Essay title - Schizotypal Personality Disorder
Schizotypal Personality Disorder (SPD) has only begun to be recognised relatively recently as a diagnostic category, it has encouraged increasing interested as it has been recognised to provide information on the etiology of schizophrenia (Siever, Koenigsberg, Harvey, Mitropoulou, Laruelle, Abi-Dargham, Goodman & Buchsbaum, 2002). SPD is characterised by the tendency of the affected person to distance themselves from situations involving social interactions. Those diagnosed with SPD tend to have problems in three particular areas: thought, affect and interpersonal relationships (Kotsaftis & Neale, 1993). Schizotypy has been known to be described as the “liability” to schizophrenia (Rossi & Daneluzzo, 2002) which can be placed within this continuum of the schizophrenic spectrum ranging from so called “normality” to schizophrenia. SPD can be characterised by a withdrawal from reality and social interactions. This withdrawal could be the starting point into developing further schizophrenic symptoms by simply a lack of social contact (Kotsaftis & Neale, 1993). Although this continuum approach to psychosis is still a debateable one.
Schizotypy is said to be an attenuated form of schizophrenia. There are different explanations of the relationship including a continuum that they are different ends of one scale differing in levels of severity. Some describe them as completely distinct disorders which are related by overlapping etiology that may account for the similarities (Siever et al, 2002). It can also be seen in previous studies that schizotypy has been shown to be related genetically to schizophrenia and by scoring highly on measures of schizoptypy an individual is at a higher risk of developing schizophrenia (Compton., Chien & Bollini, 2007). Previous literature has shown how valuable studying SPD is in the understanding of schizophrenia in the prodromal phase is (Cadenhead, Perry, Shafer & Braff, 2002). Individuals with SPD are free of possible confounding variables such as antipsychotic medication (Park & McTigue, 1997). In this case SPD and ‘psychosis proneness’ as an entity will be the main focus although findings on schizotypy can offer insight for all schizophrenia spectrum disorders.
From the days of Kraepelin and Bleuler when the term schizophrenia was being defined, it has been said that the traits exhibited by schizophrenics are distributed amongst the normal population in less extreme way this is what we know as schizotypy (Kotsaftis & Neale, 1993). Schizotypy was recognised only relatively recently by the DSM as a personality disorder where it is defined as:
"A pervasive pattern of social and interpersonal deficits marked by acute discomfort with, and reduced capacity for, close relationships as well as by cognitive or perceptual distortions and eccentricities of behavior, beginning by early adulthood and present in a variety of contexts” (American Psychological Association, 2000)
After making an initial appearance, SPD has been reevaluated giving it now nine symptoms including; ideas of reference, magical thinking, unusual perceptual experiences, suspiciousness, social anxiety, no close friends, inappropriate or constricted affect, odd speech and odd behaviour (Badcock & Dragović, 2006).
Since SPD has become more widely recognized and interest in SPD in the normal population has developed there have been increasing numbers of self report measures developed (Daneluzzo, Bustini, Stratta, Casacchia, & Rossi, 1998). These measures provide a way to test large quantities of people without incurring the huge cost of clinician fees (Bedwell & Donnelly, 2005). The number of scales is too many to mention and although they originally measured proneness to psychosis by assessing the positive or negative aspects, were reliable and valid measures they did not directly reflect the criteria determined by the DSM-IV (Compton et al. 2007). The Schizotypal Personality Questionnaire (SPQ) however does encompass all nine criteria set out in the DSM-IV. Developed by Raine (1991) it consists of 74 questions in a dichotomous (yes/no) layout (Compton et al. 2007). The questionnaire has been used widely and since its popularity a varied scale; the SPQ-B was developed comprising of the most valid and reliable scales from the SPQ (Bedwell & Donnelly, 2005). The SPQ has also been translated into many languages including Turkish, French and Italian (Daneluzzo et al. 1998) and remains a highly reliable scale.
In terms of the effect of age on the sample and levels schizotypy previous research has shown that schizophrenia has its peak onset in late adolescence and early adulthood (Badcock and Dragović, 2006). If participants do not score highly on the SPQ during early adulthood then they are unlikely to develop the disorder if assessed later on in life. It appears that mature adults score significantly lower the adolescents and young adults on the SPQ (Badcock & Dragović, 2006). Research shows that mature adults appear to hold differentiated factor structures on the SPQ demonstrating that a sample of university students would be the most appropriate.
