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CHAPTER THREE: MATERIALS AND METHODS
1. Materials and Methods 1.1 Subjects
Of the 30 subjects (15 males, 15 females; mean age=20.70±2.71 years) recruited from the university via advertisements, 15 were pseudo-randomly assigned to the Sleep group (8 males; mean age=19.67 years), and 15 to the Wake group (7 males;
mean age=21.73 years). Demographic data are presented in Table 3. Sleep group participants obtained nocturnal normal sleep with polysomnography (PSG) recording, and wake group participants kept awake all-night. Exclusion criteria included present or past history of mental illness screened through clinical interview and sleep disorder via PSG exam. Prior to procedure of experiment, they slept six to eight hours per night, and had no major disruptions of the sleep–wake cycle, as verified by sleep logs and actigraphy over three days. Volunteers followed a constant sleep schedule (sleep time 12:00 a.m. and wake time 8:00 a.m.±1 hr) three days before the day of learning phase. All were also required to refrain from alcohol and caffeine for the 3 days before and during the entire course of the study. They could receive credit for an undergraduate class or payment of money as reward for their participation. All participants provided a written informed consent to participate in the study.
1.2 Experimental Procedure
Figure 4 illustrates the experimental procedure. Before the day of learning, subjects of Sleep group arrived at 10:00 P.M. at the Sleep Lab in National Cheng-Chi University for PSG exam to rule out the sleep disorder, and to avoid first night effect (Agnew, Webb, & Williams, 1966) in the night following the experiment. Subjects of
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Wakefulness group were allowed to sleep at home monitored by actigraphy and sleep log. Both groups were obligated to sleep at 12:00 A.M. and waked up at 8:00 A.M on the days prior to experimental night.
On the day of the study, subjects were instructed to arrive at 8:00 P.M. for
preparing to hook up EEG recording. In both groups, participants were presented with the task of learning between 8:30 P.M. and 9:30 P.M. After a 10-minute break,
pre-testing was carried out between 9:40 P.M. and 10:10 P.M. The subjects then underwent either sleep with PSG recording (Sleep group) or sleep deprivation (Wakefulness group). During sleep deprivation, subject activities were limited to Internet use, e-mail, short walks, reading, movie watching and board games.
Subjects of Sleep group went to sleep at 12:00 A.M. after PSG hook-up on the learning day. Subjects of Wakefulness group were allowed to leave the laboratory at 08:00 A.M., and those of Sleep group were awoken at the same time. They were instructed to follow their usual daytime activities and to abstain from napping during the day. To prohibit nap and monitor subjects’ states, Wakefulness participants were required to call in Sleep Lab per hour till 06:00 P.M. After sleep manipulation, all subjects were allowed to have one night of recovery sleep on the following night, and then the post-test was administrated. Participants arrived at 09:00 A.M. and underwent post-test phase. The pre-test phase and post-test phase lasted about 30 minutes, and EEG recordings were carried out during both test phases. All subjects completed the Stanford Sleepiness Scale to rate the sleepiness prior to both test phases.
1.3 Paired-associates Learning List
Four hundred and eighty medium frequency two-charactered Chinese nouns (frequency range from10-20 per million) were selected from the CKIP Categorical Classification of Mandarin Chinese (1993) developed by Chinese Knowledge and
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國立 政 治 大 學
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Information Processing Group (CKIP) of Academia Sinica. The unrelated word paired-associations were formed randomly. The degree of association between
unrelated word-pairs was measured in a pilot study. One hundred subjects were asked to rate the strength of associations between a serial of word-pairs with 5-point scale.
Two hundred and forty word-pairs that were rated low in association (average 1.5 points) were selected to be the stimuli of unrelated word-pairs.
These pairs were then randomly allocated into one of three unrelated lists, and each list consisted of 80 word pairs. One list was chosen to be learning materials, and they were presented at study phase and served as old pairs at test phase. Among the old pairs, half were randomly selected to maintain their original paring and served as
“old-intact (OI)” pairs. The other half was randomly recombined and served as
“old-rearranged (OR)” pairs. The word pairs from the other two lists were served as new pairs at pre-test and post-test phases. The study list therefore contained a total of 80 word-pairs whereas each test list included 160 pairs (40 OI, 40 OR, 80 new, see figure 5a).
1.4 Stimuli Presentation
Presentation® software (Neurobehavioral System, Inc., Albany, CA, USA) was used to control both the timing of the stimuli (onset and duration) and the registration of the response. Participants sat in a comfortable chair in a sound-attenuated room. All words were presented on a 17-inch flat-panel monitor at a viewing distance of 90 cm with vertical visual angle of 15° and a horizontal visual angle ranging between 12°
and 19°.
Stimuli were presented in central vision on a computer monitor screen with a black background. During the study (learning) phase, the subjects were told to memorize each pair on the list only once for a subsequent recognition test. The
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learning phases were self-paced. On each trial, an initial fixation character, an exclamation mark “!”, was displayed, signaling that the participants could begin the trial when ready. When a response button was pressed, this character was then replaced with a second fixation character, a plus sign “+”, which displayed for a duration of 500ms (see figure 5b). Then this character was replaced with a word pair, which followed by the original fixation character. When subject finished learning this pair, they pressed the response bottom to learn the next word pair.
During the pre-test and post-test session, the random sequences of 80 studied words, which contained 40 old-intact pairs and 40 old-rearranged pairs, intermixed 80 unstudied words were presented to subjects. Each trial began with the presentation of an initial fixation point, an exclamation mark “!”, for the duration of 2s. This was immediately followed by the presentation of a second fixation point, a plus sign “+”, for a period of 1s. The screen was then blanked for 200 ms. The prime word was presented for 400 ms, followed by the target word displayed for 650 ms with an interstimulus interval (ISI) of 350 ms separating prime and target. After the offset of the target word, a question mark “?” which served as the cue to second response was presented for 3000 ms. Subjects had to make judgments on whether these two words were old-intact pairs, old-rearranged pairs or new pairs as quickly and accurately as possible by pressing one of three buttons on the response tool (see figure 4b). If the response was not made until the time of 3000 ms, the screen was replaced with the next trial. The response buttons were counter-balanced for each test session to avoid a confounding factor of the practice effect. The test list was administered in four blocs of 40 trials, with a short break intervening between each block.
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2. Electrophysiological Recording