Brain Lexicon Design
Documented on 7/25/02: JN
Purpose:
The purpose of this study is to get brain activation signatures for both individual
low-frequency nouns and verbs, as well as their combination into two-word sentences, for
use in training up a neural network on the data. The neural network will be used to
determine if individual words can be recognized via their brain signatures and whether
sentences can be identified from their component words, among other things.
Stimuli:
Sixteen low-frequency nouns and eight low-frequency verbs were chosen for use
in this study. Eight of the nouns were animate and eight were inanimate. All the verbs
had a K-F written frequency of 10 or below. All verbs but one had only verb meanings
(one had a secondary noun meaning).
Design:
This study was broken down into three phases.
Phase One:
Eight words (four nouns and four verbs) were chosen from the list of 24 words.
They appeared on the screen for one second each and were separated from each other by
a 14 second fixation (so they were presented 15 seconds apart, onset to onset). This was
in order to get the full hemodynamic response for each word. Phase one consists of two
cycles (so each word is presented twice). Each cycle was randomized. Participants’ task
in Phase One was to note whether each word presented was a noun or a verb.
8 words x 2 cycles x 15 seconds = 240 seconds (4 min)
Phase Two:
All 24 words were presented in Phase Two, repeated six times each, in six
separately randomized cycles (actually, the 16 nouns were randomized and the 8 verbs
were inserted to fit the other experimental criteria). Each word appeared on the screen
for a duration of one second and was followed by a blank screen that lasted two seconds
before the next word appeared. There were no breaks between cycles. Participants’ task
in Phase Two was to note whether each word presented was a noun or a verb.
Also, 20 sentences, created by pairing nouns and verbs together to form true and
false statements, were embedded in each cycle (3-4 sentences per cycle). These were
intended not to be noticed.
24 words x 6 cycles x 3 seconds = 432 seconds (7 min 12 sec)
Phase Three:
In Phase Three, the 20 embedded sentences from Phase Two were presented as
sentences. The two words of each sentence were presented one at a time, appearing on
the screen for one second each. There was a two second blank screen between the noun
and the verb and an eleven second fixation cross after the verb before the next sentence
appeared.
This was a surprise task that participants had not practiced. Instructions appeared
on the screen directing them to note (via a button press) whether each sentence presented
was true or false. There were 10 true sentences and 10 false sentences presented.
20 sentences x 1 cycle x 15 seconds = 300 seconds (5 min)
Surprise Instructions = 25 seconds (.42 min)
Fixations:
Four fixation periods of 30 seconds each were presented as well. One was
presented before Phase One, one after Phase One, one after Phase Two, and the final
fixation after Phase Three.
4 fixations x 30 seconds = 120 seconds (2 min)
Miscellaneous (Instructions) = 7.5 seconds (.13 min)
Total Running Time (without Scope Pulses) = 1140.5 seconds (19 min .5 sec)
**Subject Number 1279 ran through this version (called BLex) with the following
problems: Time was miscalculated for the experiment because power was out at CMU
and the time could not be checked with Scope Pulses. Also, Phase Three was typed in
the Scan Control Room and not checked or edited before being run. The surprise
instructions only appeared on the screen for 1 second, so the subject did not even know
what to do with the sentence task.
Alterations:
7/22/02:
Fixations were dropped to 24sec. P2C6 was deleted and miscellaneous
instructions were cut to 6.50sec. Even with these cuts, the expt was still too long for the
scanner (timed with SP it was at 19m). P2 was not edited to replace the lost embedded
sentences from C6. This version, run with Subject Number 1280, was called
BLex5cycles.
7/25/02:
Before Scan: Miscellaneous instructions were cut to 6s. Two sentences were
deleted (saved 30s) from P3, and more surprise instructions were included (examples and
rewording) that added 7s. This version, run with Subject Number 1281, was called
BLex5cycles2.
After Scan: P2C1-P2C5 were edited to include the lost sentences from the prior
deletion of C6 and to make changes as per the two new deleted sentences. So now P2 has
18 embedded sentences (required some reworking of the word order in those cycles) and
P3 has 18 sentences. Surprise instructions were edited and a picture of button boxes
added.
This version, first to be run on Subject Number 1282 (on 7/29/02), was called
BLex. The original BLex was renamed as BLex-OLD. The new time breakdown is as
follows:
Phase One: 240s
Phase Two: 360s
Surprise Instructions: 42s
Phase Three: 270s
Fixations: 96s
Misc Instructions: 6s
Total Time (without Scope Pulses): 1014s (16 min 54 sec)