Effect of Loudspeaker Position on Differences between Earphone and Free-Field Thresholds (MAP and MAF)

1974 ◽  
Vol 17 (4) ◽  
pp. 549-568 ◽  
Author(s):  
Richard W. Stream ◽  
Donald D. Dirks
Keyword(s):  
Free Field ◽  
Secondary Analysis ◽  
Field Measurements ◽  
Ear Canal ◽  
Pure Tones ◽  
Calibration Techniques

Free-field and earphone measurements were obtained from eight practiced listeners under monaural and binaural conditions to assess the hypothesis that a major source of the disparity between minimum audible pressure (MAP) and minimum audible field (MAF) speech thresholds was the position of the loudspeaker relative to the listener’s head. Free-field measurements were made at seven different loudspeaker positions (0, 30, 60, 90, 270, 300, and 330 degrees). Stimuli were spondaic words and pure tones at five octave intervals from 250 to 4000 Hz. The smallest monaural MAP/MAF difference for spondees occurred at 0° azimuth (2.7 dB) and the largest appeared at the 60° near-ear position (7.1 dB). Similar results emerged for spondaic words under binaural conditions, although the magnitude of the changes due to variations in loudspeaker position was reduced considerably from comparable monaural conditions. These results indicated that the disparities in MAP/MAF differences of previous investigations were due principally to the location of the loudspeaker. The differences between MAP and MAF thresholds were compared to other published results on ear-canal pressure measured in free field and under earphone. Secondary analysis of the data suggests that the MAP/MAF differences observed in this study may be related partially to the differences in calibration techniques used to specify the level of the signal in free field and under earphone.

A free field room for measuring pure tones

1981 ◽  
Vol 69 (S1) ◽  
pp. S9-S9
Author(s):  
O. L. Angevine ◽  
E. N. Angevine
Keyword(s):  
Free Field ◽  
Pure Tones

Frequency and amplitude representations in anterior primary auditory cortex of the mustached bat

1983 ◽  
Vol 50 (5) ◽  
pp. 1182-1196 ◽  
Author(s):  
A. Asanuma ◽  
D. Wong ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Second Harmonic ◽  
Free Field ◽  
Primary Auditory Cortex ◽  
Frequency Component ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Frequency Representation ◽  
Pure Tones

The orientation sound emitted by the Panamanian mustached bat, Pteronotus parnellii rubiginosus, consists of four harmonics. The third harmonic is 6-12 dB weaker than the predominant second harmonic and consists of a long constant-frequency component (CF3) at about 92 kHz and a short frequency-modulated component (FM3) sweeping from about 92 to 74 kHz. Our primary aim is to examine how CF3 and FM3 are represented in a region of the primary auditory cortex anterior to the Doppler-shifted constant-frequency (DSCF) area. Extracellular recordings of neuronal responses from the unanesthetized animal were obtained during free-field stimulation of the ears with pure tones. FM sounds, and signals simulating their orientation sounds and echoes. Response properties of neurons and tonotopic and amplitopic representations were examined in the primary and the anteroventral nonprimary auditory cortex. In the anterior primary auditory cortex, neurons responded strongly to single pure tones but showed no facilitative responses to paired stimuli. Neurons with best frequencies from 110 to 90 kHz were tonotopically organized rostrocaudally, with higher frequencies located more rostrally. Neurons tuned to 92-94 kHz were overpresented, whereas neurons tuned to sound between 64 and 91 kHz were rarely found. Consequently a striking discontinuity in frequency representation from 91 to 64 kHz was found across the anterior DSCF border. Most neurons exhibited monotonic impulse-count functions and responded maximally to sound pressure level (SPL). There were also neurons that responded best to weak sounds but unlike the DSCF area, amplitopic representation was not found. Thus, the DSCF area is quite unique not only in its extensive representation of frequencies in the second harmonic CF component but also in its amplitopic representation. The anteroventral nonprimary auditory cortex consisted of neurons broadly tuned to pure tones between 88 and 99 kHz. Neither tonotopic nor amplitopic representation was observed. Caudal to this area and near the anteroventral border of the DSCF area, a small cluster of FM-FM neurons sensitive to particular echo delays was identified. The responses of these neurons fluctuated significantly during repetitive stimulation.

Directional Hearing in the Japanese Quail (Coturnix Coturnix Japonica): II. Cochlear Physiology

1980 ◽  
Vol 86 (1) ◽  
pp. 153-170
Author(s):  
R. B. COLES ◽  
D. B. LEWIS ◽  
K. G. HILL ◽  
M. E. HUTCHINGS ◽  
D. M. GOWER
Keyword(s):  
Pressure Gradient ◽  
Free Field ◽  
Directional Hearing ◽  
Directional Sensitivity ◽  
Ear Canal ◽  
Directional Information ◽  
Cochlear Physiology ◽  
Directivity Patterns ◽  
The Difference ◽  
Sound Diffraction

The directional sensitivity of cochlear microphonics (CM) was studied inthe quail by rotating a free-field sound source (pure tones, 160-10 kHz)through 360° in the horizontal plane, under anechoic conditions. Sound diffraction by the head was monitored simultaneously by a microphone at the entrance to the ipsilateral (recorded) ear canal. Pressure-field fluctuations measured by the microphone were non-directional (≤ 4 dB) up to 4 kHz; the maximum head shadow was 8 dB at 6.3 kHz. In comparison, the CM sensitivity under went directional fluctuations ranging up to 25 dB for certain low, mid and high frequency band widths. There was noticeable variation between quail for frequencies producing maximum directional effects, although consistently poor directionality was seen near 820 Hz andto a lesser extent near 3.5 kHz. Well-defined CM directivity patterns reflected the presence of nulls (insensitive regions) at critical positions around the head and the number of nulls increased with frequency. Five major types of directivity patterns were defined using polar co-ordinates: cardioid, supercardioid, figure-of-eight, tripartite and multilobed. Such patterns were largely unrelated to head shadow effects. Blocking the ear canal contralateral to there corded ear was shown to effectively abolish CM directionality, largely by eliminating regions of insensitivity to sound. It is inferred that the quail ear functions as an asym metrical pressure gradient receiver, the pressure gradient function being mediated by the interauralcavity. It is proposed that the central auditory system codes directional information by a null detecting method and computes an unambiguous (i.e.intensity independent) directional cue. This spatial cue is achieved by the difference between the directional sensitivities of the two ears, defined as the Directional Index (DI). The spatial distribution of DI values (difference pattern) demonstrated ranges and peaks which closely reflected the extent and position of nulls determined from monaural directivity functions. Large directional cues (up to 25 dB) extended throughout most of the audible spectrum of the quail and the sharpness of difference patterns increased with frequency. Primary ‘best’ directions, estimated from peaks in difference patterns, tended to move towards the front of the head at higher frequencies; rearward secondary peaks also occurred. From the properties of directional cues it is suggested that the ability of birds to localize sound need not necessarily depend on frequency; however, spatial acuity may be both frequency and direction dependent, and include the possibility of front-torearerrors. The directional properties of bird vocalizations may need to bere assessed on the basis of the proposed mechanism for directional hearing.

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