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.     

A geometric model of the lumbar spine in the sagittal plane

This article describes a geometric model using the skin profile and five anthropometric measurements to estimate the position of S1, T12, and all lumbar vertebrae for all postures assumed in the sagittal plane. This method involves a normalization process by which different skin profiles can be compared between postures and individuals. The skin profile is transformed by taking the differences with the lumbar spine into consideration. The model was developed and validated with 20 and 7 subjects, respectively. An error analysis shows an adequate level of accuracy for the absolute (1.68-1.82 cm) and relative (0.32-0.54 cm) linear positions of vertebrae as well as their absolute (2.6-6.7 degrees) and relative (1.4-3.6 degrees) angular positions except for T12; however, the validity of the model was limited to specific angular motions in flexion for the pelvis (12 +/- 3%), the entire lumbar spine (14 +/- 13%) and the intervertebral motion of L4/L5 (13 +/- 10%). The data obtained are very useful, especially in models designed to evaluate loadings on the lumbar spine.     

Long-term use of hearing aids in patients with presbyacusis

By means of a prospective study, concerning the postoperative rate of ossification after cementless total hip replacement, it was due to prove the efficacy of radiotherapy in preventing periarticular ossification. In 1992 arthroplasty was followed by radiotherapy of 50 hip joints as regular therapy. The radiation was performed with a focal dose of 8 Gy. Patients with bilateral cementless total hip replacement and radiotherapy only at one side were of special interest in this study. Within the 24th postoperative week in 28 (56%) of the radiated hip joins no periarticular ossifications were found. In 20 (40%) we found ossifications grade 1, in 1 case ossification grade II and in 1 further case ossification grade III following the classification of Arcq. By 8 patients with former cementless total hip replacement without postoperative radiotherapy, a significant reduction of the ossification rate was found in the contralateral hip joint treated by postoperative radiotherapy. The rate of ossification was reduced by 28%. In correlation to reduction of periarticular ossification the increase on the overall range of motion in the radiated hip joins was 10.9%. By none of the patients treated by radiotherapy we found a disturbed healing process, a deep infection or an early loosening of the endoprosthesis. Postoperative radiotherapy as regular therapy for prophylaxis of periarticular ossification after Cementless total hip replacement can subsequently be recommended.     

Sound localization in large mammals: Localization of complex sounds by horses.

The idea that large mammals localize sounds more accurately than small mammals has been noted frequently and is usually explained by reference to their large interaural distance and the correspondingly broad binaural time (Δt) and spectral (Δfi) differences between their 2 ears. In Exps I and II, sound-localization thresholds for single clicks and 100-msec noise bursts were determined in 5 horses, and the magnitude of the binaural time (Δt) and spectral (Δfi) cues for sound direction were measured in Exp III with 1 horse. Results show that although Ss had relatively large interaural distances and physically broad binaural-localization cues available to them, their sound direction thresholds were markedly poorer than those of other large mammals--averaging 22° for noise and 30° for clicks. It appears that sound-localization acuity is not determined simply by the physical availability of binaural cues. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sound localization in pigeon (Columba livia).

The presence of a binaurally activated nucleus (nucleus laminaris) in the hindbrain of birds suggests that they may be capable of binaural sound localization. In this report, after verification that pigeons were capable of either homing or scanning for the source of a sound, 5 Ss were also shown to be (a) capable of localizing a single burst of noise whose duration was too brief for homing or scanning; (b) capable of using either binaural time or intensity disparities for the localization of brief tones; (c) capable of localizing a single tone-pip throughout their frequency range of hearing from 125 Hz to 8 kHz, though having considerable difficulty in their midfrequency range (1–2 kHz); and (d) capable of localizing a single brief burst of narrow band noise even in their midfrequency range. It is concluded that the capacity of pigeons to localize brief sounds and to use binaural disparity cues for doing so is not qualitatively different from that of mammals and, therefore, that the nucleus laminaris or some similar brain-stem nuclei in pigeons are probably analogous in their contribution to sound localization to the superior olivary complex in mammals. (55 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)     

Sound localization in chinchillas, III: Effect of pinna removal

Using a computerized infrared activity analysis system, the dose-response relationship, timing, and duration for stimulation of motor activity after a single dose of methylphenidate was studied in Sprague-Dawley rats. After 5 days of acclimation and 2 days of monitored baseline activity, rats received a single subcutaneous injection of vehicle or of 0.6, 2.5, 10 or 40 mg/kg methylphenidate 1 h into the dark cycle. Recording was then resumed for an additional 36 h. Five locomotor indices were analyzed. Each locomotor parameter monitored different aspects of motor activity. The doses of 2.5, 10 and 40 mg/kg significantly increased (P < 0.01) locomotor activity. The time to maximal effect (20, 50, and 90 min) and duration of effect (70, 210, and 280 min) increased with dose respectively. Ten mg/kg had the maximum effect on locomotor activity, while the largest dose, 40 mg/kg, elicited a more focused stereotyped activity that limited the amount of forward ambulation. Single injections of methylphenidate did not alter motor activity the next day. Pharmacological parameters and specific locomotor parameters describing the effects of methylphenidate at the beginning of the dark cycle can later be used in chronopharmacologic studies. They will also provide the basis for investigation of adaptive mechanisms during repeated or chronic administration of methylphenidate.     

