Intertrial-interval effects on sensitivity (A') and response bias (B") in a temporal discrimination by rats.
Shorter gaps between trials sharpen timing and raise reinforcement density, but they can also nudge learners toward long guesses.
01Research in Context
What this study did
The team worked with rats in a temporal discrimination task.
Animals chose whether a sound was short or long.
The researchers varied the quiet gap between trials from 5 to 80 seconds.
They tracked two things: how well the rats told time and whether they leaned toward long or short guesses.
What they found
Longer gaps cut the number of reinforcers per minute.
Sensitivity to time dropped as gaps grew.
Surprise: longer gaps made rats pick long more often, not less.
The bias result ran opposite to classic timing theory.
How this fits with other research
Okouchi (2003) later showed the same thing in a new way.
Rats on fixed-interval schedules worked faster when earlier sessions had short gaps, slower when they had long gaps.
Together the two studies say gap history sets the clock speed for the next session.
Santos et al. (2019) extended the idea to pigeons in a midsession reversal task.
Unequal reward rates across the session shifted timing errors, proving the rule works across species and tasks.
Wulfert (1994) added extra food between trials and saw rats choose the small-sooner reward more often.
That conceptual replication ties gap events to both timing and self-control.
Why it matters
For your learners, reinforcement density is a hidden clock.
Keep intertrial times short when you want sharp, fast discriminations.
If you must stretch gaps, expect slower responding and more long guesses.
Watch for carry-over: yesterday’s gap schedule can speed or slow today’s session.
Use steady, balanced reward rates mid-session to avoid timing errors in reversal tasks.
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02At a glance
03Original abstract
Killeen and Fetterman's (1988) behavioral theory of animal timing predicts that decreases in the rate of reinforcement should produce decreases in the sensitivity (A') of temporal discriminations and a decrease in miss and correct rejection rates (decrease in bias toward "long" responses). Eight rats were trained on a 10- versus 0.1-s temporal discrimination with an intertrial interval of 5 s and were subsequently tested on probe days on the same discrimination with intertrial intervals of 1, 2.5, 5, 10, or 20 s. The rate of reinforcement declined for all animals as intertrial interval increased. Although sensitivity (A') decreased with increasing intertrial interval, all rats showed an increase in bias to make long responses.
Journal of the experimental analysis of behavior, 1992 · doi:10.1901/jeab.1992.58-527