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Chapter 2: General methodology
Participants
Potential participants were recruited using an advertising flier which was posted around the city campus of the University of Auckland, as well as from an online research recruitment website. The initial sample included 64 volunteers who all met the strict exclusion criteria, which were: 1) being left-handed; 2) being bi-/multi-lingual with English not being their first language; 3) currently taking either anti-depressant or anti-psychotic medications; 4) having hearing deficits; 5) being outside the 18-40 years age bracket; 6) being a regular smoker; and 7) having a reading difficulty. As the main objective of this thesis was to investigate the role of schizotypy using different tasks and methods within the same group of individuals, 16 volunteers who could not complete all three experimental sessions (described below) were excluded from further testing.
In total, 48 adults participated in this study who completed all screening and experimental procedures (31 females and 17 males). All procedures for recruitment and testing were approved by the University of Auckland Human Participants Ethics Committee (Appendix A). Written informed consent to participate was obtained from all participants, who received NZ$20 (cash or a voucher equivalent) for each of the three experimental sessions as reimbursement for their time (Appendix B).
Screening procedures
Handedness assessment
The Edinburgh Handedness Inventory (EHI; Oldfield, 1971) was used to confirm that all participants were right-handed (Appendix C). There are ten items in this inventory, where the participant has to indicate their hand preference for different tasks including writing, drawing, throwing, striking a match, opening a box, and using tools such as scissors, a toothbrush, a knife (without a fork), a spoon, and a broom. Additionally, there are two items related to the dominant foot and eye. Usual hand preference is indicated by placing a cross (+) in either the left hand or the right hand column. In addition, participants can indicate a strong preference by placing two crosses in one column, or an equal preference (for either hand) by placing a cross in each column for the same task.
Handedness is calculated as a Laterality Quotient (LQ) = (R – L / R + L) × 100, where R represents the number of right hand column responses, and L the number of left hand column responses. A positive LQ indicates right hand preference while a negative LQ indicates left hand preference. All 48 participants had a LQ between +60 and +100, indicating strong right handedness.
Hearing assessment
Hearing assessment was required due to the inclusion of an auditory EEG experiment in the study, and was administered on a Dell Latitude D620 laptop running on Windows VistaTM Enterprise. Auditory threshold for each participant was checked by using an Otovation Amplitude T3 series audiometer (Otovation LLC, King of Prussia, PA). The pure tones were delivered wirelessly using the Symphony NOAH Module software Build 1.2.1.0 (Otovation LLC, King of Prussia, PA), which presented tones between 125 and 8000Hz, ranging from -10 up to around 120dB HL (decibels Hearing Level, a measure of sound sensitivity). Each ear was tested separately while background white noise was presented concurrently to the other (non-tested) ear. Participants responded to the pure tones by pressing a button on the audiometer. All tones were presented in a semi-darkened, quiet room, and repeated at least twice to ensure there were no accidental or guess responses. All participants met our cut-off of a pure-tone average threshold of 15dB HL or less for each ear.
The average dB HL for the left and right ears across all 48 participants was 7.07 and 9.02dB HL, respectively.
Schizotypy assessment
The Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE; Mason et al., 1995) was used to assess the level of schizotypy in all participants (Appendix D). The O-LIFE consists of 104 self-reported ‘yes/no’ items that load onto four factors of schizotypy, some of which are related to the positive and negative symptoms found in schizophrenia (Dinn et al., 2002). These include: unusual experiences, which refer to items that describe perceptual and hallucinatory experiments including magical thinking; cognitive disorganisation, which measures the level of social anxiety as well as poor attention, concentration, and decision making; introvertive anhedonia which describes a lack of enjoyment from both physical and social sources; and lastly, impulsive nonconformity, which consists of items that refer to impulse-driven, anti-social, and disinhibited behaviour (Mason
& Claridge, 2006). A total overall O-LIFE score is taken from the average of the four subscale scores. In addition, individual subscale scores can be taken separately if investigating a specific dimension of schizotypy, such as the positive factor (unusual experiences).
The O-LIFE was chosen to assess the level of schizotypy in the current thesis as it is based on a fully dimensional model of schizotypy where it takes a more personality-based approach, and considers schizotypal traits as part of normal personality differences (Claridge, 1997). This is in contrast to the Schizotypal Personality Questionnaire (SPQ; Raine, 1991; another well-used and validated measure in the literature), which is a questionnaire based on the DSM-III-R criteria for schizotypal personality disorder (a clinically diagnosed disorder). Therefore, the SPQ treats schizotypy as a possible precursor to schizophrenia, and follows the three-factor structure of the disorder (positive, negative, and disorganised), compared to the O-LIFE which includes a fourth impulsive behaviour factor (Asai, Sugimori, Bando, & Tanno, 2011). This difference may be due to the design of the O-LIFE, which was derived using factor-analytic studies of nonclinical personality measures, and therefore the broader nature of this questionnaire is particularly suited to testing nonclinical populations, who may provide a more stable investigative opportunity (Mason et al., 1995).
Furthermore, it also has good psychometric properties, including good test-retest reliability, good validity, high internal consistency, and acceptable levels of skewness and kurtosis (Burch, Steel, & Hemsley, 1998; Mason et al., 1995).
In the current thesis, out of the 48 participants who completed all screening and experimental procedures, only those with a total O-LIFE score of half a standard deviation above or below the mean O-LIFE score were included in the data analyses. This was to ensure that those who scored in the middle were not arbitrarily included into either the high or the low schizotypy group. Furthermore, two factors of the O-LIFE (unusual experiences and impulsive nonconformity) were examined separately in Chapters 3 and 4, in addition to the total O-LIFE. Again, from the sample of 48 participants, those who scored half a standard deviation above or below the mean on the unusual experiences factor or the impulsive nonconformity factor were included in the separate analyses. These mean scores are presented in Table 2.1.
Mean scores and standard deviations for the schizotypy measures (total O-LIFE, unusual experiences, and impulsive nonconformity) for the high and low scoring groups from an initial sample of 48 participants. The scores are listed for each gender, as well as for both.
Chapter 1: General introduction
1.1 Introduction
1.2 What is schizotypy?
1.3 The multidimensionality and assessment of schizotypy
1.4 The overlap between schizotypy and schizophrenia
1.5 Early processing deficits in schizotypy
1.6 Language laterality in schizotypy
1.7 Psychosis and creativity
1.8 Creativity and schizotypy
1.9 Structural differences in schizotypy
1.10 Thesis rationale
Chapter 2: General methodology
2.1 Participants
2.2 Screening procedures
2.3 Experimental methods and analyses
2.4 Experimental tasks
2.5 Experimental procedures
Chapter 3: P50 sensory gating deficits in schizotypy
Abstract:
3.1 Introduction
3.2 Methods
3.3 Results
3.4 Discussion
Chapter 4: Language laterality in schizotypy
Abstract:
4.1 Introduction
4.2 Methods
4.3 Results
4.4 Discussion
Chapter 5: Neural correlates of creative thinking and schizotypy
Abstract:
5.1 Introduction
5.2 Materials and methods
5.3 Results
5.4 Discussion
5.5 Limitations and future directions
5.6 Conclusions
Chapter 6: Grey matter differences in schizotypy
Abstract:
6.1 Introduction
6.2 Materials and methods
6.3 Results
6.4 Discussion
6.5 Limitations and future directions
6.6 Conclusions
Chapter 7: General discussion
7.1 Summary
7.2 Effects of schizotypy
7.3 Function-structure relationship in schizotypy
7.4 Limitations, applications, and future directions
7.5 General conclusion
References
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