Does the side of onset influence symptom severity in Parkinson's disease? A systematic review and meta-analysis.

Parkinson's disease (PD) is a neurodegenerative movement disorder characterized by motor symptoms that initially manifest unilaterally. Whilst some studies indicate that right-side onset is associated with greater symptom severity, others report no differences between right-side and left-side onset patients. The present meta-analysis was thus designed to reconcile inconsistencies in the literature and determine whether side of onset affects PD symptom severity. Following the PRISMA guidelines 1013 studies were initially identified in database and grey literature searches; following title and abstract, and full text, screening 34 studies met the stringent inclusion criteria (n = 2210). Results of the random-effects meta-analysis indicated no difference in symptom severity between PD patients with left-side (n = 1104) and right-side (n = 1106) onset. As such, the meta-analysis suggests that the side of onset should not be used to predict symptom trajectory or to formulate prognoses for PD patients. The current meta-analysis was the first to focus on the relationship between the side of onset and symptom severity in PD. However, the studies included were limited by the common exclusion of left-handed participants. Future research would benefit from exploring other factors that may influence symptom severity and disease progression in PD, such as asymmetric loss of nigrostriatal dopaminergic neurons.

Do Left-Handed Older Adults Have Superior Visual Memories?

On demanding visual memory tasks like the Rey Complex Figure Test and Recognition Trial (RCFT), left-handers often outperform right-handers and participants with mixed handedness. Left-handers' apparent visual memory superiority develops during late childhood and early adolescence and is established by young adulthood. Though many studies have examined RCFT performance in older adults and found that visual memory deteriorates with age, investigations of the relationship between handedness and visual memory abilities in older adults have been scarce. In the present study I sought to determine whether a left-handed RCFT performance advantage would be evident among older adults. I examined RCFT and handedness data from 800 older adults (Females = 152, Males = 648; M age = 69.86, SD = 5.18 years; range 60-85 years), who took part in prior research (Whitehall II Phase 11 sub-study). Among these participants, handedness predicted both immediate and delayed RCFT recall, with left-handers outperforming both mixed- and right-handers and with performance unrelated to gender. The absence of a left-handed advantage for copy accuracy suggests that the effects observed for recall do not stem from differences in participants' perceptual abilities and/or motor control. Instead, these data suggest that left-handers' superior performances stem from their advantage for visual memory. As visual memory predicts both motor learning capacity and motor skill retention in older adults, these results have potentially important implications for rehabilitation efficacy.

Putting your best face forward: Posing biases in psychologists' online portraits.

When posing for portraits the position you adopt influences perceptions. As the left hemiface (controlled by the emotion-dominant right hemisphere) expresses emotion more intensely, left cheek portraits communicate stronger emotion than right cheek portraits. This phenomenon influences perceptions of both emotional expressivity and professional specialisation: while left cheek portraits emphasise emotion, right cheek portraits appear more scientific. When professionals upload photographs online to promote their services, the cheek shown consequently influences perceptions. Given the importance of empathy in establishing a therapeutic alliance, theoretically psychologists would benefit from choosing left cheek portraits to enhance their perceived emotionality. The present study thus examined psychologists' posing biases in photographs uploaded to online "Find a Psychologist" resources. Images (N = 1230) of psychologists were drawn from professional "Find a Psychologist" online databases, and coded for gender, portrait type and cheek shown. Results confirmed that psychologists show a left cheek bias, irrespective of gender and across portrait types (upper body, full body). This distinguishes psychologists from doctors and surgeons: past research reports no cheek bias in photos uploaded to "Find a Doctor" websites. The current findings suggest that psychologists may intuitively select left cheek images to enhance the communication of empathy to potential clients.

Phylogenetic proximity influences humans' depictions of nonhuman primates on Instagram.

