Scott M. Hardie

The valence-specific laterality effect in free viewing conditions: The influence of sex, handedness, and response bias

The right hemisphere has often been viewed as having a dominant role in the processing of emotional information. Other evidence indicates that both hemispheres process emotional information but their involvement is valence specific, with the right hemisphere dealing with negative emotions and the left hemisphere preferentially processing positive emotions. This has been found under both restricted (Reuter-Lorenz & Davidson, 1981) and free viewing conditions (Jansari, Tranel, & Adophs, 2000). It remains unclear whether the valence-specific laterality effect is also sex specific or is influenced by the handedness of participants. To explore this issue we repeated Jansari et al.s free-viewing laterality task with 78 participants. We found a valence-specific laterality effect in women but not men, with women discriminating negative emotional expressions more accurately when the face was presented on the left-hand side and discriminating positive emotions more accurately when those faces were presented on the right-hand side. These results indicate that under free viewing conditions women are more lateralised for the processing of facial emotion than are men. Handedness did not affect the lateralised processing of facial emotion. Finally, participants demonstrated a response bias on control trials, where facial emotion did not differ between the faces. Participants selected the left-hand side more frequently when they believed the expression was negative and the right-hand side more frequently when they believed the expression was positive. This response bias can cause a spurious valence-specific laterality effect which might have contributed to the conflicting findings within the literature.

Vigilance in Single- and Mixed-Species Groups of Tamarins (Saguinus labiatus and Saguinus fuscicollis)

By forming larger sizes of groups, individuals benefit from a decrease in vigilance, but the collective vigilance of the group as a whole is not compromised. We examined whether this group size effect is apparent in mixed-species groups of red-bellied tamarins (S. labiatus) and saddleback tamarins (S. fuscicollis) which form stable and permanent associations in the wild. We studied general vigilance and responses to hidden threatening stimuli in five captive groups of each species, while they were housed in single- and mixed-species groups. For vigilance, the individual rate was lower in the larger mixed-species groups than in the smaller single-species groups. In addition, the amount of time when at least one individual was vigilant was higher in mixed-species groups. This suggests that the tamarins alter their vigilance behavior in the presence of the other species. In response to hidden threats, both species performed brief vigilance checks and frequencies of checking did not differ in single- and mixed-species groups. However, both species had a significant reduction in the mean duration per check, and there was a reduced total amount of time spent vigilance checking in the mixed-species groups compared to the single-species groups, demonstrating the group size effect. Overall the mixed-species groups had a higher number and mean duration of checking than the smaller single-species groups. Given that the two species share a common set of predators, and respond to each others alarm calls, these findings provide strong evidence that individuals of both tamarin species may be able to benefit from forming mixed-species groups via improved vigilance and monitoring of threats.

Are left-handers really more anxious?

Research examining anxiety and handedness is inconclusive. Davidson and Schaffer (1983) found left-handers had higher trait anxiety, while Beaton and Moseley (1991) found no state or trait differences. Such studies potentially have methodological issues, and we have argued that handedness related reactivity differences (Wright & Hardie, 2011) suggest that state anxiety needs to be measured within a context. Thus the current study investigated state and trait anxiety levels in an experimental situation. We found left-handers had significantly higher state scores, supporting the right hemispheres role in negative affect and inhibition. It also fits with predictions based on the behavioural inhibition systems role in the revised reinforcement sensitivity theory (rRST). No trait differences were found, but there was a significant relationship between trait and state anxiety. Using ANCOVA to control for the influence of trait anxiety on state anxiety, we still found a handedness effect. When participants trait anxiety levels were similar, left-handers showed a relatively larger state response. We conclude that in the context of an experiment, state anxiety was directly correlated with trait anxiety but that the relatively higher reactivity of left-handers may be a major influence on how they respond in a new situation.

Differences between left- and right-handers in approach/avoidance motivation: influence of consistency of handedness measures.

Hand preference is often viewed as a troublesome variable in psychological research, with left-handers routinely excluded from studies. Contrary to this, a body of evidence has shown hand preference to be a useful variable when examining human behavior. A recent review argues that the most effective way of using handedness as a variable, is a comparison between individuals who use their dominant hand for virtually all manual activities (consistent handers) versus those who use their other hand for at least one activity (inconsistent handers). The authors contend that researchers should only focus on degree of handedness rather than direction of preference (left versus right). However, we argue that the field suffers from a number of methodological and empirical issues. These include a lack of consensus in choice of cut-off point to divide consistent and inconsistent categories and importantly a paucity of data from left-handers. Consequentially, researchers predominantly compare inconsistent versus consistent right-handers, largely linked to memory, cognition and language. Other research on response style and personality measures shows robust direction of handedness effects. The present study examines both strength and direction of handedness on self-reported behavioral inhibition system (BIS) and behavioral activation system (BAS) scores, using evidence from a large (N = 689) dataset including more than 200 left-handers. There were degree of handedness effects on BIS and BAS-Fun Seeking, but effects are largely driven by differences between consistent left-handers and other groups. Choice of cut-off point substantively influenced results, and suggests that unless a suitable sample of left-handers is included, researchers clarify that their degree of handedness effects are applicable only to right-handers. We concur that strength of hand preference is an important variable but caution that differences related to consistency may not be identical in right and left-handers.

