The impact of affective states and traits on perceptual stability during binocular rivalry.

Affective states and traits have been associated with different measures of perceptual stability during binocular rivalry. Diverging approaches to measuring perceptual stability as well as to examination of the role of affective variables have contributed to an inconclusive pattern of findings. Here, we studied the influence of affective traits, such as depressiveness and trait anxiety, and states, which were manipulated with a musical mood induction paradigm, on different measures of perceptual stability (dominance ratios and phase durations) during binocular rivalry. Fifty healthy participants reported alternations in two conditions: a biased perception condition with an unequal probability of perceiving stimuli, using an upright versus a tilted face with a neutral expression, and a control condition with equal chances of perceiving stimuli, using Gabors of different orientations. Baseline positive state affect significantly predicted longer phase durations whereas affective traits did not yield any such effect. Furthermore, in an exploratory analysis, induced negative affect attenuated stimulus related bias in predominance ratios. Overall, we found a strong correlation between both measures of perceptual stability (phase durations and dominance ratios). Our findings thus question the distinction between different measures of perceptual stability during binocular rivalry and highlight the role of affective states in its formation.

Negative affect impedes perceptual filling-in in the uniformity illusion.

The notion of cognitive penetrability, i.e., whether perceptual contents can in principle be influenced by non-perceptual factors, has sparked a significant debate over methodological concerns and the correct interpretation of existing findings. In this study, we combined predictive processing models of visual perception and affective states to investigate influences of affective valence on perceptual filling-in in extrafoveal vision. We tested how experimentally induced affect would influence the probability of perceptual filling-in occurring in the uniformity illusion (N = 50). Negative affect led to reduced occurrence rates and increased onset times of visual uniformity. This effect was selectively observed in illusionary trials, requiring perceptual filling-in, and not in control trials, where uniformity was the veridical percept, ruling out biased motor responses or deliberate judgments as confounding variables. This suggests an influential role of affective status on subsequent perceptual processing, specifically on how much weight is ascribed to priors as opposed to sensory evidence.

Trait anxiety is linked to increased usage of priors in a perceptual decision making task.

Current predictive processing accounts consider negative affect to result from elevated rates of prediction error, thereby motivating changes in the degree with which prior expectancies and sensory evidence influence our perceptions. Trait anxiety is associated with the amount of negative affect a person is experiencing and has been linked to aberrant strategies in decision making and belief updating. Here, we assessed the degree to which induced prior expectancies influenced motion judgements in a simple perceptual decision making task in 117 healthy participants with varying levels of trait anxiety. High trait anxious individuals showed increased usage of priors, independent from the amount of sensory uncertainty that was perceived. This finding demonstrates aberrant strategies of belief updating in anxiety even in evaluating nonthreatening visual motion stimuli, and thus suggest an influential role of affective traits in processes of perceptual inference.

Category-selective processing in the two visual pathways as a function of stimulus degradation by noise.

Understanding the organising principles and functional properties of the primate brain's numerous visually responsive cortical regions is one of the major goals in cognitive neuroscience. Functional magnetic resonance imaging (fMRI) studies have revealed that neural responses in higher-order visual cortex are shaped by object categories, task context, and spatiotemporal regularities. Beyond these properties, visual processing in the ventral pathway has been shown to be tightly linked to perceptual awareness, while the evidence regarding dorsal visual processing and awareness is mixed. Most previous studies targeting the dorsal pathway have used dichotomous "visible versus invisible" experimental designs and interocular suppression paradigms to modulate stimulus visibility. In this fMRI study, we sought to investigate category-selective processing of faces and tools in the ventral and dorsal visual streams as a function of parametric stimulus degradation by noise. Both frequentist and Bayesian statistics provide strong evidence for a linear relationship between category-selective processing and stimulus information in both visual pathways. Overall, multivariate category decoding accuracies turned out to be lower in the dorsal pathway. We discuss our results within the context of the emerging notion of highly interconnected visual streams, and provide an outlook on how future studies may help to further refine our understanding of the functional role of the dorsal pathway in visual object processing.

No evidence for dorsal-stream-based priming under continuous flash suppression.

Previous studies have proposed that potentially action-relevant visual features of masked images are processed along the dorsal visual pathway, and can thus prime responses to images of man-made manipulable objects (tools). According to the "category priming by elongation" hypothesis, (invisible) stimulus elongation is the basis for how the dorsal stream can affect the categorization of tools. In our study, prime stimuli were rendered invisible using continuous flash suppression (CFS) and anaglyphs for dichoptic stimulation. We found that participants' reaction times were only weakly affected by CF-suppressed prime stimuli. If anything, the RT data were more consistent with response priming based on shape. Moreover, when prime visibility was low, participants were not able to infer the prime's category but its shape. We recommend that future CFS priming studies should use crosstalk-free setups for dichoptic stimulation, and that awareness measures should be tailored to the stimulus feature of interest.

Exploring the boundary conditions of unconscious numerical priming effects with continuous flash suppression.