Portraits of humans favour the left cheek, with emotion thought to drive this posing asymmetry. In primates the emotion-dominant right hemisphere predominantly controls the left hemiface, rendering the left cheek anatomically more expressive than the right. As perceptions of nonhuman primates vary with genetic relatedness, depictions of nonhuman primates should theoretically be influenced by their phylogenetic proximity to humans. The present study thus examined whether humans depict nonhuman primates showing the left cheek, and whether depictions vary with evolutionary distance. Photographs of nonhuman primates were sourced from Instagram's "Most recent" feed: great apes (#chimpanzee, #bonobo, #gorilla, #orangutan), lesser apes (#gibbon), Old World monkeys (#baboon, #macaque, #proboscismonkey), New World monkeys (#spidermonkey, #marmosetmonkey, #capuchin), and prosimians (#lemur, #slowloris, #tarsier). The first 500 single-subject images for each hashtag (except #slowloris for which 318 images were available) were coded for pose orientation (left, right) and portrait type (head/torso, full body). As anticipated, there was a left cheek bias for great apes but no bias for more distantly related primates. These data thus suggest that depictions of nonhuman primates are implicitly influenced by phylogenetic proximity: the more closely related the primate, the more likely we are to depict them as we do ourselves, showing the left cheek.

Instagram Advertisements Favor the Left Cheek.

The growth of social media has catalyzed a shift in marketing expenditure away from traditional print media. As Instagram posts featuring left cheek poses gain more "likes" than right cheek poses, advertisers and social media influencers would likely benefit from favoring the left cheek. While previous investigations of posing biases in print advertising present a conflicting picture, research has yet to investigate posing biases in Instagram advertisements. Given that left cheek images garner more "likes" than right cheek images, we hypothesized a left cheek bias for Instagram advertisements. Two thousand posts (F = M) were sourced by searching Instagram's "Most Recent" feed using the #ad, and coded for pose orientation, image type, and model gender. As predicted, Instagram advertisements showed a left cheek bias (59.8 percent) that was evident across genders and image types, being stronger for female than male models, and for full body than head and torso poses. As such, these data indicate that the left cheek bias that characterizes painted and photographic portraits extends to paid Instagram promotions. The difference in bias from previous investigations of posing orientation in print media advertisements may reflect the importance of emotion in driving attentional capture in social media's highly competitive and content-overloaded landscape.

Humans' left cheek portrait bias extends to chimpanzees: Depictions of chimps on Instagram.

When posing for portraits, humans favour the left cheek. This preference is argued to stem from the left cheek's greater expressivity: as the left hemiface is predominantly controlled by the emotion-dominant right hemisphere, it expresses emotion more intensely than the right hemiface. Whether this left cheek bias extends to our closest primate relatives, chimpanzees, has yet to be determined. Given that humans and chimpanzees share the same oro-facial musculature and contralateral cortical innervation of the face, it appears probable that humans would also choose to depict chimps showing the more emotional left cheek. This paper thus examined portrait biases in images of chimpanzees. Two thousand photographs were sourced from Instagram's "Most Recent" feed using the #chimpanzee, and coded for pose orientation (left, right) and portrait type (head and torso, full body). As anticipated, there were significantly more left cheek (57.2%) than right cheek images (42.8%), with the bias observed across both head and torso and full body portraits. Thus humans choose to depict chimpanzees just as we depict ourselves: offering the left cheek. As such, these data confirm that the left cheek bias is observed in both human and non-human primates, consistent with an emotion-based account of the orientation preference.

Facing the truth: are there hemifacial differences in the communication of trustworthiness?

As the right hemisphere is dominant for emotion processing, the left cheek expresses emotion more intensely than the right cheek. This prompts a leftward bias: people offer the left cheek to communicate emotion and viewers perceive left cheek poses as more emotive. Perceptions of trustworthiness are positively influenced by emotional expressivity, with smiling faces deemed more trustworthy than neutral faces. Thus as the left hemiface is more emotionally expressive than the right, the present study sought to determine whether people offer the left cheek to communicate trustworthiness, and the right to express untrustworthiness. One hundred and twenty-six participants (57 males, 69 females) completed a posing task asking them to read one of two scenarios (randomly assigned: trusted babysitter; untrustworthy car salesman), consider it for 30 seconds, and then pose for a photograph communicating their trustworthiness or untrustworthiness. Contrary to expectation, binary logistic regression results indicated no posing bias for communicating trustworthiness, however people were more likely to offer the left than right cheek when posing to communicate untrustworthiness. The novel finding of a left cheek bias for untrustworthiness is previously unreported, and highlights the need for future investigations of trustworthiness to examine both sides of the trustworthy coin.

