Social origins of executive function development

The chapters in this issue revisit the social origins of the development of executive function (EF) through both empirical examination of the contexts in which EF development occurs (in vivo), as well as its social antecedents and consequences. Importantly, they also point to new directions in studying the social foundations of neurodevelopment, novel methods that take the social context into account, and cultural influences on EF development.

Transportation of Pacific salmon carcasses from streams to riparian forests by bears

Predation on Pacific salmon by bears (genus Ursus L., 1758) can be an important ecosystem process because the spatial distribution of carcasses largely determines whether marine-derived nutrients cycle through aquatic or terrestrial pathways. Direct observations on three streams in southeastern Alaska indicated that 49% of the pink ( Oncorhynchus gorbuscha (Walbaum, 1792)) and chum ( Oncorhynchus keta (Walbaum in Artedi, 1792)) salmon killed by bears were carried into the forest. The tendency of bears to transport carcasses was independent of the sex and species of salmon, but unspawned fish were more often transported than fish that had completed spawning. Data on tagged sockeye salmon ( Oncorhynchus nerka (Walbaum in Artedi, 1792)) in one southwestern Alaska stream indicated that 42.6% of the killed salmon were transported, and that higher percentages were transported in years when salmon densities were greater. At six other streams, on average, 68.1% of the sockeye salmon killed were apparently transported away from the stream into the forest. Combining the data from all sites, the proportion of carcasses transported increased with water depth at the site. These results emphasize the role that bears play in mediating the interactions between nutrients from salmon and the terrestrial and aquatic ecosystems, and the variation in carcass distribution among streams and among years.

Does variation in selection imposed by bears drive divergence among populations in the size and shape of sockeye salmon?

Few studies have determined whether formal estimates of selection explain patterns of trait divergence among populations, yet this is one approach for evaluating whether the populations are in equilibria. If adaptive divergence is complete, directional selection should be absent and stabilizing selection should prevail. We estimated natural selection, due to bear predation, acting on the body size and shape of male salmon in three breeding populations that experience differing predation regimes. Our approach was to (1) estimate selection acting within each population on each trait based on an empirical estimate of reproductive activity, (2) test for trait divergence among populations, and (3) test whether selection coefficients were correlated with trait divergence among populations. Stabilizing selection was never significant, indicating that these populations have yet to attain equilibria. Directional selection varied among populations in a manner consistent with trait divergence, indicating ongoing population differentiation. Specifically, the rank order of the creeks in terms of patterns of selection paralleled the rank order in terms of size and shape. The shortest and least deep-bodied males had the highest reproductive activity in the creek with the most intense predation and longer and deeper-bodied males were favored in the creeks with lower predation risk.

Bilingual experience and executive functioning in young children

Advanced inhibitory control skills have been found in bilingual speakers as compared to monolingual controls (Bialystok, 1999). We examined whether this effect is generalized to an unstudied language group (Spanish-English bilingual) and multiple measures of executive function by administering a battery of tasks to 50 kindergarten children drawn from three language groups: native bilinguals, monolinguals (English), and English speakers enrolled in second-language immersion kindergarten. Despite having significantly lower verbal scores and parent education/income level, Spanish-English bilingual children's raw scores did not differ from their peers. After statistically controlling for these factors and age, native bilingual children performed significantly better on the executive function battery than both other groups. Importantly, the relative advantage was significant for tasks that appear to call for managing conflicting attentional demands (Conflict tasks); there was no advantage on impulse-control (Delay tasks). These results advance our understanding of both the generalizability and specificity of the compensatory effects of bilingual experience for children's cognitive development.

Evolutionary consequences of habitat loss for Pacific anadromous salmonids

Large portions of anadromous salmonid habitat in the western United States has been lost because of dams and other blockages. This loss has the potential to affect salmonid evolution through natural selection if the loss is biased, affecting certain types of habitat differentially, and if phenotypic traits correlated with those habitat types are heritable. Habitat loss can also affect salmonid evolution indirectly, by reducing genetic variation and changing its distribution within and among populations. In this paper, we compare the characteristics of lost habitats with currently accessible habitats and review the heritability of traits which show correlations with habitat/environmental gradients. We find that although there is some regional variation, inaccessible habitats tend to be higher in elevation, wetter and both warmer in the summer and colder in the winter than habitats currently available to anadromous salmonids. We present several case studies that demonstrate either a change in phenotypic or life history expression or an apparent reduction in genetic variation associated with habitat blockages. These results suggest that loss of habitat will alter evolutionary trajectories in salmonid populations and Evolutionarily Significant Units. Changes in both selective regime and standing genetic diversity might affect the ability of these taxa to respond to subsequent environmental perturbations. Both natural and anthropogenic and should be considered seriously in developing management and conservation strategies.

