Tiziana Vercillo

Enhanced auditory spatial localization in blind echolocators.

Echolocation is the extraordinary ability to represent the external environment by using reflected sound waves from self-generated auditory pulses. Blind human expert echolocators show extremely precise spatial acuity and high accuracy in determining the shape and motion of objects by using echoes. In the current study, we investigated whether or not the use of echolocation would improve the representation of auditory space, which is severely compromised in congenitally blind individuals (Gori et al., 2014). The performance of three blind expert echolocators was compared to that of 6 blind non-echolocators and 11 sighted participants. Two tasks were performed: (1) a space bisection task in which participants judged whether the second of a sequence of three sounds was closer in space to the first or the third sound and (2) a minimum audible angle task in which participants reported which of two sounds presented successively was located more to the right. The blind non-echolocating group showed a severe impairment only in the space bisection task compared to the sighted group. Remarkably, the three blind expert echolocators performed both spatial tasks with similar or even better precision and accuracy than the sighted group. These results suggest that echolocation may improve the general sense of auditory space, most likely through a process of sensory calibration.

Early visual deprivation severely compromises the auditory sense of space in congenitally blind children.

A recent study has shown that congenitally blind adults, who have never had visual experience, are impaired on an auditory spatial bisection task (Gori, Sandini, Martinoli, & Burr, 2014). In this study we investigated how thresholds for auditory spatial bisection and auditory discrimination develop with age in sighted and congenitally blind children (9 to 14 years old). Children performed 2 spatial tasks (minimum audible angle and space bisection) and 1 temporal task (temporal bisection). There was no impairment in the temporal task for blind children but, like adults, they showed severely compromised thresholds for spatial bisection. Interestingly, the blind children also showed lower precision in judging minimum audible angle. These results confirm the adult study and go on to suggest that even simpler auditory spatial tasks are compromised in children, and that this capacity recovers over time. (PsycINFO Database Record

The curious incident of attention in multisensory integration : bottom-up vs. top-down

The role attention plays in our experience of a coherent, multisensory world is still controversial. On the one hand, a subset of inputs may be selected for detailed processing and multisensory integration in a top-down manner, i.e., guidance of multisensory integration by attention. On the other hand, stimuli may be integrated in a bottom-up fashion according to low-level properties such as spatial coincidence, thereby capturing attention. Moreover, attention itself is multifaceted and can be described via both top-down and bottom-up mechanisms. Thus, the interaction between attention and multisensory integration is complex and situation-dependent. The authors of this opinion paper are researchers who have contributed to this discussion from behavioural, computational and neurophysiological perspectives. We posed a series of questions, the goal of which was to illustrate the interplay between bottom-up and top-down processes in various multisensory scenarios in order to clarify the standpoint taken by each author and with the hope of reaching a consensus. Although divergence of viewpoint emerges in the current responses, there is also considerable overlap: In general, it can be concluded that the amount of influence that attention exerts on MSI depends on the current task as well as prior knowledge and expectations of the observer. Moreover stimulus properties such as the reliability and salience also determine how open the processing is to influences of attention.

Attention to sound improves auditory reliability in audio-tactile spatial optimal integration.

The role of attention on multisensory processing is still poorly understood. In particular, it is unclear whether directing attention toward a sensory cue dynamically reweights cue reliability during integration of multiple sensory signals. In this study, we investigated the impact of attention in combining audio-tactile signals in an optimal fashion. We used the Maximum Likelihood Estimation (MLE) model to predict audio-tactile spatial localization on the body surface. We developed a new audio-tactile device composed by several small units, each one consisting of a speaker and a tactile vibrator independently controllable by external software. We tested participants in an attentional and a non-attentional condition. In the attentional experiment, participants performed a dual task paradigm: they were required to evaluate the duration of a sound while performing an audio-tactile spatial task. Three unisensory or multisensory stimuli, conflictual or not conflictual sounds and vibrations arranged along the horizontal axis, were presented sequentially. In the primary task participants had to evaluate in a space bisection task the position of the second stimulus (the probe) with respect to the others (the standards). In the secondary task they had to report occasionally changes in duration of the second auditory stimulus. In the non-attentional task participants had only to perform the primary task (space bisection). Our results showed an enhanced auditory precision (and auditory weights) in the auditory attentional condition with respect to the control non-attentional condition. The results of this study support the idea that modality-specific attention modulates multisensory integration.

