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 (), verbal feedback () and no feedback (). 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.
Prolonged adaptation to delayed sensory feedback to a simple motor act (such as pressing a key) seems to provoke a recalibration of sensory-motor synchronization, causing instantaneous feedback to appear to precede the motor act that caused it (Stetson et al., Neuron, 2006). We investigated whether a similar recalibration occurs in school-age children, when plasticity may be expected to be even greater than in adults. 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 light cue by pressing a key, which was accompanied by a tone played at a variable interval before or after the keypress. Subjects judged whether the tone preceded or followed the keypress. The data were fit with cumulative gaussian psychometric functions, yielding estimates of the points of perceived synchrony (mean) and precision (width). In agreement with previous studies, adults showed a shift in perceived synchrony after adaptation, so the keypress appeared to trail the auditory feedback, implying sensory-motor recalibration. However, school children of all ages (7, 8, 10 & 12 years) showed no adaptation of perceived simultaneity, although their precision in the simultaneity task was comparable with that of adults. This suggests that school-age children do not recalibrate sensory-motor simultaneity after adaptation, implying that the neural mechanisms underlying recalibration require the maturity of both the motor and sensory systems.
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.
Encoding the temporal properties of external signals that comprise multimodal events is a major factor guiding everyday experience. However, during the natural aging process, impairments to sensory processing can profoundly affect multimodal temporal perception. Various mechanisms can contribute to temporal perception, and thus it is imperative to understand how each can be affected by age. In the current study, using three different temporal order judgement tasks (unisensory, multisensory, and sensorimotor), we investigated the effects of age on two separate temporal processes: synchronization and integration of multiple signals. These two processes rely on different aspects of temporal information, either the temporal alignment of processed signals or the integration/segregation of signals arising from different modalities, respectively. Results showed that the ability to integrate/segregate multiple signals decreased with age regardless of the task, and that the magnitude of such impairment correlated across tasks, suggesting a widespread mechanism affected by age. In contrast, perceptual synchrony remained stable with age, revealing a distinct intact mechanism. Overall, results from this study suggest that aging has differential effects on temporal processing, and general impairments with aging may impact global temporal sensitivity while context-dependent processes remain unaffected.