It is widely shown throughout the psychological literature that one of the most challenging aspects accompanying SPD is the cognitive deficits. Evidence has shown that those with SPD also display cognitive deficits similar to that of schizophrenia. In order to understand whether the cognitive deficits are present prior to the onset of schizophrenia spectrum disorders, measuring cognitive dysfunction in those with SPD helps to classify whether they are primary or secondary features (Gooding, Kwapil, & Tallent, 1999). The most common deficits can be seen in that of executive functioning. Executive functioning is a higher order process therefore it influences more of the basic abilities that are used in everyday functioning. Suhr (1997) defines executive functioning as ‘ a flexible process that operates in novel, non-routine situations by inhibiting or activating other, more basic, cognitive processes’. Executive functions hold great importance for functioning normally within society they help us control and change our behaviours, they enable future planning when we are required to deal with new unfamiliar tasks and initiate or inhibit certain actions. Without executive functions we are unable to adapt to new situations we are faced with and anticipate what the result will be.
A commonly used test assessing executive functioning is the Wisconsin Card Sorting Test (WCST) (Gooding et al. 1999; Trestman, Keefe, Mitropoulou, Harvey, deVegvar, Lees-Roitman, Davidson, Aronson, Silverman & Siever, 1995; Daneluzzo et al, 1998). Although not as frequently researched (Trestman et al. 1995) a deficit in cognitive ability can also be seen in those suffering from SPD or ‘psychosis prone’ individuals; those scoring highly on self report measures of schizotypy. ‘Subtle prefrontal deficits are associated with SPD. Individuals receiving a SPD diagnosis demonstrate a greater degree of impairment on tests assessing frontal executive functioning.’ (Dinn, Harris, Aycicegi, Greene & Andover, 2002)
There is contradicting views to whether volunteers who score highly on measures of schizotypy are actually truly representative of the cognitive deficits seen in schizophrenia spectrum disorders. On one hand those high scorers do not actually meet all of the criteria set out by the DSM so in some cases this type of research has been criticised as not valid evidence for the continuum of schizophrenia (Trestman et al. 1995). The other side of the argument however is that by using volunteers we have data that is free of the huge confounding variables (Trestman et al. 1995). Individuals with these include institutionalisation and continued use of anti-psychotic medications which may contribute to the deficits. So therefore the research on those suffering from SPD or who score highly on self report measures offer invaluable data contributing to our understanding of cognitive deficits in schizophrenia and it’s spectrum disorders. Through research such as this on schizotypy, predictions can begin to be made through cognitive disorganisation and measures to aid cognitive deficits can be put into place for schizophrenic spectrum disorders. There is extensive research demonstrating this reduced cognitive functioning ability in those who are classified with SPD (Siever et al. 2002). Evidence from previous research can ‘confirm the existence of a significant relationship between psychometric schizotypy and cognitive deficits’ (Giráldez, Caro, Rodrigo, Piñeiro & González, 2000). Particularly important in executive functioning are planning, attention and language fluency, obviously there are many measures of executive functioning but the three selected have been shown as robust measures in the never ending pile of neuropsychological test battery.
There have long been associations made between most psychiatric disorders and abnormalities in language and communication (Walsh, Regan, Sowman, Parsons, & McKay, 2007). However one of the biggest difficulties in making this connection is the difficulty in deciphering whether the communication problems are due to institutionalisation and anti psychotic medication or whether they are prevalent prior to the institutionalisation. This is a discussion as to whether the dysfunction in language is ‘primary or secondary features of psychosis?’ (Tsakanikos & Claridge, 2005). Primary features are the notion that abnormalities are a development through genetic or clinical symptoms or endophenotypes or secondary features which are the side effects from treatments as mentioned earlier. The language abnormalities displayed in those with schizophrenia spectrum disorders are wide ranging but evidence has shown that verbal productivity is the main focus of the problem (Tsakanikos & Claridge, 2005).
