Research Questions

This study aimed to examine the hemispheric lateralization of emotion word processing by left-handers, FS+ and FS- right-handers. To be more specific, this study investigated whether the handedness factor influences one’s processing of emotion word in a divided visual field paradigm. Accordingly, the research questions of the current study are shown as follows:

1. Will the positive words shown in the visual field ipsilateral to the dominant hand be preferred and processed faster?

2. Will handedness (left-handers, FS+ and FS- right-handers) be an influential factor on such processing?

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Chapter Two

Literature Review

This chapter reviews the literature pertaining to the current study. First, hemispheric lateralization studies with the factor of handedness are discussed in Section 2.1, including the explicit sinistrality (i.e., left-handedness) and implicit sinistrality (i.e., familial sinistrality).

Section 2.2 introduces the body-specificity hypothesis. Section 2.3 addresses the emotion word processing.

2.1 Handedness and Hemispheric Lateralization

It is well established that in most right-handed adults the major capacity for language is located in the LH, either from clinical evidence (Sperry and Gazzaniga, 1967; Luria, 1970;

Rasmussen & Milner, 1977; Bryden, Hecaen & DeAgostini, 1983) or from experiments with healthy subjects (Knecht et al, 2000, 2003; Szaflarski et al., 2002; Tzourio et al., 1998).

However, the pattern of such functional specialization for left-handers is less consistent.

Based on the observation of neurological patients, early studies reported that only about two-thirds of the left-handed population have their language lateralized to the LH. The remainder either display a reverse lateralization (approximately 15 to 18%) or a bilateral representation pattern (about 17%) (Rasmussen & Milner, 1977; Bryden, Hecaen, & DeAgostini, 1983). But it can be argued that the patients may not be representative for the general population because they may be pathological left-handers due to the LH lesions (Rasmussen and Milner, 1977).

With the help of functional transcranial Doppler sonography, Knecht et al. (2000) were able to examine the relationship between handedness and language dominance in healthy subjects.

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They discovered that the incidence of RH language dominance was found to increase linearly with the degree of sinistrality, from 4% in strong right-handers (number in accordance with the study by Rasmussen & Milner, 1977) to 15% in ambidextrous individuals and 27% in strong left-handers. The results clearly demonstrated that there is a relationship between handedness and language dominance and that this relationship is not an artifact of cerebral pathology.

Since handedness is determined in the gene, it is natural to wonder if the factor of FS influences the linguistic lateralization among the right-handed population. As early as 1970, Luria and colleagues noted that the right-handed aphasic patients who had left-handed family members (FS+) recovered faster from LH aphasia and showed a higher incidence of RH aphasia than those without familial left-handers (FS-) (Luria, 1970). They speculated that the FS+ right-handed population has a genetic disposition towards bilateral representation for language, which can be manifested as explicit left-handedness in their family members.

Later language researchers incorporated the FS factor into their studies. At an early stage, FS was discussed within syllable or single word processing (Andrews, 1977;

McKeever & VanDeventer, 1977; McKeever et al. 1983). Andrews (1977) observed a tendency of right visual field (RVF) lateralization for meaningful words, nonsense syllables, and consonant strings but not vowel strings (all trigrams) and that this lateralization was modulated by FS. McKeever & VanDeventer (1977) also noted a RVF recognition superiority in FS+ left-handers. McKeever et al. (1983) employed an object naming task and reported a sex-FS interaction in the spatial visualization ability, that is FS- females and FS+

males performed better than FS- males and FS+ females. Though the approaches of the experiments were variant, the studies all confirmed FS’s modulation on the cerebral dominance for language processing.

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Later on, Bever et al. (1989) discovered that FS+ right-handers focused more on lexical/semantic information, whereas the FS- group relied more on syntactic information in sentence comprehension. In 2010, Hancock and Bever further looked into the FS effect via probe word recognition with subordinate clause fragments, and they observed that FS+

individuals exhibited greater RH involvement during early lexical processing of isolated words. Recently, Lee and Federmeier (2015) combined event-related potential (ERP) measures with divided visual field paradigm to invoke lateralized processing differences (Banich, 2003). They used “to” and “the” to create the syntactic expectancy of the lexical category of the following word (either a noun or verb). It was found that the RH sensitivity to the syntactic word violation was modulated by the FS factor. In sum, the FS factor exhibited a modulation effect not only on the lexical but also on the syntactic level.

Overall, the literature suggested that manifest handedness and the familial handedness have an influence on hemispheric asymmetry when individuals process language.

