Evaluación de la formación de precipitados

Evidence reviewed above (section 1.3.2) suggests that the real-life tendency in adolescence to engage in risky behaviours is partly attributable to social factors, such as peer pressure. Recent studies using laboratory-based decision-making tasks suggest that, in addition to these social factors, there is continuing development during adolescence of a number of non-social cognitive components that underlie the ability to make optimal decisions. These studies will be reviewed below. In general, it appears to be the case that sub-optimal decision-making in adolescence is particularly evident when decisions are made in an emotional context.

1.6.2.1 Performance in probabilistic decision-making tasks

A number of recent studies have shown continuing development during adolescence in performance on laboratory-based decision-making tasks. Often in these tasks, participants must take into account the rewards and reward probabilities associated with a selection of choices, and then choose so as to maximize their total rewards (e.g. money, fictitious money, or points).

For example, in the Iowa Gambling Task (IGT; Overman et al., 2004; Crone & van der Molen, 2004; Hooper et al., 2004; Huizinga et al., 2007), participants repeatedly select cards from an array of four decks with unknown reward distributions. Two of the decks yield low-magnitude, constant rewards and modest probabilistic losses, resulting in net gain across the task. The remaining two decks yield high-magnitude, constant rewards but substantial probabilistic losses, resulting in a net loss. Several studies have shown that the tendency to adopt the advantageous strategy of selecting from the former two decks continues to increase with age during adolescence (between 11 and 18+ years: Overman et al., 2004; Crone & van der Molen, 2004; Hooper et al., 2004), although

contradictory findings have been reported. In a study by van Leijenhorst et al. (2008), no differences were found between age 8-30 years in the ability to make advantageous selections in a version of the IGT.

In a study by Harbaugh et al., participants aged 5-64 made a series of decisions between a certain reward, and a gamble with equivalent expected value (EV: the sum of potential outcomes weighted by their respective probabilities; Harbaugh et al., 2002). Unlike in the many versions of the IGT, in this task participants are explicitly informed about the reward probabilities associated with each decision3. However, children and adolescents showed evidence of biased decisions in the task, relative to adults. Specifically, children and adolescents showed a lesser degree of indifference in their choice between the pairs of options with equivalent EV, relative to adults. A similar study by Levin et al. (2007), in which children (aged 5-11) and adults made a choice between gambles that differed in EV showed age-related increases in the tendency to make choices that maximised EV. The results from these two studies show that, even in relatively simple decision- making tasks in which participants are provided with all the necessary information to make optimal choices, the tendency to do so continues to develop up to (Levin et al.) and during (Harbaugh et al.) adolescence.

Several suggestions have been put forward to account for the age-related improvements in performance on these decision-making tasks. One suggestion is that, with age, adolescents become better able to take into account performance feedback (wins and losses) and use this to maintain or modify subsequent behaviour (Byrnes et al., 1999; Crone & van der Molen, 2004). This might be expected to impact on performance in tasks including the IGT, but not in the tasks used by Levin et al. and Harbaugh et al. (see preceding paragraph).

Another suggestion for the age-related improvements in performance on decision- making tasks is that the use of behavioural rules or strategies shifts during adolescence. For example, Huizinga et al. (2007) show evidence for an age-related improvement in

3

i.e. in Harbaugh et al., decisions are made under risk (probabilities of reward are known, but are less than unity), not uncertainty (probabilities of reward are unknown).

the sophistication of strategies employed during the IGT. At younger ages (e.g. 6-9 years), participants behaved in a way that was consistent with sensitivity to the frequency of loss and an insensitivity to loss magnitude, while up to and during adolescence (10-15 years), participants were increasingly likely to take into account both the frequency and magnitude of losses. This study will be discussed in more detail in Chapter 3. The suggestion that the development of decision-making proceeds via the adoption of increasingly sophisticated or unbiased strategies is in agreement with Harbaugh et al. (2002), and is also in broad agreement with some influential theories of the development of decision-making (e.g. Brainerd & Reyna, 1990).

1.6.2.2 Emotional influences on decision-making

A number of recent studies have investigated emotional influences on decision-making in adolescence. Depending on one’s conceptualisation of emotion, it could be argued that any reward-based decision-making task is, strictly, emotional (in that reward receipt, omission or termination gives rise to ‘reward-based emotions’; Rolls, 2005). However, it is possible to manipulate the level of emotional salience or emotional intensity in decision-making tasks.

In a study by Figner et al. (2009), adolescent participants aged 13-19 years and adult participants aged 20+ years played the Columbia Card Task (CCT), in which cards shown face down are sequentially turned over to win points. On a given trial, cards can be turned over as long as gains are encountered, but the game terminates as soon as the participant turns over a loss card and the amount specified on the loss card is subtracted from the total payoff. In this particular study, two versions of the game were played: an emotional or ‘hot’ version of the task, and an unemotional or ‘cold’ version of the task. In the cold version, participants decided at the start of each trial how many cards they would turn over (a single number, e.g. 15). In the hot CCT, this decision was made incrementally: After each card was turned over, the participant made a decision either to quit with their current payoff, or turn over another card. Therefore, the hot CCT provides reward feedback at each decision point. The results showed that, regardless of age, participants turned over a greater number of cards in the hot than in the cold CCT. However, the difference between the number of cards turned over in the hot version and the number of cards turned over in the cold version of the task was greater in

adolescents than in adults. The authors suggest that this effect arises due to a greater tendency for emotional factors to produce risk-seeking behaviour in adolescents, relative to adults.

In summary, a number of experimental studies have shown evidence that some basic cognitive components of decision-making continue to develop during adolescence. In addition, the impact of emotion on decision-making may be particularly high in adolescence. Chapter 2 of this thesis describes an experiment that was carried out to investigate decision-making and emotion across adolescence. In the following sections, this and subsequent experimental chapters will be summarised.