What Brain Imaging Can Tell Us About Embodied Meaning

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  • 8/9/2019 What Brain Imaging Can Tell Us About Embodied Meaning

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    In Press, To appear in M. de Vega, A. Glenberg, & A. Graesser (Eds.), Neural embodiment of sentence and word meaning

    Symbols, embodiment, and meaning. Oxford, UK: Oxford University Press.

    What Brain Imaging Can Tell Us About Embodied Meaning

    Marcel Adam JustCenter for Cognitive Brain Imaging

    Department of PsychologyCarnegie Mellon University

    Pittsburgh, PA

    Abstract: Brain imaging studies of language processing (using fMRI) can indicate under whatcircumstances the embodied aspects of language representations become activated. In particular,the processing of language is distributed across a number of cortical centers, including not onlyclassic language areas in association cortex (which might be involved in symbolic processing), butalso sensory and motor areas. A set of fMRI studies on visual imagery in sentence comprehensionreveals both the perceptual-motor and the symbolic aspects of brain function that underlie languageprocessing. Moreover, they indicate some of the conditions under which perceptual or motorrepresentations are most likely to be activated. Another set of studies on word comprehensionindicates that the neural signature of certain concrete semantic categories (tools and dwellings) andindividual category exemplars can be identified by machine learning algorithms operating on thefMRI data, and that perceptual and motor representations constitute part of the signature.

    Visual imagery in sentence comprehension

    Many types of thinking, in particular languagecomprehension, entail the use of mental imagery.

    Understanding a text on architecture or automobiledesign seems impossible without mental imagery.Language often refers to perceptually-basedinformation. For example, to evaluate a sentence likeThe number eight when rotated 90 degrees looks like

    a pair of spectacles, a reader must process thecontent of the sentence, retrieve a mental image ofthe shape of the digit 8, mentally apply a rotationtransformation to it, and then evaluate the resultingimage. In this case, there seems little doubt that aperceptually-based representation is involved in thecomprehension. This perceptually-based

    representation has sometimes been called thereferential representation or the situation model. OurfMRI studies attempt to determine the characteristicsof such representations and the conditions underwhich they are likely to be evoked or activated.

    Previous studies have indicated that mentalimagery generated by verbal instructions and byvisual encoding activate similar cortical regions(Mellet et al., 1996, 1998, & 2002; Mazoyer et al.,2002). Several studies examining mental imagery

    have observed activation of the parietal area (Just et al.,2001; Mellet et al., 1996 & 2000; Deiber et al., 1998;Ishai et al., 2000, Kosslyn et al., 1993, 1996 & 1999),particularly around the intra-parietal sulcus. Our

    imagery studies attempted to determine the conditionsunder which such activation occurs during languagecomprehension.

    There is also a possibility that the neural activityunderlying the imagery in language processing isaffected by the presentation modality of the language(i.e., written vs. spoken). For example, the neuralactivity elicited in primary visual cortex during mentalimagery following verbal vs. visual encoding wasdifferent (Mellet et al., 2000); there was less primaryvisual activation during imagery after visual encodingcompared to verbal encoding, suggesting that

    presentation modality may indeed affect later imageryprocessing. Another study by Eddy and Glass (1981)examined how the visual processes in reading might berelated to the visual imagery processes that a sentenceengenders, comparing visual and auditory sentencepresentation modes. High-imagery sentences tooklonger to verify as true or false than low-imagerysentences when the sentences were presented visually,but not when they were presented auditorily. Thesefindings again suggest that the presentation modality of

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    In Press, To appear in M. de Vega, A. Glenberg, & A. Graesser (Eds.), Neural embodiment of sentence and word meaning

    Symbols, embodiment, and meaning. Oxford, UK: Oxford University Press.

    2

    a sentence may affect the processing of thesubsequent imagery.

    Our imagery studies examined mental imageryprocesses in the context of a language comprehensiontask (Just et al., 2004). One of the main goals was toexamine the interaction between two somewhat

    separable neural systems, the mental imagery andlanguage processing systems. In the context of theembodiment debate, these studies ask not whetherembodied (perceptual or motor) activation occurs, butthe circumstances under which it occurs and how it isrelated to other more symbolic activation. Toaccomplish this goal, we used fMRI to measure notonly the activation levels but also the functionalconnectivities of the regions believed to be involvedin mental imagery, to determine the relations betweenthe two systems. A second goal was to examine theeffect of input modality, comparing the effect on the

    imagery-related activation when the sentences wereeither heard or read.

