Murray T. Maybery

Neuropsychological studies of mild traumatic brain injury: A meta-analytic review of research since 1995

A meta-analysis conducted by Binder, Rohling and Larrabee (1997) established a relationship between mild traumatic brain injury (TBI) and small reductions in cognitive functioning in individuals assessed more than 3 months post-injury. As a follow-up, this study summarized similar research that (1) was published since the previous meta-analysis, and (2) included data collected at any stage post-injury. An extensive literature search revealed 17 suitable studies from which effect sizes were aggregated. The overall effect size was g = 0.32, p < .001. Speed of processing measures had the largest effect, g = 0.47, p < .001. The merging of post-acute effect sizes with those reported in Binder et al.s review yielded a nonsignificant result, g = 0.11. Time since injury was found to be a significant moderator variable, with effect sizes tending to zero with increasing time post injury. Thanks go to the authors of papers included in this analysis who willingly provided additional data and information to assist in the completion of this meta-analysis. This study was supported by an Australian Postgraduate Award provided to K. Frencham.

Auditory hallucinations in schizophrenia: Intrusive thoughts and forgotten memories

Introduction. This paper presents a new cognitive model of auditory hallucinations in schizophrenia. We suggest that auditory hallucinations are auditory representations derived from the unintentional activation of memories and other irrelevant current mental associations. Our model proposes that a combination of deficits in intentional inhibition and contextual memory is critical to the experience of auditory hallucinations. The failure in intentional inhibition produces unwanted and uncontrollable mental events which are not recognised because they have lost the contextual cues that would normally facilitate recognition. Methods. This article amalgamates recently published data and presents a reanalysis of the findings on 43 patients with a diagnosis of schizophrenia (Badcock, Waters, Maybery, & Michie, 2005; Waters, Badcock, Maybery, & Michie, 2003a; Waters, Maybery, Badcock, & Michie, 2004a). Relative risk was also estimated to determine whether the combination of deficits increases the risk of having auditory hallucinations. Results. Almost 90% of patients currently experiencing auditory hallucinations showed the predicted combination of deficits on both inhibition and context memory, compared to only a third of patients without hallucinations. In addition, the results showed that those patients with the specified cognitive deficits were at an especially increased risk of having auditory hallucinations relative to patients without the deficits. Conclusions. The results of our investigations strongly support the role of intentional inhibition and context memory in auditory hallucinations. Critical consideration of the findings also suggests that additional cognitive processes might be important for the expression of this symptom.

Weak central coherence, poor joint attention, and low verbal ability: independent deficits in early autism

C. Jarrold, W. Butler, E. M. Cottington, and F. Jiminez (2000) proposed that weak central coherence is a primary cognitive deficit in autism and speculated that it may even account for theory of mind impairments. The current study investigated whether weak central coherence could account for deficits in 2 behaviors purported to tap capabilities fundamental to a theory of mind: joint attention and pretend play. Twenty-one children (ages 3-5 years) with autism spectrum disorders were matched to 21 control children on chronological age, nonverbal ability, and gender. Pretend play did not differentiate the groups. Weak central coherence, poor joint attention, and low verbal ability contributed significantly and independently to the prediction of autism group membership, a finding consistent with 3 independent cognitive deficits underlying autism.

Context memory and binding in schizophrenia

The current study aimed to provide evidence for the context-memory hypothesis, which proposes that schizophrenia is linked to a deficit in retrieving contextual information and in binding the different components of a memory together. A new task was developed in which memory for the content of events could be assessed in conjunction with memory for both source and temporal information. Forty-three patients with schizophrenia and 24 normal controls took part in the study. Patients were found to be less accurate in identifying the source and temporal context of events. Furthermore, whereas controls tended to identify correctly both source and temporal context of events, patients tended to have a more fractionated recollection of those events. The study provides support for the context-memory hypothesis by demonstrating that patients with schizophrenia show a fundamental deficit in binding contextual cues together to form a coherent representation of an event in memory.

Inhibition in schizophrenia: association with auditory hallucinations

The study investigated whether auditory hallucinations (AH) in schizophrenia are linked to a deficit in inhibition. Two tasks assessing the intentional suppression of cognitive events-the Hayling Sentence Completion Test (HSCT) [Neuropsychologia 34 (1996) 263] and the Inhibition of Currently Irrelevant Memories Task (ICIM) [Nature Neuroscience 2 (1999) 677]-were administered to 42 patients with schizophrenia and 24 normal controls. Presence and severity of symptoms in the patient group were examined using the Positive and Negative Syndrome Scale (PANSS). Patients performed significantly worse on the measures of inhibition compared to controls. More importantly, among patients, significant positive correlations were obtained between an index of AH severity (defined as an increase in frequency of AH on PANSS) and the number of type A errors on the HSCT and errors in the last three runs of the ICIM. An increase in AH severity was, therefore, associated with increasingly impaired control of intentional inhibition. Furthermore, no significant correlations were found between these indices of inhibition and either negative, general or positive symptoms (excluding AH scores).

