Effects of drugs of abuse and signal predictability in two models of sustained attention in pigeons.

The acute effects of ethanol, pentobarbital, D-amphetamine and nicotine were determined in two animal models of attention. This study examined if changing the predictability of the stimulus presentation modifies drug effects under two attention tasks, in male White Carneau pigeons. The first task was a continuous-trial sustained attention task. For seven pigeons, the frequency of signal presentation was constant and predictable, once every 60 s [a fixed-interval 60 s (FI-60) signal presentation]. For seven additional pigeons, the frequency of signal presentation averaged once every 60 s, but the interval between presentations was random and variable [a variable-interval 60 s (VI-60) signal presentation]. Following ethanol (0.3-3 g/kg) and pentobarbital (0.3-13 mg/kg), decreases in p(hit) and large increases in p(false alarm) occurred at doses that did not impair response rates. Following D-amphetamine (0.03-5.6 mg/kg) and nicotine (0.03-3 mg/kg), a significant decrease in p(hit) and increase in p(miss) occurred at doses that did not impair response rates. The second task was a discrete-trial attention task, under which eight pigeons were presented a constant and predictable signal and eight were presented a random and unpredictable signal. Following ethanol (0.3-3 g/kg) and pentobarbital (0.3-13 mg/kg), drug effects on accuracy occurred at doses that suppressed responding. The schedule of signal presentation did not alter the effects of ethanol or pentobarbital. Following D-amphetamine (0.03-5.6 mg/kg) and nicotine (0.03-3 mg/kg), a significant decrease in p(hit) and increase in p(error of omission) occurred at doses that did not impair response latencies, but there were no differences between pigeons responding under the predictable (FI-60) or variable (VI-60) signal presentations. The observation of differential drug effects [e.g. p(false alarms)] on performance under the continuous-trial procedure supports the validity of the procedure for measuring drug effects on attention. However, changes in signal predictability had little effect on control or drug conditions under this continuous-trial sustained attention procedure.