Evaluating dedicated and intrinsic models of temporal encoding by varying context

Abstract

Two general classes of models have been proposed to account for how people process temporal information in the milliseconds range. Dedicated models entail a mechanism in which time is explicitly encoded; examples include clock-counter models and functional delay lines. Intrinsic models, such as state-dependent networks (SDN), represent time as an emergent property of the dynamics of neural processing. An important property of SDN is that the encoding of duration is context dependent since the representation of an interval will vary as a function of the initial state of the network. Consistent with this assumption, duration discrimination thresholds for auditory intervals spanning 100 ms are elevated when an irrelevant tone is presented at varying times prior to the onset of the test interval. We revisit this effect in two experiments, considering attentional issues that may also produce such context effects. The disruptive effect of a variable context was eliminated or attenuated when the intervals between the irrelevant tone and test interval were made dissimilar or the duration of the test interval was increased to 300 ms. These results indicate how attentional processes can influence the perception of brief intervals, as well as point to important constraints for SDN models.

Figure 1

Diagram of the reset task (adapted from Karmarkar & Buonomano 2007). (i) The two-tone (2T) trials and (ii) the three-tone (3T) trials, in which an irrelevant interval (D) precedes the test interval (T), are depicted. (a) In the fixed condition, the irrelevant interval was of a fixed duration, either 100 or 300 ms, across the block. (b) In the variable condition, the duration of the irrelevant interval was variable from trial to trial.

Figure 2

Difference thresholds for experiment 1 in which the standard interval was 100 ms. (a) In the 100–100 group, the irrelevant interval was 100 ms (fix) or varied by approximately 100 ms (var). (b) In the 300–100 group, the irrelevant interval was 300 ms (fix) or varied by approximately 300 ms (var). The difference threshold corresponds to a value two times of that required to be correct on 79% of the trials.

Figure 3

Response bias analysis for experiment 1. Percentage of trials in which the participant responded ‘long’ as a function of the duration of the irrelevant interval on the 3T variable trials ((a) 100–100 group, (b) 300–100 group). The irrelevant intervals were sorted into six bins.

Figure 4

Difference thresholds for experiment 2 in which the standard interval was 300 ms. Irrelevant intervals were determined in the same way as shown in figure 2 ((a) 100–300 group, (b) 300–300 group).

Figure 5

Response bias analysis for experiment 2. Data are plotted as in figure 3 ((a) 100–300 group, (b) 300–300 group).