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PubMed2001

Navigating without vision: basic and applied research.

We describe some of the results of our program of basic and applied research on navigating without vision. One basic research topic that we have studied extensively is path integration, a form of navigation in which perceived self-motion is integrated over time to obtain an estimate of current position and orientation. In experiments on pathway completion, one test of path integration ability, we have found that subjects who are passively guided over the outbound path without vision exhibit significant errors when attempting to return to the origin but are nevertheless sensitive to turns and segment lengths in the stimulus path. We have also found no major differences in path integration ability among blind and sighted populations. A model we have developed that attributes errors in path integration to errors in encoding the stimulus path is a good beginning toward understanding path integration performance. In other research on path integration, in which optic flow information was manipulated in addition to the proprioceptive and vestibular information of nonvisual locomotion, we have found that optic flow is a weak input to the path integration process. In other basic research, our studies of auditory distance perception in outdoor environments show systematic underestimation of sound source distance. Our applied research has been concerned with developing and evaluating a navigation system for the visually impaired that uses three recent technologies: the Global Positioning System, Geographic Information Systems, and virtual acoustics. Our work shows that there is considerable promise of these three technologies in allowing visually impaired individuals to navigate and learn about unfamiliar environments without the assistance of human guides.

Animals↗
PubMed2006

Development and evaluation of the listening in spatialized noise test.

OBJECTIVE: The goal of this study was to design and develop an audiological test that provides an ecologically valid measure of speech understanding in background noise while minimizing the effects of between-listener variation in factors such as linguistic skills and attention on test performance. The Listening in Spatialized Noise Test (LISN) creates a three-dimensional auditory environment under headphones and was designed to be totally software driven, so that it can be delivered in any audiology clinic with the use of only a PC and an audiometer. The extent to which the LISN was able to simulate free-field conditions and the effect of learning on the test were also examined. DESIGN: : In a three-alternative forced choice adaptive procedure, 20 adults with normal hearing were required to indicate the intelligibility level of target continuous discourse presented at 0 degrees azimuth in the presence of distracter sentences simultaneously presented at either 0 degrees azimuth (0 degrees condition) or at both +90 degrees and -90 degrees azimuth (+/-90 degrees condition). The target story was always spoken by female 1, whereas there were three conditions of speaker for the distracter sentences: the "same female speaker" as the target (same voice condition); two "different female speakers" (different female voices condition); and a "male speaker" (male voice condition). In a separate study, 16 adults with normal hearing who had not participated in the first study were assessed on the same voice and different female voices conditions, which were presented and then retested in the same order and test session to determine the effect of practice on performance on the LISN. RESULTS: The 20 adults were able to understand the target story at a significantly lower threshold in the +/-90 degrees condition than the 0 degrees condition. The degree of this spatial separation advantage (SSA) decreased significantly as the vocal quality of speakers of the target and the distracter sentences became more different (10.4 dB in the same voice condition, compared with 5.6 dB in the different female voices condition, and only 3.3 dB in the male voice condition). The SSA for the different female voices and male voice conditions were comparable to measurements previously reported in a free-field environment. There was no significant difference in SSA between the first and second presentations for either the same voice condition (at 10.3 dB and 10.2 dB) or the different female voices condition (at 4.7 and 5.7 dB). CONCLUSIONS: For adults with normal hearing, the ability to comprehend the story in the separate condition was facilitated by the use of binaural cues, such as interaural time differences, to distinguish the target from the spatially separated distracters. When a target and masker are distinguishable on the basis of features of the various speakers' voices (such as large differences in fundamental frequency), listeners are less reliant on spatial cues to recognize the target, and the SSA in dB is reduced. The stability of test scores with practice, the comparable levels of performance to those achieved in free-field environments, and the ability of the test to utilize difference scores to assess binaural processing while minimizing differences between participants in variables such as linguistic skills make the LISN a potentially valuable tool for assessing auditory processing disorders.

Adolescent↗
PubMed2003

Between language and space: a cross-domain interaction.

We document for the first time the effect of a spatial deficit on an spoken language task. Right brain-damaged patients with and without neglect were administered a task of emphatic stress. Patients listened to 60 subject-verb-object sentence pairs. The emphatic stress could be placed on the subject, on the verb or on the object word. Patients had to judge whether the two sentences were same or different for the position of the emphatic stress. The judgements were more impaired in patients with neglect and when the stress was placed at the beginning of the sentence (on the subject word), that is to say, at the leftmost location of a hypothetical spatial representation of the heard sentence. We hypothesize that auditory language undergoes a spatial transcoding, and that this transcoding is affected by the presence of a spatial bias like that observed in patients with neglect.