A review of quantitative genetic components of fitness in salmonids: implications for adaptation to future change

Salmonine fishes are commonly subjected to strong, novel selective pressures due to anthropogenic activities and global climate change, often resulting in population extinction. Consequently, there is considerable interest in predicting the long-term evolutionary trajectories of extant populations. Knowledge of the genetic architecture of fitness traits is integral to making these predictions. We reviewed the published, peer-reviewed literature for estimates of heritability and genetic correlation for fitness traits in salmonine fishes with two broad goals in mind: summarization of published data and testing for differences among categorical variables (e.g., species, life history type, experimental conditions). Balanced coverage of variables was lacking and estimates for wild populations and behavioral traits were nearly absent. Distributions of heritability estimates were skewed toward low values and distributions of genetic correlations toward large, positive values, suggesting that significant potential for evolution of traits exists. Furthermore, experimental conditions had a direct effect on h (2) estimates, and other variables had more complex effects on h (2) and r G estimates, suggesting that available estimates may be insufficient for use in models to predict evolutionary change in wild populations. Given this and other inherent complicating factors, making accurate predictions of the evolutionary trajectories of salmonine fishes will be a difficult task.

Links between dissociation and role play in a nonclinical sample of preschool children

Children's role play activities are included in symptom checklists of dissociative disorders, yet little is known about the potential relation between individual differences in role play and dissociative behaviors in normative development. This issue was examined in a study of 147 children aged 3 and 4 from a nonclinical population. Parents completed the Child Dissociative Checklist (CDC; F. W. Putnam, K. Helmers, & P. K. Trickett, 1993) and a questionnaire about their child's role play, fears, behavior problems, and dreams. Children were also interviewed about these same items. Dissociation was significantly related to parent report of fears, problem behaviors, and nightmares. These results are consistent with the view that CDC scores reflect some degree of difficulty in children's lives. Children who engaged in role play, particularly children with imaginary companions, scored higher on the CDC than other children. However, role play was not related to the measures of fears or problem behaviors. The results suggest that a distinction between pathological and nonpathological dissociation is warranted, with role play activities being more closely linked to the latter. Measurement of dissociation in preschoolers is discussed.

Trait changes in a harvested population are driven by a dynamic tug-of-war between natural and harvest selection

Selective harvest of large individuals should alter natural adaptive landscapes and drive evolution toward reduced somatic growth and increased reproductive investment. However, few studies have simultaneously considered the relative importance of artificial and natural selection in driving trait changes in wild populations. Using 50 years of individual-based data on Windermere pike (Esox lucius), we show that trait changes tracked the adaptive peak, which moved in the direction imposed by the dominating selective force. Individual lifetime somatic growth decreased at the start of the time series because harvest selection was strong and natural selection was too weak to override the strength of harvest selection. However, natural selection favoring fast somatic growth strengthened across the time series in parallel with the increase in pike abundance and, presumably, cannibalism. Harvest selection was overridden by natural selection when the fishing effort dwindled, triggering a rapid increase in pike somatic growth. The two selective forces appear to have acted in concert during only one short period of prey collapse that favored slow-growing pike. Moreover, increased somatic growth occurred concurrently with a reduction in reproductive investment in young and small female pike, indicating a tradeoff between growth and reproduction. The age-specific amplitude of this change paralleled the age-specific strength of harvest pressure, suggesting that reduced investment was also a response to increased life expectancy. This is the first study to demonstrate that a consideration of both natural selection and artificial selection is needed to fully explain time-varying trait dynamics in harvested populations.

