8 or more SD below the normative standards. General intellectual ability Dating back to the work of Spearman,9 a distinction has been made between general and specific cognitive abilities. Two widely used indices of generalized cognitive performance have been applied in schizophrenia research: general measures of intelligence quotient, or IQ, and composite scores or profiles derived from test batteries #Gefitinib clinical trial keyword# comprising multiple neuropsychological tests. While both provide a measure of an individual’s overall cognitive

functioning, the results of these assessments often do not overlap to a substantial degree. Neuropsychological test batteries typically focus on assessment of multiple cognitive abilities, such as memory, executive functions, and attention, and these include a strong component of novelty of testing requirements. IQ tests, on the other hand, have a lesser emphasis on specific abilities and novelty and greater emphasis on the assessment of crystallized abilities.10 Schizophrenia patients show a substantial and very severe generalized impairment (Figure 1). As Inhibitors,research,lifescience,medical demonstrated by meta-analytic studies,11-16 the generalized impairment as indexed by IQ seems to be consistently greater than the one indexed by neuropsychological composite scores (Figure 1). The impairment

in performance IQ is almost 50% larger than that observed for verbal IQ.2 The impairment Inhibitors,research,lifescience,medical in general ability seems to be almost as severe as those observed for more specific neuropsychological functions, suggesting that any specific neuropsychological deficit Inhibitors,research,lifescience,medical in schizophrenia occurs in the context of a background of a very severe general intellectual impairment.2 Figure 1. Neuropsychological performance profile of schizophrenia. Summary of results from meta-analytic studies presented in effect-size units (median Inhibitors,research,lifescience,medical effect size was calculated from available meta-analyses). Specific cognitive abilities Attention Early descriptions of schizophrenia recognized attentional impairments as fundamental aspects

of schizophrenia long before the advent of formal neuropsychological testing or modern experimental psychology.17,18 It is clear that attention is not a unitary construct. Posner and Petersen19 proposed that attention should be broken down into three main functions: alerting, orienting, and executive control. Alerting is defined as achieving and maintaining an alert state; orienting below is the selection of information from sensory input; and executive control is defined as resolving conflict among responses.20 Alerting has received considerable research attention in schizophrenia, and simple reaction time studies using different versions of Continuous Performance Tests have been conducted. Meta-analytic studies suggest moderate to severe impairments in this attentional domain (Figure 1).11,12,14 Orienting has not been studied as much. It is important to remember that attentional impairments may disrupt many other cognitive functions.