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PubMed1994

Functional organization of sound direction and sound pressure level in primary auditory cortex of the cat.

1. The functional organization of neuronal tuning to the azimuthal location and sound pressure level (SPL) of noise bursts was studied in high-frequency primary auditory cortex (AI) of barbiturate-anesthetized cats. Three data collection strategies were used to map neural responses: 1) electrode penetrations oriented normal to the cortical surface provided information on the radial organization of neurons' responses; 2) neurons' responses were examined at a few points in the middle cortical layers in multiple normal penetrations across AI to produce fine-grain maps of azimuth and level selectivity; and 3) electrode penetrations oriented tangential to the cortical surface provided information on neurons' responses along the isofrequency dimension. 2. An azimuth-level data set was obtained for each single- or multiple- (multi-) unit recording; this consisted of responses to noise bursts at five SPLs (0-80 dB in 20-dB steps) from seven azimuthal locations in the frontal hemifield (-90 to +90 degrees in 30 degrees steps; 0 degree elevation). An azimuth function was derived from these data by averaging response magnitude over all SPLs at each azimuth tested. A preferred azimuth range (PAR; range of azimuths over which the response was > or = 75% of maximum) was calculated from the azimuth function and provided a level-independent measure of azimuth selectivity. Each PAR was assigned to one of four azimuth preference categories (contralateral-, midline-, ipsilateral-preferring, or broad/multipeaked) according to its location and extent. A level function obtained from the data set (responsiveness averaged over all azimuths) was classified as monotonic if it showed a decrease of < or = 25% (relative to maximum) at the highest SPL tested (usually 80 dB), and nonmonotonic if it showed a decrease of > 25%. The percentage reduction in responsiveness, relative to maximum, at the highest level tested (termed nonmonotonic strength) and the preferred level range (PLR; range of SPLs over which responsiveness was > or = 75% of maximum) of each response was also determined. 3. Normal penetrations typically showed a predominance of one azimuth preference category and/or level function type. The majority of penetrations (26/36: 72.2%) showed statistically significant azimuth preference homogeneity, and approximately one-half (17/36: 47.2%) showed significant level function type homogeneity. Over one-third (13/36) showed significant homogeneity for both azimuth preference and level function type. 4. Mapping experiments (n = 4) sampled the azimuth and level response functions at two or more depths in closely spaced normal penetrations that covered several square millimeters of AI.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

The growing-louder effect in short diotic stimuli.

Previous evidence from short monotic stimuli shows that a steady stimulus is perceived as growing louder; to be perceived as steady, the intensity of the stimulus must decrease. In the present study, 10 subjects heard a sequence of diotic tonal stimuli. Each stimulus lasted 1.5 sec. and increased, decreased, or remained steady in intensity; initial intensity was 40 dB SPL and carrier frequency was 1 kHz. Subjects made forced binary responses of "growing louder" or "growing softer" to each stimulus. Confirming the evidence from monotic stimuli, the mean value of changing intensity eliciting equal numbers of both responses was negative. Possible explanations for this growing-louder effect reside in (a) the percussive nature of many natural sounds and (b) selective responding to approaching sound-sources.

Adult↗
PubMed2002

Influence of sleep deprivation and auditory intensity on reaction time and response force.

Arousal and activation are two variables supposed to underlie change in response force. This study was undertaken to explain these roles, specifically, for strong auditory stimuli and sleep deficit. Loud auditory stimuli can evoke phasic overarousal whereas sleep deficit leads to general underarousal. Moreover, Van der Molen and Keuss (1979, 1981) showed that paradoxically long reaction times occurred with extremely strong auditory stimuli when the task was difficult, e.g., choice reaction or Simon paradigm. It was argued that this paradoxical behavior related to reaction time is due to active disconnecting of the coupling between arousal and activation to prevent false responses. If so, we predicted that for extremely loud stimuli and for difficult tasks, the lengthening of reaction time should be associated with reduction of response force. The effects of loudness and sleep deficit on response time and force were investigated in three different tasks: simple response, choice response, and Simon paradigm. According to our expectation, we found a detrimental effect of sleep deficit on reaction time and on response force. In contrast to Van der Molen and Keuss, we found no increase in reaction time for loud stimuli (up to 110 dB) even on the Simon task.

Acoustic Stimulation↗
PubMed1985

Morphology, synaptology and electrophysiology of the developing cochlea.

