Interactions of space and language: Insights from the neglect syndrome

Abstract

The current article speculates about the interrelations between space and language from the perspective of the neglect syndrome. Various conflicting findings are reviewed and the effect of cultural factors is strongly emphasised. Current scientific literature describes relationships between space and language; however, the available data render it difficult to conclude whether it is the primacy of spatial representations or the complex two-way interaction between linguistic and spatial representations that determines the nature of cognitive processing. It is hoped that studying the neglect syndrome will provide a solution to this problem. Finally, directions for future research are provided that requires bridging the gap between cognitive theorising and neuroscientific approaches.

Keywords:

• Brain damage
• cognitive processing, language
• neuropsychology

Introduction

Scientific literature shows that space and language interact. Mandler (1996), for instance, reasons (based on empirical evidence) that young children map developing linguistic concepts on a pre-existing conceptual system and space is considered as the fundamental dimension of this system. Similarly, Chatterjee, Maher, and Heilman (1995a), Chatterjee, Southwood, and Basilico (1999) claim that spatial representations that underlie spoken language reflect the way in which the human mind conceptualises events. Studies conducted to probe the interaction of space and language have mainly focussed on spatial prepositions (Crawford, Regier, & Huttenlocher, 2000; Hayward & Tarr, 1995; Logan, 1995) and demonstratives (Bonfiglioli, Finocchiaroa, Gesierich, Rositani, & Vescovia, 2009; Kemmerer, 1999, 2006) in typically functioning individuals or on spellings/words in cases of brain damage (Baxter & Warrington, 1983; Caramazza & Hillis, 1990) and other conditions like letter position dyslexia (Friedmann & Gvion, 2001) and neglect dyslexia (Riddoch, Humphreys, Cleton, & Fery, 1990). Comparisons across languages that have different writing orders (left to right vs. right to left) have also been reported in this context (see Friedmann & Gvion, 2001).

In order to better characterise the relationship between space and language we require investigations concentrated at the level of both, spoken and written sentences. This is an important task as contemporary theorists impute a special role to space reflected in theoretical conceptualisations like the “spatial registration hypothesis” which states that the location of any perceived stimulus is automatically marked with respect to one's egocentric space even when such marking is not required by the task at hand. This marking appears to have an evolutionary advantage as it facilitates interaction with the perceived stimuli in both the sensory and motor domains. Moreover, this marking with respect to egocentric coordinates is not restricted to sensory and motor domains but “spills-over” to higher level cognitive operations (Coslett, 1999). The right posterior parietal cortex is hypothesised to serve as the neural substrate for this registration process and hence damage to it impairs performance on both spatial and non-spatial tasks alike (see Chatterjee, 2001). A popular outcome of the spatial registration hypothesis is the space number association of response codes, the SNARC effect, obtained with numbers where participants are faster to respond to larger numbers with the right hand and to smaller numbers with the left hand (Dehaene, Bossimi, & Giraux, 1993). This finding implies a left to right organisation of the mental number line. Similar spatial organisation has been proposed for language and for expressing event/action sequences linguistically. For instance, the auditory trace of a spoken sentence is said to be transcoded in a spatial format with a vector running from left to right (spatial transcoding of spoken language, Rinaldi, Marangolo, & Pizzamiglio, 2003).

Damage to linguistic algorithms

Researchers posit an underlying spatial representation with a left to right trajectory that supports the verbal communication of events, a structure that is reflected in language. Consistent with this claim Chatterjee, Maher, Gonzalez Rothi, and Heilman (1995b) showed that an agrammatic patient assigned the thematic role of agent to a figure located on the left in a picture task when asked to describe the agent and recipient of a depicted action. Chatterjee and colleagues reasoned that due to the unavailability of grammatical and syntactic rules of his first language, the patient relied on the undamaged spatial representations for disambiguating action roles. Thus damage to linguistic processing in case of agrammatism exposed the underlying primitive spatial biases. This same spatial representation is hypothesised to bias the unfolding of action events from left to right in typically functioning individuals and as a result well individuals are shown to place the agent of an action closer to the left margin of a given page while the recipients are placed to the right (Chatterjee et al., 1995a). But Chatterjee et al. (1999) labelled their obtained effects as “hemispheric specialization hypothesis” which imputes a special role for the left hemisphere's overlapping language and spatial attention networks which in turn mediate the left to right directionality bias. In this account, verbs play an important role by embodying the meaning of event/action sequences linguistically and serving as the underlying basis for thematic role assignment. Therefore, the overlap of spatial attention and directional representations of events by verbs serves as the neural gateway for linking spatial and propositional representations of event(s).