Verbal Fluency is the ease to which one is able to use language, usually measured by generating words beginning with a particular letter. Verbal fluency is a measure of executive functioning and it assesses the ability to stay within the constraints of the rules and inhibit any inadequate responses (Tsakanikos & Claridge, 2005). Tests of verbal fluency have proven popular when assessing executive functioning as groups of healthy participants’ exhibit strong activation for tests. The test is also relatively time and cost effective and can produce valuable quantitative data. (van Beilen, Pijnenborg, van Zomeren, van den Nosch, Withaar & Bouma, 2004). Tests of verbal fluency are prefrontal tests and test for the reproduction of words from the semantic memory (Vollema & Postma, 2002). The verbal fluency test using letters is said to be more difficult and more sensitive to processes in the semantic memory than category fluency (Vollema & Postma, 2002). Evidence has shown however when some individuals who were measured on schizotypy and split according to this into high or low groups, the high schizotypy group actually generated more words than the low schizotypy group (Ducheme, Graves & Brugger, 1998). However in most cases those scoring highly on schizotypy perform less well than those score low or healthy controls. Vollema & Postma (2002) found that when testing controls and those more susceptible to schizophrenia the susceptible group were less able to produce as many words suggesting the deficit in executive functioning is a primary feature of psychosis (Tsakanikos & Claridge, 2005). (Barrantes-Vidal, Fañanás, Rosa, Caparrós, Riba & Obiols, 2002) also found that on tests of verbal fluency scores were lower for high schizotypes.
The Stroop task is a common measure of executive function and deficit in inhibitory control (Höfer, Casa & Feldon, 1999) or the ability to inhibit habitual responses (Henik & Salo, 2004). It was developed by John Ridley Scott who reported the effect in his PhD in 1935. Ever since then the effect has had continued interested causing it to be one of the most cited articles. The Stroop effect is basically a matter of interference and attention; this is done by measuring the difficult task of ignoring certain aspects of the presented stimuli. It is a classical paradigm measuring the inhibition of automatic responses and is frequently used to measure dysfunctions in frontal areas including Parkinson’s and Huntingdon’s diseases but namely psychiatric illnesses such as schizophrenia (Vendrell, Junqué, Pujol, Jurado, Molet & Grafman, 1995). Those with psychiatric illnesses have symptoms that include abnormalities in language and attention (Henik & Salo, 2004) the problems in language are largely due to the ‘attention deficits related to the inability to select appropriate dimension of stimulus and inhibit the irrelevant’ (Henik & Salo, 2004).
The Stroop task has been shown to be a robust measure (MacLeod & Sheehan, 2003) as ‘anyone who can read shows a decrement in the incongruent condition’. When words printed in a colour which is different from the colour expressed by the words semantic meaning a delay occurs in processing and causes a slower reaction time. Individuals scoring highly on measures of schizotypy performed less well compared to low scorers on the Stroop task (Giráldez et al. 2000; Höfer et al, 1999; Suhr, 1997) such that reaction times were worse. Girládez., Piñeiro, Caro & González, (2004) found that the high risk schizotypy group performed worse when presented with the incongruent stimuli; when the colour of the word did not represent the semantic meaning of the word. Although there is evidence for those with SPD have deficits on the Stroop task there is also contradicting evidence. Cadenhead et al. (1999) found that when comparing those with SPD to the control group there were no significant results. Trestman et al (1995) also found no effect of the Stroop task in SPD. In some cases completely contradicting results can be seen when high scorers on measures of schizotypy demonstrated faster reaction times than low scorers (Dinn et al. 2002). However, these results do seem to be anomalies when assessing the effect of cognitive inhibition and schizotypy. Most research concurs that high scorers on measures of schizotypy have slower reaction times than low scorers. Is the difference perhaps because of difficulty in remembering the constraints of the tasks though or due to deficits in attention?