The scope and limits of unconscious processing are a controversial topic of research in experimental psychology. Particularly within the visual domain, a wide range of paradigms have been used to experimentally manipulate perceptual awareness. A recent study reported unconscious numerical processing during continuous flash suppression (CFS), which is a powerful variant of interocular suppression and disrupts the conscious perception of visual stimuli for up to seconds. Since this finding of a distance-dependent priming effect contradicts earlier results showing that interocular suppression abolishes semantic processing, we sought to investigate the boundary conditions of this effect in two experiments. Using statistical analyses and experimental designs that precluded an effect of target numerosity, we found evidence for identity priming, but no conclusive evidence for distance-dependent numerical priming under CFS. Our results suggest that previous conclusions on high-level numerical priming under interocular suppression may have been premature.

Revisiting the Lissajous figure as a tool to study bistable perception.

During bistable vision perception spontaneously "switches" between two mutually exclusive percepts despite constant sensory input. The endogenous nature of these perceptual transitions has motivated extensive research aimed at the underlying mechanisms, since spontaneous perceptual transitions of bistable stimuli should in principle allow for a dissociation of processes related to sensory stimulation from those related to conscious perception. However, transitions from one conscious percept to another are often not instantaneous, and participants usually report a considerable amount of mixed or unclear percepts. This feature of bistable vision makes it difficult to isolate transition-related visual processes. Here, we revisited an ambiguous depth-from-motion stimulus which was first introduced to experimental psychology more than 80 years ago. This rotating Lissajous figure might prove useful in complementing other bistable stimuli, since its perceptual transitions only occur at critical stimulus configurations and are virtually instantaneous, thus facilitating the construction of a perceptually equivalent replay condition. We found that three parameters of the Lissajous figure - complexity, line width, and rotational speed - differentially modulated its perceptual dominance durations and transition probabilities, thus providing experimenters with a versatile tool to study the perceptual dynamics of bistable vision.

Learning to detect but not to grasp suppressed visual stimuli.

A central implication of the two-visual-systems hypothesis (TVSH) is that the dorsal visuomotor system (vision-for-action) can make use of invisible information, whereas the ventral system (vision-for-perception) cannot (Milner & Goodale, 1995). Therefore, actions such as grasping movements should be influenced by invisible information while conscious reports remain unaffected. To test this assumption, we used a dichoptic stimulation technique--continuous flash suppression (CFS)--which has the potency to render stimuli invisible for up to seconds (Tsuchiya & Koch, 2005). In two experiments using CFS, participants were asked to grasp for invisible bars of different sizes (Experiment 1) or orientations (Experiment 2), or to report both measures verbally. Target visibility was measured trial-by-trial using the perceptual awareness scale (PAS). We found no evidence for the use of invisible information by the visuomotor system despite extensive training (600 trials) and the availability of haptic feedback. Participants neither learned to scale their maximum grip aperture to the size of the invisible stimulus, nor to align their hand to its orientation. Careful control of stimulus visibility across training sessions, however, revealed a robust tendency towards decreasing perceptual thresholds under CFS. We discuss our results within the framework of the TVSH and with respect to alternative models which emphasize the close functional interaction between the dorsal and ventral visual systems.

Probing the cortical network underlying the psychological refractory period: a combined EEG-fMRI study.

Human performance exhibits strong multi-tasking limitations in simple response time tasks. In the psychological refractory period (PRP) paradigm, where two tasks have to be performed in brief succession, central processing of the second task is delayed when the two tasks are performed at short time intervals. Here, we aimed to probe the cortical network underlying this postponement of central processing by simultaneously recording electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data while 12 subjects performed two simple number-comparison tasks. Behavioral data showed a significant slowing of response times to the second target stimulus at short stimulus-onset asynchronies, together with significant correlations between response times to the first and second target stimulus, i.e., the hallmarks of the PRP effect. The analysis of EEG data showed a significant delay of the post-perceptual P3 component evoked by the second target, which was of similar magnitude as the effect on response times. fMRI data revealed an involvement of parietal and prefrontal regions in dual-task processing. The combined analysis of fMRI and EEG data-based on the trial-by-trial variability of the P3-revealed that BOLD signals in two bilateral regions in the inferior parietal lobe and precentral gyrus significantly covaried with P3 related activity. Our results show that combining neuroimaging methods of high spatial and temporal resolutions can help to identify cortical regions underlying the central bottleneck of information processing, and strengthen the conclusion that fronto-parietal cortical regions participate in a distributed "global neuronal workspace" system that underlies the generation of the P3 component and may be one of the key cerebral underpinnings of the PRP bottleneck.

[Palliative sedation]. / Palliatieve sedatie.

Palliative sedation is the intentional lowering of the level of consciousness ofa patient in the last phase of life by means of the administration of sedatives. The objective of palliative sedation is to relieve severe physical or psychological suffering that is otherwise untreatable. Sedation is used in 12% of all patients dying in the Netherlands. Refractory delirium, dyspnoea or pain are the most common indications. If deep palliative sedation is used, the estimated life expectancy should be a few days to at most one week. Midazolam is used most often for continuous sedation, usually by subcutaneous infusion; if the response is insufficient, a combination of midazolam with levomepromazine or phenobarbital or monotreatment with propofol may be used. If continuous infusion is not desired or feasible, intermittent administration of midazolam, diazepam, lorazepam or chlorpromazine may be considered. Provided that it is used under the right circumstances, palliative sedation does not shorten life.