Four decades of opposing natural and human-induced artificial selection acting on Windermere pike (Esox lucius)

The ability of natural selection to drive local adaptation has been appreciated ever since Darwin. Whether human impacts can impede the adaptive process has received less attention. We tested this hypothesis by quantifying natural selection and harvest selection acting on a freshwater fish (pike) over four decades. Across the time series, directional natural selection tended to favour large individuals whereas the fishery targeted large individuals. Moreover, non-linear natural selection tended to favour intermediate sized fish whereas the fishery targeted intermediate sized fish because the smallest and largest individuals were often not captured. Thus, our results unequivocally demonstrate that natural selection and fishery selection often acted in opposite directions within this natural system. Moreover, the two selective factors combined to produce reduced fitness overall and stronger stabilizing selection relative to natural selection acting alone. The long-term ramifications of such human-induced modifications to adaptive landscapes are currently unknown and certainly warrant further investigation.

The development of executive functioning and theory of mind. A comparison of Chinese and U.S. preschoolers

Preschoolers' theory-of-mind development follows a similar age trajectory across many cultures. To determine whether these similarities are related to similar underlying ontogenetic processes, we examined whether the relation between theory of mind and executive function commonly found among U.S. preschoolers is also present among Chinese preschoolers. Preschoolers from Beijing, China (N= 109), were administered theory-of-mind and executive-functioning tasks, and their performance was compared with that of a previously studied sample of U.S. preschoolers (N= 107). The Chinese preschoolers outperformed their U.S. counterparts on all measures of executive functioning, but were not similarly advanced in theory-of-mind reasoning. Nonetheless, individual differences in executive functioning predicted theory of mind for children in both cultures. Thus, the relation between executive functioning and theory of mind is robust across two disparate cultures. These findings shed light on why executive functioning is important for theory-of-mind development.

Developmentally sensitive measures of executive function in preschool children

Changes in executive functioning in the preschool years are recognized as playing a critical role in cognitive and social development, yet comprehensive data and recommendations about measurement of these changes are lacking. The performance of 602 preschool children on several executive function tasks was analyzed and reported as (a) age trends in performance and (b) task difficulty scales at 2, 3, 4, and 5 to 6 years of age. This analysis informs theories of executive function development and offers researchers an evidence-based guide to task selection and design.

Less Is More: Executive Function and Symbolic Representation in Preschool Children

Executive function is recognized as a critical component of children's cognitive and social development. In two studies, a measure of executive function that had been used in research with chimpanzees was adapted for preschoolers. On this task, called Less Is More, children must point to a smaller reward (two candies) to receive a larger reward (five candies). In Study 1 (N= 101), performance was significantly related to age (3 vs. 4), verbal ability, and established measures of executive function. In Study 2 (N= 128), symbolic representations substituted for real candies in this task. Three-year-olds' performance improved significantly as a function of symbolic distancing. This research has implications for the role of symbol systems in the development of executive control over thought and action.

Induction of photosensitivity by heterologous expression of melanopsin

Melanopsin has been proposed to be the photopigment of the intrinsically photosensitive retinal ganglion cells (ipRGCs); these photoreceptors of the mammalian eye drive circadian and pupillary adjustments through direct projections to the brain. Their action spectrum (lambda(max) approximately 480 nm) implicates an opsin and melanopsin is the only opsin known to exist in these cells. Melanopsin is required for ipRGC photosensitivity and for behavioural photoresponses that survive disrupted rod and cone function. Heterologously expressed melanopsin apparently binds retinaldehyde and mediates photic activation of G proteins. However, its amino-acid sequence differs from vertebrate photosensory opsins and some have suggested that melanopsin may be a photoisomerase, providing retinoid chromophore to an unidentified opsin. To determine whether melanopsin is a functional sensory photopigment, here we transiently expressed it in HEK293 cells that stably expressed TRPC3 channels. Light triggered a membrane depolarization in these cells and increased intracellular calcium. The light response resembled that of ipRGCs, with almost identical spectral sensitivity (lambda(max) approximately 479 nm). The phototransduction pathway included Gq or a related G protein, phospholipase C and TRPC3 channels. We conclude that mammalian melanopsin is a functional sensory photopigment, that it is the photopigment of ganglion-cell photoreceptors, and that these photoreceptors may use an invertebrate-like phototransduction cascade.