Differences across writing/reading systems

Work reported in the previous sections might point at the possibility that spatial representations supporting spatial registration and transcoding always have a vector from left to right. But previous studies have most often employed speakers of languages that have a reading and writing orientation running from left to right. Studies conducted with participants who use the opposite direction for reading and writing (right to left) offer different explanations for the relations shared by spatial representations and language. For example, the usual SNARC effect is not observed in Iranian participants (Dehaene et al., 1993). Furthermore, Leker and Biran (1999) contend that the right hemisphere has a special role in supporting the differential organisation of spatial patterns required for a language that reads right to left, for example, Hebrew.

In effect, writing and reading systems with an orientation from right to left might be implicated in an organisation of spatial representations with a vector that runs from right to left rather than from left to right. This differential organisation would then give rise to a “reversed directionality bias” on cognitive tasks. Consistent with this claim, Fagard and Dahmen (2003) showed that French-speaking children filled in more dots in a dot-filling task while moving from left to right, a pattern consistent with the direction of reading and writing in French. On the other hand, Tunisian children performed better when moving from right to left (see Geldmacher & Alhaj, 1999, for similar results).

Maass and Russo (2003), comparing Arabic and Italian participants, also supported the reversed directionality bias. Their Italian participants showed a bias for putting subjects of actions to the left of objects of actions in a sentence-picture matching task whereas the Arabic participants showed the opposite bias. This reversed directionality bias was obtained even though both Italian and Arabic languages share the temporal subject-verb-object order. What differs between the two languages is the direction of writing and reading with Italian following a left-right order and Arabic following the reverse. But Maass and Russo also pointed out that Italians were fastest to verify whether an action depicted in a drawing matched the action conveyed linguistically in conditions where the subject of the action was on the left and the action itself evolved from left to right. On the other hand, Arabs were fastest on the same task where the subject of action was on the right but the action itself evolved from left to right. These findings provide partial support for the hemispheric specialisation hypothesis, consolidating the claim that there is an additional tendency to direct attention from left to right over and above the biases that might emerge from specific reading/writing orientations.

Consistent with the study conducted by Maass and Russo, Chan and Bergen (2005) examined the interaction of writing directionality with spatial cognition between English, Chinese and Taiwanese participants. Chinese like English follows a left to right writing direction while Taiwanese follows a top to bottom direction. They conducted three different experiments to probe the effects of writing orientation on spatial memory, visual attention and arrangement of sequential events in space. Both English and Chinese-speaking people were more likely to remember stimuli appearing on the top left-hand side as compared to Taiwanese speakers who in turn recalled stimuli presented at the upper right-hand side better. In the visual attention task, participants were presented with two pictures (one on the left and the other on the right) and their task was to form sentences taking into account both the pictures presented. Care was taken to ensure that both pictures had similar levels of animacy as sentence subjects are usually shown to have higher level of animacy than objects (Forrest, 1993). English and Chinese participants were more inclined to use the picture presented on the left as the subject of the sentence whereas Taiwanese speakers more often chose the pictures on the right as the subject. In the third experiment, English and Chinese speakers spatially arranged a given set of pictures more often from the left to right direction. In this experiment, Taiwanese speakers displayed a mixed pattern with picture arrangement varying from top-bottom, left-right, right-left, bottom-top, clockwise and even some Chinese speakers using a top-bottom direction.

Taken together, the results supporting reversed directionality bias suggest that the orientation/direction of reading and writing modifies the spatial routines that people deploy not only for reading and writing itself but also for other cognitive functions, for example, initial direction of spatial attention, the location of preferential memorising of objects and the beginning of temporal sequences (Chan & Bergen, 2005).

Spatial registration hypothesis versus hemispheric specialisation hypothesis

Chatterjee and his colleagues studied participants for whom the orientation of writing and reading followed a left to right order and proposed the hemispheric specialisation hypothesis. Maass and Russo only provided partial support for this hypothesis underscoring the important modifying role played by reading and writing habits. Which hypothesis could better explain the interaction of space and language? Are space and linguistic representations overlapping in the left hemisphere yielding the left to right scanning bias (a basic universal feature) evident in thematic role assignment and other cognitive tasks as predicted by the hemispheric specialisation hypothesis? Or could this relation be better explained by the spatial registration hypothesis which predicts that the location of a perceived stimulus is automatically marked with respect to one's egocentric space, a function that seems localised in the right posterior parietal cortex? The spatial registration hypothesis also provides room for the influences of distinct scanning habits due to differences in reading and writing direction. The findings reported in the literature provide evidence for both hypotheses, so which research methodology should be applied to disentangle their respective contributions?

