Growth of microbial populations in nonminimal media: some considerations for modeling

Ramkrishna and his co-workers have developed so-called cybernetic models which purport to describe, among other things, how microorganisms make choices when presented with two or more functionally equivalent, or substitutable, nutrients that are sources of carbon and available energy. In general, however, organisms are presented with choices not just between nutrients that are substitutable for one another, but also between sets of nutrients some of which are by no means substitutable for one another. It is postulated herein that the main ideas of cybernetic modeling apply to these more general choices as they seem to apply to the choices considered by Ramkrishna and his co-workers. Some consequences of the postulate are worked out for steady-state growth situations where two, or in one case three, nutrients limit or potentially limit growth rate. If predicted phenomena are observed experimentally so as to verify the postulate, a significantly improved basis for understanding growth of microorganisms in practical fermentation media as well as in natural situations will be provided by this application of cybernetic modeling ideas.     

Responsibility and the limits of patient choice

Patients are generally assumed to have the right to choices about treatment, including the right to refuse treatment, which is constrained by considerations of cost-effectiveness. Independently, many people support the idea that patients who are responsible for their ill health should incur penalties that non-responsible patients do not face. Surprisingly, these two areas have not received much joint attention. This paper considers whether restricting the scope of responsibility to pre-treatment decisions can be justified, or whether a demand to hold people responsible for 'usual suspect' choices such as smoking or failure to exercise commits us to also holding people responsible for their treatment choices. I argue that there is no good reason to support this restriction: those who advocate responsibility for (some) pre-treatment choices should also advocate responsibility for (some) treatment choices. However, I also note that, as with pre-treatment choices, patients may sometimes have reason to choose in ways that do not optimize their health. As such, I also consider a process, based on the idea of public reasons, for deciding which treatment choices patients cannot legitimately be held responsible for, along with a method for considering proposed changes to this category.     

Fixation patterns in simple choice reflect optimal information sampling

Simple choices (e.g., eating an apple vs. an orange) are made by integrating noisy evidence that is sampled over time and influenced by visual attention; as a result, fluctuations in visual attention can affect choices. But what determines what is fixated and when? To address this question, we model the decision process for simple choice as an information sampling problem, and approximate the optimal sampling policy. We find that it is optimal to sample from options whose value estimates are both high and uncertain. Furthermore, the optimal policy provides a reasonable account of fixations and choices in binary and trinary simple choice, as well as the differences between the two cases. Overall, the results show that the fixation process during simple choice is influenced dynamically by the value estimates computed during the decision process, in a manner consistent with optimal information sampling.     

Harder than Expected: Increased Conflict in Clearly Disadvantageous Delayed Choices in a Computer Game

When choosing between immediate and temporally delayed goods, people sometimes decide disadvantageously. Here, we aim to provide process-level insight into differences between individually determined advantageous and disadvantageous choices. Participants played a computer game, deciding between two different rewards of varying size and distance by moving an agent towards the chosen reward. We calculated individual models of advantageous choices and characterized the decision process by analyzing mouse movements. The larger amount of participants’ choices was classified as advantageous and the disadvantageous choices were biased towards choosing sooner/smaller rewards. The deflection of mouse movements indicated more conflict in disadvantageous choices compared with advantageous choices when the utilities of the options differed clearly. Further process oriented analysis revealed that disadvantageous choices were biased by a tendency for choice-repetition and an undervaluation of the value information in favour of the delay information, making rather simple choices harder than could be expected from the properties of the decision situation.     

A selective emotional decision-making bias elicited by facial expressions

Emotional and social information can sway otherwise rational decisions. For example, when participants decide between two faces that are probabilistically rewarded, they make biased choices that favor smiling relative to angry faces. This bias may arise because facial expressions evoke positive and negative emotional responses, which in turn may motivate social approach and avoidance. We tested a wide range of pictures that evoke emotions or convey social information, including animals, words, foods, a variety of scenes, and faces differing in trustworthiness or attractiveness, but we found only facial expressions biased decisions. Our results extend brain imaging and pharmacological findings, which suggest that a brain mechanism supporting social interaction may be involved. Facial expressions appear to exert special influence over this social interaction mechanism, one capable of biasing otherwise rational choices. These results illustrate that only specific types of emotional experiences can best sway our choices.     

