The Value of Emotion: How Does Episodic Prospection Modulate Delay Discounting?

Background

Humans often show impatience when making intertemporal choice for monetary rewards, preferring small rewards delivered immediately to larger rewards delivered after a delay, which reflects a fundamental psychological principle: delay discounting. However, we propose that episodic prospection humans can vividly envisage exerts a strong and broad influence on individuals'' delay discounting. Specifically, episodic prospection may affect individuals'' intertemporal choice by the negative or positive emotion of prospection.

Methodology/Principal Findings

The present study explored how episodic prospection modulated delay discounting by emotion. Study 1 showed that participants were more inclined to choose the delayed but larger rewards when they imaged positive future events than when they did not image events; Study 2 showed that participants were more inclined to choose the immediate but smaller rewards when they imaged negative future events than when they did not image events; In contrast, study 3 showed that choice preferences of participants when they imaged neutral future events were the same as when they did not image events.

Conclusions/Significance

By manipulating the emotion valence of episodic prospection, our findings suggested that positive emotion made individuals tend to choose delayed rewards, while negative emotion made individuals tend to choose immediate rewards. Only imaging events with neutral emotion did not affect individuals'' choice preference. Thus, the valence of imaged future events'' emotion might play an important role in individuals'' intertemporal choice. It is possible that the valence of emotion may affect the changed direction (promote or inhibit) of individuals'' delay discounting, while the ability to image future events affects the changed degree of individuals'' delay discounting.     

Changes in Socioeconomic Inequality in Indonesian Children’s Cognitive Function from 2000 to 2007: A Decomposition Analysis

Background

Measuring social inequalities in health is common; however, research examining inequalities in child cognitive function is more limited. We investigated household expenditure-related inequality in children’s cognitive function in Indonesia in 2000 and 2007, the contributors to inequality in both time periods, and changes in the contributors to cognitive function inequalities between the periods.

Methods

Data from the 2000 and 2007 round of the Indonesian Family Life Survey (IFLS) were used. Study participants were children aged 7–14 years (n = 6179 and n = 6680 in 2000 and 2007, respectively). The relative concentration index (RCI) was used to measure the magnitude of inequality. Contribution of various contributors to inequality was estimated by decomposing the concentration index in 2000 and 2007. Oaxaca-type decomposition was used to estimate changes in contributors to inequality between 2000 and 2007.

Results

Expenditure inequality decreased by 45% from an RCI = 0.29 (95% CI 0.22 to 0.36) in 2000 to 0.16 (95% CI 0.13 to 0.20) in 2007 but the burden of poorer cognitive function was higher among the disadvantaged in both years. The largest contributors to inequality in child cognitive function were inequalities in per capita expenditure, use of improved sanitation and maternal high school attendance. Changes in maternal high school participation (27%), use of improved sanitation (25%) and per capita expenditures (18%) were largely responsible for the decreasing inequality in children’s cognitive function between 2000 and 2007.

Conclusions

Government policy to increase basic education coverage for women along with economic growth may have influenced gains in children’s cognitive function and reductions in inequalities in Indonesia.     

The foraging movements of bumblebees on vertical “inflorescences”: An experimental analysis

Summary The bumblebees,Bombus edwardsii, move upward while visiting consecutive flowers on artificial inflorescences. This response is unrelated to the vertical patterning of rewards in the flowers of inflorescences. However, when rewards are greatest in the bottommost flowers the bees learn to start lower and leave before reaching the topmost (empty) flowers. Conversely, when rewards are greatest in the topmost flowers they tend to start in the middle of the inflorescence and depart from the top. When rewards are equal in all flowers bees start near the bottom and depart near the top of inflorescences. These behavioral patterns tend to maximize the number of visits to rewarding flowers while minimizing visits to non-rewarding flowers, thereby enhancing foraging returns.Supported by NSF grant DEB77-08430.     

Comparison of Statistical and Clinical Predictions of Functional Outcome after Ischemic Stroke

Background

To determine whether the predictions of functional outcome after ischemic stroke made at the bedside using a doctor’s clinical experience were more or less accurate than the predictions made by clinical prediction models (CPMs).

