Speech processing asymmetry revealed by dichotic listening and functional brain imaging☆
Introduction
In this invited article we review studies on auditory laterality from our laboratories at the University of Bergen, Norway, and Uppsala University, Sweden, which were conducted over the last 25–30 years on auditory laterality. The reviewed studies and articles have in common the use of the dichotic listening paradigm. For most parts, these studies have been conducted in our laboratory at the University of Bergen, Norway, or by our collaborators. We also review, when relevant, other studies in order to emphasize a point, or clarify an issue. We have, moreover, and somewhat untraditionally, divided the paper according to separate studies. We believe that the overall pattern of findings from these studies reveals a coherent story on the laterality of auditory language processing. The review particularly focuses on studies using functional neuroimaging, conceptualized both as hemodynamic imaging (Hugdahl et al., 1999; van den Noort et al., 2008; Westerhausen et al., 2010; Kompus et al., 2012; Westerhausen et al., 2014) as well as electrophysiological and magnetoencephalographic measures (Alho et al., 2012, Davidson and Hugdahl, 1996, Eichele et al., 2005, Passow et al., 2013). These findings are further contrasted with observations in clinical populations (Carlsson et al., 1994; Pollmann et al., 2002, Pollmann et al., 2004; Hugdahl et al., 1997; Kompus et al., 2011). A focus of and core interest in our research on hemispheric asymmetry has been to reveal how bottom-up and top-down factors interact to program conscious perception, whether reflected as behavioral response or as change in brain activity patterns.
Section snippets
Bottom-up and top-down effects on auditory language laterality
With the term “bottom-up” we refer to the brain asymmetry which can be observed as a consequence of the nature of the presented stimulus and the anatomy of the ascending auditory pathways, e.g. how the acoustic–phonetic nature of a consonant–vowel (CV) syllable (like the sound /ba/) presented in isolation, and out of a semantic and syntactic context, will initially drive the neurons in the left peri-Sylvian region, including the Heschl's gyrus (HG), superior temporal gyrus (STG), superior
Outline of the review paper
Fig. 1 illustrates some of the bottom-up and top-down influences on the REA, and we will use sound intensity manipulations as an example of bottom-up, or stimulus-driven, influences, and focused attention instructions as an example of top-down, or instruction-driven, influences. We will then bring it all together by reviewing studies where both types of manipulations have been done within a single experiment, or study.
We have focused on functional neuroimaging studies in this review, and how
The classic REA and the structural model
The classic REA in dichotic listening was originally observed as a behavioral preference when there were two competing stimuli presented at the same time. The discovery of the behavioral REA for auditory perception is typically ascribed to Doreen Kimura who in two articles in the Canadian Journal of Psychology (Kimura, 1961a, Kimura, 1961b) showed superior performance in her subjects for stimulus items presented to the right ear. It should, however, be noted that Kimura in her original studies
Stimulus-driven modulation of the REA
Charles Berlin and colleagues conducted a series of pioneering parameter studies of the REA in the 1960–1970s (see Berlin (1977), for overview of the studies carried out in his laboratory in these years). One of the manipulations he and his colleagues performed was to increase the signal intensity in one ear relative to the other ear, which affected the REA in the sense that increasing the intensity in the right ear increased the REA, while the reversed manipulation decreased the REA. Tallus et
Instruction-driven modulation of the REA
Having addressed issues related to auditory laterality for language processing from a bottom-up perspective and how the REA in dichotic listening is based on the structural model originally proposed by Kimura (1967), and how it is modulated by stimulus-driven factors, like signal intensity, we now turn to a review and discussion of top-down modulatory factors.
The REA can be influenced by a variety of non-stimulus factors, like head- and eye-movements towards either the left or right ear (
The attention-executive model and dichotic listening
Hugdahl et al. (2009) proposed that focusing attention on the right or left ear induced different degrees of cognitive conflict and a corresponding need for cognitive control strategies. When attention was biased to the right side, as in the situation with instructions to focus on the right ear, labeled the forced-right, FR, condition by Hugdahl and Andersson (l986), the bottom-up and top-down influences on the REA would act synergistically to increase the number of correct reports. However,
Summary and conclusions
We have made a couple of intermediate summaries as we have proceeded through this review on the previous pages, and will therefore in this closing section only sum-up the overall take-home-message from studying auditory language laterality with a dichotic listening paradigm, using phonological stimuli, and applying various functional imaging modalities, both hemodynamic and electrophysiological, to evaluate the neuronal and neural underpinnings of the behavioral asymmetries reported from our
Acknowledgments
The authors want to thank all past and present Master and PhD students, as well as Postdocs and national and international research collaborators, as well as the technical staff at the Bergen fMRI Group, and Department of Radiology, Haukeland University Hospital, Bergen, Norway for their contributions to research reviewed in this article. The current work was funded by grants to Kenneth Hugdahl from the Research Council of Norway, Oslo, Norway Grant # 221558 and European Research Council (ERC),
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2022, Clinical NeurophysiologyCitation Excerpt :Speech processing is commonly left lateralized (Bethmann et al., 2007, Floel et al., 2005). Therefore, most people show a right ear advantage for speech processing due to the contralaterality of the auditory pathway (Hugdahl and Westerhausen, 2016). This contralaterality is reflected in a stronger response in the contralateral than in the ipsilateral auditory cortex to monaural stimulation in normal hearing listeners (Behne et al., 2005, Behne et al., 2006, Hine and Debener, 2007, Woldorff et al., 1999).
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2020, Brain and LanguageCitation Excerpt :In addition, the decrease in accuracy in the laSTG from TMS was significantly greater than that in the raSTG. Thus, results of the current study converge with those from previous investigations that examined dichotic listening and neuropsychological findings demonstrating a crucial role for the left STG in speech perception (Hugdahl & Westerhausen, 2016; Johsrude, et al., 1997; Kimura 1961; Maffei et al., 2017; Milner et al., 1968; Slevc et al., 2011; Sparks & Geschwind, 1968). Most importantly, the TMS findings supported the conclusion that the activation in the laSTG was causally related to sublexical speech perception whereas such causal evidence was lacking for the raSTG.
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The research presented in this review article was funded by the Research Council of Norway (RCN), Western Norway Health Authorities (Helse-Vest), University of Bergen, and the European Research Council (ERC).