Why Procreative Preferences May be Moral – And Why it May not Matter if They Aren't

There has been much argument over whether procreative selection is obligatory or wrong. Rebecca Bennett has recently challenged the assumption that procreative choices are properly moral choices, arguing that these views express mere preferences. This article challenges Bennett's view on two fronts. First, I argue that the Non‐Identity Problem does not show that there cannot be harmless wrongs – though this would require us to abandon the intuitively attractive ‘person‐affecting principle’, that may be a lesser cost than abandoning some more firmly‐held intuition. But, even if we accept Bennett's claim that these choices are not moral, that does not show them to be mere personal preferences. I argue that there is a class of non‐moral ‘categorical preferences’ that have much the same implications as moral preferences. If a moral preference for able‐bodied children is problematic (as Bennett claims), then so is a non‐moral categorical preference. Thus, showing that these preferences are not moral does not show that they are not problematic, since they may still be categorical.     

Farmer Choice of Sorghum Varieties in Southern Mali

In southern Mali and throughout the semiarid tropics, small-scale family farmers are faced with the challenge of producing adequate harvests in difficult biophysical and socioeconomic environments. Professional plant breeders have had much difficulty developing modern varieties that outperform farmers’ traditional varieties in these environments, in part because of an incomplete understanding of why farmers choose the varieties they grow. Improved understanding of farmers’ varietal choices can contribute to collaboration between farmers and formal plant breeders. Based on a 15-month field study in Dissan, Mali, we examine farmer's choices among their traditional sorghum varieties in terms of one or more than one variety, and short-cycle or long-cycle varieties, and the interaction between these two choices. Results support our general hypothesis that farmers choose varieties to optimize outputs in the face of variation in the growing environment and in human managed inputs such as labor and tools.     

Optimal risky choice in humans: effects of amount of variability

The present study investigated whether the predictions of an optimal risk-sensitive foraging model (the energy-budget rule) would extend to humans’ choices between high- and low-variance monetary response options. In Experiment 1, participants were presented with repeated choices between two options that had the same mean values but different variances across positive- and negative-budget conditions. In Experiment 2, a within-subject comparison was conducted to investigate choice under positive- and negative-budget conditions when the options were either (a) a fixed option and a high-variance option, or (b) a low-variance option and a high-variance option. Session-wide choices were analyzed in relation to the predictions of the energy-budget rule and sequential choices were analyzed with dynamic optimization modeling. When both options were variable choice was generally consistent with predictions of the energy-budget rule and was more risk prone under negative-budget than positive-budget conditions. Sequential choices were sensitive to local budget conditions, but choices were less consistent with optimality when both options were variable, possibly because of the greater similarity in expected earnings for optimal and nonoptimal choices in these conditions. Overall, the results provide further evidence that the energy-budget rule may have broad applicability and that it can extend to human risky choice between multiple variable response options.     

The incidence of calorie labeling on fast food choices: A comparison between stated preferences and actual choices

In order to test the effect of calorie information on fast food choices, we conducted a questionnaire employing two types of stated preferences methods (the best-worst-scaling and intentional questions) and a follow-up randomized field experiment in a sample of 119 participants. This combined approach allowed us to test the internal validity of preferences for fast food meals across elicitation scenarios. The results showed that calorie information reduces the probability of selecting high calorie meals only in the questionnaire, while it did not have any significant impact on actual purchasing behavior in the field experiment. Thus, the findings show that there is a clear difference between the role of calorie information on immediate stated preference choices, and the relatively low level of responsiveness in real choices in a restaurant. We believe that the current results are quite suggestive, indicating the limits of predicting actual fast food behavior, and may open the way to using data sources that combine stated methods with field experiments.     

Location and Color Learning in Bumblebees in a Two-Phase Conditioning Experiment

Bees use spatial and visual cues that characterize flowers to make dietary choices. If two such cues always appear together nonambiguously, they provide identical information. In such cases, do bees base dietary choices on one cue and ignore the other, or do they consider both cues? We allowed bumblebees to forage on two patches of artificial flowers that differed in location, color, and reward presence in a two-phase experiment. We switched either the display color, the location, or both the color and the location associated with the rewarding patch between phases. We tested for the effects of the switch on the bees' choices. Immediately following a switch in the location or both the location and the color of the rewarding patch, the bees' performance decreased, as they continued to visit the patch that was previously rewarding. This decrease did not occur when only the color of the rewarding patch was changed or in no-change controls. We suggest that the bees' foraging choices were guided mostly by a location cue when both the location and the color conveyed the same information.     