Rinaldi and Pizzamiglio (2006) reasoned that in order to better understand the interaction of space and language one needs to take into account careful analysis of brain damaged cases. Analysis of cases with damage to the right hemisphere which subserves spatial representations, as usually occurs in cases of hemispatial neglect, will thus be instrumental in understanding the directionality bias.

Highlights from the neglect syndrome

This section will attempt to analyse the relation between space and language from the perspective of the neglect syndrome. In neglect, patients fail to detect stimuli on the side of the space which is opposite their lesioned side despite adequate basic sensory and motor capabilities. Neglect is more commonly manifest after damage to the right posterior parietal cortex (inferior parietal lobule, Vallar, 2001). This occurs because the right posterior parietal areas are responsible for allocating attention to both the left and right sides (hemispaces or the extrapersonal space, Mesulam, 1981) while left parietal areas mediate orienting of attention only to the right side. Hence damage to the right hemisphere exaggerates attention orienting towards the right side with the result that patients are often observed as neglecting events occurring on their left side (Bartolomeo & Chokron, 2002) such as they may omit left parts of objects while drawing, leave the left half of their faces unshaved, or not eat from the left side of the plate.

If language and space share important relationships then it is implied that damage to brain areas subserving either one of them would be accompanied by corresponding processing deficits in the other. On similar grounds, patients suffering from hemispatial neglect are shown to perform poorly on aurally presented spelling where spatial position of letters interacts with errors (Baxter & Warrington, 1983; Caramazza & Hillis, 1990). The obtained errors in spelling are consistent with the proposal of “spatial transcoding” of spoken language, which implies that these spellings are subject to the same bias as other visuo-spatial stimuli in neglect.

Other researchers have studied neglect patients with language backgrounds that do not share the usual left to right order. These studies yield support for the reversed directionality bias and thereby implicate the interaction of reading/writing habits with visuo-spatial representations of the right hemisphere. The most popular task employed to investigate visuo-spatial biases in typically functioning individuals and neglect patients is the line bisection task. Typical individuals show a tendency to bisect lines by placing the bisection to the left of the geometrical midpoint when asked to indicate the middle of a visually presented line; an effect termed as pseudoneglect. This tendency is attributed to the right hemisphere's capacity to direct attention. But in cases of right brain damage, patients suffering from neglect bisect lines by placing the bisection to the right of the geometrical midpoint (Schenkenberg, Bradford, & Ajax, 1980). This tendency is attributed to the impaired search strategies supported by the right hemisphere (Weintraub & Mesulam, 1990). Consistent with this claim, Speedie et al. (2002) showed that reading/writing direction modulated performance on the line bisection task after damage to the right hemisphere with the readers of right to left language dissecting the lines closer to the geometrical centre while the readers of the left to right language bisected lines by placing the bisection to the right of the geometrical centre (see Chokron, Bartolomeo, Perenin, Helft, & Imbert, 1998, for similar results).

Elucidating the relationship between space and language beyond the level of single words and simple line bisection tasks, Rinaldi and Pizzamiglio (2006) showed that Italian right brain damaged patients with spatial heminattention (neglect concentrated on the left hemispace) committed more errors on the initial part (subject-word) of aurally presented active sentences (agent of action-action-object/or subject of sentence-verb-object for active sentences) than did participants without neglect while comparing two sentences for similar intonation patterns. Furthermore, this error pattern was inverted for passive sentences (object of action-action-agent of action) implying that neglect is mainly concentrated on the logical subject of the sentence or the doer of action. Rinaldi and Pizzamiglio therefore concluded that neglect occurs at the deep structure of the sentence which coincides with surface structure in the case of active sentences. In their study, the presence of “verbs” acted as the main mediating variable for eliciting the error patterns because in the absence of verbs, in a three-noun word condition, as well as with musical stimuli, the performance of neglect patients was comparable to that of participants without neglect. This implies that the deficient performance of neglect patients does not reflect on the general necessity of processing any sequence of event over a period of time.

The explanation provided by Rinaldi and Pizzamiglio (2006) for their findings could be contrasted with that provided by Chatterjee and colleagues. Chatterjee et al. explained their findings in terms of the hemispheric specialisation hypothesis whereas Rinaldi and Pizzamiglio focus on the spatial transcoding of linguistic input. It is important to point out that the patient studied by Chatterjee et al. did not suffer from neglect. Furthermore Dobel, Diesendruck, and Bölte (2007) provided support for the modification of spatial representational biases by the introduction of reading and writing systems. Dobel and colleagues compared pre school children from Germany (left to right system) and Israel (right to left system) on tasks where the children were asked to draw or arrange transparencies of objects and protagonists for auditorily presented agent/recipient first sentences. Results did not show a directional bias for the pre school children but did so for adults consistent with the writing directions of their respective languages where Israeli participants tended to place agents on right side of recipients while the Germans showed the opposite trend.

