Younger apes and human children plan their moves in a maze task

Abstract

20Planning defined as the predetermination of a sequence of actions towards some goal is crucial 21 for complex problem solving. To shed light on the evolution of executive functions, we 22 investigated the ontogenetic and phylogenetic origins of planning. Therefore, we presented all 23 four great apes species (N=12) as well as 4-and 5-year-old human preschoolers (N=24) with a 24 vertical maze task. To gain a reward placed on the uppermost level of the maze, subjects had to 25 move the reward to the bottom through open gaps situated at each level of the maze. In total, 26 there were ten gaps located over three of the maze's levels, and free passage through these 27 gaps could be flexibly blocked using multiple traps. Due to the decision tree design of the maze, 28 the subjects had to plan their actions depending on the trap configuration up to two steps ahead 29 to successfully retrieve the reward. We found that (1) our measure of planning was negatively 30 correlated with age in nonhuman apes, (2) younger apes as well as 5-year-old children planned 31 their moves up to two steps ahead whereas 4-year-olds were limited to plan one step ahead, 32 and (3) similar performance but different underlying limitations between apes and children. 33 Namely, while all species of nonhuman apes were limited by a lack of motor control, human 34 children exhibited a shortage in shifting their attention across a sequence of subgoals. 35 36

Looking ahead? Computerized maze task performance by chimpanzees (Pan troglodytes), rhesus monkeys (Macaca mulatta), capuchin monkeys (Cebus apella), and human children (Homo sapiens).

“…Overall, though, the data suggest that these four chimpanzees examined the mazes, noticed the potential error-causing areas within the maze, and completed the mazes even when they have to make multiple decisions within the maze. These data complement other tasks given to chimpanzees that also show they are capable of some degree of planning (e.g., Fragaszy et al, 2003, 2009; Völter & Call, 2014a). …”

“…The chimpanzees that were tested here did not seem to struggle as much with these task demands, but this could be the result of our different kind of planning maze rather than being something different about these chimpanzees. Despite some of these performance differences, which may be the result of methodological variations, our chimpanzees’ results overall complement those found in other kinds of tasks with chimpanzees with regard to showing that chimpanzees do show some degrees of planning behavior (e.g., Beran et al, 2004; Biro & Matsuzawa, 1999; Fragaszy et al, 2003; Iversen & Matsuzawa, 2001; Völter & Call, 2014a). …”

“…To provide a related but novel assessment of planning abilities across species, we designed a computerized maze task that operated visually much like the physical mazes used by Völter and Call (2014a, b) and Tecwyn et al (2013, 2014). Our mazes were completed by using a joystick to move a cursor leftward or rightward onscreen until the cursor reached gaps at each level of the maze and “fell” to the next level.…”

“…Finally, we predicted that mazes requiring movements away from the end goal or a change of direction would prove especially difficult for the monkey species based on previous research (e.g., Fragaszy et al, 2003). Such changes might also prove difficult – although to a lesser degree – for chimpanzees, given past research showing that such movements sometimes disrupted performance in other maze tasks (Iversen & Matsuzawa, 2001; Völter & Call, 2014a). …”

Is there a link between the crafting of tools and the evolution of cognition?

“…While to date the tests used in the physical domain have been based on the range of ecological tasks faced by primates in the wild, more specific tasks designed to mirror the requirements of tool manufacture, and in particular online hierarchical processing, would be very useful. Extending recent work on hierarchical planning in the great apes would be one promising direction for future research.…”