2.2 Handedness and the Body-Specificity Hypothesis

In addition to its relationship with language representation, handedness is also found to be associated with conceptual representation. Casasanto (2009) investigated the links between handedness and mental representation of abstract concepts with positive or negative valence (e.g. intelligence, sadness, bravery). He observed that right-handers tend to associate rightward space with positive ideas while the left-handers with the leftward space. The author argued that people who interact with the physical environments in systematically different ways should form different mental representations accordingly, which he named “the body-specificity hypothesis” (Casasanto, 2009). In one of his experiments, the participants received a piece of paper with a cartoon figure at the center and two boxes at each side of the figure,

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either horizontally or vertically arranged (vertical array being the control) (See Figure 1 adapted from Casasanto, 2009). Participants were instructed that the cartoon figure liked zebras and hated pandas (counterbalanced) and they were to draw the zebra in the box that best represented good things like seeing zebras and the panda in the box representing bad things (or vice versa). Results demonstrated that participants had a tendency to draw the good animal in the box at their dominant side. The results were replicated with Dutch speakers and with oral response instead of hand-drawing, which indicates that this preference was not due to the native language of the subjects or the fact that the hand drawing of the animal was the dominant hand.

Figure 1. The experimental materials adapted from Casasanto (2009)

Another experiment in the series examined whether the left-right position of the stimuli would have an implicit influence on left- and right-handers’ judgements towards positive/negative traits. Participants received a piece of paper with 12 pairs of created alien creatures. The creatures were arranged in two columns, one on each side of a list of questions printed in a center column. The task was to circle one of the creatures in the pair that best fit the question, to indicate a judgement about one of the four personal characteristics (i.e., intelligence, attractiveness, honesty, happiness). Results showed that participants’ directional

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preference was influenced by the right-left location of the creature, even though spatial location was irrelevant to the judgements.

In fact, research has demonstrated that positive emotion (pleasantness) reflects the

“approach motivation” while negative emotion links to the “avoidance motivation”

(Cacioppo & Berntson, 1994; Lang & Bradley, 2010). For example, food and drink provoke one’s motivation to approach, which is a natural instinct for survival and progeny, whereas punishment or danger motivates one to avoid. Approach motivation is thus associated with positive emotion while avoidance motivation with negative valence. Literature also pointed out that the LH is specialized for approach and the RH for avoidance motivation (Davidson &

Fox, 1982; for a review, see Harmon--Jones, Gable & Peterson, 2010). Interestingly, Brookshire and Casasanto (2012) have found that the cerebral lateralization of approach motivation is to the same hemisphere that controls the dominant hand: the hemispheric correlate of approach motivation is lateralized to the LH for the right-handers, but to the RH for the left-handers. In addition to representation of abstract concepts, the body-specificity hypothesis is also exhibited in the interaction between language and action. An fMRI study by Willems, Hagoort & Casasanto (2010) investigated whether the meanings of manual action verbs are grounded in how the particular language users perform the actions. The researchers compared the premotor activation in right- and left-handers during a lexical-decision task on manual-action verbs (e.g. grasp, throw) and non-manual-action verbs (e.g.

kneel, giggle). In the first task, participants viewed the manual-action verbs,

nonmanual-action verbs, pseudowords, and fillers in an fMRI machine. The presentation of a pseudoword or filler stimulus was followed by the screen showing a question of whether the stimulus was an extant word, and the participants should press the key for response as fast as possible.

After the critical stimuli (i.e., manual-action verbs and nonmanual-action verbs) no responses were solicited. In the second task, participants were instructed to mentally imagine

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themselves performing the action denoted by the verb. By comparing the first and the second task, the researchers were able to determine the cerebral activation of viewing the manual-action verbs was not due to the participants’ mental visualization of the verbs. After careful exclusion of the potential confounding factor -- mental imagery, they observed that each group, right- or left-handed, preferentially activated premotor areas in the hemisphere contralateral to their dominant hands, which suggested the body specificity of the motor component in action verb semantics.

In summary, people have implicit preference to their dominant side and that the approach motivation, which is associated with positive emotion, is lateralized to the dominant hemisphere. And since body-specificity has been exhibited in both conceptual representation of positive/negative characteristics and language, it would be informative to see if we can combine the two and explore whether this hypothesis can also be true for emotion word processing.

