Psychotic disorders are often preceded by impaired cognitive functioning. Self-reported psychotic symptoms during adolescence have been associated with the development of a psychotic disorder in adulthood (Poulton et al., 2000; Welham et al., 2009a; 2009b). Adolescents who report psychotic-like experiences (PLEs; the non-clinical psychosis phenotype) have been shown to share many of the same schizophrenia-related risk factors as patients with schizophrenia (the clinical psychosis phenotype; Kelleher & Cannon, 2011). The following thesis employs both behavioural and electrophysiological methods in an attempt to uncover possible correlates of PLEs in a community-based sample of young adolescent participants compared to a control group. Electroencephalographic (EEG) recording took place following a detailed clinical interview and neuropsychological testing. Neuropsychological functioning and resting state EEG data were examined. Three tasks which investigate capacities which have been proposed as trait markers for schizophrenia were chosen for use with EEG. These tasks were an Active Auditory Oddball Task, an Implicit Spatial Memory Task and a Spatial Working Memory Task. The present thesis is the first study to examine resting state data and the electrophysiological correlates of auditory and spatial processing in adolescents reporting PLEs. In Chapter 3 the MATRICS Consensus Cognitive Battery (MCCB) was employed to test group differences on a number of tests of neuropsychological functioning. Chapter 3 also examines quantitative EEG spectral power in the delta (1.5-3.5Hz), theta (3.5-7.5Hz) and alpha (7.5-12.5Hz) frequency bands during resting state recordings in which participants had their eyes open for two minutes and eyes closed for an additional two minutes. Adolescents reporting PLEs scored more poorly on two measures of speed of processing. No between-group differences were observed in the resting state data at anterior, posterior or fronto-temporal scalp locations. In Chapter 4 an Active Auditory Oddball Task was employed to test group differences in the P300 event-related potential (ERP) and the N100 auditory evoked potential (AEP). Reduced amplitude of the P300 ERP to target tones has been reported in patients with schizophrenia, first-episode psychosis (FEP), groups at genetic high risk for psychosis and, most recently, in clinical at-risk groups. Reduced amplitude of the N100 AEP to non-target tones has also been reported in schizophrenia patients and first-degree relatives of patients. An increase in the amplitude of the N100 AEP component to non-target tones was observed in the PLEs group in the present thesis. No between-group-differences in mean amplitude of the P300 component to target tones were observed; however, mean amplitude to target tones at FCz was found to be significantly greater than mean amplitude to non-target tones in the control group but not in the PLEs group at fronto-central locations. Chapters 5 and 6 investigated spatial processing and spatial working memory, respectively. No between-group differences were observed in the behavioural or electrophysiological data obtained from the Implicit Spatial Memory Task. Data from the Spatial Working Memory Task revealed no between-group differences for accuracy or reaction time. Greater reaction time variability was observed in the PLEs group relative to control group however. Reduced mean amplitude of the P300 component was observed in the PLEs group relative to the control group at parietal electrode sites. The present thesis adds to the knowledge of PLEs in early adolescence by reporting reduced P300 during spatial working memory retrieval in this group while spatial processing and memory (as assessed by the Implicit Spatial Memory Task) remain unimpaired. This reduction in P300 amplitude may reflect disrupted neural processes underlying stimulus evaluation and template matching during retrieval in the PLEs group. The finding of reduced P300 in the PLEs group on the Spatial Working Memory Task adds to previous findings of impaired spatial working memory in this group reported by Kelleher et al. (2012c), and expands existing findings of reduced P300 amplitude in adolescent onset schizophrenia (Haenschel et al., 2007) by revealing reduced P300 amplitude in the treatment-naïve extended psychosis phenotype.