Reward expectation influences audiovisual spatial integration

In order to determine the spatial location of an object that is simultaneously seen and heard, the brain assigns higher weights to the sensory inputs that provide the most reliable information. For example, in the well-known ventriloquism effect, the perceived location of a sound is shifted toward the location of a concurrent but spatially misaligned visual stimulus. This perceptual illusion can be explained by the usually much higher spatial resolution of the visual system as compared to the auditory system. Recently, it has been demonstrated that this cross-modal binding process is not fully automatic, but can be modulated by emotional learning. Here we tested whether cross-modal binding is similarly affected by motivational factors, as exemplified by reward expectancy. Participants received a monetary reward for precise and accurate localization of brief auditory stimuli. Auditory stimuli were accompanied by task-irrelevant, spatially misaligned visual stimuli. Thus, the participants’ motivational goal of maximizing their reward was put in conflict with the spatial bias of auditory localization induced by the ventriloquist situation. Crucially, the amounts of expected reward differed between the two hemifields. As compared to the hemifield associated with a low reward, the ventriloquism effect was reduced in the high-reward hemifield. This finding suggests that reward expectations modulate cross-modal binding processes, possibly mediated via cognitive control mechanisms. The motivational significance of the stimulus material, thus, constitutes an important factor that needs to be considered in the study of top-down influences on multisensory integration.     

面孔表情和声音情绪信息整合对返回抑制的影响

返回抑制(inhibition of return, IOR)与情绪刺激都具有引导注意偏向、提高搜索效率的特点, 但二者间是否存在一定的交互作用迄今为止尚不明确。研究采用“线索-目标”范式并在视听双通道呈现情绪刺激来考察情绪刺激的加工与IOR的交互作用。实验1中情绪刺激以单通道视觉面孔或一致的视听双通道呈现, 实验2通过在视听通道呈现不一致的情绪刺激进一步考察视听双通道情绪一致刺激对IOR的影响是否是由听觉通道一致的情绪刺激导致的, 即是否对听觉通道的情绪刺激进行了加工。结果发现, 视听双通道情绪一致刺激能够削弱IOR, 但情绪不一致刺激与IOR之间不存在交互作用, 并且单双通道的IOR不存在显著差异。研究结果表明仅在视听双通道呈现情绪一致刺激时, 才会影响同一阶段的IOR, 这进一步支持了IOR的知觉抑制理论。     

The influence of stimulus properties on multisensory processing in the awake primate superior colliculus.

Multisensory integration is a process whereby information converges from different sensory modalities to produce a response that is different from that elicited by the individual modalities presented alone. A neural basis for multisensory integration has been identified within a variety of brain regions, but the most thoroughly examined model has been that of the superior colliculus (SC). Multisensory processing in the SC of anaesthetized animals has been shown to be dependent on the physical parameters of the individual stimuli presented (e.g., intensity, direction, velocity) as well as their spatial relationship. However, it is unknown whether these stimulus features are important, or evident, in the awake behaving animal. To address this question, we evaluated the influence of physical properties of sensory stimuli (visual intensity, direction, and velocity; auditory intensity and location) on sensory activity and multisensory integration of SC neurons in awake, behaving primates. Monkeys were trained to fixate a central visual fixation point while visual and/or auditory stimuli were presented in the periphery. Visual stimuli were always presented within the contralateral receptive field of the neuron whereas auditory stimuli were presented at either ipsi- or contralateral locations. Many of the SC neurons responsive to these sensory stimuli (n = 66/84; 76%) had stronger responses when the visual and auditory stimuli were combined at contralateral locations than when the auditory stimulus was located on the ipsilateral side. This trend was significant across the population of auditory-responsive neurons. In addition, some SC neurons (n = 31) were presented a battery of tests in which the quality of one stimulus of a pair was systematically manipulated. A small proportion of these neurons (n = 8/31; 26%) showed preferential responses to stimuli with specific physical properties, and these preferences were not significantly altered when multisensory stimulus combinations were presented. These data demonstrate that multisensory processing in the awake behaving primate is influenced by the spatial congruency of the stimuli as well as their individual physical properties.     

