gms | German Medical Science

28. Wissenschaftliche Jahrestagung der Deutschen Gesellschaft für Phoniatrie und Pädaudiologie e. V.
2. Dreiländertagung D-A-CH

Deutsche Gesellschaft für Phoniatrie und Pädaudiologie e. V.
Schweizerische Gesellschaft für Phoniatrie; Sektion Phoniatrie der Österreichischen Gesellschaft für HNO-Heilkunde, Kopf- und Halschirurgie

09.09. - 11.09.2011, Zürich, Schweiz

Localization and unification of unimodal and multimodal objects in older adults

Poster

  • corresponding author presenting/speaker Claudia Freigang - Universität Leipzig, Leipzig, Germany
  • Marc Stöhr - Universität Leipzig, Leipzig, Germany
  • Kristina Schmiedchen - Universität Leipzig, Leipzig, Germany
  • Ines Nitsche - Universität Leipzig, Leipzig, Germany
  • Rudolf Rübsamen - Universität Leipzig, Leipzig, Germany

Deutsche Gesellschaft für Phoniatrie und Pädaudiologie. 28. Wissenschaftliche Jahrestagung der Deutschen Gesellschaft für Phoniatrie und Pädaudiologie (DGPP), 2. Dreiländertagung D-A-CH. Zürich, 09.-11.09.2011. Düsseldorf: German Medical Science GMS Publishing House; 2011. Doc11dgppP16

DOI: 10.3205/11dgpp57, URN: urn:nbn:de:0183-11dgpp577

Published: August 18, 2011

© 2011 Freigang et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Outline

Abstract

Localization of speakers and differentiation of speakers in space are demanding tasks in central object representation. The perception of spatial objects depends on the integration of sensory information from different modalities. Crossmodal interactions during perception of audio-visual objects in terms of spatial alignment/displacement have been extensively studied in young adults. Still, it is unclear how both systems interact at peripheral positions, where spatial representations of objects are less precise. In old adults central processing mechanisms are declined and crossmodal interactions might be of great significance in object localization.

The present study investigates acuity of localization of static acoustic, visual and audio-visual objects in young and old adults in free-field. Subject had to localize either acoustic or visual stimuli. The acoustic and visual signals of an audio-visual stimulus were spatially congruent or incongruent and subjects were asked to localize the acoustic signal. At frontal positions localization of audio-visual stimuli was strongly biased towards the visual signals. At peripheral positions, subjects localized the sound source at a position intermediate between the acoustic and visual signal. The results suggest that the influence of the visual system is reduced towards the periphery, while the auditory system has a stronger impact in localization in the periphery. The amount of unification increased as a function of spatial position and age. Thereby, old adults showed a higher amount of unification at largest spatial disparities. Young and old adults performed equally at the largest disparity at the most peripheral position which points to an increased match of sensory information in the peripheral, monocular visual field. These results suggest that the amount of unification depends on the dimension of spatial resolution.


Text

Introduction

Age is associated with a decline and slowing of the processing of sensory stimuli by peripheral mechanisms. Additionally, effectiveness of central cognitive and attentional networks deteriorates. As a consequence, processing of unimodal stimuli is blurred. According to the model of 'inverse effectiveness' the processing (and subjective performance) of two near-threshold stimuli is increased when they are presented as a multisensory stimuli. So far, some studies showed an enhancement of multisensory integration in older adults. The role of redundant multisensory stimuli in localization of one event in older adults still remains unclear. The present study aimed at the influence of congruent and incongruent audiovisual signals in localization of multisensory objects. Localization acuity in older adults was tested by applying unimodal (either acoustic or visual) stimuli, multisensory audiovisual stimuli – referenced to a younger age group. We hypothesise that the localization blur should be smallest in congruent multisensoryconditions compared to unimodal conditions. The effect of age on this ability is analysed and will be discussed in terms of multisensory enhancement of integration hypothesis.

Methods

Subjects

Young Adults (n=14): 23.5 (3.5) years; 8f 6m

Old Adults (n=26): 67.5 (4.5) years; 11f 15m

Screening

Audiogram and Mini-Mental Status Exam (scores >27); Experiments were pointing tasks and conducted in the free-field (Figure 1 [Fig. 1]). Stimuli: 500ms Gaussian noise bands (0.375 to 4.5 kHz).

Procedure

(i) Localization of unimodal stimuli (acoustic or visual).

(ii) Localization and unification of the acoustic part of audio-visual stimuli. Acoustic and visual parts only differed in location. The acoustic part was presented from six different standard positions (±65°; ±30°; ±9°) while the visual part was either congruent to the respective acoustic part (same direction: 0°) or incongruent (spatially disparate: ±5°; ±10°; ±15°).

Results

Localization bias and unification increased with laterality of the stimuli (Figure 2 [Fig. 2]). Old adults tended to point towards the visual stimulus or to point at positions that were in-between the acoustic and the visual part of the audio-visual stimulus and showed a higher degree of unification at each standard position, especially at frontal positions. Localization accuracy varied as a function of standard position 1 (laterality, F5,40=5.697, p=0.016), spatial disparity (F6,40=17.037, p=0.000) and spatial disparity * age (F5,40=9.881, p=0.001). Data of unification showed main effects of age (χ2 1,40=62.81, p=0.000), standard position (χ2 5,40=124.629, p=0.000) and spatial disparity (χ2 6,40=718.758, p=0.000). Additionally, inter-actions between standard position * spatial disparity (χ2 30,40=387.025, p=0.000), age * spatial disparity (χ2 6,40=76.123, p=0.000), and age * standard position (χ2 5,40=14.042, p=0.0153). Note that pointing task and unifcation task were conducted in separate experiments and hence are not directly related to each other.

Conclusion

Localization bias in unimodal conditions depended on spatial position, i.e bias increased at peripheral positions in both young and old adults.The performance in unimodal localization showed no effect of age. Localization bias and visual capturing depends on position, spatial disparity and age. While younger adults only showed visual capture effects at ±5°, acoustic localization was captured by vision to a disparity of ±10° in older adults. Difference between standard position and response angle were smaller in congruent multisensory conditions compared to unimodal conditions. Performance in older adults tends to be biased towards the visual part of the multisensory stimulus, and also at large spatial disparities between visual and acoustic part. The effects in old adults were stronger compared to young adults. This might be caused by an increased neural match of incoming sensory information. The probability of binding non-congruent sensory information is increased based on the assumption that sensory and cortical processing declines and slows down with age. Conclusively, presentation of combined acoustic and visual sensory information leads to an enhanced performance in older adults which is consistent with the enhanced multisensory integration model.