Time and Memory: Towards a Pacemaker‐free Theory of Interval Timing

Abstract

A popular view of interval timing in animals is that it is driven by a discrete pacemaker-accumulator mechanism that yields a linear scale for encoded time. But these mechanisms are fundamentally at odds with the Weber law property of interval timing, and experiments that support linear encoded time can be interpreted in other ways. We argue that the dominant pacemaker-accumulator theory, scalar expectancy theory (SET), fails to explain some basic properties of operant behavior on interval-timing procedures and can only accommodate a number of discrepancies by modifications and elaborations that raise questions about the entire theory. We propose an alternative that is based on principles of memory dynamics derived from the multiple-time-scale (MTS) model of habituation. The MTS timing model can account for data from a wide variety of time-related experiments: proportional and Weber law temporal discrimination, transient as well as persistent effects of reinforcement omission and reinforcement magnitude, bisection, the discrimination of relative as well as absolute duration, and the choose-short effect and its analogue in number-discrimination experiments. Resemblances between timing and counting are an automatic consequence of the model. We also argue that the transient and persistent effects of drugs on time estimates can be interpreted as well within MTS theory as in SET. Recent real-time physiological data conform in surprising detail to the assumptions of the MTS habituation model. Comparisons between the two views suggest a number of novel experiments.

Can we use verbal estimation to dissect the internal clock? Differentiating the effects of pacemaker rate, switch latencies, and judgment processes

“…For internal clock models, this is the pattern that one would expect from a change in switch latencies when there is no change in the rate of the pacemaker. Of course, this does not necessarily mean that the results of Experiment 1 are due to the relative size of the second marker affecting the time taken to open the switch and end the accumulation of pulses: various accounts of behavioural timing which do not assume a pacemaker-accumulator system at all might equally well explain this pattern (e.g., Machado, 1997;Staddon & Higa, 1999). However, the key point is that Experiment 1 demonstrates that the verbal estimation procedure is capable of producing an intercept effect consistent with a change in switch latencies.…”

“…Many theories of behavioural timing assume the existence of a pacemaker-accumulator system (e.g., Allan, 1998;Gibbon et al 1984;Treisman, 1963;Ulrich et al, 2006;Wearden, 1992;Zakay & Block, 1997; for contrasting accounts, see e.g., Machado, 1997;Mauk & Buonomano, 2004;Staddon & Higa, 1999;Wackermann & Ehm, 2006). There are various instantiations of this idea, but the core assumption is that timing is based on a pacemaker which emits pulses; at the start of the to-be-timed interval, a switch closes so that these pulses flow into an accumulator.…”

Multiple-interval timing in rats: Performance on two-valued mixed fixed-interval schedules.

“…This means that the data predate both the information-processing version of SET (first published in the early 1980s, e.g., by Gibbon et al, 1984, andGibbon, 1982), BeT (Killeen & Fetterman, 1988), and LeT (Machado, 1997) as well as other recent theories (e.g. Staddon & Higa, 1999). The only negative consequence of the age of our data is that we do not have some behavioral measures that might be desirable (e.g.…”

Pigeons’ timing of an arbitrary and a naturalistic auditory stimulus: tone versus cooing

“…As noted earlier, the dominant timing model postulates that the psychological representation of time changes as a linear function of time with a ratio comparison process. An alternative model, the multiple-time-scale model, proposes that timing is the result of the trace strength of a stimulus rather than an internal clock (Staddon and Higa, 1999). This model postulates that the psychological representation of time changes as a logarithmic function of time.…”

“…Although the function that best characterizes the psychological representation of time has been subject to debate (Staddon and Higa, 1999), the popular view of interval timing postulates that time is accumulated in a linear fashion and ratios are computed to determine the operant choice response (Church and Gibbon, 1982). Given the assumptions of a linear accumulation of time and a ratio comparison process, the internal clock model can account for the finding that the PSE is at the geometric mean of the two anchor durations in a temporal bisection procedure.…”