Acoustic Stimulation↗
PubMed2004

Human cortical auditory motion areas are not motion selective.

The existence of a specialized mechanism supporting auditory motion processing in humans is a matter of debate in the psychophysical literature. Recent functional neuroimaging data appear to have resolved the debate in favor of a specialized motion system in that several studies have found cortical regions that seem to be motion selective. While all these studies contrast some form of moving auditory stimulation with a stationary stimulus, none have adequately controlled for the possibility that these areas are simply computing sound-source location and not motion per se: a moving stimulus varies in spatial location as well as motion, and so a system computing spatial location (and not motion) would be activated in response to both a moving and stationary sound source. To control for this possibility, ten subjects were scanned while listening to moving stimuli and while listening to stationary stimuli that varied randomly in spatial location. Consistent with previous imaging studies, we found that a motion stimulus when contrasted with rest (scanner noise) activated STG/planum temporale (bilaterally) and right parietal lobe. However, stationary stimuli presented at varying locations activated these regions equally well, arguing against the existence of specialized motion-processing areas in human cortex.

Acoustic Stimulation↗
PubMed2006

Better time-intensity trade revealed by bilateral giant magnetostrictive bone conduction.

Sound lateralization tests were performed to compare the magnet coil bone-conduction headphone with the giant magnetostrictive bone-conduction headphone using 18 healthy participants. Although, no significant difference between these bone-conduction headphones was obtained for the interaural time difference and interaural intensity difference, a significant difference was obtained for the time-intensity trade. This revealed that the difference between the headphones is apparent in the integration of the heterogeneous sensations of the time and intensity difference at the cognitive level, but no difference is apparent between the homogeneous sensations of the discrimination of interaural time difference or interaural intensity difference at the sensory level. It was concluded that the difference at the cognitive level indicates the better performance of the giant magnetostrictive headphone.

Acoustic Stimulation↗
PubMed2006

Differential cortical processing of location and pitch changes in dichotic pitch.

The objective of this study was to determine whether the auditory mismatch negativity can be elicited by changes in spatial and nonspatial cues within dichotic pitches. Participants were presented with blocks of standard dichotic pitch stimuli in which location or pitch was occasionally varied. A mismatch negativity was reliably elicited by deviant locations; in contrast, no measurable mismatch negativity response was found for deviant pitches. A separate psychophysical screening procedure ruled out the possibility that participants could not hear the pitch deviations. The results indicate that spatial and nonspatial features of dichotic pitch receive differential processing at a preattentive level of analysis within the auditory system and are supportive of recent notions of dual processing streams in audition.

Acoustic Stimulation↗
PubMed2000

Directional encoding by fish auditory systems.

This paper reviews and discusses several investigations of the peripheral neural code for the directional axis of acoustical particle motion in the saccule of two fishes: goldfish (Carassius auratus) and toadfish (Opsanus tau). Most saccular afferents are directional in the manner of hair cells, having a cosine-shaped directional response pattern. The saccular sensory epithelia are orientated almost vertically in a parasagittal plane. In the horizontal plane, these epithelia are orientated obliquely with respect to the midline. Hair-cell stereocilia project perpendicularly. Thus, directional response patterns of saccular afferents tend to be orientated in azimuth parallel to the orientation of the epithelia in the head. The oblique angle of the toadfish saccule is greater than that of the goldfish, and the range of best directions in the horizontal plane for each species reflects those differing orientations. The azimuth of acoustical particle motion could be computed by comparing the relative activation of the two saccules, as is the case for the ears of most terrestrial vertebrates. The spatial patterns of saccular hair-cell orientation of most fishes thus appear to have little function in azimuthal source location, but for toadfish are probably most important for determining the elevation of monopole sources.

Acoustic Stimulation↗
PubMedDate not supplied

Learning directions of objects specified by vision, spatial audition, or auditory spatial language.

The modality by which object azimuths (directions) are presented affects learning of multiple locations. In Experiment 1, participants learned sets of three and five object azimuths specified by a visual virtual environment, spatial audition (3D sound), or auditory spatial language. Five azimuths were learned faster when specified by spatial modalities (vision, audition) than by language. Experiment 2 equated the modalities for proprioceptive cues and eliminated spatial cues unique to vision (optic flow) and audition (differential binaural signals). There remained a learning disadvantage for spatial language. We attribute this result to the cost of indirect processing from words to spatial representations.

Adult↗
PubMed2005

Spiking neurons learning phase delays: how mammals may develop auditory time-difference sensitivity.

