Neural Correlates of the Time Marker for the Perception of Event Timing

The moment of awareness influences the content of awareness in orientation repulsion

Through the neurally evolving process of dynamic contextual modulation of perceptual contents, it remains unclear how the content of awareness is determined. Here we quantified the visual illusion of orientation repulsion, wherein the target appears tilted against the surrounding's orientation, and examined whether its extent changed when the target awareness was quickened by a preceding flanker. Independently of spatial cueing, repulsion was reduced when the flanker preceded the target by 100 ms compared with when they appeared simultaneously. We confirmed that the preceding flanker quickened the awareness of a nearby target relative to distant ones by 40 ms. Furthermore, the preceding flanker that was greater than 7 degrees away from the target still evoked such reduction of repulsion. These findings imply that the content of awareness is determined by the temporal interaction of two distinct processes: one controls the moment of awareness, and the other represents the perceptual content.

The perceived present: What is it, and what is it there for?

It is proposed that the perceived present is not a moment in time, but an information structure comprising an integrated set of products of perceptual processing. All information in the perceived present carries an informational time marker identifying it as "present". This marker is exclusive to information in the perceived present. There are other kinds of time markers, such as ordinality ("this stimulus occurred before that one") and duration ("this stimulus lasted for 50 ms"). These are different from the "present" time marker and may be attached to information regardless of whether it is in the perceived present or not. It is proposed that the perceived present is a very short-term and very high-capacity holding area for perceptual information. The maximum holding time for any given piece of information is ~100 ms: This is affected by the need to balance the value of informational persistence for further processing against the problem of obsolescence of the information. The main function of the perceived present is to facilitate access by other specialized, automatic processes.

Neural markers of memory consolidation do not predict temporal estimates of encoded items

In contrast to the paradigms used in most laboratory experiments on interval timing, everyday tasks often involve tracking multiple, concurrent intervals without an explicit starting signal. As these characteristics are problematic for most existing clock-based models of interval timing, here we explore an alternative notion that suggests that time perception and working memory encoding might be closely connected. In this integrative model, the consolidation of a new item in working memory initiates cortical oscillations that also signal the onset of a time interval. The objective of this study was to test whether memory consolidation indeed acts as the starting signal of interval timing. Participants performed an attentional blink task in which they not only reported the targets, but also the estimated target onsets, allowing us to calculate estimated lag. In the attentional blink task, the second target (T2) in a rapid serial visual presentation is often not reported when it follows quickly after the first target (T1). However, if this fast T2 is reported, memory consolidation of T2 is presumably delayed. Consequently, if memory consolidation determines interval onset, we would expect a later estimated onset when consolidation is delayed. Furthermore, as the P3 ERP component is assumed to reflect memory consolidation, we expect that the estimated onsets and subjective lag are functions of the P3 latencies. The behavioral data show that the presumed delay in memory consolidation did not lead to later estimated onsets. In addition, the EEG results suggest that there was no relationship between P3 latency and subjective lag or estimated onset. Overall, our results suggest that there is no direct link between the encoding of items in working memory and sub-second interval timing of these items in the attentional blink task.

Piercing of Consciousness as a Threshold-Crossing Operation

Many decisions arise through an accumulation of evidence to a terminating threshold. The process, termed bounded evidence accumulation (or drift diffusion), provides a unified account of decision speed and accuracy, and it is supported by neurophysiology in human and animal models. In many situations, a decision maker may not communicate a decision immediately and yet feel that at some point she had made up her mind. We hypothesized that this occurs when an accumulation of evidence reaches a termination threshold, registered, subjectively, as an “aha” moment. We asked human participants to make perceptual decisions about the net direction of dynamic random dot motion. The difficulty and viewing duration were controlled by the experimenter. After indicating their choice, participants adjusted the setting of a clock to the moment they felt they had reached a decision. The subjective decision times (t_SDs) were faster on trials with stronger (easier) motion, and they were well fit by a bounded drift-diffusion model. The fits to the t_SDs alone furnished parameters that fully predicted the choices (accuracy) of four of the five participants. The quality of the prediction provides compelling evidence that these subjective reports correspond to the terminating process of a decision rather than a post hoc inference or arbitrary report. Thus, conscious awareness of having reached a decision appears to arise when the brain’s representation of accumulated evidence reaches a threshold or bound. We propose that such a mechanism might play a more widespread role in the “piercing of consciousness” by non-conscious thought processes.

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Perceptual decisions can arise through an accumulation of evidence to a threshold

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After a stimulus, participants set a clock to the moment they had reached a decision

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An evidence accumulation model fit to these times allowed predictions of accuracy

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The sense of having decided is mediated by a threshold on accumulated evidence