In 2020, millions of children shifted to using video chat for core aspects of education and social interaction. While video chat allows for genuine social interaction-in which the partner can see and hear you-affordances in other modalities are limited (e.g., touch). Do children understand the nuanced affordances and limitations of video chat? Here we provide evidence of these abilities at preschool age. Prior to COVID-19, we conducted an experiment with 4-year-old children (N = 44). Each child was introduced to people over video chat, in person, and in a photograph. Children judged whether each person could see, hear, feel, and physically interact with them. We found that children made nuanced judgments about the affordances of video chat, judging that a person over video chat can see, but cannot feel a touch nor physically interact through the screen. Children's answers about hearing were divided, with children answering that the person over video chat could hear more often than for a photograph, but less often than for in-person interaction. Overall, by age four, children understand that video chat has a mixture of life-like affordances and picture-like limitations, showing the presence of a necessary cognitive prerequisite to effective use of video chat in early education.

Several empirical approaches have attempted to explain perception of 2D and 3D size. While these approaches have documented interesting perceptual effects, they fail to offer a compelling, general explanation of everyday size perception. Here, we offer one. Building on prior work documenting an “Additive Area Heuristic” by which observers estimate perceived area by summing objects’ dimensions, we show that this same principle—an “additive heuristic”—explains impressions of 3D volume. Observers consistently discriminate sets that vary in “additive volume,” even when there is no true difference; they also fail to discriminate sets that truly differ (even by amounts as much as 30%) when they are equated in “additive volume.” These results suggest a failure to properly integrate multiple spatial dimensions, and frequent reliance on a perceptual heuristic instead.

How do children reason about people presented over video chat? Video chat is a representation, like a picture; but is also a real social interaction (the partner sees and hears you). Do children understand the nuanced affordances and limitations of video chat? We tested 4-year-old children’s reasoning, asking if a person over video chat (vs. a live person; photograph) could see, hear, feel, and physically interact through the screen. Children judged that a person over video chat can see, but cannot feel nor receive an object, through the screen. The person over video chat was judged to hear more often than a photograph, but less often than a live person. Preschool children are not limited to considering a stimulus fully representational, or fully present; instead, they understand video chat as a medium that blurs the boundaries of representation and reality, allowing for a mixture of life-like affordances and picture-like limitations.

Several empirical approaches have attempted to explain perception of 2D and 3D size. While these approaches have documented interesting perceptual effects, they fail to offer a compelling, general explanation of everyday size perception. Here, we offer one. Building on prior work documenting an ‘Additive Area Heuristic’ by which observers estimate perceived area by summing objects’ dimensions, we show that this same principle — an ‘additive heuristic’ — explains impressions of 3D volume. Observers consistently discriminate sets that vary in ‘additive volume’, even when there is no true difference; they also sometimes fail to discriminate sets that truly differ (even by amounts as much as 200%) when they are equated in ‘additive volume’. However, this heuristic also has limits: when volume varies to large extents, observers may rely on both ‘additive’ and true, mathematical volume to make volume judgments. These results suggest a failure to properly integrate multiple spatial dimensions, and frequent reliance on a perceptual heuristic instead.

A large and growing body of work has documented large, robust illusions of area perception in adults. To date, however, there has been surprisingly little in-depth investigation into children's area perception, despite the importance of this topic to the study of quantity perception more broadly (and to the many studies that have been devoted to studying children's number perception). Here, in order to understand the interactions of number and area on quantity perception, we study both dimensions in tandem. First, inspired by recent work showing that human adults appear to rely on an 'Additive Area Heuristic', we test whether children may rely on this same kind of heuristic. Indeed, 'additive area' explains children's area judgments better than true, mathematical area. Second, we show that children's use of 'additive area' biases number judgments. Finally, to isolate 'additive area' from number, we test children's area perception in a task where number is held constant across all trials. We find something surprising: even when there is no overall effect of 'additive area' or 'mathematical area', individual children adopt, and stick to, specific strategies throughout the task. In other words, some children appear to rely on 'additive area', while others appear to rely on true, mathematical areaa pattern of results that may be best explained by a misunderstanding about the concept of cumulative area. We discuss how these findings raise both theoretical and practical challenges of studying quantity perception in young children.