Sound localization acuity in very young infants: An observer-based testing procedure.

Infants 8 to 28 weeks of age were tested to determine the smallest sound shift off midline and along the horizontal axis that could be reliably discriminated, that is, minimum audible angle. Both sound-shift and no-shift trials were presented. For each trial, an observer decided, based solely on the infant's behavior, whether the sound shifted location (i.e., an observer-based yes–no task). To isolate sensory from nonsensory factors, analyses were performed on d′ scores. The results indicated increasing localization acuity with age. The video records revealed numerous auditory orienting behaviors (e.g., alerting, quieting, and lateral head and eye movements) and highlighted the value of not requiring that specific behavioral responses be performed on sound-shift trials. Possible factors contributing to these developmental trends are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distraction by competing speech in young and older adult listeners.

In 2 experiments, young and older adults heard target speech presented in quiet or with a competing speaker in the background. The distractor consisted either of meaningful speech or nonmeaningful speech composed of randomly ordered word strings (Experiment 1) or speech in an unfamiliar language (Experiment 2). Tests of recall for the target speech showed that older adults, but not younger adults, were impaired more by meaningful distractors than by nonmeaningful distracters, However, on a surprise recognition test, young adults were more likely than older adults to recognize meaningful distractor items. These results suggest that reduced efficiency in attentional control is an important factor in older adults' difficulty in recalling target speech in the presence of a background of competing speech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

FO processing and the separation of competing speech signals by listeners with normal hearing and with hearing loss

Normal-hearing and hearing-impaired listeners were tested to determine F0 difference limens for synthetic tokens of 5 steady-state vowels. The same stimuli were then used in a concurrent-vowel labeling task with the F0 difference between concurrent vowels ranging between 0 and 4 semitones. Finally, speech recognition was tested for synthetic sentences in the presence of a competing synthetic voice with the same, a higher, or a lower F0. Normal-hearing listeners and hearing-impaired listeners with small F0-discrimination (deltaF0) thresholds showed improvements in vowel labeling when there were differences in F0 between vowels on the concurrent-vowel task. Impaired listeners with high deltaF0 thresholds did not benefit from F0 differences between vowels. At the group level, normal-hearing listeners benefited more than hearing-impaired listeners from F0 differences between competing signals on both the concurrent-vowel and sentence tasks. However, for individual listeners, deltaF0 thresholds and improvements in concurrent-vowel labeling based on F0 differences were only weakly associated with F0-based improvements in performance on the sentence task. For both the concurrent-vowel and sentence tasks, there was evidence that the ability to benefit from F0 differences between competing signals decreases with age.     

Sound localization in a predatory rodent, the northern grasshopper mouse (Onychomys leucogaster).

A comparison of the ability of mammals to localize sound revealed that among the animals examined to date, none of the rodents have been able to localize as accurately as the carnivores. Because all of these rodents are prey animals, the question arises as to whether their poor localization acuity is a phyletic trait of Rodentia or whether it is a trait common to prey species that may be under less selective pressure than predators to localize sound accurately. To answer this question, sound localization acuity was determined in a species that is both predatory and a rodent, the northern grasshopper mouse. Localization thresholds for a single 100-ms noise burst were determined for three grasshopper mice using a conditioned avoidance procedure. Their 50% discrimination threshold of 19° is larger than that of any of the previously tested carnivores and well within the range of other rodents. However, calculations of the binaural sound localization cues available to rodents (based on their head size) suggest that the grasshopper mouse may make more efficient use of the available locus cues than other rodents. Thus, although the grasshopper mouse cannot localize as accurately as carnivores, it appears to be more accurate than predicted for a nonpredatory rodent of its size. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Regulation of contextual conditioning by the median raphe nucleus