Left cheek poses garner more likes: the effect of pose orientation on Instagram engagement.

In social media's attention economy "likes" are currency; photos showing faces attract more "likes." Previous research has established a left cheek bias in photos uploaded to social media, but whether left cheek poses induce more engagement than right cheek poses remains to be determined. The present study thus examined whether pose orientation influences the number of "likes" and comments garnered by photos uploaded to Instagram. The top 20 single-user Instagram accounts were identified, and the most recent 10 left and 10 right cheek images were selected, resulting in a total of 400 images. The number of "likes" and comments were tallied for each image, netting over 1 billion "likes" and 14 million comments for analysis. Results confirmed that pose orientation influences audience engagement: left cheek poses garner >10% more "likes" than right cheek poses. Gender did not influence "likes". Comments were not affected by either pose orientation or gender, likely reflecting the different levels of effort and motivations involved in "liking" vs. commenting on an image. These data indicate that a seemingly inconsequential turn of the head profoundly impacts audience engagement: left cheek poses gained >330,000 more "likes", offering clear implications for marketers and others in the social media economy.

Born criminal? Differences in structural, functional and behavioural lateralization between criminals and noncriminals.

Over 100 years ago Lombroso [(1876/2006). Criminal man. Durham: Duke University Press] proposed a biological basis for criminality. Based on inspection of criminals' skulls he theorized that an imbalance of the cerebral hemispheres was amongst 18 distinguishing features of the criminal brain. Specifically, criminals were less lateralized than noncriminals. As the advent of neuroscientific techniques makes more fine-grained inspection of differences in brain structure and function possible, we review criminals' and noncriminals' structural, functional, and behavioural lateralization to evaluate the merits of Lombroso's thesis and investigate the evidence for the biological underpinning of criminal behaviour. Although the body of research is presently small, it appears consistent with Lombroso's proposal: criminal psychopaths' brains show atypical structural asymmetries, with reduced right hemisphere grey and white matter volumes, and abnormal interhemispheric connectivity. Functional asymmetries are also atypical, with criminal psychopaths showing a less lateralized cortical response than noncriminals across verbal, visuo-spatial, and emotional tasks. Finally, the incidence of non-right-handedness is higher in criminal than non-criminal populations, consistent with reduced cortical lateralization. Thus despite Lombroso's comparatively primitive and inferential research methods, his conclusion that criminals' lateralization differs from that of noncriminals is borne out by the neuroscientific research. How atypical cortical asymmetries predispose criminal behaviour remains to be determined.

Consistently Showing Your Best Side? Intra-individual Consistency in #Selfie Pose Orientation.

Painted and photographic portraits of others show an asymmetric bias: people favor their left cheek. Both experimental and database studies confirm that the left cheek bias extends to selfies. To date all such selfie studies have been cross-sectional; whether individual selfie-takers tend to consistently favor the same pose orientation, or switch between multiple poses, remains to be determined. The present study thus examined intra-individual consistency in selfie pose orientations. Two hundred selfie-taking participants (100 male and 100 female) were identified by searching #selfie on Instagram. The most recent 10 single-subject selfies for the each of the participants were selected and coded for type of selfie (normal; mirror) and pose orientation (left, midline, right), resulting in a sample of 2000 selfies. Results indicated that selfie-takers do tend to consistently adopt a preferred pose orientation (α = 0.72), with more participants showing an overall left cheek bias (41%) than would be expected by chance (overall right cheek bias = 31.5%; overall midline bias = 19.5%; no overall bias = 8%). Logistic regression modellng, controlling for the repeated measure of participant identity, indicated that sex did not affect pose orientation. However, selfie type proved a significant predictor when comparing left and right cheek poses, with a stronger left cheek bias for mirror than normal selfies. Overall, these novel findings indicate that selfie-takers show intra-individual consistency in pose orientation, and in addition, replicate the previously reported left cheek bias for selfies and other types of portrait, confirming that the left cheek bias also presents within individuals' selfie corpora.

Left cheek bias for emotion perception, but not expression, is established in children aged 3-7 years.