The Towers of Hanoi (TOH) task is a widely used diagnostic tool (Goel & Grafman, 1994) to assess problem solving abilities. Similar to Towers of London task however the TOH is considered a harder version and they should not be considered direct comparisons of each other as some journals tend to do (Goel & Grafman, 1994). The TOH test is a measure of planning capacity it is considered a measure of executive functioning. The TOH task is used and cited as often as the Stroop task in terms of neuropsyhcological assessed although less frequently quoted within the study of psychopathology and executive functioning there is research showing that there is a connection between the two. Bustini, Stratta, Daneluzzo, Pollice, Prosperini & Rossi, (1999) demonstrated than schizophrenics showed deficits on the TOH task when using three or four disks, such that those with schizophrenia took significantly more moves to complete the task to the goal state. However, this deficit is expected to be shown in studies on those with SPD also but in some cases individuals with schizotypals exhibited no significant deficits on the TOH test (Suhr, 1997). Although this does not mean they have no deficit it may be due to the lack of severity that results were not significant.
This study aims to assess neurocognitive performance using measures of executive functioning including verbal fluency, Towers of Hanoi and Stroop in low and high scorers on the SPQ in the normal population. The study aims to contribute a better understanding of executive functioning deficits in schizophrenia spectrum disorders without the issue of confounding variables. The hypothesis is that individuals scoring highly on the SPQ are predicted to perform intermediate compared to the low scoring group.
The design was an experimental design, with one independent variable which was Schizotypy (high or low). There were three dependent variables; which consisted of the scores on three executive functioning tasks Stroop, verbal fluency and Towers of Hanoi.
The initial sample was an opportunistic sample consisting of 112 undergraduate students studying at Nottingham Trent University who filled in a computerised version of the Schizotypal Personality Questionnaire (SPQ). The experimental sample of participants willing to take part in the further tests of executive functioning was actually only 15 with only 14 being included in the data set inputted for analysis as the median figure was omitted from the final analysis as were extreme scores. The participants were collected through email sent out via a university organised email list asking if they wanted to take part. The participants consisted of 6 females and 8 males. The aged ranged from 18 to 24 years (mean age = 20.6).
The threshold to deciding between high and low schizotypals was decided by performing a median split of the results.
2.3.1 Schizotypal Personality Questionnaire
As a measure of schizotypy; the Schizotypal Personality Questionnaire (SPQ) (Raine, 1991) was used. The questionnaire was developed directly from the nine symptoms criteria as defined in the DSM-III-R and is the only measure of schizotypy to correspond to all nine criteria. The SPQ consists of 74 items that are answered with either a yes or no response. The SPQ was administered online from the authors website (Raine, 1991a) and as well as the 74 items the questionnaire including certain demographics including age and sex. Also participants were asked to include their student email account so they may be contacted to take part in the second cognitive aspect of the experiment. They were only asked for their student email account instead of personal email address to keep anonymity. The SPQ has been shown to have high internal reliability with a Cronbach’s alpha of 0.91 (Daneluzzo et al. 1998).
2.3.2 Executive Functioning
Three neuropsychological tests for assessing executive functioning were used dimensions of this included planning, cognitive inhibition, communication and ease of language use.
A) Towers of Hanoi
The Towers of Hanoi test is a test of planning and goal setting in executive functioning. The task consists of three pegs and four disks of varying sizes. The four disks are initially set up on the left most peg in order of size; largest at the bottom and smallest at the top. The goal of the task is to transfer all four disks onto the right most peg in the least number of moves and in the order they are to begin with; in ascending order starting with the largest at the bottom. There are however several constraints or rules upon the task: 1) participants are only allowed to place a smaller disk on top of a larger one 2) participants are only allowed to move one disk at a time and 3) when disks are not being moved they must remain on a peg. The minimum number of moves the Towers of Hanoi task can be completed using four disks is 15.
B) Stroop Test (Stroop, 1935)
The Stroop test is a measure of cognitive inhibition part of executive functioning. The stroop test consists of two trials; firstly a baseline set of words was presented and then an experimental set was presented. For the baseline trials the participants were firstly presented with a set of 25 colour words. The colour words were written in the colours that they denote, the colour words were a varied selection of a total of eight colours; red, blue, green, yellow, orange, pink, brown and white these are classed as congruent stimuli. The participant was required to read out aloud the colour that the words were written for all 25 words. The time taken to read these out aloud was measured and recorded. The second part of the Stroop task required participants to read out the colour of all 25 words on the screen exactly the same as the first trial however this time the word was not written in the same colour as the word denoted. The time taken for this part of the task was recorded, and the baseline time was subtracted from the experimental trial this was the participants final score and the one used in analysis. The test was administered using a computer program (Chudler, 1996) this calculated not only the time taken to complete the task to the goal state but also the total number of moves taken to complete.
