Perception & Action group
University of Nottingham
School of Psychology
www.cognitology.eu


-----Original Message-----
From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of Alon Hafri
Sent: 28 June 2011 21:47
To: E-Prime
Subject: eye tracking reading study

Hi, wondering if someone in the group can help me out.

I am creating an E-Prime experiment using the E-Prime Extensions for
Tobii. For each trial, the participant will read a sentence, and I
would like to record reading times for each window of size 1 to 3
words.

I have experience with using list attributes to set Slide Image
position (and therefore AOI position) at runtime, as well as with
using transparent Slide Images overtop of larger images to act as
AOIs, but I've never done a reading study before. Since the words will
vary in length for each trial, but will need to be evenly spaced (and
on multiple lines conceivably), it would be great if position for
every window would not have to be specified but could be determined by
a script.

I can think of a few solutions, but perhaps someone has an easier one?
1) create a Slide Text object for each word (or window), and so they
could act as their own AOIs.
Drawbacks: You would have to specify locations for each one, and it
could be tricky lining them up appropriately so words are evenly
spaced.

2) Have one Slide Text object for the whole sentence and have
transparent AOIs overtop as the AOIs.
Drawbacks: You would still have to specify locations for each, but the
text would be in one object so would appear normal.

3) Suggestions?

Thanks!
Alon

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