Audiotactile temporal order judgments in sighted and blind individuals

Comparison of temporal judgments in sighted and visually impaired children

AIM

We studied visually impaired and blind children to investigate the effects of visual damage on time perception.

METHODS

Sixty-three children (11 blind, 16 visually impaired, 20 sighted and 16 sighted but blindfolded) performed a temporal bisection task, which consisted of judging different temporal intervals presented in the auditory modality.

RESULTS

The visually impaired children showed lower constant error than sighted children but higher variability (Weber ratio). The blindfolded children had a temporal estimation comparable to the clinical groups and time sensitivity comparable to the controls.

CONCLUSION

These findings are interpreted in the light of inter-modality interference, assuming that the coexistence of both sensory modalities, present only in controls, leads to a trade-off between the two senses with an indirect contribution of sight, which does not happen either in the clinical groups or in the blindfolded children, despite the single sensory task.

Reciprocal Interference Between Audition and Touch in the Perception of Duration

Audition and touch interact with one another and share a number of similarities; however, little is known about their interplay in the perception of temporal duration. The present study intended to investigate whether the temporal duration of an irrelevant auditory or tactile stimulus could modulate the perceived duration of a target stimulus presented in the other modality (i.e., tactile or auditory) adopting both a between-participants (Experiment 1) and a within-participants (Experiment 2) experimental design. In a two-alternative forced-choice task, participants decided which of two events in a target modality was longer. The simultaneously distractor stimuli were presented with a duration that was either congruent or incongruent to the target’s. Results showed that both the auditory and tactile modalities affected duration judgments in the incongruent condition, decreasing performance in both experiments. Moreover, in Experiment 1, the tactile modality enhanced the perception of auditory stimuli in the congruent condition, but audition did not facilitate performance for the congruent condition in the tactile modality; this tactile enhancement of audition was not found in Experiment 2. To the best of our knowledge, this is the first study documenting audiotactile interactions in the perception of duration, and suggests that audition and touch might modulate one another in a more balanced manner, in contrast to audiovisual pairings. The findings support previous evidence as to the shared links and reciprocal influences when audition and touch interact with one another.

Walking to a multisensory beat

Living in a complex and multisensory environment demands constant interaction between perception and action. In everyday life it is common to combine efficiently simultaneous signals coming from different modalities. There is evidence of a multisensory benefit in a variety of laboratory tasks (temporal judgement, reaction time tasks). It is less clear if this effect extends to ecological tasks, such as walking. Furthermore, benefits of multimodal stimulation are linked to temporal properties such as the temporal window of integration and temporal recalibration. These properties have been examined in tasks involving single, non-repeating stimulus presentations. Here we investigate the same temporal properties in the context of a rhythmic task, namely audio-tactile stimulation during walking. The effect of audio-tactile rhythmic cues on gait variability and the ability to synchronize to the cues was studied in young adults. Participants walked with rhythmic cues presented at different stimulus-onset asynchronies. We observed a multisensory benefit by comparing audio-tactile to unimodal stimulation. Moreover, both the temporal window of integration and temporal recalibration mediated the response to multimodal stimulation. In sum, rhythmic behaviours obey the same principles as temporal discrimination and detection behaviours and thus can also benefit from multimodal stimulation.

The Sound of Vision Project: On the Feasibility of an Audio-Haptic Representation of the Environment, for the Visually Impaired

The Sound of Vision project involves developing a sensory substitution device that is aimed at creating and conveying a rich auditory representation of the surrounding environment to the visually impaired. However, the feasibility of such an approach is strongly constrained by neural flexibility, possibilities of sensory substitution and adaptation to changed sensory input. We review evidence for such flexibility from various perspectives. We discuss neuroplasticity of the adult brain with an emphasis on functional changes in the visually impaired compared to sighted people. We discuss effects of adaptation on brain activity, in particular short-term and long-term effects of repeated exposure to particular stimuli. We then discuss evidence for sensory substitution such as Sound of Vision involves, while finally discussing evidence for adaptation to changes in the auditory environment. We conclude that sensory substitution enterprises such as Sound of Vision are quite feasible in light of the available evidence, which is encouraging regarding such projects.