The development of synapses clearly differentiates the two kinds of cochlear receptors inner (IHC) and outer (OHC) hair cells. An adult-like pattern of innervation can be seen very early below the IHCs: both afferent and efferent (mainly axo-dendritic) synapses are formed before the onset of function. At the OHC level, drastic changes occur: numerous afferent dendrites retract as the large efferent endings arrive and synapse with the hair cell. This synaptic OHC remodelling coincides with maturation of compound action potential (AP) parameters, such as the "S" -shape of the input-output curves and the sharpening of AP tuning curves.

Animals↗
PubMed1993

Electrical tinnitus suppression: frequency dependence of effects.

Electrical stimulation through a round window electrode has been evaluated in 9 patients with unilateral deafness and severe tinnitus. Three subjects were permanently implanted with positive long lasting results. Analysis of the threshold of sound perception, tinnitus suppression and auditory discomfort levels as a function of current frequency revealed the advantage of low frequency stimulation. In 2 patients the loudness of electrically evoked sound perception was balanced against tones in the hearing ear. Our results can be interpreted as indicating that processes other than auditory masking are responsible for electrical tinnitus suppression.

Acoustic Stimulation↗
PubMedDate not supplied

Azimuth estimates by human subjects under free-field and headphone conditions.

Estimates of sound source directions in the horizontal plane (azimuth) were made by human subjects under acoustic free-field (loudspeaker) and dichotic stimulus conditions (headphones). The functional relationship between the binaural cues, interaural time and intensity differences (ITDs and IIDs) and azimuth angle approximately follow a quarter of a full sine wave between 0 degrees straight ahead and the maximum at 90 degrees for ITDs and, depending on frequency for IIDs, at 60-90 degrees lateral (frontal quadrant). Under free-field conditions, these physically determined, interaural difference cues are correctly translated into azimuth angles by all listeners: estimated angles correspond to presented sound directions. In contrast, when providing dichotic stimuli containing ITDs/IIDs, so that sounds come from virtual azimuth angles, only 8% of the listeners estimated according to the expected transfer function of a quarter of a sine wave. However, about 60% of the listeners ranged azimuth directly proportionally to the binaural differences introduced, systematically overestimating virtual angles by up to 20 degrees. The remaining 32% of the listeners systematically overestimated virtual small and midrange sound directions even more. Virtual 40 degrees (corresponding to 12- to 14-dB and/or 450- to 550-microseconds differences) was often estimated as almost 90 degrees. Without corrective feedback, a reduction of the systematic errors was never observed. Central neural mechanisms and conceptual strategies to accomplish the expected transfer from virtual back to free-field directions are proposed to explain the large systematic overestimates: in contrast to our lifelong 'free-acoustic field' experience, we are unable, under dichotic conditions (hence in the absence of complete pinna cues and possibly room acoustics), to use the either innate or, more likely, acquired quarter of a sine interaural difference function necessary to accomplish the correct transfer.

Adult↗
PubMed1985

The 40-Hz event-related potential as a measure of auditory sensitivity in normals.

Estimates of behavioral threshold using the 40-Hz Event-Related Potential (ERP) were obtained on sixteen normal subjects at frequencies of 500, 1000, 2000, and 4000 Hz, and compared with behavioral thresholds for the same stimuli. The mean differences were within 10 dB at the three lowest frequencies. The mean difference at 4000 Hz was 16 dB. Peak amplitude of the response did not vary significantly either with signal amplitude or test frequency, but the latency of the response varied significantly with frequency. Factors which may affect the reliability and validity of the 40-Hz ERP are discussed.

Adult↗
PubMed2005

Symbolic distance affects two processing loci in the number comparison task.

A dual-task procedure was used to investigate the attentional requirements of number processing. The results show that (1) numeric information in Task 2 can be retrieved in parallel with capacity-demanding processing in Task 1 but (2) comparing two quantities requires central capacity, which is depleted by switching from one task to another. This finding resolves an apparent discrepancy in the literature, in which digit magnitude information has not been retrieved in parallel with a second task (Logan & Schulkind, 2000), despite repeated demonstrations that this information is retrieved autonomously, even when it is deleterious to performance (Henik & Tzelgov, 1982). A model is proposed to reconcile existing findings with the new ones revealed in the present investigation.

Distance Perception↗
PubMed1997

Comparing exemplar-retrieval and decision-bound models of speeded perceptual classification.

