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| Effects of Drugs of Abuse on Timing and Choice |
| Saturday, May 28, 2005 |
| 1:00 PM–2:20 PM |
| Lake Ontario (8th floor) |
| Area: BPH |
| Chair: Lori Lieving (University of Texas - Houston Health Sciences Center) |
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| Effects of Marijuana on the Direction and Variability of Temporal Discrimination in Humans |
| Domain: Basic Research |
| LORI LIEVING (University of Texas - Houston Health Science Center), Scott D. Lane (University of Texas - Houston Health Science Center), Don R. Cherek (University of Texas - Houston Health Science Center), Oleg Tcheremissine (University of Texas - Houston Health Science Center), Sylvain Nouvion (University of Texas - Houston Health Science Center) |
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| Abstract: Marijuana has been reported to alter the discrimination of time, although the manner in which temporal discrimination is disturbed has not been well characterized. The present study used a psychophysical approach to examine the effects of marijuana on temporal discrimination in humans. Subjects responded under a discrete-trial procedure in which they were required to push one of two buttons depending on the duration of a conditional stimulus (a blue square on a computer monitor). Correct choices (“C” button after a 2-s stimulus; “A” button after a 4-s stimulus) resulted in an increase in session earnings of $0.12. Intermediate durations (probe stimuli between 2 and 4 s) were also presented. Psychophysical functions relating the probability of judging a duration as “long” (4 s) as a function of actual stimulus durations were characterized by measures of central tendency (point of subjective equality, PSE) and variability (Weber fraction, WF). Smoked marijuana (1.1% and 3.89% THC) produced an increase in the PSE (i.e., a bias to judge intervals as short) and the high dose often increased the WF (i.e., increased variability in temporal discriminations). |
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| Simultaneous Effects of d-Amphetamine on Choice and Timing in Pigeons |
| Domain: Basic Research |
| CHRISTINE E. HUGHES (University of North Carolina, Wilmington), Raymond C. Pitts (University of North Carolina, Wilmington), Randolph C. Grace (University of Canterbury, New Zealand), Anthony P. McLean (University of Canterbury, New Zealand) |
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| Abstract: Effects of d-amphetamine on choice and timing were examined in a concurrent-chains with peak-trials procedure. Four pigeons responded under a concurrent-chains schedule with variable-interval (VI) initial links and fixed-interval (FI) 10-s and 20-s terminal links. Approximately 25% of the terminal links were peak trials; trials were 80 s in length and no reinforcer was delivered during the trial. During the initial link, over 3/4 of each pigeon’s responding occurred on the key associated with the FI 10-s schedule. During the peak trials, the peak of the distribution of responses was close to the schedule value. Once performance was stable, a range of doses of d-amphetamine was administered prior to selected sessions. As the dose of d-amphetamine increased, the distribution of responses during the peak trials shifted leftward slightly, especially in the FI 20-s terminal link. The shifts in the response distributions during the peak trials occurred without a substantial change in the initial-link responding. After the dose-effect curve was determined, the terminal-link schedules were changed to FI 20 s and FI 40 s, and the dose-effect curve was redetermined. These data are relevant to theories about choice and timing and to interpretations of drug effects under procedures that involve reinforcement delay. |
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| Rapid Acquisition of Preference in Concurrent Chains: Effects of d-Amphetamine on Control by Reinforcement Delay |
| Domain: Basic Research |
| RAYMOND C. PITTS (University of North Carolina, Wilmington), We-Min Ta (University of Canterbury, New Zealand), Christine E. Hughes (University of North Carolina, Wilmington), Anthony P. McLean (University of Canterbury, New Zealand), Randolph C. Grace (University of Canterbury, New Zealand) |
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| Abstract: Effects of d-amphetamine on choice were examined using a rapid-acquisition procedure similar to that previously described by Grace, Bragason, and McLean (2003). Four pigeons responded under a concurrent-chains schedule with variable-interval (VI) initial links and fixed-interval (FI) terminal links; one terminal-link schedule always was an FI 8 s and the alternative schedule was either an FI 4 s or an FI 16 s (determined pseudorandomly). Under this procedure, the pigeons acquired a preference based upon reinforcement delay within each session. After stable acquisition was obtained, effects of several doses of d-amphetamine were tested. The primary effect of this drug was to attenuate preference for the more immediate reinforcer. That is, d-amphetamine decreased estimates of the sensitivity to reinforcement delay. These data are consistent with previous findings suggesting that stimulant drugs increase self-control choices by attenuating sensitivity to reinforcement delay. |
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