Concurrent emotional pictures modulate temporal order judgments of spatially separated audio-tactile stimuli

Although attention can be captured toward high-arousal stimuli, little is known about how perceiving emotion in one modality influences the temporal processing of non-emotional stimuli in other modalities. We addressed this issue by presenting observers spatially uninformative emotional pictures while they performed an audio-tactile temporal-order judgment (TOJ) task. In Experiment 1, audio-tactile stimuli were presented at the same location straight ahead of the participants, who had to judge "which modality came first?". In Experiments 2 and 3, the audio-tactile stimuli were delivered one to the left and the other to the right side, and participants had to judge "which side came first?". We found both negative and positive high-arousal pictures to significantly bias TOJs towards the tactile and away from the auditory event when the audio-tactile stimuli were spatially separated; by contrast, there was no such bias when the audio-tactile stimuli originated from the same location. To further examine whether this bias is attributable to the emotional meanings conveyed by the pictures or to their high arousal effect, we compared and contrasted the influences of near-body threat vs. remote threat (emotional) pictures on audio-tactile TOJs in Experiment 3. The bias manifested only in the near-body threat condition. Taken together, the findings indicate that visual stimuli conveying meanings of near-body interaction activate a sensorimotor functional link prioritizing the processing of tactile over auditory signals when these signals are spatially separated. In contrast, audio-tactile signals from the same location engender strong crossmodal integration, thus counteracting modality-based attentional shifts induced by the emotional pictures.

Positive Clinical Neuroscience

Disorders of the brain and its sensory organs have traditionally been associated with deficits in movement, perception, cognition, emotion, and behavior. It is increasingly evident, however, that positive phenomena may also occur in such conditions, with implications for the individual, science, medicine, and for society. This article provides a selective review of such positive phenomena – enhanced function after brain lesions, better-than-normal performance in people with sensory loss, creativity associated with neurological disease, and enhanced performance associated with aging. We propose that, akin to the well-established field of positive psychology and the emerging field of positive clinical psychology, the nascent fields of positive neurology and positive neuropsychology offer new avenues to understand brain-behavior relationships, with both theoretical and therapeutic implications.

Tactual perception: a review of experimental variables and procedures

This paper reviews the literature on tactual perception. Throughout this review, we will highlight some of the most relevant aspects in the touch literature: type of stimuli; type of participants; type of tactile exploration; and finally, the interaction between touch and other senses. Regarding type of stimuli, we will analyse studies with abstract stimuli such as vibrations, with two- and three-dimensional stimuli, and also concrete stimuli, considering the relation between familiar and unfamiliar stimuli and the haptic perception of faces. Under the "type of participants" topic, we separated studies with blind participants, studies with children and adults, and also performed an overview of sex differences in performance. The type of tactile exploration is explored considering conditions of active and passive touch, the relevance of movement in touch and the relation between haptic exploration and time. Finally, interactions between touch and vision, touch and smell and touch and taste are explored in the last topic. The review ends with an overall conclusion on the state of the art for the tactual perception literature. With this work, we intend to present an organised overview of the main variables in touch experiments, compiling aspects reported in the tactual literature, and attempting to provide both a summary of previous findings, and a guide to the design of future works on tactual perception and memory, through a presentation of implications from previous studies.

The role of visual experience for the neural basis of spatial cognition

Blindness often results in the adaptive neural reorganization of the remaining modalities, producing sharper auditory and haptic behavioral performance. Yet, non-visual modalities might not be able to fully compensate for the lack of visual experience as in the case of congenital blindness. For example, developmental visual experience seems to be necessary for the maturation of multisensory neurons for spatial tasks. Additionally, the ability of vision to convey information in parallel might be taken into account as the main attribute that cannot be fully compensated by the spared modalities. Therefore, the lack of visual experience might impair all spatial tasks that require the integration of inputs from different modalities, such as having to represent a set of objects on the basis of the spatial relationships among the objects, rather than the spatial relationship that each object has with oneself. Here we integrate behavioral and neural evidence to conclude that visual experience is necessary for the neural development of normal spatial cognition.

Audiotactile interactions in temporal perception

In the present review, we focus on how commonalities in the ontogenetic development of the auditory and tactile sensory systems may inform the interplay between these signals in the temporal domain. In particular, we describe the results of behavioral studies that have investigated temporal resolution (in temporal order, synchrony/asynchrony, and simultaneity judgment tasks), as well as temporal numerosity perception, and similarities in the perception of frequency across touch and hearing. The evidence reviewed here highlights features of audiotactile temporal perception that are distinctive from those seen for other pairings of sensory modalities. For instance, audiotactile interactions are characterized in certain tasks (e.g., temporal numerosity judgments) by a more balanced reciprocal influence than are other modality pairings. Moreover, relative spatial position plays a different role in the temporal order and temporal recalibration processes for audiotactile stimulus pairings than for other modality pairings. The effect exerted by both the spatial arrangement of stimuli and attention on temporal order judgments is described. Moreover, a number of audiotactile interactions occurring during sensory-motor synchronization are highlighted. We also look at the audiotactile perception of rhythm and how it may be affected by musical training. The differences emerging from this body of research highlight the need for more extensive investigation into audiotactile temporal interactions. We conclude with a brief overview of some of the key issues deserving of further research in this area.

