Are only infants held more often on the left? If so, why? Testing the attention-emotion hypothesis with an infant, a vase, and two chimeric tests, one "emotional," one not.

Most adults, especially women, hold infants and dolls but not books or packages on the left side. One reason may be that attention is more often leftward in response to infants, unlike emotionally neutral objects like books and packages. Women's stronger bias may reflect greater responsiveness to infants. Previously, we tested the attention hypothesis by comparing women's side-of-hold of a doll, book, and package with direction-of-attention on the Chimeric Faces Test (CFT) [Harris, L. J., Cárdenas, R. A., Spradlin, Jr., M. P., & Almerigi, J. B. (2010). Why are infants held on the left? A test of the attention hypothesis with a doll, a book, and a bag. Laterality: Asymmetries of Body, Brain and Cognition, 15(5), 548-571. doi:10.1080/13576500903064018]. Only the doll was held more often to the left, and only for the doll were side-of-hold and CFT scores related, with left-holders showing a stronger left-attention bias than right-holders. In the current study, we tested men and women with a doll and the CFT along with a vase as a neutral object and a "non-emotional" chimeric test. Again, only the doll was held more often to the left, but now, although both chimeric tests showed left-attention biases, scores were unrelated to side-of-hold. Nor were there sex differences. The results support left-hold selectivity but not the attention hypothesis, with or without the element of emotion. They also raise questions about the contribution of sex-of-holder. We conclude with suggestions for addressing these issues.

Why are infants held on the left? A test of the attention hypothesis with a doll, a book, and a bag.

Most adults, especially women, hold infants and objects representing infants, such as dolls, preferentially on the left side. The attention hypothesis credits the effect to left-directed attention for perception of emotionally salient targets, faces being prime examples. Support comes from studies showing stronger left visual hemispace (LVH) biases in left-holders than right-holders on the Chimeric Faces Test (CFT), but control tests with non-social/emotional objects are needed. We therefore observed young women holding a doll, a book, and a bag, and compared their scores with their performance on the CFT. We also assessed their handedness to check on its possible role. Overall, only the doll elicited a significant side bias, with 57% of all holds on the left, 2% in the middle, and 41% on the right. On the CFT, only left-holders had an LVH bias, whereas right-holders had no bias in either direction. Only the doll-hold scores were consistently related to CFT scores, and for none of the objects was handedness related to side-of-hold.

Adults' preferences for side-of-hold as portrayed in paintings of the Madonna and Child.

Most women hold infants on their left side. They do the same when depicted in works of art. Does the latter accurately reflect the real-life bias, the artist's own aesthetic preference, or something else, such as the artist's handedness, sex, direction of attentional bias, or even the artist's own side-preference for holding infants? As a first step to finding out, we showed 272 young adults (85 men, 187 women) 20 pairs of paintings of the Madonna and Child, the original on one side, its mirror-reversal on the other, and asked which one they preferred. Along with assessing the effects of the variables already mentioned, we used equal numbers of paintings originally depicting left-holds and right-holds to control for the possible effects of differences between the paintings other than side-of-hold itself, such as in their colour scheme, background details, and the type of hold shown (e.g., cradle vs seated on lap). Each pair was presented twice, once with the original on the left, once on the right, for a total of 40 trials. Women and men alike more often preferred left-hold images, but the difference was significant only for women. Preferences were also stronger for original left-hold paintings than for the mirror-reversals of original right-hold paintings, suggesting that the originals differed in ways affecting preference beyond those we tried to control. Overall preference for left-hold images was enhanced when the images were on the viewer's left. As for the other variables, they were for the most part unrelated to preferences. The reasons for the preference thus remain unclear but it is evidently affected by multiple variables, with at least some clearly different from those affecting side-of-hold preferences of real mothers holding real infants.

Probing the human brain with stimulating electrodes: the story of Roberts Bartholow's (1874) experiment on Mary Rafferty.

Roberts Bartholow's 1874 experiment on Mary Rafferty is widely cited as the first demonstration, by direct application of stimulating electrodes, of the motor excitability of the human cerebral cortex. The many accounts of the experiment, however, leave certain questions and details unexamined or unresolved, especially about Bartholow's goals, the nature and quality of the evidence, and the experiment's role in the history of theory and research on localisation of function. In this article, we try to fill these gaps and to tell the full story. We describe Bartholow's career up to 1874, review the theoretical and empirical background for the experiment, and present Bartholow's own account of the experiment as well as those of his supporters and critics. We then present our own analysis, assess the experiment's influence on contemporaneous scientific opinion about cortical excitability, and trace its citation record into our own time. We also review and assess ethical criticisms of Bartholow and their effects on his career, and we close by discussing the role we think the experiment deserves to play in the history of theory and research on cortical excitability.