Crossmodal binding: evaluating the "unity assumption" using audiovisual speech stimuli

We investigated whether the "unity assumption," according to which an observer assumes that two different sensory signals refer to the same underlying multisensory event, influences the multisensory integration of audiovisual speech stimuli. Syllables (Experiments 1, 3, and 4) or words (Experiment 2) were presented to participants at a range of different stimulus onset asynchronies using the method of constant stimuli. Participants made unspeeded temporal order judgments regarding which stream (either auditory or visual) had been presented first. The auditory and visual speech stimuli in Experiments 1-3 were either gender matched (i.e., a female face presented together with a female voice) or else gender mismatched (i.e., a female face presented together with a male voice). In Experiment 4, different utterances from the same female speaker were used to generate the matched and mismatched speech video clips. Measuring in terms of the just noticeable difference the participants in all four experiments found it easier to judge which sensory modality had been presented first when evaluating mismatched stimuli than when evaluating the matched-speech stimuli. These results therefore provide the first empirical support for the "unity assumption" in the domain of the multisensory temporal integration of audiovisual speech stimuli.     

Crossmodal binding: Evaluating the “unity assumption” using audiovisual speech stimuli

We investigated whether the “unity assumption,” according to which an observer assumes that two different sensory signals refer to the same underlying multisensory event, influences the multisensory integration of audiovisual speech stimuli. Syllables (Experiments 1, 3, and 4) or words (Experiment 2) were presented to participants at a range of different stimulus onset asynchronies using the method of constant stimuli. Participants made unspeeded temporal order judgments regarding which stream (either auditory or visual) had been presented first. The auditory and visual speech stimuli in Experiments 1–3 were either gender matched (i.e., a female face presented together with a female voice) or else gender mismatched (i.e., a female face presented together with a male voice). In Experiment 4, different utterances from the same female speaker were used to generate the matched and mismatched speech video clips. Measuring in terms of the just noticeable difference the participants in all four experiments found it easier to judge which sensory modality had been presented first when evaluating mismatched stimuli than when evaluating the matched-speech stimuli. These results therefore provide the first empirical support for the “unity assumption” in the domain of the multisensory temporal integration of audiovisual speech stimuli.     

Multisensory-mediated auditory localization

Multisensory integration is a powerful mechanism for maximizing sensitivity to sensory events. We examined its effects on auditory localization in healthy human subjects. The specific objective was to test whether the relative intensity and location of a seemingly irrelevant visual stimulus would influence auditory localization in accordance with the inverse effectiveness and spatial rules of multisensory integration that have been developed from neurophysiological studies with animals [Stein and Meredith, 1993 The Merging of the Senses (Cambridge, MA: MIT Press)]. Subjects were asked to localize a sound in one condition in which a neutral visual stimulus was either above threshold (supra-threshold) or at threshold. In both cases the spatial disparity of the visual and auditory stimuli was systematically varied. The results reveal that stimulus salience is a critical factor in determining the effect of a neutral visual cue on auditory localization. Visual bias and, hence, perceptual translocation of the auditory stimulus appeared when the visual stimulus was supra-threshold, regardless of its location. However, this was not the case when the visual stimulus was at threshold. In this case, the influence of the visual cue was apparent only when the two cues were spatially coincident and resulted in an enhancement of stimulus localization. These data suggest that the brain uses multiple strategies to integrate multisensory information.     

Multisensory identification of natural objects in a two-way crossmodal priming paradigm

The question of how vision and audition interact in natural object identification is currently a matter of debate. We developed a large set of auditory and visual stimuli representing natural objects in order to facilitate research in the field of multisensory processing. Normative data was obtained for 270 brief environmental sounds and 320 visual object stimuli. Each stimulus was named, categorized, and rated with regard to familiarity and emotional valence by N=56 participants (Study 1). This multimodal stimulus set was employed in two subsequent crossmodal priming experiments that used semantically congruent and incongruent stimulus pairs in a S1-S2 paradigm. Task-relevant targets were either auditory (Study 2) or visual stimuli (Study 3). The behavioral data of both experiments expressed a crossmodal priming effect with shorter reaction times for congruent as compared to incongruent stimulus pairs. The observed facilitation effect suggests that object identification in one modality is influenced by input from another modality. This result implicates that congruent visual and auditory stimulus pairs were perceived as the same object and demonstrates a first validation of the multimodal stimulus set.     