As the left hemiface is controlled by the emotion-dominant right hemisphere, emotion is expressed asymmetrically. Portraits showing a model's left cheek consequently appear more emotive. Though the left cheek bias is well established in adults, it has not been investigated in children. To determine whether the left cheek biases for emotion perception and expression are present and/or develop between the ages of 3 and 7 years, 145 children (71 male, 74 female; M age = 65.49 months) completed two experimental tasks: one assessing biases in emotion perception, and the other assessing biases in emotion expression. Regression analysis confirmed that children aged 3-7 years find left cheek portraits happier than right cheek portraits, and age does not predict the magnitude of the bias. In contrast when asked to pose for a photo expressing happiness children did not show a left cheek bias, with logistic regression confirming that age did not predict posing orientations. These findings indicate that though the left cheek bias for emotion perception is established by age 3, a similar bias for emotion expression is not evident by age 7. This implies that tacit knowledge of the left cheek's greater expressivity is not innate but develops in later childhood/adolescence.

Motor biases do not influence posing orientation in selfies.

When posing for portraits people tend to offer their left cheek. This bias is also evident in selfies: informal photographic self-portraits taken with a smartphone. Mechanical biases have been argued to influence selfie posing orientation (predicting that using the left hand favours a stronger left cheek bias), however this hypothesis has not been directly tested. The present study was thus designed to determine whether motor biases influence selfie pose orientation. Three hundred and twenty participants (F = 159, M = 161) were asked to pose for a selfie "as you really are," and completed a handedness measure; hand used to take the selfie and selfie pose orientation were recorded. Ordinal logistic regression confirmed that neither participant handedness nor hand used to capture the selfie predicted selfie pose orientation. Regardless of sex, handedness, or hand used, participants were more likely to present a midline (49.75%) than a left (26.53%) or right (26.72%) cheek pose. Though handedness was a strong predictor of hand used to capture the selfie (left handers favour the left, and right handers the right, hand), it did not predict posing orientation. These results confirm that selfie cheek biases are not simply a residual effect of the mechanics of taking selfies.

Celebrity chefs put their left cheek forward: Cover image orientation in celebrity cookbooks.

Portrait pose orientations influence perception: the left cheek is more emotionally expressive; females' right cheeks appear more attractive. Posing biases are established in paintings, photographs, and advertisements, however, book covers have not previously been examined. This paper assesses cover image orientation in a book genre that frequently features a cover portrait: the celebrity cookbook. If marketers intuitively choose to enhance chefs' emotional expressivity, left cheek poses should predominate; if attractiveness is more important, right cheek poses will be more frequent for females, with a left or no cheek bias for males. Celebrity cookbook covers (N = 493) were sourced online; identity, portrait orientation, photo type, and sex were coded. For celebrity cookbooks, left cheek covers (39.6%) were more frequent than right cheek (31.6%) or midline covers (28.8%); sex did not predict pose orientation. An interaction between photo type and sex bordered on significance: photo type did not influence females' pose orientation; for males, the left cheek bias present for head and torso images was absent for full body and head only photos. Overall, the left cheek bias for celebrity cookbook covers implies that marketers intuitively select images that make the chefs appear happier and/or more emotionally expressive, enhancing engagement with the audience.

Featural information is sufficient to produce a left cheek bias for happiness perception.

People perceive the left cheek as more emotionally expressive than the right. Both configural and featural information enable the evaluation of emotional expressions; whether they make equivalent contributions to the left cheek bias is undetermined. As scrambling faces disrupts configural processing whilst leaving featural information intact, we investigated whether configural information is necessary, or featural information is sufficient, to induce a left cheek bias for emotion perception. Eighty-one participants (65 F, 16 M) viewed two types of left and right cheek image pairs - normal, scrambled - and indicated which image appeared happier (half mirror-reversed to control for perceptual biases). Results indicated a left cheek bias for both normal and scrambled faces, irrespective of mirror reversal. As scrambling faces disrupts configural processing, the fact that the left cheek was perceived as more expressive even when scrambled confirms that differences between the cheeks' featural information are sufficient to induce the left cheek bias.

Do the Big Five personality traits predict individual differences in the left cheek bias for emotion perception?

