Uncovering mnestic problems in help-seeking individuals reporting subjective cognitive complaints.

In individuals with subjective cognitive impairments (SCI) the risk for the development of a neurodegenerative disease is assumed to be increased. However, it is not clear which factors contribute to the expression of SCI: Is it related to the cognitive resources already challenged, or is the psycho-affective state of more relevance? Using a novel online assessment combining self-report questionnaires and neuropsychological psychometric tests, significant predictors for the level of complaints were identified in two samples of elderly individuals: Help-seekers (HS, n = 48) consulting a memory clinic and a matched sample of non-help-seekers (nHS, n = 48). Based on the results of the online assessment, the SCI level was found to be significantly determined by the psycho-affective state (depressive mood) in the nHS group, whereas cognitive performance (cued recall) was the main predictor in the HS group. The predictive value of recall performance, however, is more-strongly expressed in memory tests which reduce the impact of compensatory strategies (face-name-association vs. word lists). Our results indicate that the problem-focused behavior of help-seeking individuals is also associated with a higher sensitivity for cognitive deficits-which can be uncovered with an appropriate psychometric test. Considering these factors, the conversion risk in individuals with SCI can probably be determined more reliably.

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.

Neural correlates of religious experience.

The commonsense view of religious experience is that it is a preconceptual, immediate affective event. Work in philosophy and psychology, however, suggest that religious experience is an attributional cognitive phenomenon. Here the neural correlates of a religious experience are investigated using functional neuroimaging. During religious recitation, self-identified religious subjects activated a frontal-parietal circuit, composed of the dorsolateral prefrontal, dorsomedial frontal and medial parietal cortex. Prior studies indicate that these areas play a profound role in sustaining reflexive evaluation of thought. Thus, religious experience may be a cognitive process which, nonetheless, feels immediate.

Attention induced motion blindness.

Recent studies have shown evidence for modulation of cortical activity by attention in visual areas involved in motion processing. Behavioural effects of this modulation have only been reported for high-order, but not for luminance-based motion. We show that attentional load can even affect the perception of a first-order motion inducing a short-termed motion blindness. The detection of transient coherent motion embedded in a rapid serial visual presentation was severely impaired if colour features were to be processed simultaneously. The findings reported here show attentional requirements can affect motion perception. This effect can not be explained by motion adaptation or priming and may instead arise from the suppression of irrelevant stimuli.

Is V1 necessary for conscious vision in areas of relative cortical blindness?

Visual field defects result from postgeniculate lesions. It is generally assumed that absolute defects are caused by total destruction or denervation of primary visual cortex (V1) and that the degraded but conscious vision that remains or returns in relative or partial defects is mediated by compromised V1 cortex that retains a sufficiently large population of functional neurons. We here report the results of three patients with long-standing postgeniculate lesions who underwent functional magnetic resonance imaging while their partial defect was stimulated with high-contrast reversing checkerboard stimuli. Although the stimulation evoked conscious visual impressions in all three, in only one patient did it activate perilesional V1. In the other two we found no evidence for perilesional activation, indicating that some conscious vision may return in the absence of functional ipsilesional V1.

Change blindness and time to consciousness.

Detection of changes in a visual scene can be substantially delayed when the original and the modified image are separated by a brief screen flicker. We used this phenomenon of "change blindness" to find when the brain detects the mismatch in relation to when the observer reports it, and whether changes in identity and position are processed similarly. Event-related brain potentials (ERPs) recorded while the subjects searched for the change in alternating series of images showed that the epoch during which they indicated detection was characterized by a marked positivity from 300 to 700 ms. Analysis of data from image presentations preceding the subjects' response revealed a similar but smaller ERP positivity one (identity) or even two (position) epochs before detection. As each epoch lasted 1500 ms, the brain may register a change as early as 3000 ms before the observer.

Characteristics of visual evoked potentials generated by motion coherence onset.

Prior studies have shown that an electrophysiological correlate of visual motion processing can be found in the N2, a transient negativity occurring at about 200 ms in the visual evoked potential (VEP). In most of the studies, N2 was triggered by the onset of a coherent motion. Results of our first experiment revealed that topography of the negative potential can be modified by motion direction information. In contrast to the onset of uncorrelated motion of pixels in a random dot kinematogram (RDK) correlated motion leads to an right hemispheric amplitude advantage. Hemispheric differences can be increased when the negativity is triggered by the onset of a coherent motion direction preceded by uncorrelated motion in RDKs. In a second experiment, we examined whether the negativity elicited by direction is related to the strength of the impression of motion direction measured psychophysically. The latter was modified by varying the percentage of correlated moving pixels in the RDK. Increasing the proportion of these 'direction signals' was associated with both an increase in the strength of the impression of motion direction and an increase in VEP amplitude. Mean correlations of electrophysiological and psychophysical data, which exceeded 0.7, revealed a higher sensitivity of the right hemisphere. The close relationship between the global motion impression and VEP negativity indicate that electrophysiological correlates of processing stages within visual motion analysis can be isolated. The recorded negativity seems to be associated primarily with the process of global motion integration.

Processing of incongruous mental calculation problems: evidence for an arithmetic N400 effect.

