Multisensory stimuli shift perceptual priors to facilitate rapid behavior

Multisensory stimuli speed behavioral responses, but the mechanisms subserving these effects remain disputed. Historically, the observation that multisensory reaction times (RTs) outpace models assuming independent sensory channels has been taken as evidence for multisensory integration (the “redundant target effect”; RTE). However, this interpretation has been challenged by alternative explanations based on stimulus sequence effects, RT variability, and/or negative correlations in unisensory processing. To clarify the mechanisms subserving the RTE, we collected RTs from 78 undergraduates in a multisensory simple RT task. Based on previous neurophysiological findings, we hypothesized that the RTE was unlikely to reflect these alternative mechanisms, and more likely reflected pre-potentiation of sensory responses through crossmodal phase-resetting. Contrary to accounts based on stimulus sequence effects, we found that preceding stimuli explained only 3–9% of the variance in apparent RTEs. Comparing three plausible evidence accumulator models, we found that multisensory RT distributions were best explained by increased sensory evidence at stimulus onset. Because crossmodal phase-resetting increases cortical excitability before sensory input arrives, these results are consistent with a mechanism based on pre-potentiation through phase-resetting. Mathematically, this model entails increasing the prior log-odds of stimulus presence, providing a potential link between neurophysiological, behavioral, and computational accounts of multisensory interactions.

Psychological functioning in survivors of COVID-19: Evidence from recognition of fearful facial expressions

Evidence about the psychological functioning in individuals who survived the COVID-19 infectious is still rare in the literature. In this paper, we investigated fearful facial expressions recognition, as a behavioural means to assess psychological functioning. From May 15th, 2020 to January 30th, 2021, we enrolled sixty Italian individuals admitted in multiple Italian COVID-19 post-intensive care units. The detection and recognition of fearful facial expressions were assessed through an experimental task grounded on an attentional mechanism (i.e., the redundant target effect). According to the results, our participants showed an altered behaviour in detecting and recognizing fearful expressions. Specifically, their performance was in disagreement with the expected behavioural effect. Our study suggested altered processing of fearful expressions in individuals who survived the COVID-19 infectious. Such a difficulty might represent a crucial sign of psychological distress and it should be addressed in tailored psychological interventions in rehabilitative settings and after discharge.

Multisensory Stimuli Shift Perceptual Priors to Favor Rapid Detection

Multisensory stimuli speed behavioral responses, but the mechanisms subserving these effects remain disputed. Historically, the observation that multisensory reaction times (RTs) outpace models assuming independent sensory channels has been taken as evidence for multisensory integration (the “redundant target effect”; RTE). However, this interpretation has been challenged by alternative explanations based on stimulus sequence effects, RT variability, and/or negative correlations in unisensory processing. To clarify the mechanisms subserving the RTE, we collected RTs from 78 undergraduates in a multisensory simple RT task. Based on previous neurophysiological findings, we hypothesized that the RTE was unlikely to reflect these alternative mechanisms, and more likely reflected pre-potentiation of sensory responses through crossmodal phase-resetting. Contrary to accounts based on stimulus sequence effects, we found that preceding stimuli explained only 3-9% of the variance in apparent RTEs. Comparing three plausible evidence accumulator models, we found that multisensory RT distributions were best explained by increased sensory evidence at stimulus onset. Because crossmodal phase-resetting increases cortical excitability before sensory input arrives, these results are consistent with a mechanism based on pre-potentiation through phase-resetting. Mathematically, this model entails increasing the prior log-odds of stimulus presence, providing a potential link between neurophysiological, behavioral, and computational accounts of multisensory interactions.

