皮亚杰的守恒任务和任务需求的影响

In the mid-twentieth century, psychologist Jean Piaget developed his conservation task, which provided researchers with a way to evaluate the logic and reasoning abilities of children, and ultimately proposed a trajectory for cognitive development.

Between the ages of 2 and 7, a period that Piaget called the pre-operational stage, children lack the mental operators—logical rules—that underlie the ability to reason about relationships between sets of properties, like objects’ sizes.

To elaborate, if adults were shown two pieces of chocolate of the same mass, and one of them happened to melt, they would use logic to conclude that the amount of chocolate in both pieces is conserved—even though another property, the shape, of one piece changed.

However, if young children were put through the same process and asked which piece has more chocolate, they’d likely say the melted one, as it appears wider and seems to take up more space.

In other words, the child may focus on the transformation of an irrelevant property of the chocolate—its shape—and not the key property that they were asked about—the amount—that didn’t change.

While Piaget’s intent was to measure the development of reasoning skills, critics have suggested that children’s poor performance in conservation tasks—like those dealing with clay instead of chocolate—is actually due to task demands, such as assumptions about the questioner’s goals and expectations when the question about the key property is repeated.

This video demonstrates how to design an experiment investigating children’s reasoning using both the classic version and a modified version of Piaget’s conservation task, and illustrates how to collect and interpret data. We also explain why researchers have questioned the validity of the conservation task, and explore how an awareness of task demands can be applied in research settings.

In this experiment, children between the ages of 4- and 6-years-old perform two types of tasks—conservation of number and length.

In the initial phase of the number task, children are shown a row of blue tokens and one of red, each with the same number.

In this case, the tokens are equally spaced: above every blue token is positioned a red one, and none of the tokens touch one another, creating the same length initially.

Children are asked whether both rows have the same number of tokens, or if one has more. Their responses at this stage serve as a preliminary judgment of number.

This is followed by the transformation phase, in which children are assigned to one of two experimental conditions: intentional or accidental.

Those in the intentional group observe the researcher move tokens in one row closer together, so that they are touching. This is the classic version of Piaget’s conservation task.

In contrast, children in the accidental group watch as the researcher uses a teddy bear to manipulate the tokens. This is a modified version of the conservation task, designed by psychologists James McGarrigle and Margaret Donaldson.

Here, the teddy bear is presented as a “rogue” agent that enjoys interfering with the tokens and ruining the experiment. Importantly, the use of a stuffed animal takes the focus off of the researcher, so children don’t take into consideration task demands—like the experimenter’s goals—in the next stage of the test.

In both experimental conditions, although the number of tokens—the key property of the task—in the modified row doesn’t change, another of its attributes—the spacing—does.

During the post-transformation phase, children are again asked if either of the rows has more tokens.

In this instance, the dependent variable is the percentage of correct post-transformation responses, in which children determine that the number of tokens in both rows is equal—an answer that requires developed reasoning skills.

The number task is followed by the length task, which follows a similar principle.

Here, children are initially shown two different-colored strings of the same length, the ends of which are aligned. They are then asked whether either of the strings is longer, or if they are both the same length.

During the transformation phase, children are assigned to the same condition they were placed in during the number task.

For the accidental group, the rogue teddy bear is brought out and used to pull the center of one of the strings so that it is curved and its ends no longer align with those of the other string. This manipulates the string in an “unintentional“ manner.

In contrast, children in the intentional group watch the researcher perform the same manipulation.

In both instances, the key attribute of the modified string—its length—is not altered, but a nonessential characteristic, its shape, is.

Finally, in the post-transformation phase, children are again asked whether either of the strings is longer.

For this task, the dependent variable is the percentage of responses in which children identify both strings as being the same length after the transformation.

Based on the previous work of Piaget, and McGarrigle and Donaldson, it is expected that—compared to the accidental group—fewer children in the intentional group will identify the objects in either task as being the same after the transformation.

This may be due to children in the intentional group misinterpreting the question asked by the researcher in the post-transformation phase. Specifically, they may think that the researcher is inquiring about the dimension they intentionally manipulated, rather than the key property.

To prepare for the experiment, gather four red and four blue tokens, all of which have the same diameter. In addition, obtain two 10-in. pieces of string in different colors, and a small teddy bear capable of being hidden in a box.

Greet the child when they arrive, and lead them to a table on which the box containing the teddy bear has been placed. Sit across from them, and remove the stuffed animal from its box. Tell the child that the bear is “naughty,” and sometimes escapes and ruins the game you will be playing.

After this introduction to the teddy bear, begin the initial phase of the number task by creating two rows of tokens in front of the child. Assure that each row consists of four of the same color tokens, and that they are evenly spaced.

Sequentially point to each row, and ask the child if either has more tokens, or if both have the same number. Record the child’s response.

For the transformation phase, manipulate the positions of the tokens in the row furthest from the child according to the condition to which they were assigned: intentional or accidental.

Afterwards, for children assigned to the accidental condition, have them place the teddy bear back in the box.

In the post-transformation phase of the number task, point to each row, and ask the child if one has more tokens. Again record their response.

Now, put away the tokens to begin the initial phase of the length task. Position two strings in front of the child so that they are parallel, and their ends are aligned.

Point to each of the strings, and ask the child whether one is longer, or if they are both the same length. Record their response.

During the transformation phase, manipulate the shape of the string further away from the child: For those in the intentional group, place your finger on the center of a straight string and pull down; and for those in the accidental group, have the teddy bear use its arms.

Sequentially point to both strings in front of the child, and ask them whether one is longer, or if they are of the same length. Finally, record their response.

To analyze the results, pool the data for the number and length tasks, and average the trials in the intentional and accidental conditions where children judged the key property of objects to be the same after transformation.

Exclude any children who answered the initial judgment questions incorrectly, as this suggests that they could not accurately gauge property equivalence.

Compare scores across the two conditions using an independent-samples t-test.

Compared to the intentional group, notice that children in the accidental group were more likely to judge the number or length of the objects to be the same after the transformation.

This may be due to the fact that, for this condition, the teddy bear was responsible for the transformation, and thus children have no reason to think that any property of an object was intentionally manipulated. Thus, children remain focused on the key property about which they were asked.

Now that you know how assumptions about researcher’s goals can influence children’s reasoning in Piaget’s conservation task, let’s look at how this issue of task demands can be applied in other contexts.

The effects of task demands are not restricted to Piaget’s conservation experiments, and are thus important for psychologists to take into consideration when they are designing research studies involving children.

For example, if a researcher repeatedly asks a child a question about what a picture is meant to represent, the child may change their response thinking that the researcher wanted them to answer differently the first time.

As a result, care must be taken to assure that children’s responses are not based on what they think the researchers want them to say or do.

In addition, the influence of task demands have provoked researchers to consider the importance of using multiple methods to measure children’s skills, so that their strengths and weaknesses can be accurately assessed.

For example, evaluating children’s spatial abilities with a task that requires them to physically manipulate objects—like having to position blocks to create a shape in a picture—may underestimate the abilities of a child whose actual difficulty is motor skills.

Thus, a more appropriate method to assess spatial abilities—one that removes confounding motor skills—would be to show children pictures of different arrangements of blocks, and ask if any two images match.

You’ve just watched JoVE’s video on Piaget’s conservation task and its modifications. By now, you should know how transforming one item in a pair of objects or object sets can be used to assess reasoning in children, and how children’s answers can be influenced by task demands.

Thanks for watching!