    The study examined brain activation whileparticipants read or listened to high-imagerysentences like The number eight when rotated 90degrees looks like a pair of spectacles or low-imagery sentences, and judged them as true or false.They included sentences requiring various types ofspatial transformation or spatial assessment such asmental rotation (like the spectacles sentence),evaluation of spatial relations (e.g., On a map,

    Nevada is to the right of California), combination of

    shapes (e.g., The number nine can be constructedfrom a circle and a horizontal line, a false example),and comparison of visual aspects of common objects(e.g.,In terms of diameter, a quarter is larger than anickel, which is larger than a dime ). Although thesesentences generally required that a spatialtransformation be mentally performed, pilot studiesindicated that understanding a complex spatialdescription without a transformation produced similarresults. The low-imagery sentences could be verifiedby referring to general knowledge, without the use ofimagery (e.g., Although they are now a sport,

    marathons started with Greek messengers bringingnews).

    The sentence imagery manipulation affected theactivation in regions (particularly the left intraparietalsulcus) that activate in other mental imagery tasks,such as mental rotation. Both the auditory and visualand auditory presentation experiments indicatedmuch more activation of the intraparietal sulcus areain the high-imagery condition as shown in Figure 1,suggesting a common neural substrate for language-

    Figure 1. The activation in the intraparietal

    sulcus area is higher for high imagerysentences (particularly in the left hemisphere),

    and the effect is similar regardless of whether

    the sentences are presented visually or

    auditorally.

    evoked imagery that is independent of the inputmodality. There was more activation in theintraparietal sulcus area in the reading than in thelistening condition (probably owing to the attentionaldemands ofdirecting spatial attention and possibly eyemovements to particular sentence locations during

    reading), but the magnitude of the imagery effect wascomparable in the two cases.

    Functional connectivity and imagery. The variousanatomical regions of the cortex involved in processinga task must be able to effectively communicate andsynchronize their processes for the system to function.In a language task, this means that the areasresponsible for executing subcomponent processesmust collaborate to synthesize the informationnecessary for comprehension. Such collaboration can

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    In Press, To appear in M. de Vega, A. Glenberg, & A. Graesser (Eds.), Neural embodiment of sentence and word meaning

    Symbols, embodiment, and meaning. Oxford, UK: Oxford University Press.

    3

    be measured in functional neuroimaging studies bycomputing the correlation of the activation timeseries in a given region with the activation time seriesof another region. The extent to which the activationlevels of two regions rise and fall in tandem is takenas a reflection of the degree to which the two regions

    are functionally connected, and the term that iswidely used to refer to the activation time seriescorrelation is functional connectivity. Previousresearch has provided some evidence that as taskdemands increase, functional connectivity alsoincreases, for example, as a function of workingmemory load (e.g., Diwadkar, Carpenter, & Just,2000), reflecting the need for tighter coordination in amore demanding condition. Functional connectivityhas also been shown to be modulated bycomprehension difficulty, and differentially so forpeople of different working memory capacity (Prat et

    al., 2007). A relation between functional andanatomical connectivity has been demonstrated inautism, where the functional connectivity betweencortical regions is correlated with the size of thecorpus callosum segment that anatomically connectsthem (Just et al., 2007).

    In addition to exhibiting higher activation levelsduring the processing of high-imagery sentences, theleft intraparietal sulcus also showed greaterfunctional connectivity in this condition with othercortical regions, particularly with languageprocessing regions, regardless of the input modality.

    The imagery manipulation affected the functionalconnectivity between the left intraparietal sulcus areaand other brain areas that are activated in this task. Italso the affected the functional connectivity betweenthe left superior temporal (Wernickes) area and otherbrain areas. These two areas are proposed to berespectively involved in the imagery processing ofhigh-imagery sentences (left intraparietal) andsemantic (symbolic) processing (Wernickes). Thefive other activated brain areas were left hemisphereareas, including areas centrally involved in languageprocessing (pars opercularis, pars triangularis,

    dorsolateral prefrontal cortex, frontal eye fields, andinferior parietal lobule). The intraparietal sulcus areahad higher functional connectivities with the fiveactivated brain areas when the sentences were highin imagery, whereas the left temporal area had higherfunctional connectivities to these five areas for low-imagery sentences. This result applies to be the visualand auditory presentation conditions , as shown inFigure 2.