Discrepant visual speech facilitates covert selective listening in "cocktail party" conditions

The presence of congruent visual speech information facilitates the identification of auditory speech, while the addition of incongruent visual speech information often impairs accuracy. This latter arrangement occurs naturally when one is being directly addressed in conversation but listens to a different speaker. Under these conditions, performance may diminish since: (a) one is bereft of the facilitative effects of the corresponding lip motion and (b) one becomes subject to visual distortion by incongruent visual speech; by contrast, speech intelligibility may be improved due to (c) bimodal localization of the central unattended stimulus. Participants were exposed to centrally presented visual and auditory speech while attending to a peripheral speech stream. In some trials, the lip movements of the central visual stimulus matched the unattended speech stream; in others, the lip movements matched the attended peripheral speech. Accuracy for the peripheral stimulus was nearly one standard deviation greater with incongruent visual information, compared to the congruent condition which provided bimodal pattern recognition cues. Likely, the bimodal localization of the central stimulus further differentiated the stimuli and thus facilitated intelligibility. Results are discussed with regard to similar findings in an investigation of the ventriloquist effect, and the relative strength of localization and speech cues in covert listening.     

Crossmodal semantic priming by naturalistic sounds and spoken words enhances visual sensitivity

We propose a multisensory framework based on Glaser and Glaser's (1989) general reading-naming interference model to account for the semantic priming effect by naturalistic sounds and spoken words on visual picture sensitivity. Four experiments were designed to investigate two key issues: First, can auditory stimuli enhance visual sensitivity when the sound leads the picture as well as when they are presented simultaneously? And, second, do naturalistic sounds (e.g., a dog's "woofing") and spoken words (e.g., /d?g/) elicit similar semantic priming effects? Here, we estimated participants' sensitivity and response criterion using signal detection theory in a picture detection task. The results demonstrate that naturalistic sounds enhanced visual sensitivity when the onset of the sounds led that of the picture by 346 ms (but not when the sounds led the pictures by 173 ms, nor when they were presented simultaneously, Experiments 1-3A). At the same SOA, however, spoken words did not induce semantic priming effects on visual detection sensitivity (Experiments 3B and 4A). When using a dual picture detection/identification task, both kinds of auditory stimulus induced a similar semantic priming effect (Experiment 4B). Therefore, we suggest that there needs to be sufficient processing time for the auditory stimulus to access its associated meaning to modulate visual perception. Besides, the interactions between pictures and the two types of sounds depend not only on their processing route to access semantic representations, but also on the response to be made to fulfill the requirements of the task.     

Perceptual congruency of audio-visual speech affects ventriloquism with bilateral visual stimuli

Many studies on multisensory processes have focused on performance in simplified experimental situations, with a single stimulus in each sensory modality. However, these results cannot necessarily be applied to explain our perceptual behavior in natural scenes where various signals exist within one sensory modality. We investigated the role of audio-visual syllable congruency on participants' auditory localization bias or the ventriloquism effect using spoken utterances and two videos of a talking face. Salience of facial movements was also manipulated. Results indicated that more salient visual utterances attracted participants' auditory localization. Congruent pairing of audio-visual utterances elicited greater localization bias than incongruent pairing, while previous studies have reported little dependency on the reality of stimuli in ventriloquism. Moreover, audio-visual illusory congruency, owing to the McGurk effect, caused substantial visual interference on auditory localization. Multisensory performance appears more flexible and adaptive in this complex environment than in previous studies.     

内外源性空间注意对多感觉整合的影响

本文采用内-外源性空间线索靶子范式, 操控内源性线索有效性(有效线索、无效线索)、外源性线索有效性(有效线索、无效线索)、目标刺激类型(视觉刺激、听觉刺激、视听觉刺激)三个自变量。通过两个不同任务难度的实验(实验1: 简单定位任务; 实验2: 复杂辨别任务)来考察内外源性空间注意对多感觉整合的影响。两个实验结果均发现外源性空间注意显著减弱了多感觉整合效应, 内源性空间注意没有显著增强多感觉整合效应; 实验2中还发现了内源性空间注意会对外源性空间注意减弱多感觉整合效应产生影响。结果表明, 与内源性空间注意不同, 外源性空间注意对多感觉整合的影响不易受任务难度的调控; 当任务较难时内源性空间注意会影响外源性空间注意减弱多感觉整合效应的过程。由此推测, 内外源性空间注意对多感觉整合的调节并非彼此独立、而是相互影响的。     

