EFFECTS OF PHENTERMINE AND PENTOBARBITAL ON CHOICE PROCESSES DURING MULTIPLE PROBABILITY-LEARNING (MPL) AND DECISION-PROCESSES MANIPULATED BY PAY-OFF CONDITIONS
Er. Volkerts et al., EFFECTS OF PHENTERMINE AND PENTOBARBITAL ON CHOICE PROCESSES DURING MULTIPLE PROBABILITY-LEARNING (MPL) AND DECISION-PROCESSES MANIPULATED BY PAY-OFF CONDITIONS, Human psychopharmacology, 12(4), 1997, pp. 379-392
The primary research question in this investigation concerned whether
arousal manipulation by a stimulant (phentermine 20 mg) and a depressa
nt (pentobarbital 100 mg) will oppositely affect choice behaviour in a
probability learning task and decision processes manipulated by pay-o
ff. A 3-source probability learning task was used for this purpose, in
that, upon the presentation of a pacing cue (every 2 s) which initiat
es a sampling response required the subject to predict which source wi
ll contain a signal. Three groups of 12 subjects received the drugs or
placebo, double-blind and crossover. One group performed the task und
er an all-or-none pay-off function (V1), wherein correct responses on
the high (0.60), medium (0.30) or low (0.10) probability source were e
qually paid; the second group performed the task under a pay-off funct
ion, approximately inversely proportional to the signal probability ra
tio (V2), wherein their gain was maximal on the low probability source
when their predictions were correct on this event; while the third gr
oup was paid according to a pay-off function (V3), closely related to
the first, in that, the maximum gain could be reached when predictions
were correct on the high or medium probability source. The results sh
owed that pentobarbital significantly increased sampling responses on
the low probability source in the V1 group, while the effects of phent
ermine did not reach significance when compared to placebo. In the V2
group, no significant treatment effects were found on sampling respons
es on the high, medium or low probability source a finding explained i
n the context of arousal theory. Further, in the V3 group relative to
placebo, both phentermine and pentobarbital marginally significantly i
ncreased and decreased sampling responses on the medium probability so
urce, respectively. These effects reached significance on the low prob
ability source for both drugs when compared to placebo. It was conclud
ed that: (1) the results generally confirm the expectations regarding
the different pay-off conditions and the general finding that full max
imization is hardly ever found in probability learning experiments; (2
) the expected effects of the drugs were overall small but consistent
and in the hypothesized direction; (3) significant drug effects were m
ostly found on the low probability source; (4) pentobarbital produced
more behavioural changes than phentermine. (C) 1997 John Wiley & Sons,
Ltd.