Detection of Auditory Signals by Frog Inferior Collicular Neurons in the Presence of Spatially Separated Noise

R. Ratnam, A. S. Feng
1998 Journal of Neurophysiology  
Ratnam, R. and A. S. Feng. Detection of auditory signals by frog auditory scenes is due to the ability to attend one talker in inferior collicular neurons in the presence of spatially separated an acoustically cluttered environment (so-called cocktailnoise. J. Neurophysiol. 80: 2848Neurophysiol. 80: -2859Neurophysiol. 80: , 1998. Psychophysical party effect) (Cherry 1953). This task, in numerous guises, studies have shown that the ability to detect auditory signals emis common to other animals
more » ... n to other animals such as frogs, which must select bedded in noise improves when signal and noise sources are widely mates calling in dense choruses. Results from psychophysiseparated in space; this allows humans to analyze complex auditory cal experiments suggest that the cocktail-party effect rescenes, as in the cocktail-part effect. Although these studies estabquires listening with two ears (binaural hearing) and is selished that improvements in detection threshold (DT) are due to verely degraded when one ear is blocked or otherwise imbinaural hearing, few physiological studies were undertaken, and very little is known about the response of single neurons to spatially paired (Cherry 1953; Hirsh 1950; Kock 1950; for review separated signal and noise sources. To address this issue we examsee Zurek 1992). ined the responses of neurons in the frog inferior colliculus (IC) Binaural hearing offers advantages over monaural hearing to a probe stimulus embedded in a spatially separated masker. in terms of sound localization because minute differences in Frogs perform auditory scene analysis because females select mates intensity and time between the two ears can be computed in dense choruses by means of auditory cues. Results of the extra-(for reviews see Blauert 1983; Durlach and Colburn 1978; cellular single-unit recordings demonstrate that 22% of neurons Mills 1972; Moore 1982). Additionally, binaural hearing (A-type) exhibited improvements in signal DTs when probe and confers improved detection thresholds (DTs), loudness demasker sources were progressively separated in azimuth. In contection, speech intelligibility, and a reduction in difference trast, 24% of neurons (V-type) showed the opposite pattern, namely, signal DTs were lowest when probe and masker were limens for both intensity and frequency discrimination at all colocalized (in many instances lower than the DT to probe alone) frequencies (Ebata et al. 1968; Flanagan and Watson 1966; and increased when the two sound sources were separated. The Gatehouse 1986; Jesteadt and Wier 1977; Kidd et al. 1995; remaining neurons demonstrated a mix of these two types of pat- Levitt and Rabiner 1967; Plomp and Mimpen 1981; Reyn-terns. An intriguing finding was the strong correlation between Aolds and Stevens 1960; Scharf 1969). type masking release patterns and phasic neurons and a weaker The importance of binaural hearing in the cocktail-party correlation between V-type patterns and tonic neurons. Although effect was demonstrated by psychophysical experiments in not decisive, these results suggest that phasic units may play a role humans (Festen and Plomp 1986; Hirsh 1950 Hirsh , 1971 ; Kock in release from masking observed psychophysically. Analysis of the data also revealed a strong and nonlinear interaction among 1950; Plomp and Mimpen 1981; Saberi et al. 1991; Santon probe, masker, and masker azimuth and that signal DTs were in-1986, 1987; Terhune and Turnbull 1989) . A listener's sound fluenced by two factors: 1) the unit's sensitivity to probe in the DT was highest when a noise and sound source were colocalpresence of masker and 2) the criterion level for estimating DT. ized but decreased when the angular separation between the For some units, it was possible to examine the interaction between two sources was increased. Separation of the two sounds in these two factors and gain insights into the variation of DTs with space allowed a decomposition of the auditory scene into masker azimuth. The implications of these findings are discussed its component sound sources, thus improving signal detecin relation to signal detection in the auditory system. tion. In humans, the improvement in DTs (release from masking) was as much as 15-18 dB for click sounds (Saberi
doi:10.1152/jn.1998.80.6.2848 pmid:9862889 fatcat:r4rbaaavpfhefjgnbzggxu7ky4