When flexibility is stable: implicit long-term shaping of olfactory preferences

Preferences are traditionally assumed to be stable. However, empirical evidence such as preference modulation following choices calls this assumption into question. The evolution of such postchoice preference over long time spans, even when choices have been explicitly forgotten, has so far not been studied. In two experiments, we investigated this question by using a variant of the free choice paradigm: In a first session, participants evaluated the pleasantness of a number of odors. We then formed pairs of similarly rated odors, and asked participants to choose their favorite, for each pair. Participants were then presented with all odors again, and asked for another pleasantness rating. In a second session 1 week later, a third pleasantness rating was obtained, and participants were again asked to choose between the same options. Results suggested postchoice preference modulation immediately and 1 week after choice for both chosen and rejected options, even when choices were not explicitly remembered. A third experiment, using another paradigm, confirmed that choice can have a modulatory impact on preferences, and that this modulation can be long-lasting. Taken together, these findings suggest that although preferences appear to be flexible because they are modulated by choices, this modulation also appears to be stable over time and even without explicit recollection of the choice. These results bring a new argument to the idea that postchoice preference modulation could rely on implicit mechanisms, and are consistent with the recent proposal that cognitive dissonance reduction could to some extent be implicit.     

Counterfactual thinking and emotions: regret and envy learning

Emotions like regret and envy share a common origin: they are motivated by the counterfactual thinking of what would have happened had we made a different choice. When we contemplate the outcome of a choice we made, we may use the information on the outcome of a choice we did not make. Regret is the purely private comparison between two choices that we could have taken, envy adds to this the information on outcome of choices of others. However, envy has a distinct social component, in that it adds the change in the social ranking that follows a difference in the outcomes. We study the theoretical foundation and the experimental test of this view.     

The neural basis of financial risk taking

Investors systematically deviate from rationality when making financial decisions, yet the mechanisms responsible for these deviations have not been identified. Using event-related fMRI, we examined whether anticipatory neural activity would predict optimal and suboptimal choices in a financial decision-making task. We characterized two types of deviations from the optimal investment strategy of a rational risk-neutral agent as risk-seeking mistakes and risk-aversion mistakes. Nucleus accumbens activation preceded risky choices as well as risk-seeking mistakes, while anterior insula activation preceded riskless choices as well as risk-aversion mistakes. These findings suggest that distinct neural circuits linked to anticipatory affect promote different types of financial choices and indicate that excessive activation of these circuits may lead to investing mistakes. Thus, consideration of anticipatory neural mechanisms may add predictive power to the rational actor model of economic decision making.     

Rationality in risk-sensitive foraging choices by starlings

Normative models of choice usually predict preferences between alternatives by computing their value according to some criterion, then identifying the alternative with greatest value. An important consequence of this procedure is captured in the economic concept of rationality, defined through a number of principles that are necessary for the existence of an ordinal scale of value upon which organisms base their choices. Violations of these principles, such as some recently reported breaches of transitivity and regularity in birds and honeybees, have strong implications for the understanding of decision mechanisms in humans and nonhumans alike. We investigated rationality in risky choice using European starlings, Sturnus vulgaris. Birds had to choose between two or three food sources, each associated with a different variance in delay to reward. In three experiments, starlings were strongly risk prone, showing regular and consistent preferences in binary and trinary choices. Preferences also satisfied weak and strong stochastic transitivity. Our results extend the generality of previous research in risk-sensitive foraging to situations where more than two alternatives are present and suggest that violations of rationality in risk-sensitive choices may be expressed only under restricted sets of conditions. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

An association between prediction errors and risk-seeking: Theory and behavioral evidence

Reward prediction errors (RPEs) and risk preferences have two things in common: both can shape decision making behavior, and both are commonly associated with dopamine. RPEs drive value learning and are thought to be represented in the phasic release of striatal dopamine. Risk preferences bias choices towards or away from uncertainty; they can be manipulated with drugs that target the dopaminergic system. Based on the common neural substrate, we hypothesize that RPEs and risk preferences are linked on the level of behavior as well. Here, we develop this hypothesis theoretically and test it empirically. First, we apply a recent theory of learning in the basal ganglia to predict how RPEs influence risk preferences. We find that positive RPEs should cause increased risk-seeking, while negative RPEs should cause risk-aversion. We then test our behavioral predictions using a novel bandit task in which value and risk vary independently across options. Critically, conditions are included where options vary in risk but are matched for value. We find that our prediction was correct: participants become more risk-seeking if choices are preceded by positive RPEs, and more risk-averse if choices are preceded by negative RPEs. These findings cannot be explained by other known effects, such as nonlinear utility curves or dynamic learning rates.     

