Papers by Morten Overgaard
Trends in Cognitive Sciences, 2016
The relation between first and higher order mental states is currently unknown. In particular, th... more The relation between first and higher order mental states is currently unknown. In particular, the relation between conscious experience and introspection is difficult as the same methods are used to investigate them. In order to make progress in the scientific understanding of consciousness, introspection or both, it is fundamental to understand whether their relation is serial (conscious experience feeds into introspec-tion) or reciprocal. Although the amount of empirical evidence directly addressing this question is sparse, the little that exists suggests a more complex situation that must be taken into account in order to characterise the relationship between first and higher order mental states. We propose a testable integrative model in an attempt to explain the existing data and to make new empirical predictions.
Journal of Vision, 2014
ABSTRACT The contents of consciousness and of short-term memory are hard to disentangle. As it se... more ABSTRACT The contents of consciousness and of short-term memory are hard to disentangle. As it seems intuitive that we represent attended objects in short-term memory and in experience, to many, it also seems intuitive to equate this content. Here we investigated memory resolution for orientation of a probed target in combination with a conscious evaluation of the experienced stimulus using the Perceptual Awareness Scale (PAS; Ramsøy & Overgaard, 2004). Observers were trained to report how they experienced a visual stimulus on a four-point scale representing their experience from "no experience" to a "clear experience" of a probed target. To assess memory resolution we used a Landolt-variation on the visual short-term memory (VSTM) resolution paradigm (e.g. Wilken & Ma, 2004). Set-sizes in the memory display were varied between 1, 2, or 4 elements. With increasing set-size we found that both the guessing parameter and the standard deviation increased, replicating patterns seen in more traditional paradigms using colors (see for example Bays, Catalao, & Husain, 2009). Moreover, we also find a decrease in guessing and standard deviation across PAS scores, showing that the resolution of content in VSTM is correlated with how it is consciously perceived by an observer. However, if we analyze the data across individual PAS scores and set-sizes, a different pattern emerges; across PAS scores we find that people are still affected by set-size in a systematic fashion. Controlling for target confusability we demonstrate that the effect cannot be explained by observers' responses to distractors, which leads us to conclude that contents of consciousness and VSTM may correlate, but are in fact not identical.Meeting abstract presented at VSS 2014
Revealing the dynamics of visual masking using a speeded saccadic choice task
Journal of Vision, 2014
Direct and indirect measures of statistical learning
Behavioral Methods in Consciousness Research, 2015
Statistical learning refers to the ability to discover systematic patterns embedded in a continuo... more Statistical learning refers to the ability to discover systematic patterns embedded in a continuous stream of auditory or visual stimuli. Infants and animal studies suggest that statistical learning may occur implicitly. Studies in adult participants, however, indicate that statistical knowledge can be used in a forced-choice task, suggesting that it is available to awareness. This conclusion is based on the unwarranted assumption that this latter task constitutes an exhaustive and exclusive measure of conscious knowledge. This chapter presents an alternative approach based on the relative sensitivity of direct and indirect tasks to the relevant acquired knowledge. We compared performance in a direct forced-choice completion task and in an indirect rapid serial visual detection task. Sensitivity to statistical regularities was only detected by the indirect task, suggesting that statistical learning can, at least partly, occur implicitly. We close by discussing the limits of these results as well as potential improvements of the method.
Frontiers in Human Neuroscience, 2015
We present a study investigating how the delay between the intention to act and the following act... more We present a study investigating how the delay between the intention to act and the following action, influenced the experience of action. In experiments investigating sense of agency and experience of action, the contrast is most often between voluntary and involuntary actions. It is rarely asked whether different types of intentions influence the experience of action differently. To investigate this we distinguished between proximal intentions (i.e., intentions for immediate actions) and delayed intentions (i.e., intentions with a temporal delay between intention and action). The distinction was implemented in an intentional binding paradigm, by varying the delay between the time where participants formed the intention to act and the time at which they performed the action. The results showed that delayed intentions were followed by a stronger binding effect for the tone following the action compared to proximal intentions. The actions were reported to have occurred earlier for delayed intentions than for proximal intentions. This effect was independent of the binding effect usually found in intentional binding experiments. This suggests that two perceptual shifts occurred in the contrast between delayed intentions and proximal intentions: The first being the binding effect, the second a general shift in the perceived time of action. Neither the stronger binding effect for tone, nor the earlier reports of action, differed across delays for delayed intentions. The results imply that delayed intentions and proximal intentions have a different impact on the experience of action.
