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Motivational lateralization hypothesis

Author: Dr Simon Moss

Overview

Many scholars have attempted to characterize how the roles and functions of each hemisphere of the brain. The motivational lateralization hypothesis, proposed by Kuhl and Kazen (2008), represents one attempt to integrate many of these perspectives and observations. The key premise is the left hemisphere evokes the motivation to seek power and the right hemisphere evokes the motivation to form affilitative bonds.

Properties of each hemisphere

Monosemantic versus polysemantic representations

According to this model, four key properties differentiate the two hemispheres. The first property relates to whether objects and events are represented as a single concept or as a network of related concepts. Specifically, the left hemisphere, at least in individuals who are right handed, seems to represent objects or event as a single concept, called monosemantic processing. In contrast, the right hemisphere seems to represent all the manifestations and associations of objects or events simultaneously.

As an analogy, in the left hemisphere, a brick might be represented as a constituent of houses, as a paperweight, as a weapon, as a means to chock a car while changing a tire, and so forth, depending on the context. In contrast, in the right hemisphere, all of these properties of the brick would, at least to some extent, be represented in simultaneously.

Sequential versus parallel processing of information

Second, as a consequence of this disparity, the processing of information differs between the hemispheres. That is, in the left hemisphere, objects and events are processed in sequence. In the right hemisphere, objects and events are processed in parallel.

Instrumental versus holistic representations

Third, the principal properties of objects or events that are represented psychologically differ between the hemispheres. Specifically, the left hemisphere primarily represents the functions and utility of objects or events--that is, how these objects and events can be used to fulfill some purpose. In contrast, the right hemisphere does not merely represent the functions and utility of object or events, but also entails a broader network of characteristics, including sensory, perceptual, affective, and temporal features.

Several strands of evidence support this proposition. For example, in a study conducted by Levy and Trevarthen (1976), drawings of objects, such as a cake, were presented to the right or left visual field of split-brain patients. Their task was to identify objects that match this drawing. When the pictures were presented to the right visual field, and thus represented in the left hemisphere, the drawings were matched to objects that were functionally related. A fork was matched to a cake, for example. When the pictures were presented to the left visual field, and thus represented in the right hemisphere, the drawings were matched to objects that were similar on more global properties. A round hat was matched to a cake, for example.

Power versus affiliative motivations

Fourth, the prevailing motivation of individuals also depends on which hemisphere is most active. When the left hemisphere is active, and thus the functions and utility of objects are salient, other individuals are perceived as a means to some end. As a consequence, this hemishpere evokes the motivation to control, utilize, or exploit other individuals to achieve some goal, called a power motivation.

In contrast, when the right hemisphere is active, other individuals are not conceptualized as a means to some end. Accordingly, motivations to interact with other individuals are broader in scope, which fosters an affilitative motivation.

Consistent with this proposition, Kuhl and Kazen (2008) found that inducing a power motivation shifted attention to the right visual field, representing the left hemisphere. In contrast, an affiliative motivation shifted attention to the left visual field, representing the right hemisphere.

In particular, participants learnt to associate schematic pictures and verbal labels, such as the words helpless or love, to specific vignettes, each epitomizing either a power or affiliative motive. For each trial, one of these schematic pictures, together with a verbal label was presented, evoking a power motivation or affiliative motivation. Next, a plus sign appeared on the right or left visual field. Participants pressed a key as soon as this symbol appeared.

Reaction times were more rapid if the plus sign was presented to the right visual field, and hence the left hemisphere, but only if a power motivation had been induced. The opposite pattern of findings were observed when an affilitative motivation had been induced.

Consistency with other findings and theories

Empathy

According to the motivational lateralization hypothesis, the right hemisphere is more likely than is the left hemisphere, in individuals who are right handed, to underpin affiliative motivations. Consistent with this premise, the right hemisphere does seem to facilitate empathy. Empathy, in turn, enables individuals to adopt the perspective of another person and coordinate their interpersonal behaviors, and thus represents an affilitative motivation (Anderson & Keltner, 2002).

