Neural responses in parietal and occipital areas in response to visual events are modulated by prior multisensory stimuli

The effect of multi-modal vs uni-modal prior stimuli on the subsequent processing of a simple flash stimulus was studied in the context of the audio-visual 'flash-beep' illusion, in which the number of flashes a person sees is influenced by accompanying beep stimuli. EEG recordings were made while combinations of simple visual and audio-visual stimuli were presented. The experiments found that the electric field strength related to a flash stimulus was stronger when it was preceded by a multi-modal flash/beep stimulus, compared to when it was preceded by another uni-modal flash stimulus. This difference was found to be significant in two distinct timeframes--an early timeframe, from 130-160 ms, and a late timeframe, from 300-320 ms. Source localisation analysis found that the increased activity in the early interval was localised to an area centred on the inferior and superior parietal lobes, whereas the later increase was associated with stronger activity in an area centred on primary and secondary visual cortex, in the occipital lobe. The results suggest that processing of a visual stimulus can be affected by the presence of an immediately prior multisensory event. Relatively long-lasting interactions generated by the initial auditory and visual stimuli altered the processing of a subsequent visual stimulus.status: publishe

An experimenter's influence on motor enhancements: the effects of letter congruency and sensory switch-costs on multisensory integration

Multisensory integration can alter information processing, and previous research has shown that such processes are modulated by sensory switch costs and prior experience (e.g., semantic or letter congruence). Here we report an incidental finding demonstrating, for the first time, the interplay between these processes and experimental factors, specifically the presence (vs. absence) of the experimenter in the testing room. Experiment 1 demonstrates that multisensory motor facilitation in response to audiovisual stimuli (circle and tone with no prior learnt associations) is higher in those trials in which the sensory modality switches than when it repeats. Those participants who completed the study while alone exhibited increased RT variability. Experiment 2 replicated these findings using the letters "b" and "d" presented as unisensory stimuli or congruent and incongruent multisensory stimuli (i.e., grapheme-phoneme pairs). Multisensory enhancements were inflated following a sensory switch; that is, congruent and incongruent multisensory stimuli resulted in significant gains following a sensory switch in the monitored condition. However, when the participants were left alone, multisensory enhancements were only observed for repeating incongruent multisensory stimuli. These incidental findings therefore suggest that the effects of letter congruence and sensory switching on multisensory integration are partly modulated by the presence of an experimenter

Top–down task-specific determinants of multisensory motor reaction time enhancements and sensory switch costs

This study was designed to investigate the complex interplay between multisensory processing, top–down processes related to the task relevance of sensory signals, and sensory switching. Thirty-five adults completed either a speeded detection or a discrimination task using the same auditory and visual stimuli and experimental setup. The stimuli consisted of unisensory and multisensory presentations of the letters ‘b’ and ‘d’. The multisensory stimuli were either congruent (e.g., the grapheme ‘b’ with the phoneme /b/) or incongruent (e.g., the grapheme ‘b’ with the phoneme /d/). In the detection task, the participants had to respond to all of the stimuli as rapidly as possible while, in the discrimination task, they only responded on those trials where one prespecified letter (either ‘b’ or ‘d’) was present. Incongruent multisensory stimuli resulted in faster responses as compared to unisensory stimuli in the detection task. In the discrimination task, only the dual-target congruent stimuli resulted in faster RTs, while the incongruent multisensory stimuli led to slower RTs than to unisensory stimuli; RTs were the slowest when the visual (rather than the auditory) signal was irrelevant, thus suggesting visual dominance. Switch costs were also observed when switching between unisensory target stimuli, while dual-target multisensory stimuli were less likely to be affected by sensory switching. Taken together, these findings suggest that multisensory motor enhancements and sensory switch costs are influenced by top–down modulations determined by task instructions, which can override the influence of prior learnt associations

Multisensory enhancement elicited by unconscious visual stimuli

The merging of information from different senses (i.e., multisensory integration) can facilitate information processing. Processing enhancements have been observed with signals that are irrelevant to the task at hand, and with cues that are non-predictive. Such findings are consistent with the notion that multiple sensory signals are sometimes integrated automatically. Multisensory enhancement has even been reported with stimuli that have been presented subliminally, though only with meaningful multisensory relations that have already been learned. The question of whether there exist cases where multisensory effects occur without either learning or awareness has, though, not been clearly established in the literature to date. Here, we present a case study of a patient with Posterior Cortical Atrophy, who was unable to consciously perceive visual stimuli with our task parameters, yet who nevertheless still exhibited signs of multisensory enhancement even with unlearned relations between audiovisual stimuli. In a simple speeded detection task, both response speed, and the variability of reaction times, decreased in a similar manner to controls for multisensory stimuli. These results are consistent with the view that the conscious perception of stimuli and prior learning are not always a prerequisite for multisensory integration to enhance human performance

The race that precedes coactivation: development of multisensory facilitation in children.