C) Verbal Fluency Task.
This is a measure executive functioning testing the ease of language production. The test requires the participant to generate as many words as possible beginning with a certain letter with 90 seconds. The target letter used was N. The participants were informed before hand of the confinements of the task. Any words were acceptable except for non-English words, names, words that were simply changed by gender and words using the same root word were ignored from the final score. For example ‘go’ would be acceptable but then ‘going’ would not be included. The participants score on this task is the total number of words generated with the letter N minus any of exceptions stated previously. The final score demonstrates not only effective use of language but the capability to remember the rules stated by the task.
Potential participants of the study were sent information regarding the aims and nature of the study, the requirements of participants and what it would involve for them in terms of time commitments and standardised instructions of what they would be asked to do. The issue of consent was also explained including their rights, they gave their consent by clicking on the link to the computerised version of the SPQ. Participants followed the online instructions and answered either ‘yes’, ‘no’ or ‘no answer’ to the 74 questions. They were also asked minimal demographics including sex, age and also a pseudonym in case they later wished to withdraw their answers from the data set. The SPQ was scored by giving one mark for every question answered with a ‘yes’ the total score for each participant was calculated by adding up the total number of yes’s. Once all participants’ scores are calculated a median split was performed to allocate participants into the high or low Schizotypy group. Both groups will take part in exactly the same tests of executive functioning. The first test was the TOH, a computerised version of the test (Mazeworks, ND) as it can effectively calculate the number of moves taken and the total time to get all disks to the end state. Participants were given a set of standardised instructions for each of the three tests then given the opportunity to ask any questions. Participants had as much time as they needed to fully complete the Towers of Hanoi task. As the task was computerised once all instructions had been fully understood the researcher kept interactions to a minimum. The second task, the Stroop task was also computerised. The first part of the Stroop involved the participants reading aloud the colour of the words on the screen. This time the colour of the word was the same as the colour it denoted. Once the participant had completed the baseline version the time taken to read all words was recorded and the participant continued on to the second part of the Stroop which again required the participant to read aloud the colour of the words here though they were different to the word the denoted. The time taken for this part of the task was recorded. To gain the total score for the Stroop task the baseline time was subtracted from the time taken for the second part of the task. The third and final executive functioning task was not computerised the participants were explained that they would be given a consonant and were required to write down as many words as they could think of in 90 seconds this was timed using a stopwatch. The participants were also told the restrictions and rules of the task. The participants were only told the consonant just before the task commenced so they were unable to begin thinking of possible words. The words were handwritten and once completed the researcher gave a mark for every word beginning with the letter N except those that violated the rules set out above.
The participant’s total mean score on the SPQ used in the final sample was 18.5 with a standard deviation of 12.33. The scores ranged from 4-44 with the maximum score of 74. Any participants who gave more than a few ‘no answer’ was discarded from the data set. Median value was 15 so therefore a score of 1-14 was classed as low schizotypy and a score of 16-44 was classed as high.
Skew and kurtosis were within limits and Box’s M indicated that the variance-covariance matrices were homogenous (Box’s M= 13.447, F(6,1043.32)=.138), p>.05). Levene’s test of homogeneity of variance was actually significant but as this was only one test out of all of them that affected the normal distribution the data was classed as not violated. If only one assumption is violated it will not affect the data, this is particularly true when the two groups have equal numbers of participants in each as is true of this case
. The scores illustrate the trend that would be expected; those with high schizotypy scores took more moves to complete the TOH task. For the Stroop task the means show that there is almost no difference between the low and high schizotypy groups although low scorers did show a slight advantage. However, verbal fluency also shows the low schizotypy group produce more words than the high schizotypy group. A multivariate analysis of variance (MANOVA) was conducted on the data with Schizotypy (high Vs low) as the independent variable and three executive functioning tasks as the dependent variables (Towers of Hanoi, Stroop and Verbal fluency). There was no significant effect of Schizotypy (Wilks’ Lambada=.256, F(1,3)=.679, >.05). Post hoc t-tests with alpha levels reduced to .0025 to cater for familywise error rates showed a significant effect of schizotypy on the towers of Hanoi performance (t(12)=1.703, p< .05) but no effect for Schizotypy on stroop (t(12)=.500, p> .05) and no effect for verbal fluency (t=(12)=1.672,p >.05). The results that individuals in the normal population scoring either high or low on the self report measure of Schizotypy have shown to have no effect on scores of executive functioning.
