Effects of Altering Spectral Cues in Infancy on Horizontal and Vertical Sound Localization by Adult Ferrets

Abstract

. Effects of altering spectral cues in infancy on horizontal and vertical sound localization by adult ferrets. J. Neurophysiol. 82: 2294Neurophysiol. 82: -2309Neurophysiol. 82: , 1999. We investigated the behavioral consequences of removing the pinna and concha of the external ear bilaterally in infancy on the sound localization ability of adult ferrets. Altering spectral cues in this manner has previously been shown to disrupt the development of the neural representation of auditory space in the superior colliculus. Using broadband noise stimuli, we tested pinnae-removed ferrets and normal ferrets in three sound localization tasks. In each case, we found that both groups of animals performed significantly better when longer duration noise bursts were used. In a relative localization task, we measured the acuity with which the ferrets could discriminate between two speakers in the horizontal plane. The speakers were placed symmetrically either around the anterior midline or around a position 45°lateral to the midline. In this task, the pinnae-removed ferrets achieved very similar scores to the normal ferrets. By contrast, in another relative localization task that measured localization ability in the midsagittal plane, pinnae-removed ferrets performed less well than normals. In an absolute localization task, 12 speakers were spaced at 30°intervals in the horizontal plane at the level of the ferrets' ears. Overall, the pinnae-removed ferrets also performed poorly in this task compared with normal ferrets: they made significantly fewer correct responses, larger localization errors and more front-back errors. Both normal and pinnae-removed animals showed an improvement in performance with practice, although the pattern of improvement differed for each group. The largest improvements in localization accuracy were achieved by the pinnae-removed ferrets, particularly at the frontal positions, and their performance eventually approached that of the normal animals. Nevertheless, some intergroup differences were still present. In particular, the pinnaeremoved ferrets continued to make significantly more front-back errors than the normals. These deficits can be attributed to differences in the spectral localization cues available to the animals. Acoustical measurements showed that, compared with normal animals, the headrelated transfer functions in the horizontal plane were largely ambiguous around the interaural axis and also contained fewer locationdependent features in the midsagittal plane.

In-flight corrections in free-flying barn owls (Tyto alba)during sound localization tasks

“…This parallels what Konishi observed in the barn owl with 50 ms bursts of sound (Konishi, 1973b). A similar result was found for ferrets approaching a sound source: the ferrets were significantly better at localizing noise bursts of 500 ms duration than those of 40 ms duration (Parsons et al, 1999). Bodson et al have tested the sound-localization performance of swimming seals (Bodson et al, 2006).…”

“…Studies on sound localization during which animals had to fixate or approach a sound source to indicate the perceived location have been conducted in several species [cat (Casseday and Neff, 1973;Casseday and Neff, 1975;Jenkins and Merzenich, 1984;Populin and Yin, 2007); bat (Aytekin et al, 2004); ferret (Kavanagh and Kelly, 1987;Kavanagh and Kelly, 1992;Parsons et al, 1999); rat (Kavanagh and Kelly, 1986); mouse (Ehret and Dreyer, 1984); and seal (Bodson et al, 2006)], whereas others have used conditioned reflexes (Ebert et al, 2008). Most of these species localize sound sources with similar or inferior accuracy when compared with the barn owl, even though many similarities in localization behavior can be found.…”

Plasticity in the neural coding of auditory space in the mammalian brain

“…Studies in mammals suggest that if the spatial cues are sufficiently degraded during development, then the map of auditory space in the SC will fail to form properly. For example, removal of the pinna and concha of the external ear disrupts the spectral localization cues such that, compared with those of normal animals, they provide much less information for discriminating between anterior and posterior sound directions (43,44). Bilateral removal of the pinna and concha in juvenile ferrets impairs both the emergence of topographic order in the auditory space map (43) and the ability of mature animals to localize broadband sounds (44).…”

Planar localisation analyses: A novel application of a centre of mass approach

“…measures ANOVA are applied (Abel and Paik, 2004;Hine, Martin et al, 1994;Kacelnik, Nodal, et al, 2006;Parsons, Lanyon, et al, 1999). Nevertheless, accuracy can be a rather blunt tool as it provides no indication about the size of the localisation errors.…”

“…Previous studies have mitigated this problem by using the mean absolute, or unsigned, error, so that the error values fall between 0° and 180°. However, these studies have used either parametric tests (Parsons, Lanyon, et al, 1999;Zahorik, Bangayan, et al, 2006) which incorrectly assume a normal distribution of the data, or non-parametric tests (Kacelnik, Nodal, et al, 2006) which offer reduced statistical power.…”