Anisotropy of lateral peripersonal space is linked to handedness.

The space immediately surrounding our bodies, i.e., peripersonal space (PPS), is a critical area for the interaction with the external world, be it to deal with imminent threat or to attain objects of interest. In the brain, a dedicated system codes PPS in motor terms for the purpose of action. Yet, humans have asymmetric motor abilities: the dominant hand has an advantage in term of movements' precision and reaction time. Furthermore, spatial attention is asymmetric and seems to be linked to a right hemispheric dominance for spatial processing. Here, we tested whether handedness and attentional asymmetries impact the detection of a tactile stimulus when an irrelevant auditory stimulus is looming towards the individual from the right or left hemispace. We examined the distance at which sound started speeding up tactile detection to estimate the morphometry of peri-trunk PPS. Our results show that right-handers' PPS is larger in the left than in the right hemispace, whereas left-handers' PPS is symmetric. The expansion of right-handers' PPS on the side of the non-dominant hand is coherent with a protective function of PPS. Left-handers' symmetric PPS can be related to the symmetric request of their motor abilities induced by living in a right-handers' world. These findings reveal that PPS is not uniform and suggest that general mechanisms of spatial processing as well as motor skills could play a role in the representation of peri-trunk PPS.

Multisensory aversive stimuli differentially modulate negative feelings in near and far space.

Affect, space, and multisensory integration are processes that are closely linked. However, it is unclear whether the spatial location of emotional stimuli interacts with multisensory presentation to influence the emotional experience they induce in the perceiver. In this study, we used the unique advantages of virtual reality techniques to present potentially aversive crowd stimuli embedded in a natural context and to control their display in terms of sensory and spatial presentation. Individuals high in crowdphobic fear navigated in an auditory-visual virtual environment, in which they encountered virtual crowds presented through the visual channel, the auditory channel, or both. They reported the intensity of their negative emotional experience at a far distance and at a close distance from the crowd stimuli. Whereas auditory-visual presentation of close feared stimuli amplified negative feelings, auditory-visual presentation of distant feared stimuli did not amplify negative feelings. This suggests that spatial closeness allows multisensory processes to modulate the intensity of the emotional experience induced by aversive stimuli. Nevertheless, the specific role of auditory stimulation must be investigated to better understand this interaction between multisensory, affective, and spatial representation processes. This phenomenon may serve the implementation of defensive behaviors in response to aversive stimuli that are in position to threaten an individual's feeling of security.

Only your eyes tell me what you like: Exploring the liking effect induced by other's gaze.

Our preferences are sensitive to social influences. For instance, we like more the objects that are looked-at by others than non-looked-at objects. Here, we explored this liking effect, using a modified paradigm of attention cueing by gaze. First, we investigated if the liking effect induced by gaze relied on motoric representations of the target object by testing if the liking effect could be observed for non-manipulable (alphanumeric characters) as well as for manipulable items (common tools). We found a significant liking effect for the alphanumeric items. Second, we tested if another type of powerful social cue could also induce a liking effect. We used an equivalent paradigm but with pointing hands instead of gaze cues. Pointing hands elicited a robust attention-orienting effect, but they did not induce any significant liking effect. This study extends previous findings and reinforces the view of eye gaze as a special cue in human interactions.

Auditory-visual integration of emotional signals in a virtual environment for cynophobia.

Cynophobia (dog phobia) has both visual and auditory relevant components. In order to investigate the efficacy of virtual reality (VR) exposure-based treatment for cynophobia, we studied the efficiency of auditory-visual environments in generating presence and emotion. We conducted an evaluation test with healthy participants sensitive to cynophobia in order to assess the capacity of auditory-visual virtual environments (VE) to generate fear reactions. Our application involves both high fidelity visual stimulation displayed in an immersive space and 3D sound. This specificity enables us to present and spatially manipulate fearful stimuli in the auditory modality, the visual modality and both. Our specific presentation of animated dog stimuli creates an environment that is highly arousing, suggesting that VR is a promising tool for cynophobia treatment and that manipulating auditory-visual integration might provide a way to modulate affect.