情绪和时间辨别任务中视听整合与预先准备效应

本研究分别在时间和情绪认知维度上考察预先准备效应对情绪视听整合的影响。时间辨别任务(实验1)发现视觉引导显著慢于听觉引导,并且整合效应量为负值。情绪辨别任务(实验2)发现整合效应量为正值;在负性情绪整合中,听觉引导显著大于视觉引导;在正性情绪整合中,视觉引导显著大于听觉引导。研究表明,情绪视听整合基于情绪认知加工,而时间辨别会抑制整合;此外,跨通道预先准备效应和情绪预先准备效应都与引导通道有关。     

Perceptual load influences auditory space perception in the ventriloquist aftereffect

A period of exposure to trains of simultaneous but spatially offset auditory and visual stimuli can induce a temporary shift in the perception of sound location. This phenomenon, known as the ‘ventriloquist aftereffect’, reflects a realignment of auditory and visual spatial representations such that they approach perceptual alignment despite their physical spatial discordance. Such dynamic changes to sensory representations are likely to underlie the brain’s ability to accommodate inter-sensory discordance produced by sensory errors (particularly in sound localization) and variability in sensory transduction. It is currently unknown, however, whether these plastic changes induced by adaptation to spatially disparate inputs occurs automatically or whether they are dependent on selectively attending to the visual or auditory stimuli. Here, we demonstrate that robust auditory spatial aftereffects can be induced even in the presence of a competing visual stimulus. Importantly, we found that when attention is directed to the competing stimuli, the pattern of aftereffects is altered. These results indicate that attention can modulate the ventriloquist aftereffect.     

When does visual perceptual grouping affect multisensory integration?

Several studies have shown that the direction in which a visual apparent motion stream moves can influence the perceived direction of an auditory apparent motion stream (an effect known as crossmodal dynamic capture). However, little is known about the role that intramodal perceptual grouping processes play in the multisensory integration of motion information. The present study was designed to investigate the time course of any modulation of the cross-modal dynamic capture effect by the nature of the perceptual grouping taking place within vision. Participants were required to judge the direction of an auditory apparent motion stream while trying to ignore visual apparent motion streams presented in a variety of different configurations. Our results demonstrate that the cross-modal dynamic capture effect was influenced more by visual perceptual grouping when the conditions for intramodal perceptual grouping were set up prior to the presentation of the audiovisual apparent motion stimuli. However, no such modulation occurred when the visual perceptual grouping manipulation was established at the same time as or after the presentation of the audiovisual stimuli. These results highlight the importance of the unimodal perceptual organization of sensory information to the manifestation of multisensory integration.     

Assessing automaticity in audiovisual speech integration: evidence from the speeded classification task

The McGurk effect is usually presented as an example of fast, automatic, multisensory integration. We report a series of experiments designed to directly assess these claims. We used a syllabic version of the speeded classification paradigm, whereby response latencies to the first (target) syllable of spoken word-like stimuli are slowed down when the second (irrelevant) syllable varies from trial to trial. This interference effect is interpreted as a failure of selective attention to filter out the irrelevant syllable. In Experiment 1 we reproduced the syllabic interference effect with bimodal stimuli containing auditory as well as visual lip movement information, thus confirming the generalizability of the phenomenon. In subsequent experiments we were able to produce (Experiment 2) and to eliminate (Experiment 3) syllabic interference by introducing 'illusory' (McGurk) audiovisual stimuli in the irrelevant syllable, suggesting that audiovisual integration occurs prior to attentional selection in this paradigm.     