Two electrophysiological components have been extensively investigated as candidate neural correl... more Two electrophysiological components have been extensively investigated as candidate neural correlates of perceptual consciousness: An early, occipitally realized component occurring 130-320 ms after stimulus onset and a late, frontally realized component occurring 320-510 ms after stimulus onset. Recent studies have suggested that the late component may not be uniquely related to perceptual consciousness, but also to sensory expectations, task associations, and selective attention. We conducted a magnetoencephalographic study; using multivariate analysis, we compared classification accuracies when decoding perceptual consciousness from the 2 components using sources from occipital and frontal lobes. We found that occipital sources during the early time range were significantly more accurate in decoding perceptual consciousness than frontal sources during both the early and late time ranges. These results are the first of its kind where the predictive values of the 2 components are quantitatively compared, and they provide further evidence for the primary importance of occipital sources in realizing perceptual consciousness. The results have important consequences for current theories of perceptual consciousness, especially theories emphasizing the role of frontal sources.
Consciousness and cognition, 2015
After decades of research, blindsight is still a mysterious and controversial topic in consciousn... more After decades of research, blindsight is still a mysterious and controversial topic in consciousness research. Currently, many researchers tend to think of it as an ideal phenomenon to investigate neural correlates of consciousness, whereas others believe that blindsight is in fact a kind of degraded vision rather than "truly blind". This article considers both perspectives and finds that both have difficulties understanding all existing evidence about blindsight. In order to reconcile the perspectives, we suggest two specific criteria for a good model of blindsight, able to encompass all evidence. We propose that the REF-CON model (Overgaard & Mogensen, 2014) may work as such a model.
Three methods for estimating unconscious processing reveal a window of subliminal perception
Visual Awareness Negativity correlates with small changes in conscious experience
Components of attention in synaesthesia‐congruent grapheme processing
Morten Overgaard (2008), Scholarpedia, 3 (5): 4953. doi: 10.4249/scholarpedia. 4953 revision# 40448 [link to/cite this article]
Introspection refers to an observation and, sometimes, a description of the contents of one&#... more Introspection refers to an observation and, sometimes, a description of the contents of one&#x27;s own consciousness. Introspection is believed to be a reflexive, metacognitive process, attending to or thinking about oneself or what is currently being experienced by oneself. It ...
The time-course of visual masking effects on saccadic responses indicates that masking interferes with reentrant processing
ABSTRACT One of the most common forms of synesthesia is between colors and graphemes (Colizoli, M... more ABSTRACT One of the most common forms of synesthesia is between colors and graphemes (Colizoli, Murre, &amp;amp; Rouw, 2012). Numerous studies have investigated different aspects of attention and synesthesia, e.g. effects of Stroop-like interference by colors that are incongruent with the synesthetic experience. Here we attempt to isolate how specific components of attention are affected by grapheme-color synesthesia. Eight carefully screened healthy participants with synesthesia reported the letters in briefly presented, post-masked arrays of letters and digits. On half the trials, the letters and digits were presented in colors congruent with the synesthetic experience. On the other half of the trials, the letters and digits were presented in colors that were incongruent with the synesthetic experience. Components of attention were estimated separately for congruent and incongruent trials by fitting the data to a mathematical model based on A Theory of Visual Attention (Bundesen, 1990). It has previously been demonstrated that color experiences in observers with synesthesia are very stable over time, and that the color experience seems to be an integrate part of the processing of letters, in for example grapheme-color synesthesia (Mattingley, 2009). Results from the present experiment show that synesthesia affects both speed of processing (C) and the number of objects that can be retained in visual short-term memory (K). Participants were faster at encoding characters that were colored congruently with their synesthesia. In addition, the capacity of the visual short-term memory increased slightly in the congruent compared to the incongruent condition. Interestingly, congruent trials compared to incongruent trials did not seem to afford benefits to attentional selectivity (α), nor did they affect the threshold for visual perception (t0). The results, therefore, indicate that synesthesia relates to a specific subset of attentional components.