Methods and Findings

A prospective cohort study of nine hundred and thirty one ischemic stroke patients recruited consecutively at the outpatient, inpatient and emergency departments of the Western General Hospital, Edinburgh between 2002 and 2005. Doctors made informal predictions of six month functional outcome on the Oxford Handicap Scale (OHS). Patients were followed up at six months with a validated postal questionnaire. For each patient we calculated the absolute predicted risk of death or dependence (OHS≥3) using five previously described CPMs. The specificity of a doctor’s informal predictions of OHS≥3 at six months was good 0.96 (95% CI: 0.94 to 0.97) and similar to CPMs (range 0.94 to 0.96); however the sensitivity of both informal clinical predictions 0.44 (95% CI: 0.39 to 0.49) and clinical prediction models (range 0.38 to 0.45) was poor. The prediction of the level of disability after stroke was similar for informal clinical predictions (ordinal c-statistic 0.74 with 95% CI 0.72 to 0.76) and CPMs (range 0.69 to 0.75). No patient or clinician characteristic affected the accuracy of informal predictions, though predictions were more accurate in outpatients.

Conclusions

CPMs are at least as good as informal clinical predictions in discriminating between good and bad functional outcome after ischemic stroke. The place of these models in clinical practice has yet to be determined.     

Informal Child Care and Adolescent Psychological Well-Being: Hong Kong’s “Children of 1997” Birth Cohort

Background

Informal child care (child care by untrained family members, relatives or employees in the home) in Western populations is often associated with poorer psychological well-being, which may be confounded by socioeconomic position. We examined the association of informal child care, common in non-Western settings, with adolescent psychological well-being, using Hong Kong’s Chinese “Children of 1997” birth cohort.

Methods

Multivariable linear regression was used to examine the adjusted associations of informal child care (at 0.5, 3, 5 and 11 years) with parent-reported Rutter score for child behavior at 11 years, self-reported Culture-Free Self-Esteem Inventories score at 11 years and self-reported Patient Health Questionnaire-9 depressive symptom score at 13 years. Model comparisons were used to identify the best representation of child care, in terms of a critical period of exposure to informal child care (independent variable) at a specific age, combination of exposures to informal child care at several ages or an accumulation of exposures to informal child care.

Results

Child care was not associated with behavioral problems. A model considering child care at 3 years best represented the association of child care with self-esteem while a model considering child care at 5 years best represented the association of child care with depressive symptoms. Informal child care at 3 years was associated with lower self-esteem (-0.70, 95% confidence interval (CI) -1.26 to -0.14). Informal child care at 5 years was associated with more depressive symptoms (0.45, 95% CI 0.17 to 0.73).

Conclusion

In a developed non-Western setting, informal child care was associated with lower self-esteem and more depressive symptoms.     

Processing of social and monetary rewards in the human striatum

Despite an increasing focus on the neural basis of human decision making in neuroscience, relatively little attention has been paid to decision making in social settings. Moreover, although human social decision making has been explored in a social psychology context, few neural explanations for the observed findings have been considered. To bridge this gap and improve models of human social decision making, we investigated whether acquiring a good reputation, which is an important incentive in human social behaviors, activates the same reward circuitry as monetary rewards. In total, 19 subjects participated in functional magnetic resonance imaging (fMRI) experiments involving monetary and social rewards. The acquisition of one's good reputation robustly activated reward-related brain areas, notably the striatum, and these overlapped with the areas activated by monetary rewards. Our findings support the idea of a "common neural currency" for rewards and represent an important first step toward a neural explanation for complex human social behaviors.     

Protection Motivation Theory in Predicting Intention to Engage in Protective Behaviors against Schistosomiasis among Middle School Students in Rural China

Background

Among millions of people who suffer from schistosomiasis in China, adolescents are at increased risk to be infected. However, there is a lack of theory-guided behavioral prevention intervention programs to protect these adolescents. This study attempted to apply the Protection Motivation Theory (PMT) in predicting intentions to engage in protective behaviors against schistosomiasis infection.

Methods

The participants were selected using the stratified cluster sampling method. Survey data were collected using anonymous self-reported questionnaire. The advanced structural equation modeling (SEM) method was utilized to assess the complex relationship among schistosomiasis knowledge, previous risk exposure and protective measures in predicting intentions to engage in protective behavior through the PMT constructs.

