Research suggests that subjects can compute the mean size of two sets of interspersed objects concurrently, but that doing so incurs a cost of dividing attention across the two sets. Alternatively, costs may arise from failing to exclude irrelevant items from the calculation of mean size. Here, we examined whether attention can be selectively deployed to prevent the inclusion of items from an irrelevant, concurrently displayed set in the computation of the relevant set's mean size. The results suggest that mean size is computed prior to the deployment of attention, failing to exclude processing of items that are irrelevant to the task. The influence of the irrelevant items is evident both with brief exposures of the set (200ms) and in a simultaneous judgment task with unlimited viewing time, suggesting that attention cannot be effectively deployed to facilitate selective averaging of the size of the relevant set. Size averaging appears to precede the deployment of selective attention, suggesting that it may be carried out automatically, without intention.

Abstract Objective: To evaluate the prevalence of food and beverage marketing on Twitch.tv (Twitch), a social media platform where individuals broadcast live audiovisual material to millions of daily users. Design: Observational analysis of the prevalence of 238 food and beverage brands in five distinct categories (processed snacks; food delivery services and restaurants; candies, energy drinks/coffees/teas; and sodas and other sugar-sweetened beverages) over the course of 18 months. Setting: Twitch streamer profiles and stream titles between January 2018 and July 2019. Twitch chat room messages during July 2019. Participants: None. Results: There was a significant increase in brand exposure on Twitch both in stream titles (sodas and candies, P < 0·05) and on streamer profiles (sodas, restaurants/food delivery services, candies, and energy drinks/coffees/teas, P < 0·05) over the 18-month study period. Energy drinks, coffees and teas had the most exposure with 1·08 billion exposure hours from profiles and 83 million exposure hours from titles. Restaurants/food delivery services and sugar-sweetened beverages were the most frequently mentioned products in chat rooms with 1·24 million messages and 1·10 million messages, respectively. Conclusions: This study is the first to demonstrate the extent by which food and beverage brands garner millions of hours of exposure on Twitch. Future studies should evaluate the impact that this level of exposure to nutrient-poor, energy-dense products may have on behavioural and health outcomes.

Perceptual averaging is a process by which sets of similar items are represented by summary statistics such as their average size, luminance, or orientation. Researchers have argued that this process is automatic, able to be carried out without interference from concurrent processing. Here, we challenge this conclusion and demonstrate a reliable cost of computing the mean size of circles distinguished by colour (Experiments 1 and 2) and the mean emotionality of faces distinguished by sex (Experiment 3). We also test the viability of two strategies that could have allowed observers to guess the correct response without computing the average size or emotionality of both sets concurrently. We conclude that although two means can be computed concurrently, doing so incurs a cost of dividing attention.

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