The authors compared the exemplar-based random-walk (EBRW) model of Nosofsky and Palmeri (1997) and the decision-bound model (DBM) of Ashby and Maddox (1994; Maddox & Ashby, 1996) on their ability to predict performance in Garner's (1974) speeded classification tasks. A key question was the extent to which the models could predict facilitation in the correlated task and interference in the filtering task, in situations involving integral-dimension stimuli. To obtain rigorous constraints for model evaluation, the goal was to fit the detailed structure of the response time (RT) distribution data associated with each individual stimulus in each task. Both models yielded reasonably good global quantitative fits to the RT distribution and accuracy data. However, the DBM failed to properly characterize the interference effects in the filtering task. Apparently, a fundamental limitation of the DBM is that it predicts that the fastest RTs in the filtering task should be faster than the fastest RTs in the control task, whereas the opposite pattern was observed in our data.

Decision Making↗
PubMed1994

The stimulus range effect: evidence for top-down control of sensory intensity in audition.

The influence of intensity range on the perceived magnitude of a stimulus is well documented and usually attributed to response biases. Recent studies, however, have suggested that the range effect might be sensory in origin. To test this notion, we had one set of subjects compare loudness intervals in three conditions: a broad-range condition (15 tones, 23-95 dB SPL), a soft short-range condition (the lowest 10 tones from the broad-range condition), and a loud short-range condition (the highest 10 tones). Nonmetric scaling showed that the broad-range and loud short-range conditions had identical loudness functions. However, the second derivative of the loudness function was larger for the soft short-range condition than for the broad-range condition. This pattern of results is consistent with the notion of a nonlinear amplifier whose gain and degree of nonlinearity are adjusted under top-down control, so as to prevent distortion and increase discriminability.

Adult↗
PubMed2005

Effect of ear canal occlusion on pure-tone threshold sensitivity.

This study sought to quantify the effects of varying the degree of ear canal occlusion on pure-tone threshold sensitivity. Thresholds were obtained from each ear of five normal-hearing adults without occlusion, with complete occlusion, and with partial occlusion estimated to be 40-60% and 60-80%. A commercial lubricant was used in the completely occluded condition to eliminate possible acoustic leakage. Results showed a reduction of threshold sensitivity in all occluded conditions, with the greatest effect in frequencies above 1000 Hz. Only in the completely occluded condition were frequencies below 1000 Hz affected. In the partially occluded conditions, thresholds decreased by an average 7.5 dB and 13.0 dB across frequency for the 40-60% and 60-80% conditions respectively. At frequencies above 1000 Hz, the average threshold shifts for the two partially occluded conditions were 10.0 dB and 16.8 dB respectively. The implications of these findings on routine pure-tone audiometric procedures, with specific relevance for industrial hearing conservation programs, are discussed.

Acoustic Stimulation↗
PubMed2002

From spectrum to space: the contribution of level difference cues to spatial receptive fields in the barn owl inferior colliculus.

Space-specific neurons in the owl's inferior colliculus have spatial receptive fields (RFs) computed from interaural time (ITD) and level (ILD) differences. Because of the shape of the owl's head, these cues vary with frequency in a manner specific for each location. We sought to determine the contribution of ILD to spatial selectivity. We measured the normal spatial receptive fields of space-specific neurons using virtual sound sources (i.e., noises filtered to simulate external sound sources, presented using headphones). The virtual-source filters were then altered so that ITD was fixed while frequency-specific ILDs varied according to location in the usual manner. The resulting "ILD-alone" RF typically revealed a horizontal band of excitation that included the normal RF. Above and below, the neurons were inhibited. Interestingly, the maxima of ILD-alone RFs were generally outside the normal RF, suggesting that space-specific neurons are not optimally tuned to the ILD spectrum occurring at the normal RF location. Congruously, frequency-specific ILD tuning, assessed with tones, better matched the ILDs at the peak of the ILD-alone RF than those at the peak of the normal RF. The firing evoked from the normal RF may thus reflect the balance of excitatory and inhibitory inputs needed to appropriately restrict the receptive field. Frequency-specific ILD tuning curves were combined with measured head-filtering characteristics to predict responses to the frequency-specific ILDs at each location. The predicted ILD-alone RFs, which are based on a simple sum of frequency-specific inputs, accounted for 56% of the variance in our measured ILD-alone RFs.

Acoustic Stimulation↗