Factors correlated with violent video game use by adolescent boys and girls.

PURPOSE: To compare the video and computer game play patterns of young adolescent boys and girls, including factors correlated with playing violent games. METHODS: Data collected in November/December, 2004 from children in grades 7 and 8 at two demographically diverse schools in Pennsylvania and South Carolina, using a detailed written self-reported survey. RESULTS: Of 1254 participants (53% female, 47% male), only 80 reported playing no electronic games in the previous 6 months. Of 1126 children who listed frequently played game titles, almost half (48.8%) played at least one violent (mature-rated) game regularly (67.9% of boys and 29.2% of girls). One third of boys and 10.7% of girls play games nearly every day; only 1 in 20 plays often or always with a parent. Playing M-rated games is positively correlated (p < .001) with being male, frequent game play, playing with strangers over the Internet, having a game system and computer in one's bedroom, and using games to manage anger. CONCLUSIONS: Most young adolescent boys and many girls routinely play M-rated games. Implications for identifying atypical and potentially harmful patterns of electronic game use are discussed, as well as the need for greater media literacy among parents.

Mothers' and fathers' lateral biases for holding their newborn infants: a study of images from the World Wide Web.

Photographic and direct-observation studies show that most adults hold infants on the left side. This basic directional effect is well established, but other details are still uncorroborated, uncertain, or inconsistent across studies. These include the overall strength of the bias, the role of the sex, parental status, and experience of the holder, and the sex and age of the infant. Given their importance for understanding the bias, we sought further information from a large sample of photographs of mothers and fathers, some of them first-time parents, others not, holding their infants in the first minutes, hours, or days after birth. The results confirmed the basic directional effect and provided information on the other variables. They also raise questions for further research, especially as it pertains to the use of photographs vs direct observation.

Most adults show opposite-side biases in the imagined holding of infants and objects.

Three hundred university undergraduates were asked to imagine holding in their arms first an object (either an "expensive vase" or an "old shoebox") and then a young infant. For all three tasks, side biases were found that were significantly different from chance and from one another: 81% of the subjects reported holding the imagined vase in their right arm, 64% reported holding the imagined shoebox in their right arm, and 66% reported holding the imagined infant in their left arm. These results further support the hypothesis that the left-side bias is unique to infants and, for the first time, establish this through direct comparisons of holding-side biases for infants and objects within subjects. The sex and handedness of the holder as well as the qualities of the imagined object also were found to contribute to the side and strength of the bias.

Task difficulty reduces the left visual hemispace bias for judgments of emotion in chimeric faces.

A prior study (Carbary, Almerigi, & Harris, 2001) of adults' judgments of emotional chimeric faces showed that the left visual hemispace (LVH) bias normally found on a free-viewing chimeric faces test is reduced when the task is judged to be difficult. Taking into account theory and research on hemispheric differences in styles, or strategies, of information processing, we proposed that the reduction was related to a change in these strategies. Two new experiments are presented that independently manipulate task difficulty and show the same task difficulty-related effect as in our prior study. Data are also presented suggesting that the strategy most commonly adopted for difficult judgments is part-based or feature-oriented, whereas the strategy most commonly adopted for easy judgments is reliance on "first impression."

The contribution of postural bias to lateral preferences for holding human infants.

When asked to hold an infant, 60-85% of adults hold on their left, so that the infant's head is to the left of their midline (Brüser, 1981; de Chateau, 1983; Saling & Tyson, 1981). The same group bias has been found even when persons are merely asked to imagine holding an infant (Nakamichi & Takeda, 1995; Harris, Almerigi, & Kirsch, 2000). A number of variables have been found to contribute modestly to the bias, including the sex and handedness of the holder. In the current study, the role of a new variable is investigated, namely, the feeling of comfort for holding an infant on a particular side as indexed by one's foot preference for acts of stabilizing or postural support. To test this hypothesis, 282 right-handed college students (218 women, 64 men) were given the imagine-hold task along with 4 questions about their foot preference for posture and balance. The results showed that, at least for women, the two measures were modestly but significantly related.