Learned Irrelevance Revisited: Pathology-Based Individual Differences, Normal Variation and Neural Correlates

Abstract

The function of the human executive system can broadly be described as the seeking out and processing of those signals and memories that are of the greatest relevance when guiding deliberate and adaptive behaviours. This task is not easy, however, since it requires almost constant shifting of attention in response to irregular alterations in the contingencies relating stimuli, responses, and environmental feedback. An individual's current belief regarding these contingencies guides response within a given context, and the representation of this belief and its consequent behaviour is often referred to as an "attentional set". Consequently, attentional set-shifting is an important executive function responsible for altering a behavioural response in reaction to the changing contingencies. Such flexibility underlies a wide range of behaviours: the better the set-shifting capacity, the more flexible the person is at adapting to change. At the other end of this continuum are many psychiatric groups, neurodegenerative groups and even healthy elderly and young subjects that have been shown repeatedly to be impaired in attentional set-shifting performance. One specific form of these impairments lies in an inability to attend to, or to learn about, information which has previously been shown to be irrelevant. This phenomenon called learned irrelevance (LI) is very mysterious, because unlike other aspects of attentional set-shifting, it appears to be neither dependent on the frontal lobe nor affected by dopamine, and, therefore, may not be coded for in the parts of the brain that are typically considered "executive" at all. The aim of this chapter is to discuss recent advances in the area of LI in humans and to show how the latest trends in executive-function research can be applied to the study of LI. The first trend is the application of experimental paradigms that provide measures of putative cognitive functions much more precisely than the measures that have been offered by "classical" neuropsychological methods. One such paradigm is the ID/ED visual discrimination learning paradigm modelled after the most prominent neuropsychological tool for studying attentional set-shifting deficits, namely Wisconsin Card Sorting Task. The ID/ED paradigm allows the operationalization of the dependent variables in a much more reliable way. It makes them much more sensitive to the effects of brain damage or pathophysiology. In the first section of this chapter, we review studies that have utilised the ID/ED paradigm to investigate normal and pathology-based individual differences in LI. The utility of such analyses is motivated by the fact that dissociable patterns of LI deficits were observed in patients with circumscribed frontal-lobe removals, and both medicated and non-medicated patients with Parkinson's disease. An understanding of these patterns may lead us to unravel the distinctive roles played by different frontal striatal circuits, or the different roles played by the cortical and striatal portions of those circuits. The second trend in executive-function research is the implementation of advanced neuroscience techniques, such as brain imaging. In the second section of the present chapter, we describe our study that aimed to investigate the neural mechanisms underlying dissociable components of attentional set-shifting, including LI. Taken together, the combined approach based on the two trends enables a finer delineation of executive functions than was possible with classical paradigms. In our opinion, the combined approach will ultimately allow us to answer the question of how the LI effect is rooted in actual neural systems. (PsycINFO Database Record (c) 2019 APA, all rights reserved)