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Biomedical subjects

B B Ballachanda

Publications and source records attributed to B B Ballachanda.

7 recordsLinked to original sources
PubMed2000

Frequency-following response: effects of interaural time and intensity differences.

This research investigated whether brainstem neural mechanisms that mediate lateralization of sounds can be extracted from the frequency-following response (FFR). Monaural and binaural FFRs were obtained from normal-hearing subjects to low-frequency (500 Hz) linearly gated tone bursts (4-4-4 msec) at 40, 50, and 60 dB SL and four interaural time differences (ITDs) (0, 333, 500, and 667 microsec). FFRs were also recorded to ITDs and intensity presented in concert and in opposition (lateralization stimuli). The results show that overall intensity and interaural time differentially affect the FFR. The FFRs evoked by ITDs and intensity (in concert and in opposition) are strikingly different. The normalized amplitudes of the binaural interaction component (BIC) are minimally altered by ITDs and intensity. The study presents strong evidence that ITDs of 0, 333, 500, and 667 microsec and lateralization stimuli, easily discriminated perceptually, evoke clearly distinguishable FFR waveforms. These ITDs provide the cues that mammals use to localize sound in a freefield. The BIC is essentially unaffected by overall intensity, ITDs, and lateralization stimuli. Based on the findings of this study, the FFR has the potential to become a tool for identification of normal and abnormal binaural processing at lower brainstem levels.

Adult↗
PubMed1997

Physiology, pathophysiology, and anthropology/epidemiology of human earcanal secretions.

Two types of glands are found in the outer third of the human earcanal: sebaceous glands that produce sebum and modified apocrine glands that produce apocrine sweat. Together, these substances make up cerumen, which serves to clean, lubricate, and, to some extent, protect the earcanal from bacteria and fungus. Excessive/impacted cerumen can cause tinnitus, vertigo, itching, pain, external otitis, and hearing loss. Two populations are known to have a high incidence of excessive/impacted cerumen: individuals with mental retardation and the elderly. Anthropologists have used cerumen type to tract human migratory patterns and epidemiologists have related cerumen type to breast cancer.

Adult↗
PubMed1997

Theoretical and applied external ear acoustics.

The external ear (pinna and earcanal) plays a major role in transforming acoustic signals from free field to the tympanic membrane in humans. It acts as a filter to reduce low frequencies, a resonator to enhance mid frequencies (2.0 to 7.0 kHz), and a direction-dependent filter at high frequencies to augment spatial perception. The external ear transfer function is altered by variations in the physical dimension of the external ear either due to individual differences or due to mechanical obstructions such as blockages, hearing aid placement, perforation of the tympanic membrane, and use of insert earphone. It is significant that any change in the characteristics of the acoustic signal can produce considerable disparity in within- and between-individual responses. The present paper examines published studies on sound pressure transfer function provided by the external ear in humans.

Acoustics↗
PubMed1994

Asymmetric frequency-following responses.

This study offers evidence of asymmetry in the frequency-following response (FFR), a brainstem evoked potential that mimics stimulus frequency. The FFRs to stimulation of one ear compared to the other are shown to have latency and amplitude dissimilarities, as well as considerable variations in waveform characteristics. The findings were obtained from eight subjects. Tone bursts at 500 Hz were delivered to the right ear, left ear, and binaurally at three sound levels. With few exceptions, subjects had asymmetric FFRs at every sensation level (SL); at some, the sound to the left ear evoked a larger response than the same sound to the right; at other levels, the right ear FFR was larger than the left. The results provide evidence that cortical processing asymmetries must, to some extent, be reflective of asymmetric mechanisms within the lower brain stem.

Acoustic Stimulation↗
PubMed1992

Adaptation of the auditory brainstem response: effects of click intensity, polarity, and position.

The aim of this research was to study the effects of several stimulus parameters on adaptation characteristics of the auditory brainstem response (ABR). Recordings were obtained from normal hearing adults to separate trains of 5 rarefaction and 5 condensation clicks with interclick intervals of 10 msec and intertrain intervals of 500 msec at three intensities. Absolute latencies for waves I, III, and V were essentially unchanged by polarity; latency shifts, however, were induced by parametric manipulations of click intensity, polarity, and position in the train. Furthermore, variations in ABR wave morphology appeared with changes in intensity and polarity. Adaptation, as measured by amplitude, was considerable; the measures of adaptation, however, were not related in a simple manner to the latency shifts. The findings indicate that adaptation of the ABR is a consequence of an interplay of central and peripheral processes to click polarity, sequence, and intensity. Finally, the results provide evidence that when fast stimulus presentation rates are used to estimate thresholds rapidly, one must be aware that certain stimulus parameters can alter the ABR waveforms.

Acoustic Stimulation↗
PubMed1990

Homo- and anti-phasic stimulation in ABR.

Effects of homo-phasic and anti-phasic stimulation on the binaurally evoked auditory brain-stem responses (ABRs) were investigated in 10 normal subjects. Clicks were presented at 47 dB SL with two in-phase (binaural condensation and binaural rarefaction) and two out-of-phase (left ear condensation, right ear rarefaction and right ear condensation, left ear rarefaction) stimulus configurations. The earlier of the latencies obtained with homo-phasic stimulation were compared with the earlier of the latencies obtained with anti-phasic stimulation. Repeated measures ANOVAs on the peaks (P) and troughs (N) of each component, revealed significantly earlier latencies for the anti-phasic condition, for components II N (p less than 0.049), III P (p less than 0.012) and VIN (p less than 0.025). Similar trends were apparent for components IVP (p less than 0.075), VP (p less than 0.099) and VIP (p less than 0.12). The results are discussed in terms of the binaural-level difference phenomenon and possible clinical applications.

Adult↗