publications

Preprints

2025

1. PsyArXiv

   The Act of Detecting a Stimulus Contaminates Measures of Conscious Experience with Unrelated Cognitive Factors

   Nicolás Sánchez-Fuenzalida, Chris Jungerius, Stephen Fleming, and 2 more authors

   May 2025

   Abs DOI

   A central challenge in consciousness research is determining whether observers truly experience a stimulus. However, present/absent detection judgments are often biased by contextual factors, making it difficult to isolate conscious perception from non-perceptual influences. Traditional psychophysical methods cannot disentangle these components. To address this, we conducted in-person experiments (N=505) in which participants detected and reproduced dim stimuli under three contextual manipulations: attentional cues, asymmetrical base rates, and payoff schemes. Using a Hurdle-Gaussian model, we separated perceptual from non-perceptual effects. We found that statistical priors (base rate) and reward structures (payoff) induced non-perceptual shifts in reproduction behavior, whereas attentional cues led to shifts that reflect changes in conscious experience. Critically, when reproduction tasks were embedded within a detection context, reports of conscious experience were contaminated by non-perceptual effects. This highlights the need for caution in using and interpreting results relying on detection judgments in consciousness research.

2. PsyArXiv

   Evidence for Unconscious Priming Using a Bayesian Single-Subject Approach

   Nicolás Sánchez-Fuenzalida, Simon Gaal, Zazie Hurk, and 2 more authors

   Nov 2025

   Abs DOI

   Although many studies have claimed the existence of unconscious priming, a valid statistical procedure for substantiating such claims is often lacking. For instance, the absence of prime awareness is often erroneously inferred from non-significant p-values, and priming and awareness are typically tested by comparing the outcomes of two separate t-tests. In a classic study by Vorberg (2003), observers were slower to identify the direction of an arrow mask when it followed an arrow prime pointing in the opposite direction (priming effect), despite being unable to identify the direction of the arrow prime (prime awareness). Using that observation as a starting point, we address several methodological shortcomings that we identified in that study (as in many other studies in the field). To overcome these shortcomings, we implemented three critical changes. First, we employed a Bayesian methodological-statistical framework to test priming effects and prime awareness at the single-subject level over multiple experimental sessions. Second, participants underwent extensive training in the prime awareness task to ensure they understood and executed the task as intended. Third, we directly compared prime awareness and the priming effect. By using this approach, we show unconscious processing at short prime-mask stimulus onset asynchronies (SOAs) in three out of six participants, replicating Vorberg et al. (2003). However, we also show that – unlike in the original study – unconscious priming was not consistently present across all SOAs, and awareness increased with increasing prime-mask SOA. Notably, priming effects were highly consistent across participants, whereas awareness showed substantial variability across participants.

Peer-Reviewed

2025

1. Commun Psychol

   Confidence Reports during Perceptual Decision Making Dissociate from Changes in Subjective Experience

   Nicolás Sánchez-Fuenzalida, Simon Gaal, Stephen M. Fleming, and 2 more authors

   Communications Psychology, May 2025

   Abs DOI

   In noisy perceptual environments, people frequently make decisions based on non-perceptual information to maximize rewards. Therefore, a central problem in psychophysics, metacognition and consciousness research is to distinguish between decisions resulting from changes in subjective experience and those arising from non-perceptual information. It has recently been proposed that confidence reports can be used to discriminate between changes in subjective experience and those arising from non-perceptual information. Here we use a Bayesian ordinal modelling framework combined with an explicit measure of subjective experience to show across two experiments (N = 204) and three bias manipulations that confidence during perceptual decision-making does not uniquely reflect subjective experience. Instead, non-perceptual manipulations affecting response bias leak into perceptual confidence reports. This occurs not only for biases resulting from changes in the base rate of stimuli (cognitive priors), but also when biasing information does not inform decision correctness (asymmetric payoff matrix). The relative strength of biases in first-order responses and confidence may help disentangle whether a given bias manipulation is perceptual in nature or not.

2023

1. PNAS

   Predictions and Rewards Affect Decision-Making but Not Subjective Experience

   Nicolás Sánchez-Fuenzalida, Simon Gaal, Stephen M. Fleming, and 2 more authors

   Proceedings of the National Academy of Sciences, Oct 2023

   Abs DOI

   To survive, organisms constantly make decisions to avoid danger and maximize rewards in information-rich environments. As a result, decisions about sensory input are not only driven by sensory information but also by other factors, such as the expected rewards of a decision (known as the payoff matrix) or by information about temporal regularities in the environment (known as cognitive priors or predictions). However, it is unknown to what extent these different types of information affect subjective experience or whether they merely result in nonperceptual response criterion shifts. To investigate this question, we used three carefully matched manipulations that typically result in behavioral shifts in decision criteria: a visual illusion (Muller-Lyer condition), a punishment scheme (payoff condition), and a change in the ratio of relevant stimuli (base rate condition). To gauge shifts in subjective experience, we introduce a task in which participants not only make decisions about what they have just seen but are also asked to reproduce their experience of a target stimulus. Using Bayesian ordinal modeling, we show that each of these three manipulations affects the decision criterion as intended but that the visual illusion uniquely affects sensory experience as measured by reproduction. In a series of follow-up experiments, we use computational modeling to show that although the visual illusion results in a distinct drift-diffusion (DDM) parameter profile relative to nonsensory manipulations, reliance on DDM parameter estimates alone is not sufficient to ascertain whether a given manipulation is perceptual or nonperceptual.