A brief history of the studies on the selection task

In this section, I present just a few highlights of the history of the studies on the selection task, focusing on some of its modified versions in which most subjects make the correct selection (p and not-q cards). The results of these researches show that subjects’ selections vary in terms of how the problem presentation is formulated. In particular, when the selection task is framed in certain ways (about which we will speak in more details in this section), we can expect that most subjects (usually over 70% of them) will give the correct response.

Experiments based on the standard version of the selection task were replicated more than once and the data obtained were almost the same (see, e.g., Wason & Johnson-Laird 1972), confirming thereby the robustness of Wason’s findings. However, Wason and Shapiro (1971) found that using thematic content in the task helps subjects to make the correct selection. In an experimental study subjects were asked to verify the conditional statement “If I go to Manchester [p], then I travel by car [q]” by examining four cards with the city destination on the one side and the transport used on the other side. The visible faces of the cards showed respectively: “Manchester” (p), “Leeds” (not-p), “Car” (q) and

“Train” (not-q). The experimental results showed that this version of the task elicits a greater number of correct responses, that is, the p (Manchester) and not-q (train) cards (Wason & Shapiro 1971: 68). In order to explain this result, Wason and Shapiro propose a

hypothesis, which Griggs and Cox (1982) have subsequently dubbed “thematic facilitation effect”, according to which the use of realistic material facilitates subjects to consider different combinations of cards in order to identify the normatively appropriate solution.

Consider another modified version of the selection task. In a task devised by Philip Johnson-Laird, Paolo Legrenzi and Maria Sonino Legrenzi (1972), subjects were asked to imagine they were Post Office workers who had to check envelopes for violations of the conditional rule “If a letter is sealed [p], then it has a 5d stamp on it [q]”. Four envelopes (instead of the usual cards) were presented in front of the subjects. Subjects could see the back side of two envelopes and the front side of the other two. As to the first two, one envelope was sealed (p) and the other was not (not-p). The other two had respectively a 5d stamp (q) and a 4d stamp (not-q) on their visible faces (both envelopes had an address printed on them). Approximately 90% of the subjects made the correct choice: they selected the sealed envelop (p) and that with a 4d stamp (not-q) (Johnson-Laird et al. 1972). This finding was confirmed by subsequent studies using both Italian and British stamps with their respective units of currency (in both cases, the subjects were English). Johnson-Laird and his colleagues interpreted these results as confirming the “thematic facilitation effect”

hypothesis. But subsequent studies have shown that using realistic materials does not always elicit the correct response in the selection task (see, e.g., Manktelow & Evans 1979;

Pollard 1982).

In a replication of the experiment based on the postal task, Griggs and Cox (1982: 411-414) discovered that most American subjects tended to select the sealed envelope (p) and the one with the stamp that corresponds to that cited in the conditional rule (q) (experimenters replaced the British stamps with American ones). Griggs and Cox held that the significant differences between choices made by British and American subjects was due to the fact that, while the former had had direct experience with that type of postal rule

(indeed, a similar postal rule existed in the British postal regulation before the seventies), American subjects had never experienced that rule before because there was no postal regulation in the United States concerning amount of postage and the sealing of envelopes (Griggs and Cox 1982: 417). This explanation was confirmed by an experimental study made by Evelyn Goldman, who presented the same task to a group of British subjects who had never met the postal rule cited before because of their ages (indeed, this type of postal rule was eliminated in the seventies in Great Britain). The result of Goldman’s experimental studies showed that only few subjects gave the correct response (reported by Griggs and Cox 1982: 418n). In order to account for such results, Griggs and Cox (1982:

417) proposed the “memory-cueing” hypothesis, according to which in certain versions of the selection task people give the correct response because they can retrieve from their memory relevant counter-examples to the rules to be tested.

Subsequent studies showed that the improvement in subjects’ performance has to do with the nature and structure of the task, not with its thematic content or with its degree of familiarity (see, e.g., Manktelow & Over 1991; 1995). In particular, some experimental studies have shown that when asked to reason about certain kind of rules or regulations, most subjects give the normatively appropriate response. A well-known example of this kind of tasks is the “drinking age problem” (Griggs & Cox 1982). In this task, subjects were asked to pretend to be police officers being in a bar and checking whether the following conditional rule is being obeyed:

If a person is drinking beer [p], then the person must be over 19 years of age [q].

In this experiment the cards represented drinkers, showing the drink on one side and their ages on the other side. The visible sides of the cards were: “Drinking a beer” [p], “Drinking coke” [not-p], “16 years of age” [q] and “22 years of age” [not-q]. The correct choice is to turn over the cards whose visible sides are “drinking beer” [p] and “16 years of age”

[not-q]. Griggs and Cox (1982: 414-417) found that around 75% of the subjects made the correct selection. While they thought that this result confirmed their “memory-cueing” hypothesis, other studies have demonstrated that this and other similar versions of the task elicit good responses because of their logical structure. In particular, subjects drastically improve their performances when the task is framed in such a way that what they are asked to check is concerned with permissions, prohibitions and obligations (see, e.g., Manktelow & Over 1991). Starting from these empirical results, many researchers have argued that people are good at reasoning with deontic conditionals because they possess domain-specific cognitive mechanisms which are specialized to handle with permissions and obligations (see, e.g., Cheng & Holyoak 1985; Cummins 1996). As seen in the third chapter, Leda Cosmides and John Tooby have proposed the so-called Cheater-Detection Hypothesis in the context of their evolutionary perspective on human mind (Cosmides 1989; Cosmides & Tooby 1992;

see Chapter 3, Section 2). According to them, the empirical data obtained from experiments based on the selection task show that subjects have a particular mental module whose domain of application is restricted to conditional rules that involve the detection of cheaters. In their view, in the “drinking age problem” an underage drinking beer can be taken to be a cheater. So, the structure of the task activates the mental module for cheater detection, leading to the correct selection of the cards. It is noteworthy that, according to Cosmides and Tooby, the module for detecting cheaters can be applied to all the versions of the selection task which involve social regulations, but not to the standard one.

Accordingly, they hold that correct performances in this kind of tasks should not be attributed to a strictly logical interpretation of the task.