We investigated if incongruent solutions of simple multiplication problems would elicit similar event-related brain potentials as inappropriate words in sentences. In Experiment I, 12 subjects verified the appropriateness of solutions of multiplication problems or of final words in short sentences. Both incongruent solutions and incongruent words evoked a phasic negative shift between 300 and 500 ms having a similar topography. In Experiment II, we tested with another sample of 13 subjects if the amplitude of this arithmetic N400 effect was affected differently by different stimulus onset asynchronies (SOA = 200 and 500 ms) and by errors that were either table-related or table-unrelated to the preceding operands. Again, incorrect solutions elicited an arithmetic N400 effect whose amplitude depended on both the relatedness of the solution and the SOA. The ascending part of the N400 effect was always larger for unrelated than for related errors independently of the SOA, whereas the maximum of the N400 effect was larger for unrelated errors in case of a long SOA only. This pattern of effects was similar to that observed with semantic material varying lexical associations. These results suggest that arithmetic incongruencies are handled by the system in a manner functionally similar to that of semantic incongruencies.

Motion evoked brain potentials parallel the consistency of coherent motion perception in humans.

The perception of global coherent motion perception in complex motion patterns containing different direction vectors was investigated. Random dot kinematograms (RDK), plaids and fragmented plaid pattern were presented in which direction vectors of the moving elements were varied. In order to elicit coherent motion perception, all elements were displaced in the same direction (delta0 degrees). In a second condition, fifty percent of the elements were moved diagonally downwards to the left, with the remaining elements moving orthogonally (delta 90 degrees). Simultaneously with psychophysical judgements on the perceived motion direction, visual evoked potentials (VEPs) were recorded at occipital electrode positions. Onset of a global coherent motion was associated with a VEP negativity occurring at about 200 ms. The amplitude of this component was clearly reduced when local ambiguous signals could not be integrated to produce the perception of global coherent motion.

[Memory traces in EEG]. / Gedächtnisspuren im EEG.

The paper gives a brief overview of five experimental approaches in which memory processes were studied by means of event-related brain potentials (ERPs). Some of the results were already published in English (Study 1), while others are new and will be reported in greater length as full paper elsewhere (Studies 2, 3, 4, and 5). Study 1 revealed that retrieval of information from episodic long-term memory is accompanied by a systematic slow negative potential. The topography of this slow wave depends on the quality of the reactivated information (spatial vs. verbal), and its amplitude reflects the difficulty of the retrieval process. In experiment 2 ERPs were recorded while subjects acquired either explicit or implicit knowledge about a sequential stimulus-response pattern. The data suggest that explicit learners who posses verbalizable knowledge about sequential dependencies have formed both perceptual and motor representations, while implicit learners have formed motor representations only. In study 3 fact retrieval in mental arithmetic was activated by a verification task. Incongruent solutions evoked an arithmetic N400-effect whose amplitude varied with the associative distance between an expected and an actually perceived solution to a multiplication problem. In study 4 ERPs were recorded during mental rotation tasks. A set of experiments revealed that mental rotation is always accompanied by a systematic negative variation over the parietal cortex. The amplitude of this "rotation specific negativity" increases with an increasing angular disparity between a perceived sign and its normal upright template. It was shown that this negativity is functionally distinct from a P300-complex which is often superimposed on it within the same latency window. Finally, study 5 examined ERPs in a sentence reading task in which grammatically legal but infrequent sentence constructions had to be processed. A left-anterior negativity was observed whenever an explicit case marker (the definite article in German) signalled a nominal phrase at a noncanonical position. The LAN phenomenon appears to be a manifestation of a syntax processor which performes a first-pass formal analysis of a sentence and which possibly allocates working memory resources whenever a word cannot be assigned immediately to an expected propositional role.

Processing of visual motion direction in the fronto-parallel plane in the stationary or moving observer.

To examine the effect of concurrent self-motion on the perception of the direction of object-motion, random-dot kinematograms were employed in which the strength of the directional signal was manipulated by varying the percentage of coherently moving pixels. The subject's task was to indicate the motion direction of briefly presented displays while undergoing whole body rotations with angular accelerations of 0, 5, 15, or 45 degrees/s2. The perception of the direction of visual motion in the horizontal plane was impaired only when visual and vestibular motion directions were incongruous. The impairment increases with both increasing angular acceleration and decreasing percentage of coherently moving pixels. For object-motion in the vertical plane, an impairment was found for both congruous and incongruous combination of visual and vestibular stimulation, although not as pronounced for the latter (i.e., visual upward, vestibular downward stimulation, and vice versa). These results are discussed in terms of postnatal development and neurophysiological optimization processes resulting from intersensory 'updating' through every-day experience of object-motion during self-motion.

Motion aftereffects with random-dot chequerboard kinematograms: relation between psychophysical and VEP measures.

A random-dot chequerboard kinematogram was used to investigate the effect of motion adaptation both on evoked potentials and on motion aftereffects (MAEs). The experimental paradigm used allowed simultaneous measurement of both variables. Each adaptation period was followed by a series of 5 short test stimuli to which evoked potentials were recorded. Motion aftereffects were observed in the intervals between test stimuli. An inverse relationship between mean N2-P1 amplitude and mean reported MAEs was found as a function of adaptation durations of 1.4, 5.6, and 17.5 s. When the shortest and longest adaptation durations were compared, this relationship held for thirteen of fourteen subjects tested when adaptation-motion and test-motion directions corresponded and for twelve of fourteen subjects when they were opposed. The possibility that the effect of motion adaptation on N2-P1 amplitude was due to local luminance-contrast adaptation is discussed and shown to be unlikely. The suitability of this paradigm for the combined psychophysical and electrophysiological assessment of disturbances in motion perception is discussed.