Pause before you respond: handedness influences response style on the Tower of Hanoi task

Comparative laterality research has indicated that marmoset monkeys with a right‐hand preference take less time to respond to novel objects within a novel environment (Cameron & Rogers, 1999). This suggests that right hemisphere dominance may be associated with a more cautious cognitive style in novel situations. The present study tested this hypothesis using right‐ and left‐handed human participants to complete a three‐disk Tower of Hanoi (TOH) task. It was hypothesised that left‐handers would be slower to initiate responding. A total of 84 participants (42 left‐handers, 42 right‐handers) took part and the time taken to make the first move, completion time, and the number of moves taken to complete the task were recorded. Analysis of Variance revealed a significant main effect of handedness, with left‐handers taking longer to move the first disk and significantly fewer moves to complete the task. However, left‐handers were not significantly faster at completing the TOH, although males completed the task more quickly than females. These initial findings support the hypothesis that left‐hand dominance is associated with a more cautious cognitive style in novel problem‐solving situations.

Distribution and Forest Utilization of Saguinus and Other Primates of the Pando Department, Northern Bolivia

We carried out a 4-month census of primates in the Pando Department of northern Bolivia with special emphasis on Saguinus species. Contrary to a previous report by Izawa and Bejarano (1981), there was no evidence for the presence of the two populations of Saguinus mystax that they reported, or that Lagothrix occurs in the Pando. In addition, we found the distribution of Saguinus imperator to be more restricted than they suggested. We confirm the presence of Cebuella south of the Río Tahuamanu (cf. Brown and Rumiz, 1986) and report two new locations for Callimico goeldii. We present data on group sizes, habitat utilization, and locomotor behavior of the primates and compare them with previous studies in the Pando. Differences in body size, diet, foraging techniques, and vertical use of the forest appear to be key factors in both sympatry and in the formation of polyspecific associations.

Analysing the effects of group size and food competition on Japanese macaque social relationships

Socio-ecological models predict group size to be one major factor affecting the level of food competition. The aims of this study were to analyse how grooming distribution and reconciliation were affected by differences in group size and food competition in a habitat where predation risk is absent. Data were collected on two groups of different size of wild Japanese macaques (Macaca fuscata yakui), living on Yakushima Island, Japan. The large group faced a greater level of intra-group scramble and a lower level of inter-group food competition. However, intra-group food competition appeared to be greater in the small group as evidenced by the stronger rank-related effects on diet composition in the small group. Grooming and reconciliation were more matrilineally kin-biased and more directed toward close-ranking monkeys in the small group than in the large group. Reconciliation was more frequent in the small group, but monkeys in the large group spent more time grooming and had a greater number of grooming partners. These results indicate that social relationships within the two groups were the result of the combination of group size differences and of the balance between the benefits and costs of a lower/greater level of inter- and intra-group food competition.

Tamarin Mixed-Species Groups: An Evaluation of a Combined Captive and Field Approach

The geographical distributions of the tamarins Saguinus mystax, S. imperator and S. lahiatus do not overlap, but each of these species is sympatric with

Responses of Captive Single- and Mixed-Species Groups of Saguinus to Novel Nonthreatening Objects

The provision of novel objects allows one to probe for behavioural differences among species. This is particularly relevant when studying species that form mixed-species groups, as divergent responses may provide clues to the advantages that individuals gain from associating. We compared the responsiveness to novel objects in captive single- and mixed-species groups of saddleback (Saguinus fuscicollis) and red-bellied (Saguinus labiatus) tamarins to determine the influence of a congener. We tested groups with novel objects placed near the top, the middle, and on the floor of their enclosures and measured latency to approach and touch them. We tested predictions related to differences in lifestyle patterns under natural conditions. As we predicted, S.labiatus, which usually occur at a higher mean height in the forest than their congeners, responded to objects placed near the top of the enclosure significantly quicker in both single- and mixed-species groups. S. fuscicollis responded to objects placed on the floor quicker, and in mixed-species groups S. fuscicollis approached them before S. labiatus did. There were specific differences in median touch–approach time (T-A): Saguinus fuscicollis had a shorter T-A time than that of S. labiatus, which can be related to their manipulative foraging style. Reaction times decreased in mixed-species trials for both species, suggesting that the reaction of one species may effect the congener. Both species may benefit through association, though the dominance of Saguinus labiatus over S. fuscicollis may limit the advantages to S. fuscicollis. Over all our study supports the idea that cross-specific social facilitation is an important consequence of mixed-species groups of Saguinus.

The enigma of facial asymmetry: is there a gender-specific pattern of facedness?

Although facial symmetry correlates with facial attractiveness, human faces are often far from symmetrical with one side frequently being larger than the other (Kowner, 1998). Smith (2000) reported that male and female faces were asymmetrical in opposite directions, with males having a larger area on the left side compared to the right side, and females having a larger right side compared to the left side. The present study attempted to replicate and extend this finding. Two databases of facial images from Stirling and St Andrews Universities, consisting of 180 and 122 faces respectively, and a third set of 62 faces collected at Abertay University, were used to examine Smiths findings. Smiths unique method of calculating the size of each hemiface was applied to each set. For the Stirling and St Andrews sets a computer program did this automatically and for the Abertay set it was done manually. No significant overall effect of gender on facial area asymmetry was found. However, the St Andrews sample demonstrated a similar effect to that found by Smith, with females having a significantly larger mean area of right hemiface and males having a larger left hemiface. In addition, for the Abertay faces handedness had a significant effect on facial asymmetry with right-handers having a larger left side of the face. These findings give limited support for Smiths results but also suggest that finding such an asymmetry may depend on some as yet unidentified factors inherent in some methods of image collection.