Implications for space and language

What can we conclude from the studies of neglect and their comparison with typically functioning individuals with respect to the relation between space and language? It is quite evident that different studies have produced results that are in contrast with each other. The study conducted by Rinaldi and Pizzamiglio (2006) shows that neglect shifts with the logical subject of the sentence (active/passive). It is important to keep in mind that these sentences were presented in an auditory format but even auditorily presented linguistic input interacts with the orientation of writing as shown by Chan and Bergen (2005). At the moment, it is difficult to distinguish among the two possibilities given the lack of data from neglect patients for whom the direction of writing differs from English or other western languages that typically follow a left to right order. On the other hand, Chatterjee and colleagues conclude that spatial representations play the most important role, however, their conclusions are based on tasks that present pictures to their experimental participants (both brain damaged and well). Therefore, it is premature to draw conclusions about on the origin of the directionality bias. Following reasoning advanced by Chatterjee et al. and the partial support provided by Mass and Russo for the hemispheric specialisation hypothesis, it would be reasonable to expect patients to show neglect concentrated on the left side irrespective of the direction of writing (but here again it is important to keep in mind that we would require both active and passive sentences in such an investigation). This brings us closer to examining the Whorf-Sapir linguistic relativity hypothesis (see Whorf, 1956) according to which the nature of language affects spatial processing. Many researchers have produced evidence against this hypothesis. Li and Gleitman (2002), for instance, showed that language does not play a key role in determining spatial perspectives for their English-speaking participants.

Investigating patients suffering from neglect syndrome more minutely will provide important insights into the nature of the relationship shared by language and space and can help us understand whether the interaction is uni- or bi-directional in nature. By carefully following the disorder we hope to disentangle the contributions made by nature and nurture. There are many important questions that need to be considered before embarking upon this agenda:

•	Is it that the spatial representations (as mediated by the right hemisphere) constrain cognitive processing on linguistic, non-linguistic and other motor and sensory tasks or is it the effect of individual language learning peculiarities that in interaction with spatial representations determine cognitive processing?
•	How strong is the spatial bias afforded by the left hemisphere in linguistic and non-linguistic tasks?
•	Finally, we need to simultaneously follow these two questions to obtain a fuller picture on action, space and attention as the processing of verbs that embody the meaning of action events, seems to be affected the most in case of neglect. Thus, how far can we connect the spatial representation required for physical actions to spatial representations needed for the understanding of actions signalled by linguistic inputs?

Therefore, it is imperative that we not only study neglect patients more closely but we also need to contrast patients with differing backgrounds of writing/reading orientations. Even if it is possible to test such patients, we need to control and manipulate several factors before we conclude about relations between space and language. For instance, the nature of tasks administered to the patients is critical because different types of task could gauge different biases as noted above (e.g., picture matching tasks, comparing heard sentences for intonation, written linguistic input, spellings vs. sentences). Finally, it is important to disentangle the effects of the logical and the grammatical subjects of the sentences. At the same time, it is imperative to keep the animacy of subjects and objects equivalent in line with Forrest (1993).

It is an important concern to correlate the nature of impairments obtained with the extent of damaged brain areas in patients. This becomes important if one were to think of neglect occurring at different levels of abstractions. It is quite possible that neglect that occurs at a higher level of abstraction, where linguistic and spatial representations are abstract in nature, is different from neglect at lower levels of abstraction where linguistic and spatial representations are concrete in nature for example, single words that stand for concrete objects as observed for letter position dyslexia and neglect dyslexia. This kind of endeavour will also provide information about the brain areas supporting each type of interaction between language and space.

Conclusions

We need a thorough program of research to better understand the nature of relationship between space and language at different levels of abstraction. Many studies have focussed on primitive levels by investigating the nature of deficient performance by neglect patients for the processing of single words. We need to move on from this level and include sentences in our focus of enquiry in order to connect findings about deficient linguistic processing that is required for the understanding of action events conveyed linguistically with findings about action and spatial attention tasks. Careful analysis of data from patients with brain damage representing different cultures with different reading orientations will be instrumental in disentangling the contributions of nature and nurture to the interactions of space and language which in case of typical individuals are hard to separate.

Acknowledgments

The author is supported by Deutsche Forschungsgemeinschaft (DFG) grant managed through the Graduate School of the Centre of Excellence “Cognitive Interaction Technology,” University of Bielefeld, Germany.

I am greatly indebted to Lori J. Altmann and Cristina M. Rinaldi for their helpful comments.