Principal Findings

Approximately 70% of participants reported they were always aware of schistosomiasis before exposure to water with endemic schistosomiasis, 6% of the participants reported frequency of weekly or monthly prior exposure to snail-conditioned water. 74% of participants reported having always engaged in protective behaviors in the past three months. Approximately 7% were unlikely or very unlikely to avoid contact with snail-conditioned water, and to use protective behaviors before exposure. Results from SEM analysis indicated that both schistosomiasis knowledge and prior exposure to schistosomiasis were indirectly related to behavior intentions through intrinsic rewards and self-efficacy; prior protective behaviors were indirectly related to behavior intentions through severity, intrinsic rewards and self-efficacy, while awareness had an indirect relationship with behavior intentions through self-efficacy. Among the seven PMT constructs, severity, intrinsic rewards and self-efficacy were significantly associated with behavior intentions.

Conclusions

The PMT can be used to predict the intention to engage in protective behaviors against schistosomiasis. Schistosomiasis intervention programs should focus on the severity, intrinsic rewards and self-efficacy of protection motivation, and also increase the awareness of infection, and enrich the contents of schistosomiasis education.     

Competition for trophies triggers male generosity

Background

Cooperation is indispensable in human societies, and much progress has been made towards understanding human pro-social decisions. Formal incentives, such as punishment, are suggested as potential effective approaches despite the fact that punishment can crowd out intrinsic motives for cooperation and detrimentally impact efficiency. At the same time, evolutionary biologists have long recognized that cooperation, especially food sharing, is typically efficiently organized in groups living on wild foods, even absent formal economic incentives. Despite its evident importance, the source of this voluntary compliance remains largely uninformed. Drawing on costly signaling theory, and in light of the widely established competitive nature of males, we hypothesize that unique and displayable rewards (trophies) out of competition may trigger male generosity in competitive social environments.

Principal Findings

Here, we use a controlled laboratory experiment to show that cooperation is sustained in a generosity competition with trophy rewards, but breaks down in the same environment with equally valuable but non-unique and non-displayable rewards. Further, we find that males'' competition for trophies is the driving force behind treatment differences. In contrast, it appears that female competitiveness is not modulated by trophy rewards.

Significance

Our results suggest new approaches to promoting cooperation in human groups that, unlike punishment mechanisms, do not sacrifice efficiency. This could have important implications in any domain where voluntary compliance matters — including relations between spouses, employers and employees, market transactions, and conformity to legal standards.     

Serotonin differentially regulates short- and long-term prediction of rewards in the ventral and dorsal striatum

Background

The ability to select an action by considering both delays and amount of reward outcome is critical for maximizing long-term benefits. Although previous animal experiments on impulsivity have suggested a role of serotonin in behaviors requiring prediction of delayed rewards, the underlying neural mechanism is unclear.

Methodology/Principal Findings

To elucidate the role of serotonin in the evaluation of delayed rewards, we performed a functional brain imaging experiment in which subjects chose small-immediate or large-delayed liquid rewards under dietary regulation of tryptophan, a precursor of serotonin. A model-based analysis revealed that the activity of the ventral part of the striatum was correlated with reward prediction at shorter time scales, and this correlated activity was stronger at low serotonin levels. By contrast, the activity of the dorsal part of the striatum was correlated with reward prediction at longer time scales, and this correlated activity was stronger at high serotonin levels.

Conclusions/Significance

Our results suggest that serotonin controls the time scale of reward prediction by differentially regulating activities within the striatum.     

Willingness-to-Pay for Community-Based Health Insurance among Informal Workers in Urban Bangladesh

Introduction

Reliance on out-of-pocket payment for healthcare may lead poor households to undertake catastrophic health expenditure, and risk-pooling mechanisms have been recommended to mitigate such burdens for households in Bangladesh. About 88% of the population of Bangladesh depends on work in the informal sector. We aimed to estimate willingness-to-pay (WTP) for CBHI and identify its determinants among three categories of urban informal workers rickshaw-pullers, shopkeepers and restaurant workers.

Methods

The bidding game version of contingent valuation method was used to estimate weekly WTP. In three urban locations 557 workers were interviewed using a structured questionnaire during 2010 and 2011. Multiple-regression analysis was used to predict WTP by demographic and household characteristics, occupation, education level and past illness.