This study tested the hypothesis that deficits in executive function are prominent within a sample of young adults scoring highly on self report measures of schizotypy. Several neurocognitive tests were chosen from a battery to demonstrate where the anomalies were. In terms of the hypothesis the results contradicted what was expected there was no significant effect for schizotypy on measures of executive functions. These contradict previous findings that those with SPD or those who are ‘psychosis prone’ have executive functioning deficits (Trestman et al, 1995; Dinn et al, 2002). However, when the executive functions tests were broken down further using post-hoc t-tests they demonstrated trends to the predicted effect. The TOH test was the only one to give significant results for dysfunction comparing the high and low schizotypy groups and the high schizotypy group showed impairment on this planning and goal setting task. The deficit in TOH task could be due to a number of reasons. The participants scoring highly on schizotypy measures do not take longer to plan but respond impulsively to the task before the plan has been fully designed (Bustini et al, 1999). The problems with functioning in this task may also be due to the ability to retain the context of the task; remembering the constraints of the tasks and sub dividing the goals. The cognitive deficit high schizotypes possess may be associated with ‘contextual reasoning’. The deficit may be in retaining the rules and information of the task therefore more of a deficit in memory not in the actual planning and executing.
The Stroop task is considered a highly effective tool when measuring neuropsychological functions as most will show an impaired performance on the incongruent stimuli condition. However, in this experiment there was no significant difference between the low and high schizotypy conditions. When observing the means a trend can be seen that the low schizotypy group performed better than the high schizotypy group although the differences were relatively minimal compared to the other executive functioning tasks. Although results for the Stroop task were not significant the trend does show that high schizotypes had more difficulty inhibiting their automatic responses during the incongruent condition as reaction times were slightly larger for the high scorers. Although the trend should be interpreted with caution we can suggest that it does provide evidence for previous work combining the Stroop task and Schizotypy. Suhr, 1997; Giráldez et al. 2000; Höfer et al, 1999 all show evidence for those scoring high on measures of schizotypy have slower reaction times to the incongruent stimuli condition. The Stroop task has been used in conjunction with schizophrenia spectrum disorders to evaluate cognitive dysfunction for over 40 years so there is extensive evidence for it. Imaging studies have also provided evidence suggesting neuronal structures differ in the brains of those with schizophrenia spectrum disorders. The study would benefit from a replication using a larger sample and increased number of trials. Due to the Stroop task’s age there are varied versions of the task by using a more comprehensive version of the task the deficits exhibited in the high schizotypy group may be demonstrated to a greater degree, as in this case time and sample restraints gave problems.
The results for the tests of verbal fluency and schizotypy were insignificant although again if the means are observed show a definite trend that high sschizotypy scorers produce less words compared to the low scorers. The means show that the low scorers were able to generate on average seven more words than the high scoring group in the 90 seconds given to provide words beginning with the letter ‘n’. The trend shown suggests that the high schizotypy group have prefrontal deficits which affect reproduction of words from semantic memory. Verbal fluency tests assess the ability to stay within the constraints of the rules and inhibit any inadequate responses (Tsakanikos & Claridge, 2005). The trend in the results illustrates that the high schizotypy group have difficulty with the ease of use of language. Also the constraints of the task as with the Stroop task may have been the problem, while generating words the participant must be able to remember and access the rules. With the pattern of the trend the results provide evidence for previous verbal fluency studies including Barrantes-Vidal et al. (2002). Due to constraints to the experiment participants were only tested on one test of verbal fluency to provide more powerful conclusions using a selection of letters and using the mean verbal fluency score may be more robust.
