Capacity Limit of Simultaneous Temporal Processing: How Many Concurrent ‘Clocks’ in Vision?

Abstract

A fundamental ability for humans is to monitor and process multiple temporal events that occur at different spatial locations simultaneously. A great number of studies have demonstrated simultaneous temporal processing (STP) in human and animal participants, i.e., multiple ‘clocks’ rather than a single ‘clock’. However, to date, we still have no knowledge about the exact limitation of the STP in vision. Here we provide the first experimental measurement to this critical parameter in human vision by using two novel and complementary paradigms. The first paradigm combines merits of a temporal oddball-detection task and a capacity measurement widely used in the studies of visual working memory to quantify the capacity of STP (CSTP). The second paradigm uses a two-interval temporal comparison task with various encoded spatial locations involved in the standard temporal intervals to rule out an alternative, ‘object individuation’-based, account of CSTP, which is measured by the first paradigm. Our results of both paradigms indicate consistently that the capacity limit of simultaneous temporal processing in vision is around 3 to 4 spatial locations. Moreover, the binding of the ‘local clock’ and its specific location is undermined by bottom-up competition of spatial attention, indicating that the time-space binding is resource-consuming. Our finding that the capacity of STP is not constrained by the capacity of visual working memory (VWM) supports the idea that the representations of STP are likely stored and operated in units different from those of VWM. A second paradigm confirms further that the limited number of location-bound ‘local clocks’ are activated and maintained during a time window of several hundreds milliseconds.

Exaggerated groups: amplification in ensemble coding of temporal and spatial features

“…Also, our findings are relevant for studies in the context of time perception. The effective number of flickering discs that were integrated—around two to four items presented in different spatial locations—might reflect the maximum number of temporal events that can be tracked simultaneously [ 32 , 33 ]. The ensemble representation of visual flicker may be critical for the parallel perception of multiple temporal signals.…”

An investigation of the spatial selectivity of the duration after-effect

“…One possibility is that attentional selection plays a role in the processing of multiple durations. A study by Cheng, Yang, Han, Ding, and Fan (2014) showed that human observers are able to process up to four multiple durations at once. Furthermore, duration tracking performance dropped steadily when attention had to be spread over a larger amount of different duration stimuli.…”

It’s About Time: Studying the Encoding of Duration

“…Given the role of attention in the selective encoding of duration, it is likely that attentional limits dictate the extent to which multiple durations can be effectively selected. In line with this idea, several studies have reported behavioral detriments when processing multiple, temporally overlapping durations (Ayhan, Revina, Bruno, & Johnston, 2012;Cheng et al, 2014;Morgan, Giora, & Solomon, 2008;van Rijn & Taatgen, 2008). Together with the current results, these findings point towards attentional limits in the encoding of duration, suggesting that duration processing is an effortful process with a limited capacity.…”

“…A recent study demonstrated localized duration compression following adaptation to the non-temporal features (i.e. orientation) of visual stimuli (Cheng et al, 2014). While we designed our experiments to reduce adaptation to non-temporal features by introducing spatial separation of adaptation and test stimuli, it is possible that some adaptation to non-temporal features occurred.…”