Global Visual Processing and Self-Rated Autistic-like Traits

The current research investigated, firstly, whether individuals with high levels of mild autistic-like traits display a similar profile of embedded figures test (EFT) and global motion performance to that seen in autism. Secondly, whether differences in EFT performance are related to enhanced local processing or reduced global processing in the ventral visual stream was also examined. Results indicated that people who scored high on the Autism-spectrum Quotient (AQ) were faster to identify embedded figures, and had poorer global motion and global form thresholds than low AQ scorers. However, the two groups did not differ on a task assessing lower-level input to the ventral stream. Overall the results indicate that individuals with high levels of autistic-like traits have difficulties with global integration in the visual pathways, which may at least partly explain their superior EFT performance.

Characteristics of the broader phenotype in autism: A study of siblings using the children's communication checklist-2

Non‐autistic relatives of people with autistic disorder have an increased risk of social and communicative difficulties: this is known as the “broad phenotype.” Better methods for characterizing the broad phenotype are needed to facilitate identification of risk genes for autism. 29 siblings of 20 children with autistic disorder, 13 siblings of 9 children with PDDNOS, and 46 typically developing control children from 26 families were assessed by parental report using the Childrens Communication Checklist‐2 (CCC‐2). Groups were matched on age and IQ and siblings with autism were excluded. Group mean scores on the CCC‐2 differed on only one subscale, syntax. However, siblings of children with autism or PDDNOS were over‐represented in the tails of the distributions of several scales, and 10 (24%) scored more than 2 SD below the control mean on a total score based on all 10 subscales. Only two of these 10 children scored above threshold on one or more scales of the Autism Diagnostic Interview—Revised (ADI‐R). Children with abnormal scores on the CCC‐2 total were characterized by low‐verbal IQ and their fathers tended to score high on the social and communication scales of the Autism Quotient, a measure of the broad phenotype in adults. The CCC‐2 shows promise as a quick screening device for the broad phenotype in non‐autistic siblings of children with autism.

Auditory hallucinations: failure to inhibit irrelevant memories

Introduction. The frequency of auditory hallucinations (AH) is associated with efficiency in inhibiting irrelevant memories, suggesting that the presence of AH may be related to the intrusion of strongly activated representations in memory. Therefore, we hypothesised that the inability to suppress irrelevant memories would be found only in patients currently experiencing AH. Method. Performance on a repeated, continuous recognition task was examined in 23 schizophrenia patients with AH present, 20 schizophrenia patients with AH absent, and 24 healthy controls. Results. Patients with current AH made significantly more inappropriate responses (false alarms) to distractors seen on previous runs of the task than nonhallucinating patients. The ability to detect targets (hits) was significantly better in healthy controls than schizophrenia patients, however, there was no significant difference between the two patient subgroups. Conclusions. The findings confirm that the presence of AH involves a failure to suppress memories that are not relevant to ongoing reality. We propose that a combination of deficits in inhibition and (episodic) memory provides a useful model of AH, which can accommodate many of the characteristic features of the symptom and fits well with the neuroanatomical circuitry that is believed to underlie the occurrence of AH.

Grouping of list items reflected in the timing of recall: implications for models of serial verbal memory

Three experiments examined the effect of temporal grouping on the timing of recall in verbal serial memory. Compared to an ungrouped condition, recall in a grouped condition produced a peak in latency between the groups (Experiment 1). However, the ratio of within- to between-group intervals at presentation was not reflected in recall (Experiment 2), contrary to the predictions of some oscillator models (Brown, Preece, & Hulme, 2000; Burgess & Hitch, 1999). In Experiment 3, grouped and ungrouped lists of different lengths were compared to assess a recent version of the ACT-R model applied to serial recall (Anderson, Bothell, Lebiere, & Matessa, 1998). Recall latencies showed a cost at group onset related to group size and a cost for all items of the first group associated with carriage of a second group. Results are discussed with reference to oscillator models, the ACT-R model, and augmented versions of it.

Vision in developmental disorders: Is there a dorsal stream deficit?

The main aim of this review is to evaluate the proposal that several developmental disorders affecting vision share an impairment of the dorsal visual stream. First, the current definitions and common measurement approaches used to assess differences in both local and global functioning within the visual system are considered. Next, studies assessing local and global processing in the dorsal and ventral visual pathways are reviewed for five developmental conditions for which early to mid level visual abilities have been assessed: developmental dyslexia, autism spectrum disorders, developmental dyspraxia, Williams syndrome and Fragile X syndrome. The reviewed evidence is broadly consistent with the idea that the dorsal visual stream is affected in developmental disorders. However, the potential for a unique profile of visual abilities that distinguish some of the conditions is posited, given that for some of these disorders ventral stream deficits have also been found. We conclude with ideas regarding future directions for the study of visual perception in children with developmental disorders using psychophysical measures.