Early- and Late-Onset Blindness Both Curb Audiotactile Integration on the Parchment-Skin Illusion

It has been shown that congenital blindness can lead to anomalies in the integration of auditory and tactile information, at least under certain conditions. In the present study, we used the parchment-skin illusion, a robust illustration of sound-biased perception of touch based on changes in frequency, to investigate the specificities of audiotactile interactions in early- and late-onset blind individuals. Blind individuals in both groups did not experience any illusory change in tactile perception when the frequency of the auditory signal was modified, whereas sighted individuals consistently experienced the illusion. This demonstration that blind individuals had reduced susceptibility to an auditory-tactile illusion suggests either that vision is necessary for the establishment of audiotactile interactions or that auditory and tactile information can be processed more independently in blind individuals than in sighted individuals. In addition, the results obtained in late-onset blind participants suggest that visual input may play a role in the maintenance of audiotactile integration.

Audiotactile interactions in front and rear space

The last few years have seen a growing interest in the assessment of audiotactile interactions in information processing in peripersonal space. In particular, these studies have focused on investigating peri-hand space [corrected] and, more recently, on the functional differences that have been demonstrated between the space close to front and back of the head (i.e., the peri-head space). In this review, the issue of how audiotactile interactions vary as a function of the region of space in which stimuli are presented (i.e., front vs. rear, peripersonal vs. extra-personal) will be described. We review evidence from both monkey and human studies. This evidence, providing insight into the differential attributes qualifying the frontal and the rear regions of space, sheds light on an until now neglected research topic and may help to contribute to the formulation of new rehabilitative approaches to disorders of spatial representation. A tentative explanation of the evolutionary reasons underlying these particular patterns of results, as well as suggestions for possible future developments, are also provided.

Audio-tactile superiority over visuo-tactile and audio-visual combinations in the temporal resolution of synchrony perception

To see whether there is a difference in temporal resolution of synchrony perception between audio-visual (AV), visuo-tactile (VT), and audio-tactile (AT) combinations, we compared synchrony-asynchrony discrimination thresholds of human participants. Visual and auditory stimuli were, respectively, a luminance-modulated Gaussian blob and an amplitude-modulated white noise. Tactile stimuli were mechanical vibrations presented to the index finger. All the stimuli were temporally modulated by either single pulses or repetitive-pulse trains. The results show that the temporal resolution of synchrony perception was similar for AV and VT (e.g., approximately 4 Hz for repetitive-pulse stimuli), but significantly higher for AT approximately 10 Hz). Apart from having a higher temporal resolution, however, AT synchrony perception was similar to AV synchrony perception in that participants could select matching features through attention, and a change in the matching-feature attribute had little effect on temporal resolution. The AT superiority in temporal resolution was indicated not only by synchrony-asynchrony discrimination but also by simultaneity judgments. Temporal order judgments were less affected by modality combination than the other two tasks.

Multisensory contributions to the perception of vibrotactile events

We argue that audio-tactile interactions during vibrotactile processing provide a promising, albeit largely neglected, benchmark for the systematic study multisensory integration. This article reviews and discusses current evidence for multisensory contributions to the perception of vibratory events, and proposes a framework to address a number of relevant questions. First, we highlight some of the features that characterize the senses of hearing and touch in terms of vibratory information processing, and which allow for potential cross-modal interactions at multiple levels along the functional architecture of the sensory systems. Second, we briefly review empirical evidence for interactions between hearing and touch in the domain of vibroactile perception and related stimulus properties, covering behavioural, electrophysiological and neuroimaging studies in humans and animals. Third, we discuss the vibrotactile discrimination task, which has been successfully applied in the study of perception and decision processes in psychophysical and physiological research. We argue that this approach, complemented with computational modeling using biophysically realistic neural networks, may be a convenient framework to address auditory contributions to vibrotactile processing in the somatosensory system. Finally, we comment on a series of particular issues which are relevant in multisensory research and potentially addressable within the proposed framework.