Biomedical subjects

Stefan Wiens

Publications and source records attributed to Stefan Wiens.

8 recordsLinked to original sources

PubMed2006

Subliminal emotion perception in brain imaging: findings, issues, and recommendations.

Many theories of emotion propose that emotional input is processed preferentially due to its relevance for the organism. Further, because consciousness has limited capacity, these considerations imply that emotional input ought to be processed even if participants are perceptually unaware of the input (subliminal perception). Although brain imaging has studied effects of unattended, suppressed (in binocular rivalry), and visually masked emotional pictures, conclusions regarding subliminal perception have been mixed. The reason is that subliminal perception demands a concept of an awareness threshold or limen, but there is no agreement on how to define and measure this threshold. Although different threshold concepts can be identified in psychophysics (signal detection theory), none maps directly onto perceptual awareness. Whereas it may be tempting to equate unawareness with the complete absence of objective discrimination ability (d'=0), this approach is incompatible with lessons from blindsight and denies the subjective nature of consciousness. This review argues that perceptual awareness is better viewed as a continuum of sensory states than a binary state. When levels of awareness are characterized carefully in terms of objective discrimination and subjective experience, findings can be informative regarding the relative independence of effects from awareness and the potentially moderating role of awareness in processing emotional input. Thus, because the issue of a threshold concept may never be resolved completely, the emphasis is to not prove subliminal perception but to compare effects at various levels of awareness.

Attention↗

PubMed2006

Current concerns in visual masking.

Theories of emotion postulate that emotional input is processed independently from perceptual awareness. Although visual masking has a long tradition in studying whether emotional pictures are processed below a supposed threshold of perceptual awareness (subliminal perception), a consensus has yet to be reached. This article reviews current concerns in the use of visual masking. These include a reliable presentation method, the role of masking pictures, common definitions of awareness and their problems, current models of awareness, and neural mechanisms. A useful strategy may be the study of dose-response relationships between awareness and emotion processing that avoids a dichotomous view of awareness and allows conclusions about the relative independence of emotional processing from awareness.

Affect↗

PubMed2005

Visual masking in magnetic resonance imaging.

When a brief target picture is followed by another picture (mask), people often report that they are not consciously aware of the target. Thus, visual masking can be used to manipulate perceptual awareness of target pictures. To avoid interference with magnetic resonance imaging, pictures have been presented on liquid crystal device (LCD) and thin film transistor (TFT) projectors that were placed outside of the scanner room. However, we found that display devices with LCD/TFT technology exhibit poor accuracy in presenting pictures at brief durations [Wiens, S., Fransson, P., Dietrich, T., Lohmann, P., Ingvar, M., Ohman, A., 2004. Keeping it short: A comparison of methods for brief picture presentation. Psychological Science, 15, 282--285]. In this paper, we present a reliable and valid masking procedure involving two LCD/TFT projectors in combination with mechanical shutters. Because LCD/TFT projectors present pictures in steady state at longer durations (e.g., after 70 ms), picture presentation is more ecologically valid than for common cathode ray tube (CRT) monitors that present pictures in multiples of refresh cycles. Also, because picture presentation with mechanical shutters is instantaneous and reliable in terms of onset, rise time, and duration, shutters can be used to control picture durations precisely in steps of milliseconds. In this paper, we also discuss risks for confounding effects from unreliable picture presentations in masking. Our findings and arguments recommend the use of mechanical shutters in front of LCD/TFT projectors in imaging studies of visual masking.

Humans↗

PubMed2005

Interoception in emotional experience.

