Neuroanatomical basis of binaural phase-difference analysis for sound localization: A comparative study.

4 varieties of mammals whose medial superior olives range from large to none at all were tested for their ability to localize single, brief tone pips at various frequencies. Ss were 2 hedgehogs, 2 Charles River white rats, 2 tree shrews, and 1 cat. Although each animal could localize high-frequency tone pips, their ability to localize middle- and low-frequency tone pips corresponded to the size of their medial superior olive (MSO). Since this latter range of frequencies is the one in which binaural phase-difference cues predominate, this anatomical-behavioral correspondence supports the idea that MSO is the chief binaural time analyzing center for sound localization. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The normalized correlation: accounting for binaural detection across center frequency

Bernstein and Trahiotis [L. R. Bernstein and C. Trahiotis, J. Acoust. Soc. Am. 100, 1754-1763 (1996)] recently reported the results of experiments designed to determine the form of interaural correlation that accounts for listeners' sensitivities to interaural disparities within high-frequency stimuli. Overall, those results demonstrated that listeners' abilities to discriminate changes in the interaural correlation of the envelope (from a base correlation of 1.0) were well accounted for by the use of the normalized correlation. The purpose of this study was to determine how well the normalized correlation computed subsequent to half-wave rectification and low-pass filtering could account for binaural detection data at low, intermediate, and high frequencies, respectively. In a four-interval, two-alternative task, listeners detected which interval contained a tone (between 500 Hz and 2 kHz) added antiphasically to diotic, 100-Hz-wide, noise (NoS pi). "Nonsignal" intervals contained the tone added homophasically (NoSo). Performance was measured for signal-to-noise ratios between -30 and +30 dB. Results indicated that a low-pass filter function based on physiological measures of synchrony in cochlear nerve fibers in conjunction with the assumption of half-wave, square-law rectification, accounted for typically 80% of the variance in the behavioral data.     

The nature and distribution of errors in sound localization by human listeners

Measurement of localization performance will reflect errors that relate to the sensory processing of the cues to sound location and the errors associated with the method by which the subject indicates the perceived location. This study has measured the ability of human subjects to localize a short noise burst presented in the free field with the subject indicating the perceived location by pointing their nose towards the source. Subjects were first trained using a closed loop training paradigm which involved instantaneous feedback as to the accuracy of head pointing which resulted in the reduction of residual localization errors and a rapid acquisition of the task by the subjects. Once trained, 19 subjects localized between 4 and 6 blocks of 76 target locations. The data were pooled and the distribution of errors associated with each target location was examined using spherical methods. Errors in the localization estimates for about one third of the locations were rotationally symmetrical about their mean but the remaining locations were best described by an elliptical distribution (Kent distributed). For about one half of the latter locations the orientations of the directions of the greatest variance of the distributions were not aligned with the azimuth and elevation coordinates used for describing the spatial location of the targets. The accuracy (systematic errors) and the distribution of the errors (variance) in localization for our population of subjects were also examined for each test location. The size of the data set and the methods of analysis provide very reliable measures of important baseline parameters of human auditory localization.     

Behavioral studies of sound localization in the cat

Using the magnetic search coil technique to measure eye and ear movements, we trained cats by operant conditioning to look in the direction of light and sound sources with their heads fixed. Cats were able to localize noise bursts, single clicks, or click trains presented from sources located on the horizontal and vertical meridians within their oculomotor range. Saccades to auditory targets were less accurate and more variable than saccades to visual targets at the same spatial positions. Localization accuracy of single clicks was diminished compared with the long-duration stimuli presented from the same sources. Control experiments with novel auditory targets, never associated with visual targets, demonstrated that the cats localized the sound sources using acoustic cues and not from memory. The role of spectral features imposed by the pinna for vertical sound localization was shown by the breakdown in localization of narrow-band (one-sixth of an octave) noise bursts presented from sources along the midsagittal plane. In addition, we show that cats experience summing localization, an illusion associated with the precedence effect. Pairs of clicks presented from speakers at (+/-18 degrees,0 degrees ) with interclick delays of +/-300 microsec were perceived by the cat as originating from phantom sources extending from the midline to approximately +/-10 degrees.     

