Threshold and suprathreshold temporal integration effects in the crossed and uncrossed human acoustic stapedius reflex

Abstract

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold TI measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%-4%, p greater than 0.05) but were significantly larger in the crossed condition at higher criterion levels (5%-6%, p less than 0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.

Temporal integration of the contralateral acoustic-reflex threshold and its age-related changes

“…Acoustic-reflex latencies for tonal and BBN activators are prolonged in older adults as compared with younger adults ͑Bosatra et al, 1984͒. Numerous studies have been done on temporal integration ͑threshold-duration function͒ for the ART ͑Woodford et al, 1975;Barry and Resnick, 1976;Morgan et al, 1977;Stelmachowitz and Seewald, 1977;Cacace et al, 1991;Zwislocki, 2003͒. These studies yielded variable results in all likelihood because of small samples and/or lack of control for age.…”

Short-term poststimulatory response characteristics of the human acoustic stapedius reflex: Monotic and dichotic stimulation

“…Anatomical evidence from animals suggests that at least one interneuron is interposed between the primary auditory-nerve fiber and the seventh-nerve motoneuron in stapedius-reflex pathways (Borg, 1973;M411er, 1984 for review). Moreover, evidence exists that both threshold and suprathreshold temporal integration effects operate in crossed and uncrossed pathways of human acoustic stapedius reflex (Cacace et al, 1991 ). In this context, consider the situation in which two acoustic stimuli are presented in temporal sequence to activate the stapedius reflex, such as in the paradigm used in experiments 1 and 2.…”

Contralateral-noise effects on cochlear responses in anesthetized mice are dominated by feedback from an unknown pathway

“…Assays of MOC reflex strength typically use high-level contralateral noise, to maximize sound-evoked activation of contralaterally responsive MOC neurons, coupled with lowlevel ipsilateral stimuli, to keep the cochlear responses in a range where the cochlear amplifier has maximum effect and thus in a range where any sound-evoked MOC feedback can produce a robust suppression (Puria et al 1996). Indeed, in unanesthetized CBA/CaJ mice, there is a robust contra-noise suppression of low-level DPOAEs that largely disappears in the ␣9 knockout mouse (Chambers et al 2011). The magnitude of the OC-mediated suppression in unanesthetized wild-type mice (5-6 dB) is significantly greater than the mean effects in the present study (Fig.…”

“…When activated, these MOC fibers suppress the OHC's contributions to cochlear amplification, thereby decreasing the ipsilaterally evoked OAEs. Interpreting the contra-noise suppression assay is complicated, because contralateral sound can also activate the middle-ear muscle reflex (Cacace et al 1991), especially the stapedius muscle, which can reduce sound transmission into the ipsilateral cochlea and attenuate cochlear responses (Goodman and Keefe 2006). In humans, the relative contributions can be teased apart by careful analysis of the OAE response phase (Guinan et al 2003) or the ear's input impedance, which is increased by middle-ear muscle contraction (Goodman and Keefe 2006).…”