PURPOSE OF REVIEW: Many theories of emotion have postulated a close relationship of the feedback of physiological changes and their perception with emotional experience. This paper reviews recent advances in theory and brain-imaging research on this topic of interoception and describes a hypothetical model of the potential mechanisms. RECENT FINDINGS: Research from patients with spinal-cord injuries and pure autonomic failure suggests that emotion-related peripheral autonomic changes are not necessary for emotional experience. However, in support of a role for centrally integrated feedback from the whole body, imaging studies found that activations in areas commonly associated with interoception and emotion (anterior insula and anterior cingulate) were correlated with individual differences in interoception (heartbeat detection) and trait measures of emotion. Because recent theory distinguishes between two levels of emotional experience (phenomenology and awareness), this paper proposes a hypothetical model of the effects of interoception on phenomenology and awareness. This model classifies interoception into the central representation of feedback from the whole body, the perception of actual physiological changes as well as the perception of illusory changes. SUMMARY: Consistent with recent theories of emotion, evidence from brain imaging supports the notion that centrally integrated feedback from the whole body plays a role in emotional experience. Because research on neural correlates of emotional experience is at an early stage, the hypothesized model of potential causal links between interoception and emotional experience might serve as a helpful guide to future research.

Autonomic Nervous System↗

PubMed2004

Neural systems supporting interoceptive awareness.

Influential theories of human emotion argue that subjective feeling states involve representation of bodily responses elicited by emotional events. Within this framework, individual differences in intensity of emotional experience reflect variation in sensitivity to internal bodily responses. We measured regional brain activity by functional magnetic resonance imaging (fMRI) during an interoceptive task wherein subjects judged the timing of their own heartbeats. We observed enhanced activity in insula, somatomotor and cingulate cortices. In right anterior insular/opercular cortex, neural activity predicted subjects' accuracy in the heartbeat detection task. Furthermore, local gray matter volume in the same region correlated with both interoceptive accuracy and subjective ratings of visceral awareness. Indices of negative emotional experience correlated with interoceptive accuracy across subjects. These findings indicate that right anterior insula supports a representation of visceral responses accessible to awareness, providing a substrate for subjective feeling states.

Acoustic Stimulation↗

PubMed2004

Keeping it short: a comparison of methods for brief picture presentation.

Research has shown that backward masking is a powerful tool for studying unconscious mental processes. Whereas studies have traditionally presented stimuli using cathode-ray tube (CRT) monitors or mechanical shutters together with slide projectors, recent studies (mainly in functional magnetic resonance imaging, fMRI) have begun to use methods based on liquid crystal displays (LCDs) and thin-film transistor (TFT) technology. However, because of differences in technology, all methods may not be equally suited for masking. When methods were compared for their accuracy in presenting pictures at short durations, LCD and TFT presentations had poor accuracy, but shutter and CRT presentations had better accuracy. Because CRTs interfere with the imaging process in fMRI, we recommend the use of mechanical shutters. However, our results may not generally apply to all displays, so we advise researchers to validate the presentation parameters of their displays. The procedure described here may be useful for that purpose.

Consciousness↗

PubMed2003

Effects of trial order and differential conditioning on acquisition of differential shock expectancy and skin conductance conditioning to masked stimuli.

Research suggests that when people are fear conditioned to masked spiders and snakes (electric shocks are contingent on only spiders or snakes), they acquire a conditional skin conductance response and can predict the occurrence of shocks even though they are unable to identify the masked spiders and snakes. Because in prior studies trial order was not completely random, it is unclear if findings were due to the contingencies from differential conditioning or a restricted trial order or both. When participants were assigned to four groups to disentangle effects of trial order and differential conditioning to masked pictures in acquisition, effects were obtained only for trial order. These findings demonstrate that trial order can result in conditioning. However, because effects were observed even for participants who reported unawareness of the contingency from trial order, results are consistent with the notion of hunches or gut feelings.

Adult↗

PubMed2002

Unawareness is more than a chance event: comment on Lovibond and Shanks (2002).

P. F. Lovibond and D. R. Shanks (2002) suggested that expectancy of the unconditional stimulus and emotional ratings are valid indexes of awareness in Pavlovian conditioning and that participants are aware if they can discriminate the conditional stimuli. However, research suggests that processes that are irrelevant to awareness affect these measures. Further, as awareness refers to conscious experience, a valid measures needs to index subjective state rather than discrimination ability. In support, research using subjective measures has demonstrated qualitatively different effects depending on whether participants reported being aware or unaware of the stimuli. In this research, participants reported being unaware of the stimuli even though they were clearly able to discriminate the stimuli. These findings question the validity of Lovibond and Shanks' concept of awareness and their suggestion of a close association between conditioning and awareness.

Awareness↗