Hakwan Lau

Publications of Hakwan Lau

• Does response interference depend on the subjective visibility of flanker distractors?

  Authors: Brian Maniscalco, Joo Won Bang, Laila Iravani, Franc Camps-Febrer, Hakwan Lau

  Attention, perception & psychophysics. 04/2012;

  Response interference (or response conflict) refers to the phenomenon whereby response times to a target stimulus are longer in the presence of distractor stimuli that indicate contrary motorResponse interference (or response conflict) refers to the phenomenon whereby response times to a target stimulus are longer in the presence of distractor stimuli that indicate contrary motor responses. Response interference has been observed even when the distractor stimuli cannot be discriminated above chance levels. These results raise the question of whether response interference might be driven automatically by the physical distractor stimuli, independently of one's subjective perception of the distractors. Using a modified version of the Eriksen flanker task, we applied metacontrast masks to the flanker stimuli and measured their subjective visibility after each trial. We found converging lines of evidence that the subjective perception of flankers contributed to response interference, over and above the contribution of automatic processing of the stimulus itself. A factorial analysis revealed that the objective, physical congruency of target and flankers and the subjective, perceptual congruency of target and flankers make additive, noninteracting contributions to target response interference, suggesting that the two interference effects originate from independent levels or stages of cognitive processing.

• Subliminal stimuli in the near absence of attention influence top-down cognitive control.

  Authors: Dobromir A Rahnev, Elliott Huang, Hakwan Lau

  Attention, perception & psychophysics. 12/2011; 74(3):521-32.

  Recent research has shown that visual stimuli can influence cognitive control functions, even if subjects are unaware of the identity of the stimuli. However, in those previous studies, subjectsRecent research has shown that visual stimuli can influence cognitive control functions, even if subjects are unaware of the identity of the stimuli. However, in those previous studies, subjects actively attended to the location of the subliminal stimuli. Here we assessed the role of endogenous spatial attention in such paradigms. We required subjects to quickly prepare for one of two numerical judgment tasks on the basis of the direction of motion in patches of moving dots presented in cued spatial locations. We found that irrelevant motion patches presented in the uncued spatial locations also influenced task performance. Motion in the uncued patches was weak and did not affect the perception of the cued patches. Further analyses suggested that the effect of priming by the uncued stimuli was present even for subjects who could only discriminate such stimuli at chance level. Three additional experiments confirmed that subjects paid minimal attention to the uncued locations, in that the subjects could not perform simple discriminations of conjunctions of features in those locations.

• Direct injection of noise to the visual cortex decreases accuracy but increases decision confidence.

  Authors: Dobromir Asenov Rahnev, Brian Maniscalco, Bruce Luber, Hakwan Lau, Sarah H Lisanby

  Journal of neurophysiology. 12/2011;

  The relationship between accuracy and confidence in psychophysical tasks has been traditionally assumed to be mainly positive, i.e. the two typically increase or decrease together. However, recentThe relationship between accuracy and confidence in psychophysical tasks has been traditionally assumed to be mainly positive, i.e. the two typically increase or decrease together. However, recent studies have reported examples of exceptions where confidence and accuracy dissociate from each other. Explanations for such dissociations often involve dual-channel models in which a cortical channel contributes to both accuracy and confidence, while a sub-cortical channel only contributes to accuracy. Here we show that a single-channel model derived from signal detection theory (SDT) can also account for such dissociations. We applied transcranial magnetic stimulation (TMS) to the occipital cortex to disrupt the internal representation of a visual stimulus. The results showed that, consistent with previous research, occipital TMS decreased accuracy. However, counter-intuitively, it also led to an increase in confidence ratings. The data were predicted well by a single-channel SDT model which posits that occipital TMS increased the variance of the internal stimulus distributions. A formal model comparison analysis that used information theoretic methods confirmed that this model was preferred over single-channel models in which occipital TMS changed the signal strength, or dual-channel models which assume two different processing routes. Thus, our results show that dissociations between accuracy and confidence can, at least in some cases, be accounted for by a single-channel model.

• Attention induces conservative subjective biases in visual perception.

  Authors: Dobromir Rahnev, Brian Maniscalco, Tashina Graves, Elliott Huang, Floris P de Lange, Hakwan Lau

  Nature neuroscience. 12/2011; 14(12):1513-5.

  Although attention usually enhances perceptual sensitivity, we found that it can also lead to relatively conservative detection biases and lower visibility ratings in discrimination tasks. TheseAlthough attention usually enhances perceptual sensitivity, we found that it can also lead to relatively conservative detection biases and lower visibility ratings in discrimination tasks. These results are explained by a model in which attention reduces the trial-by-trial variability of the perceptual signal, and we determined how this model led to the observed behavior. These findings may partially reflect our impression of 'seeing' the whole visual scene despite our limited processing capacity outside of the focus of attention.