Several studies imply what empathy relates to the right hemisphere. For example, recognizing the emotional expressions of other individuals seems to be associated with somatosensory regions in the right hemisphere (Adolphs, Damasio, Tranel, Cooper, & Damasio, 2000). Second, performance on tasks that reflect empathy, such as theory of mind, declines when the ventromedial prefrontal cortex of the right hemisphere is damaged (Shamay-Tsoory, Tomer, Berger, & Aharon-Peretz, 2003). Finally, right smell identification, which is primarily underpinned by right hemispheric processing, but not left smell identification, is correlaed with measures of empathy (Spinella, 2002).

Emotional processing

Many other disparities between the right and left hemispheres can also be ascribed to this motivational lateralization hypothesis. To illustrate, many studies indicate that perhaps the right hemisphere is more likely to underpin the expression and interpretation of emotions. The capacity to express emotions, as well as to interpret the mannerisms and facial expressions of someone else, is perhaps integral to affiliation.

To illustrate this disparity between the right and left hemisphere, in one study, conducted by Nicholls, Clode, Wood, and Wood (1999), some participants were asked to express their emotions while they were photographed. Other participants were asked to conceal their emotions, posing as a scientist, while they were photographed. Interestingly, compared to participants who concealed their emotions, participants who expressed their emotions were more likely to direct the left side of their face towards the camera.

This finding is consistent with the proposition that regions in the right, rather than left, hemisphere primarily underpin the expression of emotions. That is, expressions on the left side of the face are primarily governed by the right hemisphere. As a consequence, if the right hemisphere underpins the expression of emotions, the left side of the face might be more expressive. Indeed, several studies indicate the left side is more expressive (see Borod, Haywood, & Koff, 1997).

Attention

The distribution of attention is underpinned by both the right and left hemispheres. Nevertheless, some facets of attention--in particular, alertness, vigilance, sustained attention, and perhaps divided attention are primarily mediated by regions of the right hemisphere, whereas focused attention is primarily mediated by regions of the left hemisphere (for a review, see McGilchrist, 2009).

Many studies, for example, indicate that lesions to the right hemisphere are more likely than lesions to the left hemisphere to compromise vigilance and sustained attention. To illustrate, as Wilkins, Shallice, and McCathy (1987) showed, lesions to the right frontal lobes are especially likely to affect sustained attention.

In contrast, research indicates that selective or focused attention, in which individuals need to disregard distracters, are more likely to be mediated by the left hemisphere rather than the right hemisphere. Regions like the left caudate or left anterior cingulate are particularly likely to underpin performance on tasks that demand selective attention (Godefroy & Rousseaux, 1996).

These findings are broadly consistent with the proposition that circuits in the right hemisphere are needed to direct attention broadly to novel and unexpected stimuli. In contrast, circuits in the left hemisphere are needed to confine attention to familiar stimuli or concepts. This finding is also consistent with the notion that circuits in the left hemisphere do not process stimuli as holistically& the context is often disregarded.

Skill under pressure

If the left hemisphere tends to represent actions or events sequentially rather than holistically, this hemisphere may disrupt the execution of complex skills--sets of movements that are often executed in parallel. To illustrate, under pressure, many people direct conscious attention to their skills. This attention may be mediated by the left hemisphere and, therefore, compromises the holistic execution of these skills. Activation of the right hemisphere may thus offset this problem and improve performance under pressure.

This possibility was proposed and validated by Beckmann, Gropel, and Ehrlenspiel (2013). In one study, experienced soccer players attempted to kick the ball at holes in a wall--either alone, under limited pressure, or in front of a crowd, under considerable pressure. Before they attempted these kicks, they squeezed a soft ball in either their left or right hand for 30 seconds, intended to activate frontal regions of the right and left hemisphere respectively. Pressure hindered performance only in the people who squeezed their right hand. The right hemisphere, therefore, seemed to override the detrimental effect of pressure on performance. Subsequent studies demonstrated the same pattern is observed in Taekwondo practitioners, performing a combination of kicks, and in badminton players performing serves.