TMS of V1 eliminates unconscious processing of chromatic stimuli

Some of the neurological patients with primary visual cortex (V1) lesions can guide their behavior based on stimuli presented to their blind visual field. One example of this phenomenon is the ability to discriminate colors in the absence of awareness. These so-called patients with blindsight must have a neural pathway that bypasses the V1, explaining their ability to unconsciously process stimuli. To test if similar pathways function in neurologically healthy individuals or if unconscious processing depends on the V1, we disturbed the visibility of a chromatic stimulus with metacontrast masking (Experiment 1) or transcranial magnetic stimulation (TMS) of the V1 (Experiment 2). We measured unconscious processing using the redundant target effect (RTE), which is the speeding up of reaction times in response to dual stimuli compared with one stimulus, when the task is to respond to any number of stimuli. An unconscious chromatic RTE was found when the visibility of the redundant chromatic stimulus was suppressed with a visual mask. When TMS was applied to the V1 to disturb the perception of the redundant chromatic stimulus, the RTE was eliminated. Based on our results and converging evidence from previous studies, we conclude that the unconscious processing of chromatic information depends on the V1 in neurologically healthy participants.

Task dependent anatomical connections underlie multisensory processing

Our senses interact in daily life through multisensory integration, facilitating perceptual processes and behavioral responses. Numerous multisensory regions have been identified in humans and animals, raising the question of whether a single mechanism can support the dynamic range of experiences and behaviors multisensory processing engenders. The most common neural mechanisms proposed to underlie multisensory processing include anatomical connections directly linking early sensory areas, indirect connections to higher-order multisensory regions, and functional connectivity between cortical areas. Here we examine the relationship between white matter connectivity, as assessed with diffusion tensor imaging and individual differences in two divergent forms of multisensory processing: the redundant-target effect (RTE), in which subjects’ behavior is facilitated by congruent multisensory information, and the sound-induced illusory flash (SIIF) paradigm, in which incongruent multisensory information elicits a novel percept. Behavioral results demonstrated strong intra-subject reliability of the RTE and SIIF paradigms, but no correlation in performance between the two tasks. Consistent with this behavioral finding, we identified distinct anatomical networks underlying these two forms of multisensory processing. Using a whole-brain analysis and contrasting anatomical models of multisensory processing, increased behavioral performance on the RTE was associated with increased connectivity between the superior parietal lobe and early sensory regions. Conversely, increased incidence of illusion on the SIIF paradigm was associated with increased connectivity directly between early auditory and visual areas. These results implicate a broad network of anatomical connections involved in task-dependent multisensory processes.

Redundancy gains in audio–visual search

This study concerns stimuli-driven perceptual processes involved in target search among concurrent distractors with a focus on comparing auditory, visual, and audio–visual search tasks. Previous works, concerning unimodal search tasks, highlighted different preattentive features that can enhance target saliency, making it ‘pop-out’, e.g., a visually sharp target among blurred distractors. A cue from another modality can also help direct attention towards the target. Our study investigates a new kind of search task, where stimuli consist of audio–visual objects presented using both audio and visual modalities simultaneously. Redundancy effects are evaluated, first from the combination of audio and visual modalities, second from the combination of each unimodal cue in such a bimodal search task. A perceptual experiment was performed where the task was to identify an audio–visual object from a set of six competing stimuli. We employed static visual blur and developed an auditory blur analogue to cue the search. Results show that both visual and auditory blurs render distractors less prominent and automatically attracts attention toward a sharp target. The combination of both unimodal blurs, i.e., audio–visual blur, also proved to be an efficient cue to facilitate bimodal search task. Results also showed that search tasks were performed faster in redundant bimodal conditions than in unimodal ones. That gain was due to redundant target effect only without any redundancy gain due to the cue combination, as solely cueing the visual component was sufficient, with no improvement found by the addition of the redundant audio cue in bimodal search tasks.

Coactive Processing of Dimensionally Redundant Targets Within the Auditory Modality?

Previous reaction time studies have demonstrated coactivation processes within the visual modality for redundant stimuli that differ in two dimensions (e.g., shape and color). The present study provides novel results of analogous processes within the auditory modality. A redundant-target effect (RTE) was obtained in a Go/NoGo experiment using tones that differed in location and/or frequency. Participants were asked to respond to a specific tone location (e.g., left) and/or tone frequency (e.g., 200 Hz) of auditory stimuli. For redundant targets (e.g., a 200 Hz tone presented to the left), an RTE was observed which was too large to be explained by mere statistical facilitation. Therefore, responses to redundant targets were triggered by a combined activation of the target dimensions. The results are consistent with the modular hybrid account of Mordkoff and Yantis (1993) .