Results

WTP for a CBHI scheme was expressed by 86.7% of informal workers. Weekly average WTP was 22.8 BDT [Bangladeshi Taka; 95% confidence interval (CI) 20.9–24.8] or 0.32 USD and varied significantly across occupational groups (p = 0.000) and locations (p = 0.003). WTP was highest among rickshaw-pullers (28.2 BDT or 0.40 USD; 95% CI: 24.7–31.7), followed by restaurant workers (20.4 BDT 0.29 USD; 95% CI: 17.0–23.8) and shopkeepers (19.2 BDT or 0.27 USD; 95% CI: 16.1–22.4). Multiple regression analysis identified monthly income, occupation, geographical location and educational level as the key determinants of WTP. WTP increased 0.196% with each 1% increase in monthly income, and was 26.9% lower among workers with up to a primary level of education versus those with higher than primary, but less than one year of education.

Conclusion

Informal workers in urban areas thus are willing to pay for CBHI and socioeconomic differences explain the magnitude of WTP. The policy maker might think introducing community-based model including public-community partnership model for healthcare financing of informal workers. Decision making regarding the implementation of such schemes should consider worker location and occupation.     

Informal Exchange Networks in Formal Systems: A Theoretical Model

Studies of the informal economy in the Third World have evolved toward defining the informal sector in relationship to the state. This article analyzes some activities that escape the control of the state, with special attention to centrally planned economies. Informal exchanges include bureaucratic favors ("connections"), clientelism, different forms of corruption, and the "parallel" system of production and marketing. I show that economic laws are not sufficient to understand the logic of these economies.     

Changes in Health Care Expenditure after the Loss of a Spouse: Data on 6,487 Older Widows and Widowers in the Netherlands

Background

In ageing populations, informal care holds great potential to limit rising health care expenditure. The majority of informal care is delivered by spouses. The loss of informal care due to the death of the spouse could therefore increase expenditure levels for formal care.

Objective

To investigate the impact of the death of the spouse on health care expenditure by older people through time. Additionally, to examine whether the impact differs between socio-demographic groups, and what health services are affected most.

Design

Longitudinal data on health care expenditure (from July 2007 through 2010) from a regional Dutch health care insurer was matched with data on marital status (2004–2011) from the Central Bureau of Statistics. Linear mixed models with log transformed health care expenditure, generalized linear models and two-part models were used to retrieve standardized levels of monthly health care expenditure of 6,487 older widowed subjects in the 42 months before and after the loss of the spouse.

Results

Mean monthly health care expenditure in married subjects was €502 in the 42 months before the death of the spouse, and expenditure levels rose by €239 (48%) in the 42 months after the death of the spouse. The increase in expenditure after the death of the spouse was highest for men (€319; 59%) and the oldest old (€553; 82%). Expenditure levels showed the highest increase for hospital and home care services (together €166).

Conclusions

The loss of the spouse is associated with an increase in health care expenditure. The relatively high rise in long-term care expenses suggests that the loss of informal care is an important determinant of this rise.     

Informal Urban Settlements and Cholera Risk in Dar es Salaam,Tanzania

Background

As a result of poor economic opportunities and an increasing shortage of affordable housing, much of the spatial growth in many of the world''s fastest-growing cities is a result of the expansion of informal settlements where residents live without security of tenure and with limited access to basic infrastructure. Although inadequate water and sanitation facilities, crowding and other poor living conditions can have a significant impact on the spread of infectious diseases, analyses relating these diseases to ongoing global urbanization, especially at the neighborhood and household level in informal settlements, have been infrequent. To begin to address this deficiency, we analyzed urban environmental data and the burden of cholera in Dar es Salaam, Tanzania.

Methodology/Principal Findings

Cholera incidence was examined in relation to the percentage of a ward''s residents who were informal, the percentage of a ward''s informal residents without an improved water source, the percentage of a ward''s informal residents without improved sanitation, distance to the nearest cholera treatment facility, population density, median asset index score in informal areas, and presence or absence of major roads. We found that cholera incidence was most closely associated with informal housing, population density, and the income level of informal residents. Using data available in this study, our model would suggest nearly a one percent increase in cholera incidence for every percentage point increase in informal residents, approximately a two percent increase in cholera incidence for every increase in population density of 1000 people per km² in Dar es Salaam in 2006, and close to a fifty percent decrease in cholera incidence in wards where informal residents had minimally improved income levels, as measured by ownership of a radio or CD player on average, in comparison to wards where informal residents did not own any items about which they were asked. In this study, the range of access to improved sanitation and improved water sources was quite narrow at the ward level, limiting our ability to discern relationships between these variables and cholera incidence. Analysis at the individual household level for these variables would be of interest.