The median raphe nucleus (MRN) has been suggested as the origin of a behavioral inhibition system that projects to the septum and hippocampus. Electrical stimulation of this mesencephalic area causes behavioral and autonomic manifestations characteristic of fear such as, freezing, defecation and micturition. In this study we extend these observations by analyzing the behavioral and autonomic responses of rats with lesions in the MRN submitted to a contextual conditioning paradigm. The animals underwent electrolytic or sham lesions of the median raphe nucleus. One day (acute) or 7 days (chronic) later they were tested in an experimental chamber where they received 10 foot-shocks (0.7 mA, 1 s with 20-s interval). The next day, sham and MRN-lesioned animals were tested again either in the same or in a different experimental chamber. During this, the duration of freezing, rearings, bouts of micturition and number of fecal boli were recorded. Sham-operated rats placed in the same chamber showed more freezing than rats exposed to a different context. This freezing behavior was clearly suppressed in rats with acute or chronic lesions in the MRN. MRN lesions also reduced the bouts of micturition and number of fecal boli. These rats showed a reduced number of rearings than sham-lesioned rats. This effect is probably the result of the displacement effect provoked by freezing since no significant differences in the number of rearings could be observed between these animals and the NMR-lesioned rats tested in an open field. This lesion produced higher horizontal locomotor activity in this test than the controls (sham-lesioned rats). These results point to the importance of the median raphe nucleus in the processing of fear conditioning with freezing being the most salient feature of it. Behavioral inhibition is also under control of MRN but its neural substrate seems to be dissociated from that of contextual fear.     

Effects of stimulus variability on speech perception in listeners with hearing impairment

Traditional word-recognition tests typically use phonetically balanced (PB) word lists produced by one talker at one speaking rate. Intelligibility measures based on these tests may not adequately evaluate the perceptual processes used to perceive speech under more natural listening conditions involving many sources of stimulus variability. The purpose of this study was to examine the influence of stimulus variability and lexical difficulty on the speech-perception abilities of 17 adults with mild-to-moderate hearing loss. The effects of stimulus variability were studied by comparing word-identification performance in single-talker versus multiple-talker conditions and at different speaking rates. Lexical difficulty was assessed by comparing recognition of "easy" words (i.e., words that occur frequently and have few phonemically similar neighbors) with "hard" words (i.e., words that occur infrequently and have many similar neighbors). Subjects also completed a 20-item questionnaire to rate their speech understanding abilities in daily listening situations. Both sources of stimulus variability produced significant effects on speech intelligibility. Identification scores were poorer in the multiple-talker condition than in the single-talker condition, and word-recognition performance decreased as speaking rate increased. Lexical effects on speech intelligibility were also observed. Word-recognition performance was significantly higher for lexically easy words than lexically hard words. Finally, word-recognition performance was correlated with scores on the self-report questionnaire rating speech understanding under natural listening conditions. The pattern of results suggest that perceptually robust speech-discrimination tests are able to assess several underlying aspects of speech perception in the laboratory and clinic that appear to generalize to conditions encountered in natural listening situations where the listener is faced with many different sources of stimulus variability. That is, word-recognition performance measured under conditions where the talker varied from trial to trial was better correlated with self-reports of listening ability than was performance in a single-talker condition where variability was constrained.     

Temporal analysis and stimulus fluctuation in listeners with normal and impaired hearing

The first experiment investigated the effects of mild to moderate sensorineural hearing impairment on temporal analysis for noise stimuli of varying bandwidth. Tasks of temporal gap detection, amplitude modulation (AM) detection, and AM discrimination were examined. Relatively high levels of stimulation were used in order to reduce the possibility that the results of the listeners with hearing impairment would be influenced strongly by audibility. A general summary of results was that there was relatively great interlistener variation among the listeners with hearing impairment, with most listeners showing normal performance and some showing degraded performance, regardless of the bandwidth of the stimulus carrying the temporal information. A second experiment investigated the hypothesis that listeners with sensorineural hearing impairment might have poor gap detection due to loudness recruitment. Here, gap markers were presented at levels where loudness growth was steeper for the listeners with hearing impairment than for the listeners with normal hearing. Although gap detection was sometimes poorer in listeners with hearing impairment than in listeners with normal hearing, there was no clear relation between gap detection performance and loudness recruitment in listeners with mild to moderate sensorineural hearing impairment.     

A behavioral measure of basilar-membrane nonlinearity in listeners with normal and impaired hearing

This paper examines the possibility of estimating basilar-membrane (BM) nonlinearity using a psychophysical technique. The level of a forward masker required to mask a brief signal was measured for conditions where the masker was either at, or one octave below, the signal frequency. The level of the forward masker at masked threshold provided an indirect measure of the BM response to the signal, as follows. Consistent with physiological studies, it was assumed that the BM responds linearly to frequencies well below the characteristic frequency (CF). Thus the ratio of the slopes of the masking functions between a masker at the signal frequency and a masker well below the signal frequency should provide an estimate of BM compression at CF. Results obtained from normally hearing listeners were in quantitative agreement with physiological estimates of BM compression. Furthermore, differences between normally hearing listeners and listeners with cochlear hearing impairment were consistent with the physiological effects of damage to the cochlea. The results support the hypothesis that BM nonlinearity governs the nonlinear growth of the upward spread of masking, and suggest that this technique provides a straightforward method for estimating BM nonlinearity in humans.