RATIONALE: The facilitating effect of multisensory integration on motor responses in adults is much larger than predicted by race-models and is in accordance with the idea of coactivation. However, the development of multisensory facilitation of endogenously driven motor processes and its relationship to the development of complex cognitive skills in school-age children is largely unexplored. METHOD: Twenty adults and 95 children where allocated into six age groups: 6, 7, 8, 9, 10-11 and adults. Participants' motor reaction times (MRTs) and accuracy in response to the detection of auditory, visual and audiovisual stimuli were recorded. Children's reading accuracy and nonverbal IQ were also assessed. RESULTS: In general, MRTs of children were significantly slower with greater variability than those of adults. Although the average level of multisensory facilitation was similar for all age groups, mean cumulative density functions (CDFs) showed that multisensory facilitation in 6 and 10-11-year-olds is within the predictive limits of race-models. Where coactivation was seen in the CDF of individual children it was not as strong or as consistent as that in adults. The degree of multisensory facilitation did not correlate with age, reading accuracy or IQ. CONCLUSION: The average level of multisensory facilitation to endogenously driven motor responses does not change gradually with age nor is it related to intelligence or reading accuracy. In general, multisensory integration remains immature until 10-11 years of age and lies within the predicted confines of race-models

The Accuracy of Source Monitoring Across the Auditory, Visual and Action Modalities

This study investigated the effect of imagination on source monitoring errors across three modalities (action, audition and vision), and the effects of increased number of imaginings (once compared to five times) on source monitoring performance. Thirty-four participants were exposed to 25 action, 25 auditory and 25 visual items. The items were either actually presented or imagined. Of the 25 items, 15 items were actually presented once, while five items were presented for imagining once and five items were presented for imagining five times. Following a 15-minute distractor task, participants were required to recognise items and to ascertain whether each item was actually presented or had been imagined. No significant difference was found between the conditions of items actually presented and items imagined only once. An increase in the number of imaginings did not significantly influence source monitoring errors for action items, but did result in a significant decrease in source monitoring errors for auditory and visual items. These findings support the notion that different processes may be involved in source monitoring across different modalities

The application of quantitative analysis-parameters to detect and quantify the lung emphysema with HR-CT data

Das Ziel der vorliegenden HR-CT Untersuchung war die Detektion und Quantifizierung des Lungenemphysems mithilfe der computerbasierten Analyseparameter Emphysemindex, fraktale Dimension, Lungenvolumen und Lungendichte. In diese Studie gingen die HR-CT-Daten von 51 COPD Patienten und 23 gesunden Probanden ein. Mit Hilfe einer semiautomatischen Software wurden die HR-CT Bildserien segmentiert und analysiert. Für die fraktalen Dimensionen wurden anhand verschiedener Schwellenwerte fünf Analysebereiche festgelegt und mit der Masse-Radius Methode berechnet. Der Grenzwert für den Emphysemindex wurde bei -950 HE festgelegt. Die Ergebnisse zeigen hoch signifikante Korrelationen zwischen den einzelnen Parametern, insbesondere wenn die Gruppe der COPD Patienten separat betrachtet wird. Für die fraktale Dimension erreicht der Schwellenwertbereich von Th [-1000, -900] HE die höchsten Korrelationen. Darüber hinaus können signifikante Unterschiede zwischen den COPD Patienten und den gesunden Probanden für den Emphysemindex, das Lungenvolumen und die Lungendichte gefunden werden. Für das Anfangsstadium der COPD GOLD I resultierten keine signifikanten Ergebnisse. Die Berechnungen für die fraktale Dimension ergaben durchweg keine signifikanten Ergebnisse. Eine differenzierte Betrachtung zeigte, dass der Emphysemindex einen großen Überschneidungsbereich zwischen beiden Gruppen aufweist. Gesunde Probanden und COPD Patienten verfügen über einen Empyhsemindex von bis zu 12,3 %; dieser Bereich scheint somit noch physiologisch zu sein. In einer neuen Gruppeneinteilung wurde der Emphysemindex von 12,3 % als Grenzwert verwendet und anschließend erneut auf Unterschiede hinsichtlich der fraktalen Dimension untersucht. Es resultieren hoch signifikante Ergebnisse. Die Analyseparamter Emphysemindex, Lungenvolumen und -dichte sind geeignet um zwischen COPD Patienten und gesunden Probanden zu differenzieren. Schwierigkeiten bestehen in der reliablen Detektion milder Emphysem- Erscheinungsformen. Die neue Gruppeneinteilung führte auch bei der fraktalen Dimension zu signifikanten Ergebnissen, sodass auch dieser Parameter das Lun- genemphysem erfolgreich zu quantifizieren scheint.The purpose of this HR-CT study was the detection and quantification of pulmonary emphysema with computer-based parameters such as emphysema index, fractal dimension, lung volume and lung density. In this restrospective study, the HR-CT images of 51 COPD Patients and 23 healthy subjects were segmented and analyzed by a semi-automatically operating software. For the fractal dimensions five areas of analysis where defined based on different thresholds. They were calculated with the mass-radius-method. A cut-off threshold of -950 Hounsfield Units was used for the emphysema index. The results show highly significant correlations between the different parameters, especially when COPD patients were considered separately. For the fractal dimen- sion the highest correlation was achieved with a threshold of [-1000, -900] HU. In addition, significant differences were found between COPD patients and healthy subjects regarding emphysema index, lung volume and lung density. No significant results were found for the initial stage of COPD GOLD I. The calculation of the fractal dimension showed no significant results. A detailed analysis displayed a big overlap for the emphysema index between both groups. The emphysema index of the healthy subjects and COPD patients ranged up to 12,3 %;; thus this range can be considered physiological. Within a new group classification the emphysema index of 12,3 % was used as threshold and subsequently analyzed on differences in the fractal dimension. The results were of great significant. The parameters emphysema index, lung volume, and lung density are appropriate to distinguish between COPD patients and healthy subjects. Difficulties occur in the reliable detection of mild emphysema manifestations. The new group classification also led to significant results in the fractal dimension. On this account it seems to be a successful parameter to quantify pulmonary emphysema

