For the Last Time: Temporal Sensitivity and Perceived Timing of the Final Stimulus in an Isochronous Sequence

Abstract

An isochronous sequence is a series of repeating events with the same inter-onsetinterval. A common finding, is that as a the length of a sequence increases, so does temporal sensitivity to irregularities -that is, the detection of deviations from isochrony is better with a longer sequence. Several theoretical accounts exist in the literature as to how the brain processes sequences for the detection of irregularities, yet there remains to be a systematic comparison of the predictions that such accounts make. To compare the predictions of these accounts, we asked participants to report whether the last stimulus of a regularly-timed sequence appeared 'earlier' or 'later' than expected. Such task allowed us to separately analyse bias and performance.Sequences lengths (3, 4, 5 or 6 beeps) were either randomly interleaved or presented in separate blocks. We replicate previous findings showing that temporal sensitivity increases with longer sequence in the interleaved condition but not in the blocked condition (where performance is higher overall). Results also indicate that there is a consistent bias in reporting whether the last stimulus is isochronous (irrespectively of how many stimuli the sequence is composed of). Such result is consistent with a perceptual acceleration of stimuli embedded in isochronous sequences. From the comparison of the models' predictions we determine that the improvement in sensitivity is best captured by an averaging of successive estimates, but with an element that limits performance improvement below statistical optimality. None of the models considered, however, provides an exhaustive explanation for the pattern of results found.3

Optimal Perceived Timing: Integrating Sensory Information with Dynamically Updated Expectations

“…Stimuli presented isochronously are instead perceptually accelerated both in cases where participants reported if stimuli are perceived to be isochronous (Experiment 1) or whether the final stimulus appears to be presented early or late22. The magnitude of the acceleration of isochronous stimuli is very similar when measured with these two tasks, but it is somewhat smaller than the acceleration effect found with the temporal-order judgment paradigm of Experiment 2.…”

“…Interval-based models assert that the time between two stimuli is represented as a discrete interval duration that is compared with subsequent intervals15161718. The representation is refined when more stimuli are presented, leading to increased performance19202122. In contrast, entrainment models advocate that the phase and frequency of temporal patterns is the important aspect.…”

“…For all these approaches, sensitivity to temporal irregularities should increase as a function of the number of stimuli composing a sequence 19 20 21 22 23 . Moreover, according to interval-based models, the presence of a stimulus sequence should not have an influence on perceptual judgments based on the perceived timing of individual stimuli; only tasks based on perceived duration should be affected.…”

“…We wanted to disambiguate such predictions and characterize the ways in which presenting stimuli in a sequence influences perceived timing. To do this, we asked participants to estimate the perceived timing of events embedded in a regular sequence either by reporting their regularity 22 or by reporting their order with respect to a probe stimulus in another sensory modality. In comparing the results obtained with these two paradigms, we assume that the sequence could have an influence on the expected timing of stimuli thus influencing judgments of regularity.…”

TRF1: It Was the Best of Time(s)…

“…Previous work highlighted that the precision with which we can discriminate isochrony in auditory sequences improves with longer sequences, according to the predictions of computational models of perception(Li, Rhodes, & Di Luca, 2016). Despite the increase in precision, there is an associated decrease in accuracy, which is captured by the prediction of prior entry, where attentional facilitation speeds up perception(Sternburg & Knoll, 1973).…”