Conclusions/Significance

Our results suggest that ongoing global urbanization coupled with urban poverty will be associated with increased risks for certain infectious diseases, such as cholera, underscoring the need for improved infrastructure and planning as the world''s urban population continues to expand.     

Effect of Familiarity on Reward Anticipation in Children with and without Autism Spectrum Disorders

Background

Previous research on the reward system in autism spectrum disorders (ASD) suggests that children with ASD anticipate and process social rewards differently than typically developing (TD) children—but has focused on the reward value of unfamiliar face stimuli. Children with ASD process faces differently than their TD peers. Previous research has focused on face processing of unfamiliar faces, but less is known about how children with ASD process familiar faces. The current study investigated how children with ASD anticipate rewards accompanied by familiar versus unfamiliar faces.

Methods

The stimulus preceding negativity (SPN) of the event-related potential (ERP) was utilized to measure reward anticipation. Participants were 6- to 10-year-olds with (N = 14) and without (N = 14) ASD. Children were presented with rewards accompanied by incidental face or non-face stimuli that were either familiar (caregivers) or unfamiliar. All non-face stimuli were composed of scrambled face elements in the shape of arrows, controlling for visual properties.

Results

No significant differences between familiar versus unfamiliar faces were found for either group. When collapsing across familiarity, TD children showed larger reward anticipation to face versus non-face stimuli, whereas children with ASD did not show differential responses to these stimulus types. Magnitude of reward anticipation to faces was significantly correlated with behavioral measures of social impairment in the ASD group.

Conclusions

The findings do not provide evidence for differential reward anticipation for familiar versus unfamiliar face stimuli in children with or without ASD. These findings replicate previous work suggesting that TD children anticipate rewards accompanied by social stimuli more than rewards accompanied by non-social stimuli. The results do not support the idea that familiarity normalizes reward anticipation in children with ASD. Our findings also suggest that magnitude of reward anticipation to faces is correlated with levels of social impairment for children with ASD.     

SYSTEMATICS AND BIOGEOGRAPHY OF THE AUSTRALIAN "GREEN ASH" EUCALYPTS (MONOCALYPTUS)

Abstract— A cladistic analysis of the "green ash" eucalypts, informal subgenus " Monocalyptus ", is presented- As a first step, ordination methods of principal coordinates analysis and multidimensional scaling delineated some terminal taxa. The cladistic analysis, applying parsimony methods to the unweighted data set, yielded 25 equally parsimonious trees, each with a consistency index of 0.57.
Farris' successive approximations approach to character weighting produced one tree with a consistency index of 0.74.
An informal classification of the group, superseries Eucalyptus , is based on that cladogram. The biogeographic history of superseries Eucalyptus is interpreted from the cladogram as having been caused by lour vicariant events in southeastern Australia, in combination with a suite of ecological features that overlie the biogeographic area-pattern.     

The neural basis of following advice

Learning by following explicit advice is fundamental for human cultural evolution, yet the neurobiology of adaptive social learning is largely unknown. Here, we used simulations to analyze the adaptive value of social learning mechanisms, computational modeling of behavioral data to describe cognitive mechanisms involved in social learning, and model-based functional magnetic resonance imaging (fMRI) to identify the neurobiological basis of following advice. One-time advice received before learning had a sustained influence on people's learning processes. This was best explained by social learning mechanisms implementing a more positive evaluation of the outcomes from recommended options. Computer simulations showed that this "outcome-bonus" accumulates more rewards than an alternative mechanism implementing higher initial reward expectation for recommended options. fMRI results revealed a neural outcome-bonus signal in the septal area and the left caudate. This neural signal coded rewards in the absence of advice, and crucially, it signaled greater positive rewards for positive and negative feedback after recommended rather than after non-recommended choices. Hence, our results indicate that following advice is intrinsically rewarding. A positive correlation between the model's outcome-bonus parameter and amygdala activity after positive feedback directly relates the computational model to brain activity. These results advance the understanding of social learning by providing a neurobiological account for adaptive learning from advice.     

