Cognitive Neuropsychology Of Thinking

Until relatively recently there has been little research on the cognitive neuropsychology of thinking (Shallice, 1988). This gap in the field must have been due to the complexity of thought in its reliance on many diverse lower-level systems (e.g., attention, working memory, and language). Because thinking violated many of the assumptions of modularity some theorists ruled it out as a meaningful area of study from the neuroscience perspective (Fodor, 1983). Happily, the development of more advanced neuroimaging techniques combined with the better understanding of lower-level processes has led to rapid advances in our understanding.

For some time it has been proposed that the prefrontal cortex was implicated in higher-level activities like thinking. While people with prefrontal damage often show no obvious decrease in IQ measures, they have obvious difficulties in managing and planning their lives; they fail to plan for future events, and meet difficulties in carrying out routine plans like shopping for food. Recent research has confirmed the importance of the prefrontal cortex in different forms of thinking, from problem solving to reasoning, planning, and analogical thinking (Duncan et al., 1996; Halford, Wilson, & Phillips, 1998; Johnson-Laird, 1995a, b; Shallice, 1988; Wharton & Grafman, 1998).

One argument that has been made is that the prefrontal cortex, which has greatly expanded in human evolution (Benson, 1993), is the seat of processes that manipulate and integrate complex relational representations, a fundamental process that underlies diverse forms of reasoning, problem solving, and planning (Holyoak & Kroger, 1995; Robin & Holyoak, 1995). Whether one is doing means-ends analysis with problem states, combining the premises of a logical argument, planning a meal, or making analogical inferences, a fundamental step is this ability to integrate complex, relational representations. There appears to be a big developmental and evolutionary step from understanding the single relation "Bill is taller than Charles" to integrating multiple relations; integrating "Bill is taller than Charles" and "Abe is taller than Bill" to form the transitive inference that "Abe is taller than Charles" (Halford, 1992; Halford & Wilson, 1980; Halford et al, 1998). In children, the integration of multiple relations to make a transitive inference reliably only appears after the age of 5 (Halford, 1984). In animals, the abilities of the brightest chimps to reason relationally severely trails human abilities (Tomasello & Call, 1997). In later chapters, we will return to the specific results for analogical thinking (Chapter 15) and reasoning (Chapter 16). In this section, we will consider some of the findings on puzzles and insight problems.

Shallice (1982) made use of a variant of the Tower of Hanoi problem, called the Tower of London problem, to assess planning and problem-solving impairments in brain-damaged patients. Typically, instructions were given to pre-plan the whole sequence of moves to be carried out mentally before executing the sequence. Thus, the poor performance of frontal-lobe patients on these is usually interpreted as the inability to pre-plan effectively (Owen, 1997; Owen et al., 1990; Shallice, 1982). However, recently aspects of this simple pre-planning account have become more complex (Owen, 1997; Phillips et al., 1999; Ward & Allport, 1997). Ward and Allport (1997) have emphasised the importance of conflicts that occurred between goals and subgoals in the problem, where they characterised a subgoal as a set of moves that were essential to the solution of the problem but which did not place a disk in its final goal position. Several studies have shown that goal-subgoal conflicts are particularly difficult for frontal-lobe patients (Goel & Grafman, 1995; Morris et al., 1997). Other research has suggested that pre-planning may be less important than the on-line planning of moves—planning of moves during the execution of a solution rather than pre-planning (Phillips et al., 1999). Phillips et al. looked at working memory effects on the task by using verbal and visuospatial executive secondary tasks (see Chapter 6) and found that pre-planning was less important than executive processing involving the execution and monitoring of on-line planning.

Unfortunately, there has been a lot less work on the cognitive neuropsychology of insight problems. The studies that have been done have also been considered successful from this perspective in assessing the hemispheric difference of relevance to them, supporting some of the theoretical proposals made about spreading activation and insight. Most notably, Bowden and Beeman (1998) have shown hemispheric differences when hints to the solutions of insight problems are presented to the left or right visual field, hence being processed by either the right or left hemisphere, respectively. Specifically, priming of the solution was more effective when the presented information was processed by the right rather than the left hemisphere, a result they explained as being due to the coarse-coded nature of semantic information in this hemisphere.

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