The SPQ is a robust measure of SPD with high internal reliability with a Cronbach’s alpha of 0.91. However, as the sample used include just university students results on the SPQ only reached a maximum score of 44 out of 74 which meant that the classification of high and low schizotypy did not show as much disparity as would be expected. Therefore the median value used for the median split to differentiate the two groups was relatively low only 15. This suggests that the majority of scores on the SPQ were relatively low this may be the reason that the results were insignificant for the MANOVA was because high and low schizotypy group were not separated by a great amount as would be expected. A way to resolve this would be to compare more diverse groups for example a collection of participants diagnosed with SPD, a group genetically prone to the disorder such as relatives of schizophrenics and a control group as this would give a far wider ranging set of results. Another suggestion which may be helpful in reducing time constraints would be to use the SPQ-B consisting of a collection of the most reliable measures although the problem again of separating the two groups would be worse unless a high and low percentile could be used instead of a median split. Also another reason for the lack of diversity of results may be due to the fact participants may be unwilling to admit to certain aspects of the SPQ as they believe they may be seen as psychotic. Some participants may be more inclined to choose what they believe are socially desirable answers resulting in a higher proportion of low schizotypy individuals than is truly representative.
The problem with assessing neuropsychological performance like this is there tends to be limitations as more than one test of executive functioning is used. This is an important factor when assessing executive functioning as there are many aspects of the higher order functioning including planning, attention, memory to name but a few; one test would not suffice. Previous assessments of schizotypy and executive functioning have used the popular WCST and although results have been significant it does not offer a break down of functioning and is typically used in conjunction with other stimuli. The limitations of this experiment included the time and resources, tests were not able to be replicated and include larger trials. This could be built upon and improved in the future, also if time and resources permitted a more extensive neuropsychological test battery could be incorporated. There are many other aspects of executive functioning which have not been accessed in this experiment but provide huge implications for functioning within society including motor skills.
As explained above they are many ways in which to assess aspects of executive functioning however another problem is the diversity of the deficits associated with executive functioning. For example one person being assessed may have difficulty on tests of verbal fluency but function normally on tests of attention or vice versa. Clearly it is not a simple thing to examine, but it is important to as all these higher order functions classed as executive functions influence all aspects of our interactions, how we process and organise information and our ability to adapt when novel situations arise. This research provides evidence although not statistically significant it does illustrate the trends which can be expected when looking at schizotypy and executive functioning. The conclusion that can be made from the trends observed through this research help provide an insight into the question asked earlier whether cognitive dysfunction is a primary or secondary feature of psychosis. As the high schizotypy group showed impaired functioning compared to the low schizotypy group it can be suggested that cognitive dysfunction is a secondary feature as the participants had none of the confounding variables such as medication or institutionalisation. This is an important finding as tests of executive functioning show anomalies in a healthy population, so could be used as an indicator for schizophrenia spectrum disorder ranging for SPD to schizophrenia as research has demonstrated that all of the spectrum exhibit cognitive dysfunction the only variation is the severity. Although the findings from this research should be viewed with caution as they are the general trends not significant findings they do provide an insight into how higher order functions are approached and processed and how schizotypy may affect prefrontal functions.
In terms of where the research can go from here there are many options to further our understanding. The obvious is to increase sample sizes and number of trials should resources permit this. Another idea mention above would be to diversify the groups used instead of just separating high and low schizotypes from the normal population but to integrate individuals diagnosed with schizophrenia spectrum disorders. Also to help understand the etiology of schizophrenia spectrum disorders it may be interesting to compare individuals with schizophrenia with and without medication and contrast this with SPD individuals and healthy controls this would give us a better understanding. Also in terms of etiology to combine a piece of research like this with the use of imaging techniques would help provide a biological perspective to executive functioning, as previous literature has touched on the idea that differences may occur in the temporal-limbic circuits (Vollema & Postma, 2002). There really are endless routes to pursue as cognitive dysfunction is an important factor in schizophrenia-spectrum disorders and could be a useful indicator of future risk of psychosis. Ideally through more research a package of the most reliable executive functioning tests could be used to evaluate adolescents and hopefully become some sort of predictor to future risk of schizophrenia spectrum disorders. This would be most beneficial to individuals more at risk i.e. individuals with a history of mental illness.
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