Auditory roughness elicits defense reactions.

Auditory roughness elicits aversion, and higher activation in cerebral areas involved in threat processing, but its link with defensive behavior is unknown. Defensive behaviors are triggered by intrusions into the space immediately surrounding the body, called peripersonal space (PPS). Integrating multisensory information in PPS is crucial to assure the protection of the body. Here, we assessed the behavioral effects of roughness on auditory-tactile integration, which reflects the monitoring of this multisensory region of space. Healthy human participants had to detect as fast as possible a tactile stimulation delivered on their hand while an irrelevant sound was approaching them from the rear hemifield. The sound was either a simple harmonic sound or a rough sound, processed through binaural rendering so that the virtual sound source was looming towards participants. The rough sound speeded tactile reaction times at a farther distance from the body than the non-rough sound. This indicates that PPS, as estimated here via auditory-tactile integration, is sensitive to auditory roughness. Auditory roughness modifies the behavioral relevance of simple auditory events in relation to the body. Even without emotional or social contextual information, auditory roughness constitutes an innate threat cue that elicits defensive responses.

Capturing the dynamics of peripersonal space by integrating expectancy effects and sound propagation properties.

BACKGROUND: Humans perceive near space and far space differently. Peripersonal space (PPS), i.e. the space directly surrounding the body, is often studied using paradigms based on audiotactile integration. In these paradigms, reaction time (RT) to a tactile stimulus is measured in the presence of a concurrent auditory looming stimulus. NEW METHOD: We propose here to refine the experimental procedure by disentangling behavioral contributions of the targeted audiotactile integration mechanisms from expectancy effects. To this aim, we added to the protocol a baseline with a fixed sound distance. Furthermore, in order to improve the relevance of the audiotactile integration measures, we took into account sound propagation properties and assessed RTs for logarithmically spaced auditory distances. RESULTS: Expectation contributed significantly to overall behavioral responses. Subtracting it isolated the audiotactile effect due to the stimulus proximity. This revealed that audiotactile integration effects have to be tested on a logarithmic scale of distances, and that they follow a linear variation on this scale. COMPARISON WITH EXISTING METHOD(S): The current method allows cleaner and more pertinent sampling measures for evaluating audiotactile integration phenomena linked to PPS. Furthermore, most of the existing methods propose a sigmoid fitting, which rests on the intuitive framework that PPS is an in-or-out zone. Our results suggest that behavioral effects follow a logarithmic decrease, thus a response graduated in space. CONCLUSIONS: The proposed protocol design and method of analysis contribute to sharpen the experimental investigation of the factors influencing and modifying multisensory integration phenomena in the space surrounding the body.

Social coding of the multisensory space around us.

Multisensory integration of stimuli occurring in the area surrounding our bodies gives rise to the functional representation of peripersonal space (PPS). PPS extent is flexible according to the affective context and the target of an action, but little is known about how social context modulates it. We used an audiotactile interaction task to investigate PPS of individuals during social interaction. Participants had to detect as fast as possible a tactile stimulus while task-irrelevant looming sounds were presented, while they were paired as collaborative dyads and as competitive dyads. We also measured PPS in participants seated near an inactive individual. PPS boundaries were modulated only when participants collaborated with a partner, in the form of an extension on the right hemispace and independently of the location of the partner. This suggests that space processing is modified during collaborative tasks. During collective actions, a supra-individual representation of the space of action could be at stake in order to adapt our individual motor control to an interaction as a group with the external world. Reassessing multisensory integration in the light of its potential social sensitivity might reveal that low-level mechanisms are modified by the need to interact with others.

Auditory Sketches: Very Sparse Representations of Sounds Are Still Recognizable.