Children do not recalibrate motor‐sensory temporal order after exposure to delayed sensory feedback

Prolonged adaptation to delayed sensory feedback to a simple motor act (such as pressing a key) causes recalibration of sensory-motor synchronization, so instantaneous feedback appears to precede the motor act that caused it (Stetson, Cui, Montague & Eagleman, 2006). We investigated whether similar recalibration occurs in school-age children. Although plasticity may be expected to be even greater in children than in adults, we found no evidence of recalibration in children aged 8-11 years. Subjects adapted to delayed feedback for 100 trials, intermittently pressing a key that caused a tone to sound after a 200 ms delay. During the test phase, subjects responded to a visual cue by pressing a key, which triggered a tone to be played at variable intervals before or after the keypress. Subjects judged whether the tone preceded or followed the keypress, yielding psychometric functions estimating the delay when they perceived the tone to be synchronous with the action. The psychometric functions also gave an estimate of the precision of the temporal order judgment. In agreement with previous studies, adaptation caused a shift in perceived synchrony in adults, so the keypress appeared to trail behind the auditory feedback, implying sensory-motor recalibration. However, school children of 8 to 11 years showed no measureable adaptation of perceived simultaneity, even after adaptation with 500 ms lags. Importantly, precision in the simultaneity task also improved with age, and this developmental trend correlated strongly with the magnitude of recalibration. This suggests that lack of recalibration of sensory-motor simultaneity after adaptation in school-age children is related to their poor precision in temporal order judgments. To test this idea we measured recalibration in adult subjects with auditory noise added to the stimuli (which hampered temporal precision). Under these conditions, recalibration was greatly reduced, with the magnitude of recalibration strongly correlating with temporal precision.

Intercepting a sound without vision

Visual information is extremely important to generate internal spatial representations. In the auditory modality, the absence of visual cues during early infancy does not preclude the development of some spatial strategies. However, specific spatial abilities might result impaired. In the current study, we investigated the effect of early visual deprivation on the ability to localize static and moving auditory stimuli by comparing sighted and early blind individuals’ performance in different spatial tasks. We also examined perceptual stability in the two groups of participants by matching localization accuracy in a static and a dynamic head condition that involved rotational head movements. Sighted participants accurately localized static and moving sounds. Their localization ability remained unchanged after rotational movements of the head. Conversely, blind participants showed a leftward bias during the localization of static sounds and a little bias for moving sounds. Moreover, head movements induced a significant bias in the direction of head motion during the localization of moving sounds. These results suggest that internal spatial representations might be body-centered in blind individuals and that in sighted people the availability of visual cues during early infancy may affect sensory-motor interactions.

Early visual deprivation prompts the use of body-centered frames of reference for auditory localization

The effects of early visual deprivation on auditory spatial processing are controversial. Results from recent psychophysical studies show that people who were born blind have a spatial impairment in localizing sound sources within specific auditory settings, while previous psychophysical studies revealed enhanced auditory spatial abilities in early blind compared to sighted individuals. An explanation of why an auditory spatial deficit is sometimes observed within blind populations and its task-dependency remains to be clarified. We investigated auditory spatial perception in early blind adults and demonstrated that the deficit derives from blind individuals reduced ability to remap sound locations using an external frame of reference. We found that performance in blind population was severely impaired when they were required to localize brief auditory stimuli with respect to external acoustic landmarks (external reference frame) or when they had to reproduce the spatial distance between two sounds. However, they performed similarly to sighted controls when had to localize sounds with respect to their own hand (body-centered reference frame), or to judge the distances of sounds from their finger. These results suggest that early visual deprivation and the lack of visual contextual cues during the critical period induce a preference for body-centered over external spatial auditory representations.