Pinna movements of the cat during sound localization

We measured the movements of the external ear, or pinna, using the magnetic search coil technique in cats trained to look at auditory and visual targets for a food reward. No behavioral contingencies were placed on pinna movements. Prominent pinna movements accompany eye movements when the animal orients to either auditory or visual stimuli. In visual trials the pinna movements are coordinated with eye movements, suggesting that they are part of the general orientation response of the animal. In auditory trials the pinna response was composed of two movements: short- and long-latency components. Whereas the long-latency component seemed to occur with the eye movement to the target, the short-latency component was coupled to the onset of the stimulus. The short-latency component ( approximately 25 msec) was highly asymmetrical, being largest in the pinna ipsilateral to the stimuli. In one animal it persisted after >10(5) trials.     

Use of binaural cues for sound localization in two species of Phyllostomidae: The Greater spear-nosed bat (Phyllostomus hastatus) and the Short-tailed fruit bat (Carollia perspicillata).

Unlike humans, not all mammals use both of the binaural cues for sound localization. Whether an animal uses these cues can be determined by testing its ability to localize pure tones; specifically, low frequencies are localized using time-difference cues, and high frequencies are localized using intensity-difference cues. We determined the ability to use binaural cues in 2 New World bats, Phyllostomus hastatus, large omnivores, and Carollia perspicillata, small frugivores, by testing their tone-localization ability using a conditioned avoidance procedure. Both species easily localized high-frequency tones, indicating that they could use the interaural intensity-difference cue. However, neither species was able to use the phase-difference cue to localize either low-frequency pure tones or amplitude-modulated tones (which provided an envelope for additional time analysis). We now know of 3 bat species that cannot use binaural time cues and 2 that can. Further exploration of localization in bats may provide insight into the neural analysis of time cues in species that do not hear low frequencies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural coding of sound frequency by cricket auditory receptors

Crickets provide a useful model to study neural processing of sound frequency. Sound frequency is one parameter that crickets use to discriminate between conspecific signals and sounds made by predators, yet little is known about how frequency is represented at the level of auditory receptors. In this paper, we study the physiological properties of auditory receptor fibers (ARFs) by making single-unit recordings in the cricket Teleogryllus oceanicus. Characteristic frequencies (CFs) of ARFs are distributed discontinuously throughout the range of frequencies that we investigated (2-40 kHz) and appear to be clustered around three frequency ranges (/=18 kHz). A striking characteristic of cricket ARFs is the occurrence of additional sensitivity peaks at frequencies other than CFs. These additional sensitivity peaks allow crickets to detect sound over a wide frequency range, although the CFs of ARFs cover only the frequency bands mentioned above. To the best of our knowledge, this is the first example of the extension of an animal's hearing range through multiple sensitivity peaks of auditory receptors.     

Measurement of the ultrasonic attenuation of fat at high frequency

RATIONALE AND OBJECTIVES: High-frequency ultrasound devices are often limited by a decreased depth of acoustic imaging caused by the increased attenuation of tissue at high frequencies. We investigated the role of adipose tissue in this phenomenon. METHODS: A substitution technique was used to calculate the ultrasonic attenuation (decibels per centimeter) of fresh samples of sheep rumen, omental fat, and back fat and swine back fat and various concentrations of bovine milk fat at 22 degrees C and 37 degrees C for frequencies of 15 and 20 MHz. RESULTS: The attenuation was significantly higher for sheep adipose tissue than for the intestinal wall, in descending order, omental fat, back fat, and rumen wall (P < 0.01). A correlation was found between bovine milk fat concentrations and attenuation at both frequencies (R2 > 0.9). The attenuation of adipose tissues decreased significantly with an increase in temperature (P < 0.01), whereas the attenuation of sheep rumen showed no significant change (P > 0.1). CONCLUSIONS: The ultrasonic attenuation of fat may contribute to limitations on the use of high-frequency ultrasound in clinical situations in which adipose tissue is present.     

The effects of spatial frequency overlap on face recognition.