Preschool children's performance in task switching on the dimensional change card sort task: separating the dimensions aids the ability to switch

Fifty-seven children (53% female) at 3 ages (2 1/2, 3, and 3 1/2 years) were tested on the standard Dimensional Change Card Sort (DCCS) task with integrated stimuli (e.g., a red truck) and on a separated-dimensions version where colorless shapes were presented on a colored background (e.g., a black truck on a red background). Roughly twice as many children successfully switched sorting dimensions when color was a property of the background than when color was a property of the shape itself. Children succeeded 6 months earlier in switching sorting criteria when the dimensions were separated. When evidence of both indecision and accuracy was taken into account, a clear and rich developmental progression emerged. These results support an inhibitory control interpretation of preschoolers' problems on the DCCS task. Diamond theorized that young children can have difficulty integrating features not part of a single object and separating features of a single object so that the object can be categorized first by one attribute and then by another. Preschoolers remain stuck in thinking about objects according to the objects' initially relevant attribute (attentional inertia; Kirkham, Cruess, & Diamond, 2003). To switch perspectives, the old way of thinking about the objects must be inhibited. Separating color and shape reduced the need for such inhibition; a truck was always a truck, and the background was always red.

Gesture as a Window on Children's Beginning Understanding of False Belief

Given that gestures may provide access to transitions in cognitive development, preschoolers' performance on standard tasks was compared with their performance on a new gesture false belief task. Experiment 1 confirmed that children (N=45, M age=54 months) responded consistently on two gesture tasks and that there is dramatic improvement on both the gesture false belief task and a standard task from ages 3 to 5. In 2 subsequent experiments focusing on children in transition with respect to understanding false beliefs (Ns=34 and 70, M age=48 months), there was a significant advantage of gesture over standard and novel verbal-response tasks. Iconic gesture may facilitate reasoning about opaque mental states in children who are rapidly developing concepts of mind.

Reproductive life-span and sources of mortality for alternative male life-history strategies in sockeye salmon, Oncorhynchus nerka

In anadromous salmonid fishes, a fraction of the males ("jacks") spend fewer years at sea than females and most males in the population. It has been hypothesized that the higher survival rates of jacks at sea are balanced by their reduced reproductive success. One component of reproductive success is in-stream longevity, and jacks were reported to have a shorter reproductive life-span than older males. To test this hypothesis, we examined the interactions between arrival date, mode of death (senescent, bear-killed, gull-killed, stranded), and reproductive life-span of male sockeye salmon, Oncorhynchus nerka (Walbaum in Artedi, 1792), in a small Alaskan creek. Of the senescent males, early-arriving fish lived longer than later arrivals, and jacks and older males had similar reproductive life-spans (p = 0.932). Jacks were less susceptible to premature mortality (mostly from bears and gulls) than older males. The life-span of fish that died prematurely was greater for jacks than non-jacks (p < 0.001). Considering all sources of mortality (both premature and senescent), jacks had a greater mean life-span than older males (5.84 vs. 3.12 days; p < 0.001). Despite this fact, jacks are scarce (1.7% in this population), suggesting that they suffer in other components of fitness such as proportion of eggs fertilized.

Individual differences in executive functioning and theory of mind: An investigation of inhibitory control and planning ability

This research examined the relative contributions of two aspects of executive function-inhibitory control and planning ability-to theory of mind in 49 3- and 4-year-olds. Children were given two standard theory of mind measures (Appearance-Reality and False Belief), three inhibitory control tasks (Bear/Dragon, Whisper, and Gift Delay), three planning tasks (Tower of Hanoi, Truck Loading, and Kitten Delivery), and a receptive vocabulary test (Peabody Picture Vocabulary Test [PPVT-3]). Multiple regression analyses indicated that two inhibition tasks (Bear/Dragon and Whisper) were significantly related to theory of mind after accounting for age, receptive vocabulary, and planning. In contrast, the planning tasks did not share unique variance with theory of mind. These results increase our understanding of the specific nature of executive function-theory of mind relations during early childhood.

