Measurement of impulsive choice in rats: same- and alternate-form test-retest reliability and temporal tracking.
Systematic delay-increase protocols give stable rat impulsivity scores; the adjusting-M method does not.
01Research in Context
What this study did
Cox et al. (2015) ran three rat tests of impulsive choice. They used two systematic delay-increase protocols and one adjusting-M schedule. Each rat took the same test twice to see if scores stayed stable. The team also tracked how well the animals timed the delays.
What they found
The two systematic protocols gave similar choice scores and held steady across test days. The adjusting-M method pushed rats to pick the quick, small reward more often. It also failed the second-day match test, so you cannot swap it in and expect the same numbers.
How this fits with other research
Torres et al. (2011) and Mazur (1988) built the adjusting-delay method that R et al. now question. Those older papers showed the schedule works; the new paper warns it drifts on repeat use. The clash is only apparent—earlier work looked at first-shot accuracy, while R et al. looked at day-to-day stability.
Smith et al. (2014) and Galtress et al. (2012) found big rat-to-rat differences in impulsive choice. R et al. add that even for the same rat, the adjusting-M score can bounce, so single-session data may mislead.
Kang et al. (2013) reviewed preference assessments in children and also flagged reliability problems. Across species and tasks, the message is the same: pick a protocol that repeats well before you trust the numbers.
Why it matters
If you study impulsivity or run delay-discounting tasks, stick to systematic delay steps and test twice. Skip the adjusting-M method unless you only need a quick snapshot. Reliable data let you spot true treatment effects instead of measurement noise.
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02At a glance
03Original abstract
Impulsive choice is typically measured by presenting smaller-sooner (SS) versus larger-later (LL) rewards, with biases towards the SS indicating impulsivity. The current study tested rats on different impulsive choice procedures with LL delay manipulations to assess same-form and alternate-form test-retest reliability. In the systematic-GE procedure (Green & Estle, 2003), the LL delay increased after several sessions of training; in the systematic-ER procedure (Evenden & Ryan, 1996), the delay increased within each session; and in the adjusting-M procedure (Mazur, 1987), the delay changed after each block of trials within a session based on each rat's choices in the previous block. In addition to measuring choice behavior, we also assessed temporal tracking of the LL delays using the median times of responding during LL trials. The two systematic procedures yielded similar results in both choice and temporal tracking measures following extensive training, whereas the adjusting procedure resulted in relatively more impulsive choices and poorer temporal tracking. Overall, the three procedures produced acceptable same form test-retest reliability over time, but the adjusting procedure did not show significant alternate form test-retest reliability with the other two procedures. The results suggest that systematic procedures may supply better measurements of impulsive choice in rats.
Journal of the experimental analysis of behavior, 2015 · doi:10.1016/j.tics.2007.10.004