A sample of 156 participants from the PRISM (Psychiatric Ratings using Intermediate Stratified Markers) Study (http://prism-project.eu) was used.20,21 The sample comprised four groups of participants: individuals with schizophrenia (SZ; n = 53, 71.70% men; m = 30.45 years, sd = 6.06); participants with a probable diagnosis of Alzheimer’s disease (AD; n = 46, 55.56% men; m = 68.80 years, sd = 7.13); and two age-matched control groups (SZc: n = 29, 58.62% men; m = 28.72 years, sd = 7.40; ADc: n = 28, 53.57% men; m = 68.80 years, sd = 7.13). All the participants performed a face emotion decoding task. Diagnosis of SZ participants was confirmed according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)22 by means of the MINI International Neuropsychiatric Interview.23 The diagnosis of AD patients was confirmed according to the criteria of AD as outlined by the National Institute on Aging (NIA) and the Alzheimer’s Association (AA).24 Participants with either a current diagnosis of major depressive disorder or high levels of depressive symptoms (QIDS ≥ 16) were excluded.
The sample was recruited from two hospitals in Spain (Gregorio Maranon University Hospital and La Princesa University Hospital) and three centres in the Netherlands (University Medical Center Utrecht, VU University Medical Center Amsterdam and Leiden University Medical Center). All the study protocols were approved by the Clinical Research Ethics Committee of the research sites (i.e., Gregorio Maranon University Hospital, La Princesa University Hospital, University Medical Center Utrecht, VU University Medical Center Amsterdam and Leiden University Medical Center). Moreover, all the participants (or their legal guards) provided a signed written consent form to participate in this study. informed consent was obtained from all participants and/or their legal guardians. All the study protocols were performed in accordance with the Declaration of Helsinki.
Data collection instruments and tasks
All the data used in this study were collected in the Assessment visit 1 of the PRISM study.20 First, a semi-structured interview on sociodemographic and medical data was conducted (i.e., age, sex, race, years of education). Where available, medical notes provided further detail of mental and physical diseases and medication. The MINI International Neuropsychiatric Interview, Screening version (M.I.N.I.-Screen)25 was used to explore the presence of psychiatric disorders among study participants. The interview was administered by trained psychiatric researchers.
Three scales were administered to measure social functioning: the social engagement/withdrawal and the interpersonal behaviour subscales (α = .76, for both subscales) of the Social Functioning Scale (SFS)26 and the Loneliness and Affiliation Scale (LAS; α = .88).27 Other scales used were: the Quick Inventory of Depressive Symptomatology, Self-reported version (QIDS-SR16) to assess depressive symptoms (Cronbach’s α = .86);28 the Positive and Negative Syndrome Scale (PANSS) to measure psychotic symptoms in the SZ sample (Cronbach’s α between .83 and .87);29 and the Mini-Mental State Examination (MMSE) to screen cognitive impairment in the AD sample (Livingston’s r between .79 and .80).30,31
Two performance tasks were carried out, both delivered on the online P1vital® ePRO system. The Digit Symbol Substitution Task (DSST) was used to measure general cognition.32 The task draws on aspects of cognition, including speed of processing and working memory. The task involves individual matching symbols to numbers according to a key. A score is constructed by adding up the number of correct symbols coded within 90 seconds. Afterwards, participants completed the computer-generated task Facial Expression Recognition Task (FERT).20,33,34 An individual is asked to indicate whether the depicted face (displayed very briefly, 0.5s each) is showing either an emotion of happiness, sadness, fear, disgust, surprise, anger; or no emotional expression (i.e., neutral face). The pictures of faces displayed the emotional expressions at 10 different intensities (10% to 100% in steps of 10%). Patients were asked to categorise the expression of the faces as one of the emotions listed above. Emotion presentation order was random. Emotion presentation order was random. Two main endpoints can be obtained from the FERT task, for each emotion: accuracy rate (number of the emotion responses when presented divided by the number of times faces with this emotion is presented, expressed as a percentage) and misclassification rate (number of the emotion responses when not presented divided by the number of times other emotions or neutral faces are presented, expressed as a percentage).
Participants were recruited when attending either neurology or psychiatry unit visits at the abovementioned healthcare centres. Participants were asked to complete the screening instruments (sociodemographic interview, QIDS-SR16, MMSE, PANSS) in the Assessment visit 1, upon completion of informed consent forms. Additionally, the psychiatric interview (M.I.N.I.-Screen) was conducted. A second visit was scheduled. This visit involved participants completing the questionnaires on social functioning factors (LAS, SFS) and the performance tasks (DSST and FERT). Further details on all protocols implemented in the PRISM study are displayed elsewhere.20
Two multivariate analyses of covariance (ANCOVA) were conducted to study between-group differences on emotion recognition performance (accuracy rate and misclassification rate). A multivariate ANCOVA was conducted for positive emotion recognition, and another for negative emotion outcomes. The study group (with three levels: SZ, AD, controls) was considered as a between-group factor for both ANCOVAs. Age group (younger participants vs. older) was used as a covariate. Bonferroni corrected t tests were used to ascertain pairwise differences between study groups, considering the four groups (SZ, AD, SZc, ADc), setting the multiple-comparion p value, .05/6 = .0083. Effect size estimates were the h2partial and Cohen’s d.
Multilevel linear regression was used to study the influence of social isolation factors on emotional face decoding (accuracy rate and misclassification rate outcomes). This approach allows for studying the fixed effect of these factors controlling for random effects derived from a grouping (level) factor. Sociodemographic factors (sex and age), general cognition (DSST score), comorbidity with emotional disorders, depressive symptoms (QIDS-SR16 score) and the social isolation scores were used as covariates. The study group was used as a level factor. The recruitment site was used as a weighting factor. A model comparison rationale was followed. The full regression model (sociodemographic, DSST score, comorbidity with emotional disorders, depressive symptoms and social functioning covariates) was compared with an unconstrained model and a model with sociodemographic (sex and age) covariates. The Akaike information criterion (AIC) was used for model comparison (lower AIC values indicating better model fit) and the conditional R2 as an effect size estimate.35
All the analyses were performed by using the R software x64 3.0.1.