The effects of spatial frequency overlap between pairs of low-pass versus high-pass images on face recognition and matching were examined in 6 experiments. Overlap was defined as the range of spatial frequencies shared by a pair of filtered images. This factor was manipulated by processing image pairs with high-pass/low-pass filter pairs whose 50% cutoff points varied in their separation from one another. The effects of the center frequency of filter pairs were also investigated. In general, performance improved with greater overlap and higher center frequency. In control conditions, the image pairs were processed with identical filters and thus had complete overlap. Even severely filtered low-pass or high-pass images in these conditions produced superior performance. These results suggest that face recognition is more strongly affected by spatial frequency overlap than by the frequency content of the images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The nature of word frequency effects on perceptual identification.

Four experiments, using a study–test paradigm, examined the effects of event presentation frequency on perceptual identification. In each cycle, subjects studied a list with different items presented from one to four or more times, then received identification tests of studied and nonstudied items. Pseudoword repetition (Experiments 1 and 4) produced a priming effect, that is, enhanced identification for presented items, and a repetition effect, that is, incremental improvements in identification for repeated items. In contrast, word repetition (Experiment 2, 3, and 4) produced priming but not repetition effects, a pattern that was not due to learning asymptotes or scaling distortions. We conclude that presentation frequency effects act on at least two distinct processing paths, selected on the basis of processing and task demands. Under conditions of simple exposure, perceptual enhancement is mediated, for codified events like words, primarily by nodal activation, and, for noncodified events like pseudowords, by information accumulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hearing in the elephant (Elephas maximus): Absolute sensitivity, frequency discrimination, and sound localization.

Tested a young female Indian elephant to determine sensitivity and frequency-discrimination and sound-localization thresholds. S was found to have an audibility curve similar to that of other mammals but one that was more sensitive to low frequencies and less sensitive to high frequencies than any other mammalian audiogram, including human's. S's sensitivity to frequency differences at low frequencies equaled that of humans. S was accurate at localizing sounds in the azimuthal plane, with thresholds around 1° for broadband noise. S's ability to localize pure tones suggested that it could use both binaural time- and intensity-difference cues to localize sound. (62 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sound localization and use of binaural cues by the gerbil (Meriones unguiculatus).

Noise-localization thresholds and the ability to localize pure tones at 60° separation were determined for gerbils. The gerbils were trained using a two-choice procedure with observing response in which the gerbils made a left or right response to sounds emanating from their left or right side in order to obtain food. The average 75% correct localization threshold of 5 gerbils for a 100-ms noise burst was 27° with chance performance (p?>?.01) reached at 12°. The ability of 4 gerbils to localize both low- and high-frequency pure tones indicates that gerbils are able to use both phase- and intensity-difference locus cues. The frequency at which tone localization was poorest was 2.8 kHz, well below the theoretical frequency of ambiguity of the phase cue but within the frequency range at which phase locking declines in the mammalian auditory system. The sound localization ability of gerbils is typical of small rodents, and there is no obvious sign that it is affected by the degenerative disorder of the central auditory system which has been recently discovered in gerbils. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of high intensity intermittent sound on performance, feeling and physiology.

There has been in recent literature some evidence indicating that intermittent sound as opposed to steady sound sources has a more disturbing effect on Ss. This paper includes those studies which have appeared since 1950 and indicates that high intensity or intermittent sound generally produces symptoms of discomfort, instability, and distraction. In addition decrements in performance may be related to the level of the sound as well as its intermittency. Changes in blood pressure, respiration, EEG, pulse rate, etc., as a result of sound have been reported in some studies. Some theoretical issues are included in the discussion. 80 refs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of auditory cortical lesions on pure-tone sound localization by the albino rat.

Used 2-choice and 3-choice tests to evaluate the effects of bilateral auditory cortical lesions on pure-tone sound localization by 10 male albino rats. Both tests required that Ss approach a distant sound source to obtain water reinforcement. Stimuli were single noise and tone bursts, 65 msec in duration including 20-msec rise and fall times. Tone frequencies were 2, 4, 8, 16, and 32 kHz adjusted to 40 dB (sound pressure level) above the S's absolute threshold. Five Ss were tested in the 2-choice situation following bilateral ablation of auditory cortex. Some reduction in performance was observed relative to normals, but impairments were not severe. Similar results were obtained for 2 brain-damaged Ss tested in the 3-choice situation. Thus, the ability to localize sounds in space remained intact after complete destruction of auditory cortex, and there was no indication of a frequency-dependent deficit. Findings are considered in relation to the more severe deficits observed in other mammals after lesions of the auditory cortex. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)