• A signal detection theoretic approach for estimating metacognitive sensitivity from confidence ratings.

  Authors: Brian Maniscalco, Hakwan Lau

  Consciousness and cognition. 11/2011; 21(1):422-30.

  How should we measure metacognitive ("type 2") sensitivity, i.e. the efficacy with which observers' confidence ratings discriminate between their own correct and incorrect stimulus classifications?How should we measure metacognitive ("type 2") sensitivity, i.e. the efficacy with which observers' confidence ratings discriminate between their own correct and incorrect stimulus classifications? We argue that currently available methods are inadequate because they are influenced by factors such as response bias and type 1 sensitivity (i.e. ability to distinguish stimuli). Extending the signal detection theory (SDT) approach of Galvin, Podd, Drga, and Whitmore (2003), we propose a method of measuring type 2 sensitivity that is free from these confounds. We call our measure meta-d', which reflects how much information, in signal-to-noise units, is available for metacognition. Applying this novel method in a 2-interval forced choice visual task, we found that subjects' metacognitive sensitivity was close to, but significantly below, optimality. We discuss the theoretical implications of these findings, as well as related computational issues of the method. We also provide free Matlab code for implementing the analysis.

• The higher-order view does not require consciously self-directed introspection: response to Malach.

  Authors: Hakwan Lau, David Rosenthal

  Trends in cognitive sciences. 10/2011;

• Awareness-related activity in prefrontal and parietal cortices in blindsight reflects more than superior visual performance.

  Authors: Navindra Persaud, Matthew Davidson, Brian Maniscalco, Dean Mobbs, Richard E Passingham, Alan Cowey, Hakwan Lau

  NeuroImage. 09/2011; 58(2):605-11.

  Many imaging studies report activity in the prefrontal and parietal cortices when subjects are aware as opposed to unaware of visual stimuli. One possibility is that this activity simply reflectsMany imaging studies report activity in the prefrontal and parietal cortices when subjects are aware as opposed to unaware of visual stimuli. One possibility is that this activity simply reflects higher signal strength or the superior task performance that is associated with awareness. To find out, we studied the hemianope GY who has unilateral destruction of almost all primary visual cortices. He exhibits 'blindsight', that is, he claims to have no conscious visual phenomenology (i.e., no visual qualia), for stationary stimuli presented to his right visual field (the blind field), although he can press keys to distinguish between different stimuli presented there. We presented to him a visual discrimination task, and equated performance for stimuli presented to the left or right visual field by presenting low contrast stimuli to his normal (left) field and high contrast stimuli to his blind (right) field. Superior accuracy can be a serious confound, and our paradigm allows us to control for it and avoid this confound. Even when performance was matched, and the signal strength was lower, visual stimulation to the normal (conscious) field led to higher activity in the prefrontal and parietal cortices. These results indicate that the activity in the prefrontal and parietal areas that has been reported in previous studies of awareness is not just due to a (signal strength or performance) confounds. One possibility is that it reflects the superior 'metacognitive' capacity that is associated with awareness, because GY was better able to distinguish between his own correct and incorrect responses for stimuli presented to his normal field than to his blind field.

• Empirical support for higher-order theories of conscious awareness.

  Authors: Hakwan Lau, David Rosenthal

  Trends in cognitive sciences. 08/2011; 15(8):365-73.

  Higher-order theories of consciousness argue that conscious awareness crucially depends on higher-order mental representations that represent oneself as being in particular mental states. TheseHigher-order theories of consciousness argue that conscious awareness crucially depends on higher-order mental representations that represent oneself as being in particular mental states. These theories have featured prominently in recent debates on conscious awareness. We provide new leverage on these debates by reviewing the empirical evidence in support of the higher-order view. We focus on evidence that distinguishes the higher-order view from its alternatives, such as the first-order, global workspace and recurrent visual processing theories. We defend the higher-order view against several major criticisms, such as prefrontal activity reflects attention but not awareness, and prefrontal lesion does not abolish awareness. Although the higher-order approach originated in philosophical discussions, we show that it is testable and has received substantial empirical support.

• Prior expectation modulates the interaction between sensory and prefrontal regions in the human brain.

  Authors: Dobromir Rahnev, Hakwan Lau, Floris P de Lange

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 07/2011; 31(29):10741-8.