Spatial modulation of motor-sensory recalibration in early deaf individuals

&NA; Audition dominates other senses in temporal processing, and in the absence of auditory cues, temporal perception can be compromised. Moreover, after auditory deprivation, visual attention is selectively enhanced for peripheral visual stimuli. In this study, we assessed whether early hearing loss affects motor‐sensory recalibration, the ability to adjust the timing of an action and its sensory effect based on the recent experience. Early deaf participants and hearing controls were asked to discriminate the temporal order between a motor action (a keypress) and a visual stimulus (a white circle) before and after adaptation to a delay between the two events. To examine the effects of spatial modulation, we presented visual stimuli in both central and peripheral visual fields. Results showed overall higher temporal JNDs (Just Noticeable Difference) for deaf participants as compared to hearing controls suggesting that the auditory information is important for the calibration of motor‐sensory timing. Adaptation to a motor‐sensory delay induced distinctive effect in the two groups of participants, with hearing controls showing a recalibration effect for central stimuli only whereas deaf individuals for peripheral visual stimuli only. Our results suggest that auditory deprivation affects motor‐sensory recalibration and that the mechanism underlying motor‐sensory recalibration is susceptible to spatial modulation. HighlightsEarly auditory loss affects motor‐sensory integration.Adaptation to a motor‐sensory delay induced opposite effect in deaf and hearing individuals.Hearing controls show a recalibration effect for central but not peripheral stimuli.Deaf individuals show a recalibration effect for peripheral visual stimuli only.Motor‐sensory recalibration is susceptible to spatial modulation.Early auditory deprivation compromises precision in sensory‐motor temporal judgments.

Restoring an allocentric reference frame in blind individuals through echolocation

Recent psychophysical studies have described task-specific auditory spatial deficits in congenitally blind individuals. We investigated auditory spatial perception in congenitally blind children and adults during different auditory spatial tasks that required the localization of brief auditory stimuli with respect to either external acoustic landmarks (allocentric reference frame) or their own body (egocentric reference frame). Early blind participants successfully represented sound locations with respect to their body. However, they showed relative poor precision when compared to sighted participants during the localization of sound with respect to external auditory landmarks, suggesting that vision is crucial for an allocentric representation of the auditory space. In a separate study, we tested three congenitally blind individuals who used echolocation as a navigational strategy, to assess the benefit of echolocation on auditory spatial perception. Blind echolocators did not show the same impairment in...

Tactile feedback improves auditory spatial localization

We recently showed that congenitally blind adults have severely impaired thresholds in an auditory spatial bisection task, pointing to the importance of vision in constructing auditory spatial maps. To explore strategies that may improve the auditory spatial sense of the blind, we investigated the impact of tactile feedback on spatial auditory localization in 29 blindfolded sighted subjects, assigned at random to one of three groups: tactile feedback ( n = 11 ), verbal feedback ( n = 8 ) and no feedback ( n = 10 ). For all groups, auditory bisection thresholds were first measured by playing three consecutive sounds at 500 ms intervals, and subjects judged whether the second sound was spatially closer to the first or to the third. The tactile-feedback group was given two audio-tactile training sessions of 100 trials, where each auditory trial was followed by the same spatial sequence played on the subject’s forearm; auditory spatial bisection thresholds were evaluated after each session. The no-feedback group did the same sequence of trials, with no feedback. In the verbal-feedback condition, the positions of the sounds was verbally reported to the subject after each training trial. Interestingly, subject performance improved significantly only after the audio-tactile training, on average by a factor of 2.5. The no-feedback sessions, and those with verbal feedback produced no statistically significant improvement. The results suggest that direct tactile feedback interacts with the auditory spatial localization system, possibly by a process of cross-sensory recalibration. More generally, the results encourage the possibility of designing rehabilitation programs to help blind individuals establish a robust sense of space.