Consciousness and introspection
Distinct MEG correlates of conscious experience, perceptual reversals and stabilization during binocular rivalry
NeuroImage, 2014
During binocular rivalry, visual perception alternates spontaneously between two different monocu... more During binocular rivalry, visual perception alternates spontaneously between two different monocular images. Such perceptual reversals are slowed or halted if stimuli are presented intermittently with inter-stimulus intervals larger than ~400 ms--a phenomenon called stabilization. Often, the neural correlates of reversal and stabilization are studied separately, and both phenomena in turn are studied separately from the neural correlates of conscious perception. To distinguish the neural correlates of perceptual content, stabilization and reversal, we recorded MEG signals associated with each in the same group of healthy humans observing repeated trials of intermittent presentation of a dichoptic stimulus. Perceptual content correlated mainly with modulation of stimulus-specific activity in occipital/temporal areas 150-270 ms after stimulus onset, possibly reflecting inhibition of the neural populations representing the suppressed image. Stability of perception reflected a gradual build-up of this modulation across at least 10 trials and was also, to some extent, associated with parietal activity 40-90 ms and 220-270 ms after stimulus onset. Perceptual reversals, in contrast, were associated with parietal (150-270 ms) and temporal (150-210 ms) activity on the trial before the reversal and a gradual change in perception-specific activity in occipital (150-270 ms) and temporal (220-420 ms) areas across at least 10 trials leading up to a reversal. Mechanistically, these findings suggest that stability of perception during rivalry is maintained by modulation of activity related to the two monocular images, and gradual adaptation of neuronal populations leads to instability that is eventually resolved by signals from parietal and late sensory cortices.
Frontiers in Psychology, 2014
Exclusion tasks have been proposed as objective measures of unconscious perception as they do not... more Exclusion tasks have been proposed as objective measures of unconscious perception as they do not depend upon subjective ratings. In exclusion tasks, participants have to complete a task without using a previously presented prime. Use of the prime is taken as evidence for unconscious processing in the absence of awareness, yet it may also simply indicate that participants have weak experiences but fail to realize that these affect the response or fail to counter the effect on the response. Here, we tested this claim by allowing participants to rate their experience of a masked prime on the perceptual awareness scale (PAS) after the exclusion task. Results showed that the prime was used almost as often when participants reported having seen a "weak glimpse" of the prime as when they claimed to have "no experience" of the prime, thus suggesting participants frequently have weak (possibly contentless) experiences of the stimulus when failing to exclude. This indicates that the criteria for report of awareness is lower (i.e., more liberal) than that for exclusion and that failure to exclude should not be taken as evidence of complete absence of awareness.
Frontiers in Psychology, 2014
Frontiers in Human Neuroscience
In a recent commentary published in Frontiers in Human Neuroscience, Catmur (2014) raises several... more In a recent commentary published in Frontiers in Human Neuroscience, Catmur (2014) raises several important questions for discussion about a study we published earlier this year (Michael et al., 2014). In the following, however, we point out that her criticism is based upon two inferences that we do not find convincing, and we maintain that the conservative claim made in our original article is more appropriate than Catmur’s alternative interpretation.
Consciousness and neural plasticity
Frontiers Research Topics, 2012
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Papers by Morten Overgaard