Multisensory processing in event-based prospective memory

Failures in prospective memory (PM) – that is, the failure to remember intended future actions – can have adverse consequences. It is therefore important to study those processes that may help to minimize such cognitive failures. Although multisensory integration has been shown to enhance a wide variety of behaviors, including perception, learning, and memory, its effect on prospective memory, in particular, is largely unknown. In the present study, we investigated the effects of multisensory processing on two simultaneously-performed memory tasks: An ongoing 2- or 3-back working memory (WM) task (20% target ratio), and a PM task in which the participants had to respond to a rare predefined letter (8% target ratio). For PM trials, multisensory enhancement was observed for congruent multisensory signals; however, this effect did not generalize to the ongoing WM task. Participants were less likely to make errors for PM than for WM trials, thus suggesting that they may have biased their attention toward the PM task. Multisensory advantages on memory tasks, such as PM and WM, may be dependent on how attention resources are allocated across dual tasks

Multisensory enhancement elicited by unconscious visual stimuli

The merging of information from different senses (i.e., multisensory integration) can facilitate information processing. Processing enhancements have been observed with signals that are irrelevant to the task at hand, and with cues that are non-predictive. Such findings are consistent with the notion that multiple sensory signals are sometimes integrated automatically. Multisensory enhancement has even been reported with stimuli that have been presented subliminally, though only with meaningful multisensory relations that have already been learned. The question of whether there exist cases where multisensory effects occur without either learning or awareness has, though, not been clearly established in the literature to date. Here, we present a case study of a patient with Posterior Cortical Atrophy, who was unable to consciously perceive visual stimuli with our task parameters, yet who nevertheless still exhibited signs of multisensory enhancement even with unlearned relations between audiovisual stimuli. In a simple speeded detection task, both response speed, and the variability of reaction times, decreased in a similar manner to controls for multisensory stimuli. These results are consistent with the view that the conscious perception of stimuli and prior learning are not always a prerequisite for multisensory integration to enhance human performance

Multisensory perceptual biases for social and reward associations

Linking arbitrary shapes (e.g., circles, squares, and triangles) to personal labels (e.g., self, friend, or stranger) or reward values (e.g., £18, £6, or £2) results in immediate processing benefits for those stimuli that happen to be associated with the self or high rewards in perceptual matching tasks. Here we further explored how social and reward associations interact with multisensory stimuli by pairing labels and objects with tones (low, medium, and high tones). We also investigated whether self and reward biases persist for multisensory stimuli with the label removed after an association had been made. Both high reward stimuli and those associated with the self, resulted in faster responses and improved discriminability (i.e., higher <i>d'</i>), which persisted for multisensory stimuli even when the labels were removed. However, these self- and reward-biases partly depended on the specific alignment between the physical tones (low, medium, and high) and the conceptual (social or reward) order. Performance for reward associations improved when the endpoints of low or high rewards were paired with low or high tones; meanwhile, for personal associations, there was a benefit when the self was paired with either low or high tones, but there was no effect when the stranger was associated with either endpoint. These results indicate that, unlike reward, social personal associations are not represented along a continuum with two marked endpoints (i.e., self and stranger) but rather with a single reference point (the self vs. other)