The role of premature evidence accumulation in making difficult perceptual decisions under temporal uncertainty

Abstract

The computations and neural processes underpinning decision making have primarily been investigated using highly simplified tasks in which stimulus onsets cue observers to start accumulating choice-relevant information. Yet, in daily life we are rarely afforded the luxury of knowing precisely when choice-relevant information will appear. Here, we examined neural indices of decision formation while subjects discriminated subtle stimulus feature changes whose timing relative to stimulus onset (‘foreperiod’) was uncertain. Joint analysis of behavioural error patterns and neural decision signal dynamics indicated that subjects systematically began the accumulation process before any informative evidence was presented, and further, that accumulation onset timing varied systematically as a function of the foreperiod of the preceding trial. These results suggest that the brain can adjust to temporal uncertainty by strategically modulating accumulation onset timing according to statistical regularities in the temporal structure of the sensory environment with particular emphasis on recent experience.

Multifaceted adaptation of the neural decision process with prior knowledge of time constraints and stimulus probability

“…Our model also highlights that these components of non-decision time can undergo distinct adjustments; for example, accumulator onset is delayed in the LoCoh regime while motor time is quickened. Further, the decoupling of accumulation onset time from the time that informative evidence is encoded provides a mechanism for anticipatory accumulation in advance of the evidence, which, as we have recently shown, can play a significant role in some circumstances such as when evidence onsets are almost imperceptible and very uncertain in their timing (Devine et al 2019).…”

Evidence accumulation relates to perceptual consciousness and monitoring

“…We developed an evidence accumulation model to fit the behavioral and EEG data, assuming that participants attempted to detect the stimulus by continuously accumulating evidence during a 3 s stimulation window (from trial onset until the response cue). To model the time uncertainty in our task (participants did not know when a stimulus could be applied), we assumed that participants started accumulating evidence before the stimulus onset 41 . This was modeled as a null drift rate across time except for a short-lasting boost triggered by the stimulus.…”

“…No neurological or cognitive abnormality, or anxiety were reported by the clinical team and the patient’s mood was stable. To ensure adequate power, the sample size of the EEG experiment was pre-determined on the basis of prior experimental works assessing perceptual decisions under temporal uncertainty 41 . Eighteen healthy participants (seven females; age: 25.2 years, SD = 4.1) took part in Experiment 4 for a monetary compensation.…”

Temporal expectation hastens decision onset but does not affect evidence quality

“…Our finding of a cue-validity effect on CPP onset latency is consistent with the notion that temporal expectation hastens sensory encoding. However, an alternative possibility is that on validly cued (versus invalidly cued) short-CTI trials, when the target was expected to appear after the short CTI, participants engaged in premature sampling (of noise) on a proportion of the trials Laming, 1979;Devine et al, 2019). That is, participants may anticipate the arrival of a target stimulus and speed up responses by starting to sample information from the display at the moment when they think the stimulus will be presented.…”

“…In contrast, valid and invalid trials did not differ in CPP slope, suggesting that temporal expectation did not affect the quality of the sensory evidence or other processes influencing the rate of decision formation. Control analyses excluded premature sampling of the stimulus array prior to target onset Laming, 1979;Devine et al, 2019) as an alternative explanation of these results.…”