However, before we move on to the literature about emotion word processing, it is important to note that positive/negative valence has not always been associated with left-right distinction. In fact, in many languages such as English and Chinese, metaphorical expressions tend to associate positive and negative valence with the top and bottom of a vertical spatial continuum (Lakoff & Johnson, 1980, 1999). A happy individual has “high” spirit, but a sad person feels “down.” In Chinese, a smart person has “high” IQ (“高”智商), but a foolish person is “an idiot” (“低”能兒 (literal translation: low ability)). An object of great quality is of “top” class (“頂”級). This High Is Good mapping associates the source domain of physical space with abstract target domain that is of positive valence. These mental metaphors import the inferential structure of source domains like space into target domains, which allows language users to envision, measure and compare the height of excitement or the depth of sadness. (Boroditsky, 2000; Casasanto, 2008; Pinker, 1997)

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It is still under debate as to whether mental metaphors arise from correlations (1) in linguistic experience or (2) in bodily experience. On the first account, it is proposed that mental metaphors are established through experience by using linguistic metaphors. Using spatial words in both literal and metaphorical contexts (e.g., a high shelf, a high standard) in daily life could induce a transfer effect of the structural elements from the concrete source domain to the abstract target domain representations in mind via analogical processes that are not necessarily “embodied” (Boroditsky, 2000; Gentner et al., 2001). For example, in the experiment by Meier & Robinson (2004), participants were faster to judge words like polite and rude as having positive or negative valence when positive words were presented at the top and negative words at the bottom of a computer screen. Linguistic conventions associating valence with vertical space are reinforced by other non-linguistic cultural conventions, such as the “thumbs up” and “thumbs down” gestures signaling approval and disapproval. This account believes that once these linguistic and non-linguistic conventions are part of a culture, they can serve as the basis for metaphorical mappings in the minds of individual learners, diminishing the role of direct bodily experience (Casasanto, 2009).

On the second account, it is said that mental metaphors like Positive Is Up and Negative Is Down could be established as people implicitly learn associations between physical experiences and emotional states that typically co-occur. For instance, people stand tall and raise the chin when feeling proud, slouching and dropping the head when feeling frustrated (Lakoff & Johnson, 1999). Linguistic metaphors later encode the pre-existing mental metaphors developed on the basis of these relationships between different types of bodily experiences. In one experiment, participants assuming an upright posture persisted longer in a puzzle-solving task, as compared to a slouching posture (Riskind & Gotay, 1982), and in another study participants expressed more pride in their test performance after sitting upright during the critical phase of the experiment than after slouching (Stepper & Strack,

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1993). This account proposes that mental metaphors are developed by the implicit reinforcement of the repeated co-occurrence of bodily experience and emotional states.

In sum, although testing the left vs. right preference (i.e. the body-specificity hypothesis) on emotion word processing is the focus of the current study, it is important to note that up vs. down preference might be another interesting topic to pursue to complement the current study.

2.3 Emotion Word Processing

Emotion words are different from non-emotion words. The strong effect of emotional connotation in word reading and writing was confirmed by several studies (Borod, 1992;

Borod et al., 1992; Cicero et al., 1999; Landis, 2006). For example, Landis et al. (1982) reported that aphasic patients, when shown an emotion or non-emotion word, pronounced the emotion word relatively easily. This clearly demonstrated the importance of emotion in language.

Abundant literature has shown greater RH involvement in processing affective words (e.g. Atchley et al., 2003; Graves et al., 1981; Landis, 2006). Atchley et al. (2003) investigated hemispheric lateralization of emotion processing by comparing the performance of clinically depressed, previously depressed, and control individuals on a divided visual field task. The researchers used person-descriptive adjectives (of positive/negative valence) to form a prime-target pair. The pair was either matching for valence, termed related (e.g.

SMART-BRAVE, both positive valence), or not, termed unrelated (e.g. SMART-DIRTY).

All words were presented as white lettering on a black background. A trial consisted of a fixation cross presented for 500 ms, followed by a centrally presented prime displayed for 300ms. A flash mask followed prime presentation. The unilateral targets were then presented

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for 185ms. Specifically, the word presented at the right side of the screen would be in the subject’s right visual field (RVF) and projected to the LH, while the left side of the screen was in the subject’s LVF and words appeared in the LVF would project to the RH. After 185ms the targets were then also masked. Following the presentation of the targets, participants made valence judgement by pressing the key as soon as possible. Results showed no difference between groups in the RVF/LH. However, both the past-depressed and current-depressed groups showed shorter response time (RT) and higher accuracy on negative words presented in the LVF/RH, whereas the non-depressed controls exhibited shorter RT and higher accuracy on positive words in the LVF/RH.