Sounds in our environment like voices, animal calls or musical instruments are easily recognized by human listeners. Understanding the key features underlying this robust sound recognition is an important question in auditory science. Here, we studied the recognition by human listeners of new classes of sounds: acoustic and auditory sketches, sounds that are severely impoverished but still recognizable. Starting from a time-frequency representation, a sketch is obtained by keeping only sparse elements of the original signal, here, by means of a simple peak-picking algorithm. Two time-frequency representations were compared: a biologically grounded one, the auditory spectrogram, which simulates peripheral auditory filtering, and a simple acoustic spectrogram, based on a Fourier transform. Three degrees of sparsity were also investigated. Listeners were asked to recognize the category to which a sketch sound belongs: singing voices, bird calls, musical instruments, and vehicle engine noises. Results showed that, with the exception of voice sounds, very sparse representations of sounds (10 features, or energy peaks, per second) could be recognized above chance. No clear differences could be observed between the acoustic and the auditory sketches. For the voice sounds, however, a completely different pattern of results emerged, with at-chance or even below-chance recognition performances, suggesting that the important features of the voice, whatever they are, were removed by the sketch process. Overall, these perceptual results were well correlated with a model of auditory distances, based on spectro-temporal excitation patterns (STEPs). This study confirms the potential of these new classes of sounds, acoustic and auditory sketches, to study sound recognition.

Cynophobic fear adaptively extends peri-personal space.

Peri-personal space (PPS) is defined as the space immediately surrounding our bodies, which is critical in the adaptation of our social behavior. As a space of interaction with the external world, PPS is involved in the control of motor action as well as in the protection of the body. The boundaries of this PPS are known to be flexible but so far, little is known about how PPS boundaries are influenced by unreasonable fear. We hypothesized that unreasonable fear extends the neural representation of the multisensory space immediately surrounding the body in the presence of a feared object, with the aim of expanding the space of protection around the body. To test this hypothesis, we explored the impact of unreasonable fear on the size of PPS in two groups of non-clinical participants: dog-fearful and non-fearful participants. The sensitivity to cynophobia was assessed with a questionnaire. We measured participants' PPS extent in the presence of threatening (dog growling) and non-threatening (sheep bleating) auditory stimuli. The sound stimuli were processed through binaural rendering so that the virtual sound sources were looming toward participants from their rear hemi-field. We found that, when in the presence of the auditory dog stimulus, the PPS of dog-fearful participants is larger than that of non-fearful participants. Our results demonstrate that PPS size is adaptively modulated by cynophobia and suggest that anxiety tailors PPS boundaries when exposed to fear-relevant features. Anxiety, with the exception of social phobia, has rarely been studied as a disorder of social interaction. These findings could help develop new treatment strategies for anxious disorders by involving the link between space and interpersonal interaction in the approach of the disorder.

Auditory-visual aversive stimuli modulate the conscious experience of fear.

In a natural environment, affective information is perceived via multiple senses, mostly audition and vision. However, the impact of multisensory information on affect remains relatively undiscovered. In this study, we investigated whether the auditory-visual presentation of aversive stimuli influences the experience of fear. We used the advantages of virtual reality to manipulate multisensory presentation and to display potentially fearful dog stimuli embedded in a natural context. We manipulated the affective reactions evoked by the dog stimuli by recruiting two groups of participants: dog-fearful and non-fearful participants. The sensitivity to dog fear was assessed psychometrically by a questionnaire and also at behavioral and subjective levels using a Behavioral Avoidance Test (BAT). Participants navigated in virtual environments, in which they encountered virtual dog stimuli presented through the auditory channel, the visual channel or both. They were asked to report their fear using Subjective Units of Distress. We compared the fear for unimodal (visual or auditory) and bimodal (auditory-visual) dog stimuli. Dog-fearful participants as well as non-fearful participants reported more fear in response to bimodal audiovisual compared to unimodal presentation of dog stimuli. These results suggest that fear is more intense when the affective information is processed via multiple sensory pathways, which might be due to a cross-modal potentiation. Our findings have implications for the field of virtual reality-based therapy of phobias. Therapies could be refined and improved by implicating and manipulating the multisensory presentation of the feared situations.