Coding of sound location and frequency in the auditory midbrain of diurnal birds of prey, families accipitridae and falconidae

Calford, Michael B.; Wise, Lisa; Pettigrew, John D.

doi:10.1007/bf01350024

Cited by 31 publications

(27 citation statements)

References 29 publications

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“…It is far from clear that a neural space map of the kind seen in barn owls generalizes to other predatory birds (Calford et al, 1985), including other owls (e.g., great horned owls, which lack the asymmetric ear orientation, and also lack spatial receptive fields limited in the elevation dimension: Volman and Konishi, 1989). There is no direct evidence for a space map of the barn owl's kind in the auditory cortex of any mammal studied to date.…”

Section: Statement Of the Problemmentioning

confidence: 97%

A perceptual architecture for sound lateralization in man

Phillips

2008

Hearing Research

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Section: Statement Of the Problemmentioning

confidence: 97%

A perceptual architecture for sound lateralization in man

Phillips

2008

Hearing Research

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“…Changing IID shifts ITD similarly in the optic tectum of the barn owl (Olsen et al, 1989). In a physiological study of 3 diurnal raptors, Calford et al (1985) found that units in ICx (or nMLD1 in their nomenclature) also had broader frequency ranges and were more spatially selective than were units in ICC (central nMLD). These spatially selective units, however, had distinct medial boundaries only.…”

Section: Azimuth (Degrees)mentioning

confidence: 99%

Spatial selectivity and binaural responses in the inferior colliculus of the great horned owl

Volman

Konishi

1989

J. Neurosci.

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In this study we have investigated the processing of auditory cues for sound localization in the great horned owl (Bubo virginianus). Previous studies have shown that the barn owl, whose ears are asymmetrically oriented in the vertical plane, has a 2-dimensional, topographic representation of auditory space in the external division of the inferior colliculus (ICx). As in the barn owl, the great horned owl's ICx is anatomically distinct and projects to the optic tectum. Neurons in ICx respond over only a small range of azimuths (mean = 32 degrees), and azimuth is topographically mapped. In contrast to the barn owl, the great horned owl has bilaterally symmetrical ears and its receptive fields are not restricted in elevation. The binaural cues available for sound localization were measured both with cochlear microphonic recordings and with a microphone attached to a probe tube in the auditory canal. Interaural time disparity (ITD) varied monotonically with azimuth. Interaural intensity differences (IID) also changed with azimuth, but the largest IIDs were less than 15 dB, and the variation was not monotonic. Neither ITD nor IID varied systematically with changes in the vertical position of a sound source. We used dichotic stimulation to determine the sensitivity of ICx neurons to these binaural cues. Best ITD of ICx units was topographically mapped and strongly correlated with receptive-field azimuth. The width of ITD tuning curves, measured at 50% of the maximum response, averaged 72 microseconds. All ICx neurons responded only to binaural stimulation and had nonmonotonic IID tuning curves. Best IID was weakly, but significantly, correlated with best ITD (r = 0.39, p less than 0.05). The IID tuning curves, however, were broad (mean 50% width = 24 dB), and 67% of the units had best IIDs within 5 dB of 0 dB IID. ITD tuning was sensitive to variations in IID in the direction opposite to that expected for time-intensity trading, but the magnitude of this effect was only 1.5 microseconds/dB IID. We conclude that, in the great horned owl, the spatial selectivity of ICx neurons arises primarily from their ITD tuning. Except for the absence of elevation selectivity and the narrow range of best IIDs, ICx in the great horned owl appears to be organized much the same as in the barn owl.

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“…Isolation of single-unit responses using a template-matching procedure was not possible because the action potential shape of neurons near the electrode tip were too similar for satisfactory discrimination. Nonetheless, multiunit recordings from the IC are expected to provide valuable insight into the response properties of this nucleus because previous studies have demonstrated robust anatomical gradients in both spectral and temporal response properties (Calford et al 1985;Langner and Schreiner 1988;Langner et al 2002;Baumann et al 2011;but see Seshagiri and Delgutte 2007). Neighboring single neurons in cat IC, for example, have similar BF, frequency tuning bandwidth, and temporal integration statistics (Chen et al 2012).…”

Section: Neurophysiological Recording Proceduresmentioning

confidence: 99%

Midbrain Synchrony to Envelope Structure Supports Behavioral Sensitivity to Single-Formant Vowel-Like Sounds in Noise

Henry

Abrams

Forst

et al. 2016

JARO

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Vowels make a strong contribution to speech perception under natural conditions. Vowels are encoded in the auditory nerve primarily through neural synchrony to temporal fine structure and to envelope fluctuations rather than through average discharge rate. Neural synchrony is thought to contribute less to vowel coding in central auditory nuclei, consistent with more limited synchronization to fine structure and the emergence of average-rate coding of envelope fluctuations. However, this hypothesis is largely unexplored, especially in background noise. The present study examined coding mechanisms at the level of the midbrain that support behavioral sensitivity to simple vowel-like sounds using neurophysiological recordings and matched behavioral experiments in the budgerigar. Stimuli were harmonic tone complexes with energy concentrated at one spectral peak, or formant frequency, presented in quiet and in noise. Behavioral thresholds for formant-frequency discrimination decreased with increasing amplitude of stimulus envelope fluctuations, increased in noise, and were similar between budgerigars and humans. Multiunit recordings in awake birds showed that the midbrain encodes vowel-like sounds both through response synchrony to envelope structure and through average rate. Whereas neural discrimination thresholds based on either coding scheme were sufficient to support behavioral thresholds in quiet, only synchrony-based neural thresholds could account for behavioral thresholds in background noise. These results reveal an incomplete transformation to average-rate coding of vowel-like sounds in the midbrain. Model simulations suggest that this transformation emerges due to modulation tuning, which is shared between birds and mammals. Furthermore, the results underscore the behavioral relevance of envelope synchrony in the midbrain for detection of small differences in vowel formant frequency under real-world listening conditions.

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Coding of sound location and frequency in the auditory midbrain of diurnal birds of prey, families accipitridae and falconidae

Cited by 31 publications

References 29 publications

A perceptual architecture for sound lateralization in man

A perceptual architecture for sound lateralization in man

Spatial selectivity and binaural responses in the inferior colliculus of the great horned owl

Midbrain Synchrony to Envelope Structure Supports Behavioral Sensitivity to Single-Formant Vowel-Like Sounds in Noise

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