International Journal of Comparative Psychology

Long-interval timing fills the gap between the traditional range of short-interval timing (i.e., seconds to minutes) and the limited range of circadian entrainment (i.e., approximately a day).  A number of reports suggest that rats time long intervals.  However, a recent report proposed that anticipation of long, but noncircadian, intervals is highly constrained.  We tested the hypothesis that long-interval timing is highly constrained by examining a number of cases:  7, 8, 9, 11, 12, and 13 hour intermeal intervals.  We found evidence for long interval timing in each case.  Long interval timing appears to be robust.