In a study similar to the above, Walsh et al. (2010) also recruited previously-depressed and never-previously-depressed individuals, all right-handed. The previously-depressed subjects were subdivided into Selective Serotonin Reuptake Inhibitors (SSRIs) respondents and SSRIs non-respondents. Participants were instructed to fixate their gaze at the center cross while a mixture of positively and negatively valenced words of high and low arousal appeared one after another on the right or left side to the central cross. The central cross was presented for 1000ms and the target word appeared for 185ms. Then it was followed by a pattern mask (########). The degree of visual angle to the inner edge of the lateralized stimuli was 2°.

After the target onset, the participants had 2500ms to press the key to indicate whether the stimulus was positive or negative. Upon receiving the response from the subject, the experiment automatically moved onto the next trial. The participants were instructed to respond as fast as they could. Any response exceeding 2500ms was deemed incorrect. They found that positive words showed a RVF/LH advantage. Critically the results indicated that the SSRIs non-respondents showed a strong bias toward negative evaluation of words presented to the LVF/RH.

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These two studies confirmed greater RH involvement in processing emotion words, which echoes to previous studies (Graves et al, 1981; Landis, 2006). However, the converging evidence of RH involvement on emotion word processing all came from right-handed participants. Since left-handers represent a population with different cerebral lateralization, it would be illuminating to look into the difference of emotion word processing between right- and left-handers. Therefore, this study adopted the divided visual field paradigm and similar experimental procedure of the above two experiments but included both right-handed and left-handed populations.

2.4 Summary

This chapter first discussed some studies on handedness and its interaction with hemispheric lateralization and then introduced the body-specificity hypothesis before reviewing literature on emotion word processing. To begin with, Section 2.1 discussed manifest handedness as well as familial handedness and their interaction with cerebral lateralization of language. In other words, studies reviewed in this section confirmed the modulation effect of handedness when individuals process language. Section 2.2 introduced the body-specificity hypothesis (Casasanto, 2009), which proposed that individuals with different dominant hands might form different mental representations in that they interact with the physical environment consistently in a different fashion. Specifically, the studies indicated that individuals not only preferred the objects shown at their dominant side of space but also associated positive ideas with their dominant side of space. Aside from the left-right space preference, this section also discussed the top-down associations with positive and negative valence common in the metaphorical expressions (Lakoff & Johnson, 1980, 1999).

Finally Section 2.3 reviewed research on emotion word processing, which exhibited a RH

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advantage in right-handed subjects and also reported different behavioral results with depressed and non-depressed participants.

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Chapter Three

Methods

This chapter illustrates the methods of the current experiment. First of all, the characteristics of the target participants and how they were divided into groups are described in Section 3.1. Experimental materials are introduced in Section 3.2. Then Section 3.3 illustrates how the experiment proceeded. Lastly, how the data were analyzed is depicted in Section 3.4.

3.1 Participants

This study recruited 37 left-handed and 68 right-handed participants, aged 20 to 40 (mean age = 27, 32 males). All of them were native speakers of Mandarin Chinese. All participants were required to have normal or corrected-to-normal vision for the experiment.

Participants with neurological or psychiatric disorders were not considered.

All of the subjects were verified by the Edinburgh handedness inventory (Oldfield, 1971, see Appendix A). Right-handers were further divided into either having familial sinistrals (FS+) or not (FS-) based on whether any of their blood relatives (including parents, siblings, grandparents, uncles, aunts or cousins) was left-handed: the participants who had at least one left-handed family member were categorized as the FS+ group, and the participants who reported no known left-handed family members were in the FS- group.

Aside from the Edinburgh handedness inventory (Oldfield, 1971), the participants also completed the Beck Depression Inventory-second edition in Chinese (BDI-II, see

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Appendix B) to measure the level of depression in the participants since previous research has shown that people who suffered from depression responded to the negative verbal stimuli in the LVF differently from people without depression (Atchley et al, 2003; Walsh et al, 2010). BDI-II is a self-report questionnaire based on Beck et al. (1961). It has 21 questions of

Appendix B) to measure the level of depression in the participants since previous research has shown that people who suffered from depression responded to the negative verbal stimuli in the LVF differently from people without depression (Atchley et al, 2003; Walsh et al, 2010). BDI-II is a self-report questionnaire based on Beck et al. (1961). It has 21 questions of