Like language, emotion is a lateralized function. Because the right hemisphere typically dominates emotion processing, people express stronger emotion on the left side of their face. This prompts a left cheek bias: we offer the left cheek to express emotion and rate left cheek portraits more emotionally expressive than right cheek portraits. Though the majority of the population show this left cheek bias (60-70%), individual differences exist but remain largely unexplained. Given that people with higher self-rated emotional expressivity show a stronger left cheek bias, personality variables associated with increased emotional expressivity and emotional intelligence, such as extraversion and openness, may help account for individual differences. The present study thus examined whether the Big Five traits predict left cheek preferences. Participants (M = 58, F = 116) completed the NEO-Five Factor Personality Inventory (NEO-FFI) [Costa, P. T. J., & McCrae, R. R. (1992). NEO PI-R professional manual. Odessa, FL: Psychological Assessment Resources] and viewed pairs of left and right cheek images (half mirror-reversed); participants made forced-choice decisions, indicating which image in each pair looked happier. Hierarchical regression indicated that neither trait extraversion nor openness predicted left cheek selections, with NEO-FFI personality subscales accounting for negligible variance in preferences. As the Big Five traits have been discounted, exploration of other potential contributors to individual differences in the left cheek bias is clearly needed.

The perception of positive and negative facial expressions by unilateral stroke patients.

There remains conflict in the literature about the lateralisation of affective face perception. Some studies have reported a right hemisphere advantage irrespective of valence, whereas others have found a left hemisphere advantage for positive, and a right hemisphere advantage for negative, emotion. Differences in injury aetiology and chronicity, proportion of male participants, participant age, and the number of emotions used within a perception task may contribute to these contradictory findings. The present study therefore controlled and/or directly examined the influence of these possible moderators. Right brain-damaged (RBD; n=17), left brain-damaged (LBD; n=17), and healthy control (HC; n=34) participants completed two face perception tasks (identification and discrimination). No group differences in facial expression perception according to valence were found. Across emotions, the RBD group was less accurate thanthe HC group, however RBD and LBD group performancedid not differ. The lack of difference between RBD and LBD groups indicates that both hemispheres are involved in positive and negative expression perception. The inclusion of older adults and the well-defined chronicity range of the brain-damaged participants may have moderated these findings. Participant sex and general face perception ability did not influence performance. Furthermore, while the RBD group was less accurate than the LBD group when the identification task tested two emotions, performance of the two groups was indistinguishable when the number of emotions increased (four or six). This suggests that task demand moderates a study's ability to find hemispheric differences in the perception of facial emotion.

The influence of left and right hemisphere brain damage on configural and featural processing of affective faces.

The literature about the lateralization of facial emotion perception according to valence (positive, negative) is conflicting; investigating the underlying processes may shed light on why some studies show right-hemisphere dominance across valence and other studies demonstrate hemispheric differences according to valence. This is the first clinical study to examine whether the use of configural and featural cues underlies hemispheric differences in affective face perception. Right brain-damaged (RBD; n = 17), left brain-damaged (LBD; n = 17) and healthy control (HC; n = 34) participants completed an affective face discrimination task that tested configural processing using whole faces and featural processing using partial faces. No group differences in expression perception according to valence or processing strategy were found. Across emotions, the RBD group was less accurate than the HC group in discriminating whole faces, whilst the RBD and LBD groups were less accurate than HCs in discriminating partial faces. This suggests that the right hemisphere processes facial expressions from configural and featural information, whereas the left hemisphere relies more heavily on featural facial information.

Reduced interhemispheric interaction in non-autistic individuals with normal but high levels of autism traits.

People with autism spectrum disorder (ASD) show superior performance for tasks requiring detail-focused processing. Atypical neural connectivity and reduced interhemispheric communication are posited to underlie this cognitive advantage. Given recent conceptualization of autism as a continuum, we sought to investigate whether people with normal but high levels of autism like traits (AQ) also exhibit reduced hemispheric interaction. Sixty right-handed participants completed the AQ questionnaire (Baron-Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001) and a lateralised letter matching task that assessed unilateral and bilateral performance in response to simple (physical) and complex (identity) matches. Whereas people with low self-rated AQ scores showed a bilateral advantage for the more complex task, indicating normal interhemispheric interaction, people in the high AQ group failed to show a bilateral gain for the computationally demanding stimuli. This finding of disrupted interhemispheric interaction converges with a dimensional conceptualisation of ASD, suggesting that the structural anomalies of ASD extend to non-autistic individuals with high levels of autism traits.