A game-theoretic model of kleptoparasitic behavior in polymorphic populations

Kleptoparasitism, the stealing of food by one animal from another, is a widespread biological phenomenon. In this paper we build upon earlier models to investigate a population of conspecifics involved in foraging and, potentially, kleptoparasitism. We assume that the population is composed of four types of individuals, according to their strategic choices when faced with an opportunity to steal and to resist an attack. The fitness of each type of individual depends upon various natural parameters, for example food density, the handling time of a food item and the probability of mounting a successful attack against resistance, as well as the choices that they make. We find the evolutionarily stable strategies (ESSs) for all parameter combinations and show that there are six possible ESSs, four pure and two mixtures of two strategies, that can occur. We show that there is always at least one ESS, and sometimes two or three. We further investigate the influence of the different parameters on when each type of solution occurs.     

Experimental analysis of the thermal and salinity preferences of glass-eels, Anguilla anguilla (L.), before and during the upstream migration

During their upstream migration European glass-eels, Anguilla anguilla (L.), encounter a series of varying environmental situations. The migration requires a sequence of physiological adaptations determined by the different chemico-physical conditions they meet. Temperature and salinity are two of the most important factors. It is reasonable that glass-eels may utilize them as cues to orientation. Laboratory experiments were designed to elucidate the thermal and salinity preferences of glass-eels. These were assessed by examining the choices of specimens caught either at sea and then kept in salt water (33%), or in the Arno river and then reared in fresh water. Water flows, triggering the rheotactic reaction, prompted glass-eels to choose between two different salinities and/or temperatures. The results confirm the preference of glass-eels for flows whose temperature does not differ from that of acclimation. Specimens tested towards two water flows, both at different temperatures from that of acclimation, preferred the colder. Fresh water was usually preferred to salt water, this preference being not so marked in the case of the glass-eels caught at sea and thus not yet adapted to fresh water. Clear-cut choices were recorded when one of the tested flows presented both the preferred temperature and preferred salinity. When only one of the two parameters reproduced the preferred situation, the choices were differently affected by temperature and salinity at different values of temperature. When the temperature of both flows was below 11–12°C, glass-eels preferred fresh water; at higher temperatures the colder of the two flows was preferred, even if salty.     

Anticipation and Choice Heuristics in the Dynamic Consumption of Pain Relief

Humans frequently need to allocate resources across multiple time-steps. Economic theory proposes that subjects do so according to a stable set of intertemporal preferences, but the computational demands of such decisions encourage the use of formally less competent heuristics. Few empirical studies have examined dynamic resource allocation decisions systematically. Here we conducted an experiment involving the dynamic consumption over approximately 15 minutes of a limited budget of relief from moderately painful stimuli. We had previously elicited the participants’ time preferences for the same painful stimuli in one-off choices, allowing us to assess self-consistency. Participants exhibited three characteristic behaviors: saving relief until the end, spreading relief across time, and early spending, of which the last was markedly less prominent. The likelihood that behavior was heuristic rather than normative is suggested by the weak correspondence between one-off and dynamic choices. We show that the consumption choices are consistent with a combination of simple heuristics involving early-spending, spreading or saving of relief until the end, with subjects predominantly exhibiting the last two.     

Discriminative proprieties of Vary and Repeat contingencies

Pigeons were trained on an arbitrary matching-to-sample task in which Vary and Repeat contingencies served as sample stimuli. During the sample component, two keys were lit red and a four-peck sequence was reinforced if its frequency was less than a certain threshold (Vary sample) or if it comprised one of two target sequences (Repeat sample). During the comparison component, two keys were lit white and green, and correct choices depended on the previous sample contingency. Pigeons learned to emit high and low variability levels during the sample, and correct matching choices were obtained. In two discrimination testing phases, the requirement of variation (Vary sample) or of repetition (Repeat sample) was parametrically manipulated such that behavioral variability became undifferentiated between samples (low sample disparity) and then differentiated (high sample disparity) again. Accurate choices fell to chance under low sample disparity conditions, but improved under high disparity conditions. The results provide evidence that high and low variability levels can be produced in the absence of antecedent cues and that pigeons can accurately report whether they had experienced a Vary or a Repeat contingency, thus indicating that those contingencies may serve discriminative functions.