Time differences between the two ears are an important cue for animals to azimuthally locate a sound source. The first binaural brainstem nucleus, in mammals the medial superior olive, is generally believed to perform the necessary computations. Its cells are sensitive to variations of interaural time differences of about 10 micros. The classical explanation of such a neuronal time-difference tuning is based on the physical concept of delay lines. Recent data, however, are inconsistent with a temporal delay and rather favor a phase delay. By means of a biophysical model we show how spike-timing-dependent synaptic learning explains precise interplay of excitation and inhibition and, hence, accounts for a physical realization of a phase delay.

Action Potentials↗
PubMed1998

A real-time experimental prototype for enhancement of vision rehabilitation using auditory substitution.

The rehabilitation of blindness, using noninvasive methods, requires sensory substitution. A theoretical frame for sensory substitution has been proposed which consists of a model of the deprived sensory system connected to an inverse model of the substitutive sensory system. This paper addresses the feasibility of this conceptual model in the case of auditory substitution, and its implementation as a rough model of the retina connected to an inverse linear model of the cochlea. We have developed an experimental prototype. It aims at allowing optimization of the sensory substitution process. This prototype is based on a personal computer which is connected to a miniature head-fixed video camera and to headphones. A visual scene is captured. Image processing achieves edge detection and graded resolution. Each picture element (pixel) of the processed image is assigned a sinusoidal tone; weighted summation of these sinewaves builds up a complex auditory signal which is transduced by the headphones. On-line selection of various parameters and real-time functioning of the device allow optimization of parameters during psychophysical experimentations. Assessment of this implementation has been initiated, and has so far demonstrated prototype usefulness for pattern recognition. An integrated circuit of this system is to be developed.

Adaptation, Physiological↗
PubMed1998

The NavBelt--a computerized travel aid for the blind based on mobile robotics technology.

This paper presents a new concept for a travel aid for the blind. A prototype device, called the NavBelt, was developed to test this concept. The device can be used as a primary or secondary aid, and consists of a portable computer, ultrasonic sensors, and stereophonic headphones. The computer applies navigation and obstacle avoidance technologies that were developed originally for mobile robots. The computer then uses a stereophonic imaging technique to process the signals from the ultrasonic sensors and relays their information to the user via stereophonic headphones. The user can interpret the information as an acoustic "picture" of the surroundings, or, depending on the operational mode, as the recommended travel direction. The acoustic signals are transmitted as discrete beeps or continuous sounds. Experimental results with the NavBelt simulator and a portable prototype show that users can travel safely in an unfamiliar and cluttered environment at speeds of up to 0.8 m/s.

Acoustics↗
PubMed1999

Extraction of fluorescent dot traces from a scanning laser ophthalmoscope image sequence by spatio-temporal image analysis: Gabor filter and radon transform filtering.

The scanning laser ophthalmoscope (SLO) allows the tracking of fluorescent dot motion, thereby enabling the flow velocities in perimacular capillaries to be directly measured. These can serve as an important index of local retinal soundness or reflect the whole body circulation status in disorders such as diabetes. Although it is possible to perceive moving fluorescent dots with the human eye, they are so faint and unstable that it is difficult to detect them by conventional digital still-image processing methods. To solve this problem, we generated spatio-temporal images of the fluorescent dots in a capillary and applied Gabor filters tuned to the direction of the traces in order to detect them. Finally, by discriminating and integrating the output using two levels of threshold, we were able to extract their traces. Because the medium-size Gabor filter requires a considerable amount of time for two-dimensional convolution calculation, we prove that there is a certain equivalence between the Gabor filter, the radon transform, and the Hough transform. In the light of this, we propose a form of radon transform filtering that includes a radon transform Gabor filter as a very long Gabor filter. This allows a whole trace to be detected in a single step with a one-dimensional convolution, thereby shortening the processing time. In an experiment, 60% of the traces could be detected without error, which is sufficient to allow the mean flow velocity in a capillary to be measured.

Filtration↗
PubMed2004

Objective detection of the central auditory processing disorder: a new machine learning approach.

The objective detection of binaural interaction is of diagnostic interest for the evaluation of the central auditory processing disorder (CAPD). The beta-wave of the binaural interaction component in auditory brainstem responses has been suggested as an objective measure of binaural interaction and has been shown to be of diagnostic value in the CAPD diagnosis. However, a reliable and automated detection of the beta-wave capable of clinical use still remains a challenge. We propose a new machine learning approach to the detection of the CAPD that is based on adapted tight frame decompositions which are tailored for support vector machines with radial kernels. Using shift-invariant scale and morphological features of the binaurally evoked brainstem potentials, our approach provides at least comparable results to the beta-wave detection in view of the discrimination of subjects being at risk for CAPD and subjects being not at risk for CAPD. Furthermore, as no information from the monaurally evoked potentials is necessary, the measurement cost is reduced by two-thirds compared to the computation of the binaural interaction component. We conclude that a machine learning approach in the form of a hybrid tight frame-support vector classification is effective in the objective detection of the CAPD.