  How do expectations about the identity of a forthcoming visual stimulus influence the neural mechanisms of perceptual decision making in the human brain? Previous investigations into this issue haveHow do expectations about the identity of a forthcoming visual stimulus influence the neural mechanisms of perceptual decision making in the human brain? Previous investigations into this issue have mostly involved changing the subjects' attentional focus or the behavioral relevance of certain targets but rarely manipulated subjects' prior expectation about the likely identity of the stimulus. Also, because perceptual decisions were often paired with specific motor responses, it has been difficult to dissociate neural activity that reflects perceptual decisions from motor preparatory activity. Here we designed a task in which we induced prior expectations about the direction of a moving-dot pattern and withheld the stimulus-response mapping until the subjects were prompted to respond. In line with current models of perceptual decision making, we found that subjects' performance was influenced by their expectation about upcoming motion direction. The integration of such information into the decision process was reflected by heightened activity in the dorsolateral prefrontal cortex. Activity in this area reflected the degree to which subjects adjusted their decisions based on the prior expectation cue. Furthermore, there was increased effective connectivity between sensory regions (motion-sensitive medial temporal area MT+) and dorsolateral prefrontal cortex when subjects had a prior expectation about the upcoming motion direction. Dynamic causal modeling suggested that stimulus expectation modulated both the feedforward and feedback connectivity between MT+ and prefrontal cortex. These results provide a mechanism of how prior expectations may affect perceptual decision making, namely by changing neural activity in, and sensory drive to, prefrontal areas.

• Neuroscience. Should confidence be trusted?

  Authors: Hakwan Lau, Brian Maniscalco

  Science (New York, N.Y.). 09/2010; 329(5998):1478-9.

• Direct assessment of qualia in a blindsight participant.

  Authors: Navindra Persaud, Hakwan Lau

  Consciousness and cognition. 10/2008; 17(3):1046-9.

  Experimenters generally infer whether participants have visual experiences based on metacognitive responses. We showed a well-studied blindsight participant, GY, several definitions of the termExperimenters generally infer whether participants have visual experiences based on metacognitive responses. We showed a well-studied blindsight participant, GY, several definitions of the term "qualia" and then questioned him about whether he felt or he experienced qualia in his normal and blind fields. We found, contrary to others who have used different methods for measuring qualia, that GY does not have qualia for stationary stimuli in his blind field. This novel method for directly assessing qualia embraces the idea that experiences should be related by the experiencer, not the experimenter.

• How the brain translates money into force: a neuroimaging study of subliminal motivation.

  Authors: Mathias Pessiglione, Liane Schmidt, Bogdan Draganski, Raffael Kalisch, Hakwan Lau, Ray J Dolan, Chris D Frith

  Science (New York, N.Y.). 06/2007; 316(5826):904-6.

  Unconscious motivation in humans is often inferred but rarely demonstrated empirically. We imaged motivational processes, implemented in a paradigm that varied the amount and reportability ofUnconscious motivation in humans is often inferred but rarely demonstrated empirically. We imaged motivational processes, implemented in a paradigm that varied the amount and reportability of monetary rewards for which subjects exerted physical effort. We show that, even when subjects cannot report how much money is at stake, they nevertheless deploy more force for higher amounts. Such a motivational effect is underpinned by engagement of a specific basal forebrain region. Our findings thus reveal this region as a key node in brain circuitry that enables expected rewards to energize behavior, without the need for the subjects;awareness.

• Dissociating response selection and conflict in the medial frontal surface.

  Authors: Hakwan Lau, Robert D Rogers, Richard E Passingham

  NeuroImage. 02/2006; 29(2):446-51.

  Response conflict and random response selection have both been associated with activations on the medial frontal surface. Random response selection was typically studied using a 'free selection'Response conflict and random response selection have both been associated with activations on the medial frontal surface. Random response selection was typically studied using a 'free selection' paradigm, in which subjects have to select between equally legitimate responses which are in competition with each other. Therefore, one interpretation is that the generation of spontaneous actions is merely a special case of the induction of response conflict. It has been reported that the generation of spontaneous actions is tightly associated with activity in the pre-supplementary motor area (pre-SMA). Most studies of response conflict, on the other hand, suggest that activations in a different and more ventral area, the anterior cingulate, reflect response conflict. Nonetheless, contradictory results have also been reported. To clarify this issue, in this experiment, we have put together a version of the Eriksen flanker task and a free selection task to allow for a direct comparison. We confirmed our hypothesis that free selection is associated with the pre-SMA, whereas response conflict is associated in the anterior cingulate. The two clusters of activation do not overlap, and the peaks of them were about 30 mm apart. We conclude that the activity in the pre-SMA is related to the endogenous generation of action rather than response conflict.