The effect of visual threat on spatial attention to touch

Viewing a threatening stimulus can bias visual attention toward that location. Such effects have typically been investigated only in the visual modality, despite the fact that many threatening stimuli are most dangerous when close to or in contact with the body. Recent multisensory research indicates that a neutral visual stimulus, such as a light flash, can lead to a tactile attention shift towards a nearby body part. Here, we investigated whether the threat value of a visual stimulus modulates its effect on attention to touch. Participants made speeded discrimination responses about tactile stimuli presented to one or other hand, preceded by a picture cue (snake, spider, flower or mushroom) presented close to the same or the opposite hand. Pictures of snakes led to a significantly greater tactile attentional facilitation effect than did non-threatening pictures of flowers and mushrooms. Furthermore, there was a correlation between self-reported fear of snakes and spiders and the magnitude of early facilitation following cues of that type. These findings demonstrate that the attentional bias towards threat extends to the tactile modality and indicate that perceived threat value can modulate the cross-modal effect that a visual cue has on attention to touch.     

Bimodal and trimodal multisensory enhancement: effects of stimulus onset and intensity on reaction time

Manual reaction times to visual, auditory, and tactile stimuli presented simultaneously, or with a delay, were measured to test for multisensory interaction effects in a simple detection task with redundant signals. Responses to trimodal stimulus combinations were faster than those to bimodal combinations, which in turn were faster than reactions to unimodal stimuli. Response enhancement increased with decreasing auditory and tactile stimulus intensity and was a U-shaped function of stimulus onset asynchrony. Distribution inequality tests indicated that the multisensory interaction effects were larger than predicted by separate activation models, including the difference between bimodal and trimodal response facilitation. The results are discussed with respect to previous findings in a focused attention task and are compared with multisensory integration rules observed in bimodal and trimodal superior colliculus neurons in the cat and monkey.     

Behold the voice of wrath: cross-modal modulation of visual attention by anger prosody

Emotionally relevant stimuli are prioritized in human information processing. It has repeatedly been shown that selective spatial attention is modulated by the emotional content of a stimulus. Until now, studies investigating this phenomenon have only examined within-modality effects, most frequently using pictures of emotional stimuli to modulate visual attention. In this study, we used simultaneously presented utterances with emotional and neutral prosody as cues for a visually presented target in a cross-modal dot probe task. Response times towards targets were faster when they appeared at the location of the source of the emotional prosody. Our results show for the first time a cross-modal attentional modulation of visual attention by auditory affective prosody.     

Cross-modal integration of emotional face and voice in congruous and incongruous pairs: The P2 ERP effect

The study investigates cross-modal simultaneous processing of emotional tone of voice and emotional facial expression by event-related potentials (ERPs), using a wide range of different emotions (happiness, sadness, fear, anger, surprise, and disgust). Auditory emotional stimuli (a neutral word pronounced in an affective tone) and visual patterns (emotional facial expressions) were matched in congruous (the same emotion in face and voice) and incongruous (different emotions) pairs. Subjects (N=31) were required to watch and listen to the stimuli in order to comprehend them. Repeated measures ANOVAs showed a positive ERP deflection (P2), more posterior distributed. This P2 effect may represent a marker of cross-modal integration, modulated as a function of congruous/incongruous condition. Indeed, it shows an ampler peak in response to congruous stimuli than incongruous ones. It is suggested P2 can be a cognitive marker of multisensory processing, independently from the emotional content.     

Effects of audio-visual integration on the detection of masked speech and non-speech sounds

Integration of simultaneous auditory and visual information about an event can enhance our ability to detect that event. This is particularly evident in the perception of speech, where the articulatory gestures of the speaker's lips and face can significantly improve the listener's detection and identification of the message, especially when that message is presented in a noisy background. Speech is a particularly important example of multisensory integration because of its behavioural relevance to humans and also because brain regions have been identified that appear to be specifically tuned for auditory speech and lip gestures. Previous research has suggested that speech stimuli may have an advantage over other types of auditory stimuli in terms of audio-visual integration. Here, we used a modified adaptive psychophysical staircase approach to compare the influence of congruent visual stimuli (brief movie clips) on the detection of noise-masked auditory speech and non-speech stimuli. We found that congruent visual stimuli significantly improved detection of an auditory stimulus relative to incongruent visual stimuli. This effect, however, was equally apparent for speech and non-speech stimuli. The findings suggest that speech stimuli are not specifically advantaged by audio-visual integration for detection at threshold when compared with other naturalistic sounds.