The rightward bias in seat choice

In movies, most individuals prefer to sit on the left side of the screen (Karev, 2000). According to Karev (2000), this finding might align with the proposition that emotional, social, and visual information is primarily processed in the right hemisphere. In particular, when individuals sit on the right side of a movie cinema, most of this information is presented to the left side of individuals and thus processed by the right hemisphere. Furthermore, this information can facilitate the pursuit of affiliation. This bias in seat choice, thus, is arguably consistent with the proposition that regions in the right, rather than left, hemisphere underpin affiliation rather than power.

Nevertheless, alternative explanations have been proposed. According to Weyers, Milnik, Muller, and Pauli (2006), individuals who prefer to use their right hand--the majority of participants--might simply prefer the right side in general. That is, this preference to sit on the right might not be related to whether or not emotional, social, and visual information is presented.

Okubo (2010), however, challenged this alternative explanation and, instead, demonstrated the predilection towards right seats is confined to contexts in which individuals want to process the social and emotional information of the movie. In one study, for example, some participants were informed the movie was recommended by friends. The other participants were informed the movie, although recommended, is depressing and they, hence, should prefer to avoid watching this film. Finally, a seating chart was presented& participants specified their preferred seat on this chart.

If participants had been told they would prefer to avoid this movie, the usual preference to sit on the right side diminished (Okubo, 2010). Presumably, these participants did not want to process the emotional and social information that was depicted in this movie. Therefore, to inhibit this information, they become more inclined to sit on the left side& the information would then be presented to the right side of participants, processed by the left hemisphere, curbing the emotional impact of the movie.

Furthermore, if participants were not right handed, whether or not they were told they would prefer to avoid this movie did not affect the location they chose. When individuals are left rather than right handed, the functions of the left and right hemispheres tend to be similar (see Christman, 1995, for example). Thus, whether these left handed individuals sit on the left or right side of the cinema should not greatly affect their experience.

In a subsequent study, if participants were informed the movie was sad and depressing, but not encouraged to avoid this film, the usual bias in right handed participants was restored. That is, 75% of these participants preferred to sit on the right side of the cinema (Okubo, 2010). Hence, in the previous study, the aversion to sadness, and not the sadness itself, encouraged some participants to avoid the right side of the cinema.

Similarly, Morton, Wearne, Kershner, and McLean (1993) examined the cognitive preferences of individuals who sit on the right or left of a classroom. Participants who sat on the right tended to be more artistic. In contrast, participants who sat on the left tended to be more analytical, reflective of the left hemisphere. Presumably, because they prefer to process information analytically, they sit on the left side to ensure most of the information they receive is directed to the left hemisphere of the brain.

Caveats

Kuhl and Kazen (2008) recognize that many other properties might differentiate the hemispheres. For example, the left hemisphere seems to be related to approach and the right hemisphere seems to be related to avoidance (Davidson, 2003). Furthermore, the left hemisphere seems to be associated with conceptual processing and the right hemisphere seems to be associated with emotional processing (e.g., Gainotti, 2005). The motivational lateralization hypothesis seems to overlap, but not supercede, these dichotomies.

Furthermore, the Kuhl and Kazen (2008) acknowledge the hemispheres should not be conceptualized as unified systems. Instead, each hemisphere entails a set of functional networks (see Kolb & Wishaw, 2003).

Finally, the motivational lateralization hypothesis does not specify whether achievement motivation, the third of the key needs (McClelland, 1985), is related to the left or right hemisphere. Kuhl and Kazen (2008) suspect that achievement motivation might be related to both hemispheres.

Left handed individuals

The motivational lateralization hypothesis most likely applies to only right handed participants. Many studies indicate that functions of the left and right hemisphere are relatively similar in left, rather than right, handed participants (e.g., Bourne, 2008& Christman, 1995). To illustrate, in right handed participants, language is primarily processed by the left hemisphere, and facial expressions as well as spatial relations are primarily processed by the right hemisphere. These disparities between the hemispheres, however, diminish in left handed individuals (Hellige, Bloch, Cowin, Eng, Eviatar, & Sergent, 1994).

References

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Last Update: 5/24/2016