Mechanisms of unimodal and cross-modal interference

Background: In everyday life we must frequently ignore distractions arising from multiple senses. However, most of our understanding about this cognitive process (known as interference control) is derived from unimodal paradigms, in which relevant and irrelevant information are presented in the same sense. Thus, it remains unclear whether the mechanisms proposed to underpin unimodal interference control generalise to cross-modal contexts. Aims: The aim of this thesis was to identify whether similar mechanisms underlie unimodal and cross-modal interference control. To answer this question, I compared patterns of unimodal and cross-modal interference in development and ageing, and compared the processing levels at which unimodal and cross-modal interference occurred. Furthermore, I explored whether some senses are given priority over others (i.e. sensory dominance), whether this differs between age groups, and whether this is associated with susceptibility to distraction from different senses. Experimental chapters (3 – 9): In Chapter 3, I introduce a Stroop paradigm designed to separate interference occurring at stimulus-encoding and response-selection. Using this paradigm I compared unimodal and cross- modal Stroop interference in children, young adults and older adults. In Chapter 4, I investigated whether some ageing effects in Stroop performance can be attributed to colour vision loss, and set up the experimental protocol for deriving event-related potentials (ERPs) associated with different stages of processing. In Chapter 5, I used ERPs in a group of young adults to assess whether unimodal and cross-modal interference occurred at different processing stages. In Chapter 6, I validated whether portable electroencephalography (EEG) could be used to assess interference control in the real world. Following this, I focus on sensory dominance measures and how they might be related to cross-modal interference. In Chapter 7, I perform a meta- analysis of studies using one measure of sensory dominance, the Colavita effect, to assess the robustness of this measure and whether it is influenced by age. In Chapter 8 I asked whether developmental shifts in sensory dominance are also evident in multisensory illusions (i.e. the McGurk effect). Finally, in Chapter 9 I used an exploratory, correlational approach to identify whether individual differences in sensory dominance were associated with unimodal and cross-modal interference. Conclusions: Findings suggested that different mechanisms underlie unimodal and cross-modal interference. Unimodal and cross-modal interference showed different patterns of development and decline in childhood and ageing. Unimodal interference control is poor in childhood and old age, whilst cross-modal interference control is poor in childhood but spared in ageing. Cross-modal interference also occurs mainly at stimulus- encoding stages, whilst unimodal interference also occurs at the level of response selection. Following this, I found measures of sensory dominance appeared robust and modulated by age. A developmental shift from auditory to visual dominance was seen in the existing literature studying the Colavita effect and my empirical investigation using the McGurk effect. However, there was no correlation between sensory dominance (measured with the Colavita task) and cross-modal distractibility in a group of young adults. Those that were more visually dominant were more susceptible to unimodal, visual, Stroop interference. I discuss the findings of this thesis with respect to the theoretical implications of findings, the gaps in literature this experimental work addresses and directions for future research