Effects of risk as a within-subject variable in probability learning

Abstract

Levels of risk were varied within Ss in a two-choice probability learning experiment. Contrary to the results of studies where risk was varied between Ss, the probability of predicting the more frequent event, P(All. was significantly greater at high than at low risk. A second finding was that P(A l ) was significantly higher for male than for female Ss, regardless of risk level. ProblemIn a recent reviewofthe literature on animal learning, Pubols (1960) concluded that variation in incentive magnitude has no significant effect on time-independent measures of learning when an absolute method is used (i. e., each S receives only a single incentive level), but that incentive effects are obtained when a differential method is employed (i. e., each S experiences more than one incentive level). Experiments involving the effects of risk on human choice behavior have yielded results which are consistent with Pubols' conclusions regarding the absolute method. For example, Myers et al (1963) reported that the probability of choosing the more frequent of two events was not significantly greater for a 10 cent-than for a 1 cent-risk group. The purpose of the present study was to determine whether the differential method of incentive presentation would affect human choice behavior. More specifically, on each trial Ss were first informed which of two amounts was to be risked, and then required to predict which of two events would occur. MethodIn the first of two experiments, six male and six female Ss, undergraduate volunteers from the University of Massachusetts, were required to predict which of two events would occur on each of 500 trials. The two events were low-associative nonsense syllables with probabilities of occurrence of .6 (E l ) and .4 (E 2 ). On half the trials, S was informed he would gain 10 cents for a correct event prediction, or lose 10 cents for an incorrect one. On the remaining trials, the level of risk was 1 cent. The sequence of risks was random with the restriction that half the E1 trials, and half the E2 trials were 10 cent risk and the remainder were 1 cent risk. The events were recorded on a 100-card deck which was shuffled before each trial block. Each S was given an initial stake oUl.OO in chips. He was told there was no pattern in the event sequence, and that he would receive all money won during the experimental session. The S kept track of his wins and losses by taking or

An analysis of the interaction of incentive magnitude and relative event frequency in probability learning.

“…At the start of the session, S was given 200 chips and told to try to maximize his winnings. No monetary value was given to the chips since the within-Ss incentive effect had previously been obtained both with dimes and pennies (Lipkin et al, 1965) and with chips alone (Schnorr et al, 1966). As in the previous within-Ss incentive studies, the 100-card deck was divided evenly between 10-chip and 1-chip risks.…”

Simultaneous and successive contrast effects in human-probability learning.

“…performance with a between-Ss incentive design. Significant differences in PA anticipation (Harley, 1965b) and in the probability of choosing the more frequent event P(A t ) (Lipkin, Schnorr, Suydam, & Myers, 1965) have been obtained from a within-.S's design. Similar effects with within-5s designs have been demonstrated by 1 This research was supported by National Institute of Mental Health Grant MH 14102-01... ..-.…”

Effects of incentive as a within- and between-subjects variable in risk-taking

“…Myers, Fort, Katz, & Suydam (1963) found in a probability matching task that Ss' risk-taking in a 10c group did not differ from Ss' behavior in a I c group. However, in an analogous task, Lipkin, Schnorr, Suydam, & Myers (1965) found a significant difference between IOc and Ic risk conditions when all Ss experienced both levels of risk, i.e., when magnitude of incentive was a within-Ss variable. Schnorr, Lipkin, & Myers (1965) investigated the effects of incentive as a within-Ss variable and as a between-Ss variable in a probability learning task and found differential effects.…”

“…However, in an analogous task, Lipkin, Schnorr, Suydam, & Myers (1965) found a significant difference between IOc and Ic risk conditions when all Ss experienced both levels of risk, i.e., when magnitude of incentive was a within-Ss variable. Schnorr, Lipkin, & Myers (1965) investigated the effects of incentive as a within-Ss variable and as a between-Ss variable in a probability learning task and found differential effects. The Ss' behavior did not vary when Ss were exposed to only one level of risk, but did vary when Ss were exposed to both levels of risk.…”