Many preschoolers don't distinguish the possible from the impossible in a marble-catching task

Abstract

Understanding what possibilities are involves being able to tell the difference between things that could happen and things that can’t happen. How does the ability to distinguish the possible from the impossible emerge over ontogenesis? The current study modified the “Y-shaped tube task” (Redshaw & Suddendorf 2016) to test children’s ability to distinguish the possible from the impossible. In the Y-shaped tube task, the experimenter holds a ball above a tube shaped like an upside-down “Y” and asks a participant to catch it. A participant who sees that there are two possible places for the ball to come out should cover the openings under each branch of the Y. But children might cover both openings for other reasons as well: for example, because there are exactly two good places to put one’s hands. If children cover both openings because they understand that the ball could come out either way, then they should also find efficient, effective solutions to two new trial types presented in this paper. The “U-shaped” tube is shaped like an upside-down “U”, with an opening at the end of each leg. However, the U-shaped tube was designed with one obviously impossible opening. In order to come out from the impossible opening, a ball would need to levitate upward and pass through a block of solid wood at the top. If children can distinguish possibilities from impossibilities, they should only cover the possible opening. The “Critical tube” has three openings at the bottom, but only two are possible; again, in order to come out from the impossible opening, a ball would need to levitate upward and pass through a block of solid wood. If children can distinguish possibilities from impossibilities, they should cover both possible openings, avoiding the impossible opening. Twenty four 36-month-olds and 24 48-month-olds were tested on all three tubes. Results indicate that less than 20% of 36-month-olds and at most about half of 48-month-olds distinguish the possible from the impossible. This result converges with several other findings in the literature that suggest that the ability to choose actions that account for multiple incompatible possibilities often emerges after the fourth birthday.

Can chimpanzees conceive of mutually exclusive future possibilities? A Comment on: ‘Chimpanzees prepare for alternative possible outcomes’ (2023), by Engelmann et al.

“…We have raised concerns about Engelmann et al .’s [5] article on three grounds: (i) the rationale implies without sufficient evidence that chimpanzees’ poor performance on similar previous tasks can be entirely explained by physical difficulties, (ii) the chimpanzees’ high rate of balancing two platforms in the control condition shows that this behaviour need not reflect a rational analysis of possibilities, and (iii) the chimpanzees might have approached the task as if it involved a straightforward AND relation between two rewards rather than an exclusive-OR relation between two possibilities, with the relatively greater performance in the experimental condition driven by increased attention to the two rewards when there was a tube exit above each. And although our own positive evidence from human children [6,8,15] remains open to other explanations that do not entail an understanding of exclusive-OR relations [16,17], it is clear that children do acquire this understanding at some point during development—with many studies (including our own) pointing to a critical transition period between 3 and 5 years.…”

“…While we have found little evidence that non-human primates and 2-year-old human children can consistently prepare for two mutually exclusive possibilities on these tasks, we have found that children typically become able to do so between 3 and 5 years of age [6,8,15]. There may of course be other simple routes (unrelated to AND relations) by which a proportion of children pass this task, for instance by matching each hand with each exit without evaluating the possibilities entailed [16], or by representing the left and right exits as two independent possibilities ( maybe left, maybe right ) without representing the exclusive-OR relation that links them [17]. As we explicitly acknowledged in our original report, we are open to ‘leaner accounts of the older children’s performance’ [6].…”

“…[22]—which sampled from the same population of chimpanzees as in their Biology Letters study—found no compelling evidence of such understanding in a logical reasoning task that children convincingly pass by 5 years [19]. Notably, it has been proposed that the mixed evidence from primates [5,6,8–10,22–24] (and very young children [25–29]) can be explained by the notion that some tasks are more readily solved without understanding exclusive-OR relations than others [2,11,16,30].…”

“…As we explicitly acknowledged in our original report, we are open to ‘leaner accounts of the older children’s performance’ [6]. Reassuringly, however, it is around 3–5 years that children also demonstrate increasing competence on other tasks designed to measure understanding of exclusive-OR relations [7,16–21] (although it remains to be seen whether children’s performances on these tasks are correlated).…”

Three-year-olds’ ability to plan for mutually exclusive future possibilities is limited primarily by their representations of possible plans, not possible events

“…They found that 4-year-old children spontaneously and consistently placed a hand under each exit of the inverted y-shaped tube, while 3-year-olds were more likely to spontaneously place their hands under only one opening (for replications, see Redshaw et al, 2018Redshaw et al, , 2019Suddendorf et al, 2017). Later work suggested that, when younger children do spontaneously cover both exits, they do not necessarily do so because they recognize that it is the correct strategy (Leahy, 2024).…”