Executive Function and Theory of Mind: Stability and Prediction From Ages 2 to 3

Several studies have demonstrated a relation between executive functioning (EF) and theory of mind (ToM) in preschoolers, yet the developmental course of this relation remains unknown. Longitudinal stability and EF-ToM relations were examined in 81 children at 24 and 39 months. At Time 1, EF was unrelated to behavioral measures of ToM but was significantly related to parent report of children's internal-state language, independent of vocabulary size. At Time 2, behavioral batteries of EF and ToM were significantly related (r=.50, p<.01). Furthermore, EF (Time 1) significantly predicted ToM (Time 2), independent of several controls. A reciprocal relation (internal-state language --> EF at Time 2) was nonsignificant with the controls included. Individual differences in EF were relatively stable.

The Characteristics and Correlates of Fantasy in School-Age Children: Imaginary Companions, Impersonation, and Social Understanding

Past research with 152 preschoolers found that having an imaginary companion or impersonating an imaginary character was positively correlated with theory of mind performance. Three years later, 100 children from this study were retested to assess the developmental course of play with imaginary companions and impersonation of imaginary characters and how these types of role play were related to emotion understanding, self-perception, and personality. The results showed that school-age children interact with imaginary companions and impersonate imaginary characters as much as preschoolers. Overall, 65% of children up to the age of 7 had imaginary companions at some point during their lives. School-age children who did not impersonate scored lower on emotion understanding. Theory of mind at age 4 predicted emotion understanding 3 years later.

Individual differences in inhibitory control and children's theory of mind

This research examined the relation between individual differences in inhibitory control (IC; a central component of executive functioning) and theory-of-mind (ToM) performance in preschool-age children. Across two sessions, 3- and 4-year-old children (N = 107) were given multitask batteries measuring IC and ToM. Inhibitory control was strongly related to ToM, r = .66, p < .001. This relation remained significant controlling for age, gender, verbal ability, motor sequencing, family size, and performance on pretend-action and mental state control tasks. Inhibitory tasks requiring a novel response in the face of a conflicting prepotent response (Conflict scale) and those requiring the delay of a prepotent response (Delay scale) were significantly related to ToM. The Conflict scale, however, significantly predicted ToM performance over and above the Delay scale and control measures, whereas the Delay scale was not significant in a corresponding analysis. These findings suggest that IC may be a crucial enabling factor for ToM development, possibly affecting both the emergence and expression of mental state knowledge. The implications of the findings for a variety of executive accounts of ToM are discussed.

The role of inhibitory processes in young children's difficulties with deception and false belief

This research examines whether children's difficulties with deception and false belief arise from a lack of inhibitory control rather than from a conceptual deficit. In 3 studies, 3-year-olds deceived frequently under conditions requiring relatively low inhibitory control (e.g., misleading pictorial cues or arrows) but failed to do so under conditions of high inhibitory control (deceptive pointing). Study 2 ruled out that the findings were due to social intimidation: Children were equally successful using an arrow to deceive under anonymous and public conditions. Study 3 indicated that, under well-controlled conditions, children did not reveal greater understanding of false belief in deceptive than nondeceptive conditions. The results of these studies suggest that children may have greater deceptive abilities than some earlier studies indicated, and that the source of their difficulty on deceptive pointing tasks lies in a failure of inhibitory control. More generally, it is argued that children's performance on false belief tasks is also likely to be affected by inhibition deficits.

The relation between individual differences in fantasy and theory of mind

The relation between early fantasy/pretense and children's knowledge about mental life was examined in a study of 152 3- and 4-year-old boys and girls. Children were interviewed about their fantasy lives (e.g., imaginary companions, impersonation of imagined characters) and were given tasks assessing their level of pretend play and verbal intelligence. In a second session 1 week later, children were given a series of theory of mind tasks, including measures of appearance-reality, false belief, representational change, and perspective taking. The theory of mind tasks were significantly intercorrelated with the effects of verbal intelligence and age statistically controlled. Individual differences in fantasy/pretense were assessed by (1) identifying children who created imaginary characters, and (2) extracting factor scores from a combination of interview and behavioral measures. Each of these fantasy assessments was significantly related to the theory of mind performance of the 4-year-old children, independent of verbal intelligence.