Artificial Intelligence↗
PubMed2003

Sonification of range information for 3-D space perception.

We present a device that allows three-dimensional (3-D) space perception by sonification of range information obtained via a point laser range sensor. The laser range sensor is worn by a blindfolded user, who scans space by pointing the laser beam in different directions. The resulting stream of range measurements is then converted to an auditory signal whose frequency or amplitude varies with the range. Our device differs from existing navigation aids for the visually impaired. Such devices use sonar ranging whose primary purpose is to detect obstacles for navigation, a task to which sonar is well suited due to its wide beam width. In contrast, the purpose of our device is to allow users to perceive the details of 3-D space that surrounds them, a task to which sonar is ill suited, due to artifacts generated by multiple reflections and due to its limited range. Preliminary trials demonstrate that the user is able to easily and accurately detect corners and depth discontinuities and to perceive the size of the surrounding space.

Acoustics↗
PubMed2000

Involuntary listening aids seeing: evidence from human electrophysiology.

It is well known that sensory events of one modality can influence judgments of sensory events in other modalities. For example, people respond more quickly to a target appearing at the location of a previous cue than to a target appearing at another location, even when the two stimuli are from different modalities. Such cross-modal interactions suggest that involuntary spatial attention mechanisms are not entirely modality-specific. In the present study, event-related brain potentials (ERPs) were recorded to elucidate the neural basis and timing of involuntary, cross-modal spatial attention effects. We found that orienting spatial attention to an irrelevant sound modulates the ERP to a subsequent visual target over modality-specific, extrastriate visual cortex, but only after the initial stages of sensory processing are completed. These findings are consistent with the proposal that involuntary spatial attention orienting to auditory and visual stimuli involves shared, or at least linked, brain mechanisms.

Acoustic Stimulation↗
PubMed2003

Speech shadowing while driving: on the difficulty of splitting attention between eye and ear.

We investigated the role of cross-modal links in spatial attention in modulating the efficiency of dual-task performance. The difficulty of combining speech shadowing with a simulated driving task was modulated by the spatial location from which the speech was presented. In both single- and dual-task conditions, participants found it significantly easier to shadow one of two auditory streams when the relevant speech was presented from directly in front of them, rather than from the side. This frontal speech advantage was more pronounced when participants performed the demanding simulated driving task at the same time as shadowing than when they performed the shadowing task alone. These results demonstrate that people process auditory information more efficiently (with a lower overall dual-task decrement) when relevant auditory and visual stimuli are presented from the same, rather than different, spatial locations. These results are related to recent findings showing that there are extensive cross-modal links in spatial attention, and have clear implications for the design of better user interfaces.

Adult↗
PubMed2003

Visual motion influences the contingent auditory motion aftereffect.

In this study, we show that the contingent auditory motion aftereffect is strongly influenced by visual motion information. During an induction phase, participants listened to rightward-moving sounds with falling pitch alternated with leftward-moving sounds with rising pitch (or vice versa). Auditory aftereffects (i.e., a shift in the psychometric function for unimodal auditory motion perception) were bigger when a visual stimulus moved in the same direction as the sound than when no visual stimulus was presented. When the visual stimulus moved in the opposite direction, aftereffects were reversed and thus became contingent upon visual motion. When visual motion was combined with a stationary sound, no aftereffect was observed. These findings indicate that there are strong perceptual links between the visual and auditory motion-processing systems.

Attention↗
PubMed2003

Attentional blink modulation during sustained and after discrete lead stimuli presented in three sensory modalities.

Previous studies found larger attentional modulation of acoustic blinks during task-relevant than during task-irrelevant acoustic or visual, but not tactile, lead stimuli. Moreover, blink modulation was larger overall during acoustic lead stimuli. The present experiment investigated whether these results reflect modality specificity of attentional blink modulation or effects of continuous stimulation. Participants performed a discrimination and counting task with acoustic, visual, or tactile lead stimuli. Stimuli were presented sustained or consisted of two short discrete stimuli. The sustained condition replicated previous results. In the discrete condition, blinks were larger during task-relevant than during task-irrelevant stimuli in all groups regardless of lead stimulus modality. Thus, previous results that seemed consistent with modality-specific accounts of attentional blink modulation reflect effects of continuous stimulus input.

Acoustic Stimulation↗

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