    Figure 2. The average functionalconnectivity of the left intraparietal sulcusROI (LIPS) and the left temporal ROI(LT) and with five left hemisphere ROIs:

    pars opercularis, pars triangularis, theinferior parietal lobule, dorsolateralprefrontal cortex, and frontal eye fields.The functional connectivity between LIPSand these areas is greater for high-imagery sentences. The opposite is truefor LT, which is not involved in imageryprocessing. The same pattern occurs forboth visual and auditory presentation ofsentences.

    The result provides important convergingevidence for implicating the intraparietal sulcus inimagery processing in sentence comprehension, andmore directly indicates the higher degree of functionalinteraction between this embodied imageryrepresentation and some of the other key activatedregions in the high imagery condition.

    Sentence imagery in autism. In a recent study, weexamined the processing of such high- and low-imagery sentences in adults with high-functioning

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    In Press, To appear in M. de Vega, A. Glenberg, & A. Graesser (Eds.), Neural embodiment of sentence and word meaning

    Symbols, embodiment, and meaning. Oxford, UK: Oxford University Press.

    4

    autism, in comparison to age- and IQ-matchedcontrols. This study provides the opportunity todetermine whether the use of imagery (or embodiedrepresentations) in sentence comparison might bedisrupted in a special neurological population. Canmeaning embodiment be disrupted or modulated by a

    neurological disorder?First, consider the effect of imagery on the

    control participants, which is very similar to the studydescribed above. Figure 3 shows the imagery effect(high imagery minus low), displaying the prominentextra activation in the parietal area, as well as somein the prefrontal and inferior temporal areas.

    Figure 3. High minus low imagery effectof visual sentence comprehension incontrol participants, displaying a largeimagery effect in parietal, prefrontal, andinferior temporal areas.

    What of people with high-functioning autism?There have been frequent suggestions thatspatial/perceptual processing is spared (or sometimes

    even enhanced) in autism. For example, Shah andFrith (1983; 1993) found that participants with autismhave an advantage at certain types of spatial tasks.When a task is amenable to either a visual or a verbalstrategy, there is a suggestion that people with autismprefer a visual strategy. There are many informalreports that individuals with autism arepredominantly visual thinkers (Grandin, 1995).Temple Grandin, an accomplished professional withhigh-functioning autism, entitled her book Thinking

    in Pictures. In an fMRI letter n-back study, Koshino etal. (2005) found of more visual coding of letters inautism compared to a verbal coding strategy in thecontrols. Similar results were also found in a facesworking memory task (Koshino et al., in press). Thesestudies indicate that there is a tendency in people with

    autism to use more visuospatial regions by recruitingposterior brain regions in accomplishing varied tasks,including language tasks.

    The group with autism showed similar activationto the controls in the processing of high-imagerysentences (prominent activation in the parietal area,particularly around the intraparietal sulcus). It is

    Figure 4. High minus low imagery effectof visual sentence comprehension in peoplewith autism, displaying a negligibleimagery effect.

    reasonable to conclude that in the high-imagerycondition, which can be said to make use of embodied(perceptual) representations, the processing of the

    autism group resembled the processing of the controlgroup. However, the interesting new result was thatunlike the control group, the autism group displayed asimilar amount of parietal imagery-related activationeven in the low-imagery condition. Figure 4 shows theminimal imagery effect (the subtraction of high minuslow imagery). It appears that the autism group usesembodied representations even in contexts wherecontrol participants do not.

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    In Press, To appear in M. de Vega, A. Glenberg, & A. Graesser (Eds.), Neural embodiment of sentence and word meaning

    Symbols, embodiment, and meaning. Oxford, UK: Oxford University Press.

    5

    The tentative account for why this occurs is thatthe cortical connectivity of the neural system iscompromised in autism (the main tenet of theunderconnect...