Biomedical subjects

Ranil R Sonnadara

Publications and source records attributed to Ranil R Sonnadara.

3 recordsLinked to original sources

PubMed2006

Occasional changes in sound location enhance middle latency evoked responses.

Rapid processing of sound location is critical for orienting attention. The present study investigated whether contextually sensitive early neural responses elicited by occasional changes in sound location could be measured. Using an oddball paradigm with stimuli consisting of brief noise bursts whose location was occasionally varied using head-related transfer functions, we found significant enhanced negativities in the event-related potentials elicited by deviant stimuli as early as 25 ms after stimulus onset, in addition to the differences around 125 ms which have previously been reported. Recent research suggests that occasional changes in auditory location information are processed in areas beyond primary auditory cortex. Our data suggest that any such processing is in fact preceded by activation in primary auditory cortex.

Acoustic Stimulation↗

PubMed2006

Effects of spatial separation and stimulus probability on the event-related potentials elicited by occasional changes in sound location.

The ability to extract information about the spatial location of sounds plays an important role in auditory scene analysis. The present study examined the effects of spatial separation and stimulus probability on auditory event-related potentials (ERPs) to changes in sound location. In Experiment 1, we found that difference waves between ERPs elicited by standard and deviant stimuli showed a biphasic negative-positive response peaking around 126 and 226 ms after deviant onset. The amplitude of both responses increased with decreasing deviant stimulus probability, and increasing stimulus deviance. When the same stimuli were presented with equal probability for all locations (Experiment 2), there were no significant differences in the ERP amplitude and latency. These results suggest that the data reported in Experiment 1 are the result of contextual changes, rather than changes in simple acoustic features. Brain electrical source analyses are consistent with generators located in auditory cortices posterior to Heschel's gyrus. Although occasional changes in sound location elicit earlier peaks than the mismatch negativity (MMN) response reported for other types of deviation, their topographical distribution and behavior are consistent with MMN. The early latency of MMN for changes in sound location is interpreted in the context of an early-warning system to alert the organism to new sound sources in the environment.

Acoustic Stimulation↗

PubMed2005

Perceived intensity effects in the octave illusion.

We showed that there is an intensity aspect to the octave illusion in addition to the pitch and location aspects originally reported by Deutsch (1974). In Experiment 1, we asked participants to directly compare the stimulus giving rise to the illusion (ILLU) with one mimicking its most commonly reported percept (illusion consistent; IC) and showed that they were easily able to distinguish between the two. In Experiment 2, we demonstrated a clear difference between the perceived loudness of ILLU and IC when IC follows ILLU, but not when IC precedes ILLU. In Experiments 3 and 4, we showed that this effect depends on the alternation of high and low tones between the ears in an extended pattern. In Experiment 5, we showed that this difference in perceived loudness disappears if the interval between the ILLU and IC stimuli is sufficiently large.

Adult↗