Poorer inhibitory control was related to greater food intake across meals varying in portion size: A randomized crossover trial

Individuals eat more food when larger portions are served, and this portion size effect could be influenced by inhibitory control (the ability to suppress an automatic response). Inhibitory control may also relate to obesogenic meal behaviors such as eating faster, taking larger bites, and frequent switching between meal components (such as bites of food and sips of water). In a randomized crossover design, 44 adults ate lunch four times in the laboratory. Lunch consisted of a pasta dish that was varied in portion size (400, 500, 600, or 700 g) along with 700 g of water. Meals were video-recorded to assess meal duration and bite and sip counts, which were used to determine mean eating rate (g/min), mean bite size (g/bite), and number of switches between bites and sips. Participants completed a food-specific stop-signal task, which was used to calculate Stop-Signal Reaction Time (SSRT). Across participants, SSRT values ranged from 143 to 306 msec, where greater SSRT indicates poorer inhibitory control. As expected, serving larger portions increased meal intake (p < 0.0001); compared to the smallest portion, intake of the largest increased by 121 ± 17 g (mean ± SEM). SSRT did not moderate the portion size effect (p = 0.34), but individuals with poorer inhibitory control ate more across all meals: 24 ± 11 g for each one SD unit increase in SSRT (p = 0.035). SSRT was not related to eating rate or bite size (both p > 0.13), but poorer inhibitory control predicted greater switching between bites and sips, such that 1.5 ± 0.7 more switches were made during meals for each one SD unit increase in SSRT (p = 0.03). These findings indicate that inhibitory control can contribute to overconsumption across meals varying in portion size, potentially in part by promoting switching behavior.

When to be discrete: the importance of time formulation in understanding animal movement

Animal movement is essential to our understanding of population dynamics, animal behavior, and the impacts of global change. Coupled with high-resolution biotelemetry data, exciting new inferences about animal movement have been facilitated by various specifications of contemporary models. These approaches differ, but most share common themes. One key distinction is whether the underlying movement process is conceptualized in discrete or continuous time. This is perhaps the greatest source of confusion among practitioners, both in terms of implementation and biological interpretation. In general, animal movement occurs in continuous time but we observe it at fixed discrete-time intervals. Thus, continuous time is conceptually and theoretically appealing, but in practice it is perhaps more intuitive to interpret movement in discrete intervals. With an emphasis on state-space models, we explore the differences and similarities between continuous and discrete versions of mechanistic movement models, establish some common terminology, and indicate under which circumstances one form might be preferred over another. Counter to the overly simplistic view that discrete- and continuous-time conceptualizations are merely different means to the same end, we present novel mathematical results revealing hitherto unappreciated consequences of model formulation on inferences about animal movement. Notably, the speed and direction of movement are intrinsically linked in current continuous-time random walk formulations, and this can have important implications when interpreting animal behavior. We illustrate these concepts in the context of state-space models with multiple movement behavior states using northern fur seal (Callorhinus ursinus) biotelemetry data.

Egocentric framing - one way people may fail in a switch dilemma: evidence from excessive lane switching

To study switching behavior, an experiment mimicking the state of a driver on the road was conducted. In each trial participants were given a chance to switch lanes. Despite the fact that lane switching had no sound rational basis, participants often switched lanes when the speed of driving in their lane on the previous trial was relatively slow. That tendency was discerned even when switching behavior had been sparsely reinforced, and was especially marked in almost a third of the participants, who manifested it consistently. The findings illustrate a type of behavior occurring in various contexts (e.g., stocks held in a portfolio, conduct pertinent for residual life expectancy, supermarket queues). We argue that this behavior may be due to a fallacy reminiscent of that arising in the well-known "envelopes problem", in which each of two players holds a sum of money of which she knows nothing about except that it is either half or twice the amount held by the other player. Players may be paradoxically tempted to exchange assets, since an exchange fallaciously appears to always yield an expected value greater than whatever is regarded as the player's present assets. We argue that the fallacy is due to egocentrically framing the problem as if the "amount I have" is definite, albeit unspecified, and shows that framing the paradox acentrically instead eliminates the incentive to exchange assets. A possible psychological source for the human disposition to frame problems in a way that inflates expected gain is discussed. Finally, a heuristic meant to avert the source of the fallacy is proposed.