Effects of nectar volume and concentration on sugar intake rates of Australian honeyeaters (Meliphagidae)

Summary Sugar intake rates of captive Australian honeyeaters (Meliphagidae) feeding at artificial flowers varied across species, and as a function of nectar volume and concentration within each species. Red Wattlebirds (Anthochaera carunculata, 110 g), achieved higher intake rates than New Holland Honeyeaters (Phylidonyris novaehollandiae, 20 g), and both achieved higher rates than Eastern Spinebills (Acanthorhynchus tenuirostris, 10 g). These results reflect differences in bill and tongue dimensions as well as in body mass. Sugar intake rates for all three species increased with volume (5–50 l) at any given concentration (10–60% mass/mass sucrose). For a given volume, sugar intake rates peaked at intermediate concentrations: 40–50% for the two larger species, and 30–40% for the smallest species. Published studies for other nectarivores foraging at unlimited volume feeders also show optimal nectar concentrations of 30–50%. However, biophysical theory predicts optima at 20–26% for small volumes, and plants presumed to be adapted for bird-pollination often have dilute nectar (20–30%). To explore this discrepancy further, we presented New Holland Honeyeaters with a range of sucrose concentrations (10–50%) using two presentation schemes. In the first we varied concentration but kept volume constant, thus varying gross sugar reward available in each concentration. This gave maximum sugar intake rates at 50%. In the second we varied both volume and concentration so that gross sugar rewards were equal for all solutions, decoupling high concentrations and large sugar rewards. This gave optima at 20%. We argue that variation among plants in nature more closely resembles the latter, equal sugar presentation scheme, and therefore, that dilute nectars may indeed represent adaptations for bird pollination.     

Discriminant conditioning of foragers in the Asian honey bees Apis cerana and A.dorsata

Abstract.

• 1 Nectivore foraging environments are typically modelled as choices among non-fluctuating rewards, but in reality they often consist of intermittent daily nectar and pollen sources. Intermittent rewards create two distinct foraging problems for colonial nectivores: re-recruitment (periodically returning to intermittent rewards) and re-allocation (finding new rewards).
• 2 The role of scent in learning and remembering the locations of discontinuous nectar rewards was examined by testing re-recruitment efficiency of Apis cerana and A.dorsata to reward-correlated scents (odour discriminant self-conditioning). Experiments examined the responses of non-naive foragers to an odour correlated with prior reward, and to odours not correlated with prior rewards, by placing different scents into a colony and observing the number of bees re-recruited to a feeding station.
• 3 Re-recruitment of non-naive foragers in both species was significantly greater in response to the conditioning scent than to the experimental controls. However, species behaviour differed in one aspect; re-recruited A.cerana foragers landed on the feeding station when unscented reward was offered, whereas re-recruited A.dorsata foragers returned but would not land without conditioning scent present in the reward.

     

Amphetamine Administration into the Ventral Striatum Facilitates Behavioral Interaction with Unconditioned Visual Signals in Rats

Background

Administration of psychomotor stimulants like amphetamine facilitates behavior in the presence of incentive distal stimuli, which have acquired the motivational properties of primary rewards through associative learning. This facilitation appears to be mediated by the mesolimbic dopamine system, which may also be involved in facilitating behavior in the presence of distal stimuli that have not been previously paired with primary rewards. However, it is unclear whether psychomotor stimulants facilitate behavioral interaction with unconditioned distal stimuli.

Principal Findings

We found that noncontingent administration of amphetamine into subregions of the rat ventral striatum, particularly in the vicinity of the medial olfactory tubercle, facilitates lever pressing followed by visual signals that had not been paired with primary rewards. Noncontingent administration of amphetamine failed to facilitate lever pressing when it was followed by either tones or delayed presentation or absence of visual signals, suggesting that visual signals are key for enhanced behavioral interaction. Systemic administration of amphetamine markedly increased locomotor activity, but did not necessarily increase lever pressing rewarded by visual signals, suggesting that lever pressing is not a byproduct of heightened locomotor activity. Lever pressing facilitated by amphetamine was reduced by co-administration of the dopamine receptor antagonists SCH 23390 (D1 selective) or sulpiride (D2 selective).

Conclusions

Our results suggest that amphetamine administration into the ventral striatum, particularly in the vicinity of the medial olfactory tubercle, activates dopaminergic mechanisms that strongly enhance behavioral interaction with unconditioned visual stimuli.