Introduction to the special issue on fluid intelligence

Intelligence has been conceptualized as crucial for adaptive problem-solving. For example, Wechsler (1944) defined intelligence as “the aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his environment” (p. 3). The assessment of intelligence is important to establish a selection and placement criterion as well as an aid in diagnosis and treatment, including as a baseline of overall mental function against which more specific cognitive skills may be compared.

An influence on David Wechsler’s development of intelligence tests may have been that his older brother (Israel Wechsler) was a neurologist (Chief of Neurology at Bellevue Hospital in New York City) and there was a clinical need for an intelligence test to assess children and adults who were neurological patients (Wechsler, 1944). It is noteworthy that David Wechsler did author a chapter on psychological testing in his older brother’s textbook on the brain.

Recently the fifth edition of the Wechsler Intelligence Scale for Children-Fifth Edition (WISC-V) (Wechsler, 2014) has been published. The WISC-V is designed to assess children from ages 6 to 16 and 11 months. The WISC-V contains Primary Index Scales based on a WISC-V factor analysis that showed five factors. The five factors are Verbal Comprehension, Visual Spatial, Fluid Reasoning, Working Memory, and Processing Speed. The 5 Primary Index Scales are each made up of two subtests that corresponded to that factor in the factor analysis. An innovation was the elimination of the Perceptual Reasoning Index (PRI) and its’ replacement with the Visual Spatial Index (VSI) and Fluid Reasoning Index (FRI) Scales. The Fluid Reasoning Primary Index Scale was made up of the Matrix Reasoning and Figure Weights subtests.

The WISC-V Technical and interpretative Manual (2014) noted that “Fluid reasoning is related to executive functioning, the prefrontal and frontal cortex, and connections between the frontal cortex and other regions” (p. 26). Moreover, the WISC-V Manual also averred that “Fluid reasoning tasks require involvement of the frontal-parietal networks in conjunction with various cortical and subcortical processes. There is a tendency towards greater activation to the right hemisphere than the left in fluid reasoning tasks; however, this may be due to the use of visual rather than verbal stimuli in fluid reasoning tasks” (p. 26).

Given this assertion of the concept or cognitive domain of fluid reasoning or fluid intelligence, it was thought that the time was appropriate for a careful consideration of what exactly is fluid reasoning or fluid intelligence? To that end, Lenard Koziol PsyD, ABN, ABPdN was requested by the Editor-in-Chief to develop a Special Issue on Fluid Intelligence for publication in Applied Neuropsychology: Child (AN:C). Dr. Koziol had already developed a number of well received Special Issues for AN:C in the past. Dr. Koziol did his usual superb job in inviting a number of noted child neuropsychology researchers and practitioners to submit manuscripts and carefully edited the manuscripts. Unfortunately, Dr. Koziol had to abruptly step down from the role of editor of the Special Issue on Fluid Intelligence due to a reason he wishes to remain confidential.

Nonetheless, the Special Issue is a collection of superb contributions. Phillip Kent, PsyD begins the Special Issue of Fluid Intelligence with an insightful history of Fluid Intelligence. Then, Tulio M. Otero, PhD and Lauren A. Barker, PhD discuss the conceptualization, neurobasis, and applications of Fluid Reasoning. Arthur Joyce, PhD follows with a consideration of how the basal ganglia system (BGS) and cerebrocerebellar system (CCS) interact within large scale brain networks including the dorsal attention network (DAN), ventral attention network (VAN), default mode network (DMN), and frontoparietal network (FPN). Next, Paula Prince, PhD, ABN addresses the important developmental aspects of Fluid Reasoning. Then, Theodore Wasserman, PhD, ABPP, ABPdN and Lori Drucker Wasserman, PhD, ABPdN address the importance of understanding Fluid Intelligence as a problem solving network that works as a system rather than a set of independent skills. Next, Lisa Grant, MA and Paula Prince, PhD, ABN focus on the important academic implications and applications of Fluid Reasoning. Then, Milton J. Dehn, PhD. describes the supporting role of Working Memory (WM) enabling Fluid Reasoning. Last, Alisa Williams, MA and Paula Prince, PhD, ABN move the focus from cognitive to emotion in discussing how anxiety influences Fluid Reasoning.

In all, the manuscripts provide a most interesting group of perspectives on Fluid Intelligence or Fluid Reasoning. All of the authors are thanked for their interesting manuscripts and impressive conceptual and methodological contributions to the field of clinical child neuropsychology. To a great extent, also the Special Issue on Fluid Intelligence is an eloquent testimony to the conceptual brilliance and keen intelligence of Dr. Koziol who invited the authors to contribute and edited the manuscripts. Dr. Koziol’s many important contributions clinical child neuropsychology are very much appreciated. Also, thanks are due to Maria Flaccavento, our hard working production editor at Taylor & Francis.