Time Interval Estimation: Internal Clock or Attentional Mechanism?

Time Interval Estimation: Internal Clock or Attentional Mechanism? Niels Taatgen 1,2 (taatgen@cmu.edu), John Anderson 1 (ja@cmu.edu), Daniel Dickison 1 (danieldickison@cmu.edu) and Hedderik van Rijn 2 (hedderik@ai.rug.nl) Carnegie Mellon University, Department of Psychology, 5000 Forbes Av. Pittsburgh, PA 15213 USA University of Groningen, Department of Artificial Intelligence, Grote Kruisstraat 2/1 NL-9712 TS Groningen, Netherlands Abstract reproduced interval. On the other hand, if they have to do a demanding task during the reproduction of the interval, their cognitive counting is slower resulting in a longer interval. The human ability to accurately estimate time intervals in the order of 0 to 20 seconds can be explained by two seemingly incompatible theories: the internal clock and the attentional counter theory. Based on a dual timing task experiment we conclude that a symbiosis of both theories is necessary to explain all the phenomena found in our experiment and in the experiments we review. This conclusion is supported by the computational models we present of the experiments. Interval Estimation The human ability to routinely estimate short time intervals plays an important role in everyday life. Time estimates play a role in situations where we take an action and expect some response, for example when we click on a link in a web-browser, in real-world decisions, for example judging whether we should brake for a yellow traffic light or not, and in multi-tasking situations where we have to strategically switch between tasks, for example using a mobile phone in a car. There are at least two theories that address interval estimation, the attentional counter theory and the internal clock theory. The attentional counter theory (Hick et al, 1977; Thomas & Weaver, 1975) assumes that there is a cognitive timer that counts subjective time events. Increasing the counter is a process that requires attention. As a consequence, if there are other processes competing for attention, the counter is increased less often, “stretching” time. For example, in an experiment by Zakay (1993), participants had to estimate a 12 second interval. In one condition, they had to estimate the interval while doing a secondary task, and had to reproduce it while doing nothing else. In the other condition, they had to estimate the interval while doing nothing else, but had to reproduce it while doing a secondary task. The secondary tasks were, in increasing level of complexity: - No secondary task (ET, empty time) - Reading color words (printed in black) (W) - The Stroop task: Naming the color names of color words printed in incongruent ink (CW) - Color-word associations: like the Stroop task, but now participants had to name a word associated with the ink color (CWA) Figure 1 shows the results of this experiment. In the relatively easy ET and W conditions there is no effect of the secondary task, but in the more demanding CW and CWA tasks, time estimates are affected. According to the attentional counter theory, when the participants have to do a demanding secondary task during presentation of an interval, they can devote less attention to keeping track of time, resulting in a lower cognitive count and a shorter Figure 1: Results of Zakay’s (1993) experiment. The internal clock theory (i.e., Matell & Meck, 2000) states that the brain has devoted several areas that implement a time estimation system. The general idea is that certain stimuli can synchronize neurons in a certain area of the cortex, effectively acting as a starting sign. As each of the neurons produces its own particular pattern of activation over time, each interval is associated with a unique pattern of activation. These patterns can then be read out by other brain areas in the basal ganglia. Contrary to the attentional counter theory, the timing system does not require any attention, and errors in time estimation are mainly due to noise. In a typical interval timing experiment (Rakitin et al, 1998) participants were presented with intervals of 8, 12 and 21 seconds, which they then had to reproduce. Figure 2 shows the results of this experiment in terms of the distributions of the responses. Although the variance increases for larger intervals, the peaks of each of the distributions are exactly at the duration of the interval that the participants had to estimate. An important difference between the Zakay (1993) and Rakitin et al. (1998) experiments is that in the Zakay experiment each participant produced exactly one time interval, while in the Rakitin et al. experiment they produced 80 intervals with feedback on the true duration every few trials. Although in the Rakitin task there is a secondary task to prevent participants from counting, this task is always the same and doesn’t produce the distortions in time perception in the Zakay experiment. When just looking at these two experiments, the attentional counter theory is consistent with both, but the internal clock theory only with the Rakitin experiment. On the other hand, many