Biomedical subjects

Pavel Zahorik

Publications and source records attributed to Pavel Zahorik.

4 recordsLinked to original sources

PubMed2006

Perceptual recalibration in human sound localization: learning to remediate front-back reversals.

The efficacy of a sound localization training procedure that provided listeners with auditory, visual, and proprioceptive/vestibular feedback as to the correct sound-source position was evaluated using a virtual auditory display that used nonindividualized head-related transfer functions (HRTFs). Under these degraded stimulus conditions, in which the monaural spectral cues to sound-source direction were inappropriate, localization accuracy was initially poor with frequent front-back reversals (source localized to the incorrect front-back hemifield) for five of six listeners. Short periods of training (two 30-min sessions) were found to significantly reduce the rate of front-back reversal responses for four of five listeners that showed high initial reversal rates. Reversal rates remained unchanged for all listeners in a control group that did not participate in the training procedure. Because analyses of the HRTFs used in the display demonstrated a simple and robust front-back cue related to energy in the 3-7-kHz bandwidth, it is suggested that the reductions observed in reversal rates following the training procedure resulted from improved processing of this front-back cue, which is perhaps a form of rapid perceptual recalibration. Reversal rate reductions were found to generalize to untrained source locations, and persisted at least 4 months following the training procedure.

Acoustic Stimulation↗

PubMed2002

Assessing auditory distance perception using virtual acoustics.

In most naturally occurring situations, multiple acoustic properties of the sound reaching a listener's ears change as sound source distance changes. Because many of these acoustic properties, or cues, can be confounded with variation in the acoustic properties of the source and the environment, the perceptual processes subserving distance localization likely combine and weight multiple cues in order to produce stable estimates of sound source distance. Here, this cue-weighting process is examined psychophysically, using a method of virtual acoustics that allows precise measurement and control of the acoustic cues thought to be salient for distance perception in a representative large-room environment. Though listeners' judgments of sound source distance are found to consistently and exponentially underestimate true distance, the perceptual weight assigned to two primary distance cues (intensity and direct-to-reverberant energy ratio) varies substantially as a function of both sound source type (noise and speech) and angular position (0 degrees and 90 degrees relative to the median plane). These results suggest that the cue-weighting process is flexible, and able to adapt to individual distance cues that vary as a result of source properties and environmental conditions.

Adult↗

PubMed2002

Direct-to-reverberant energy ratio sensitivity.

Although the ratio of direct-to-reverberant sound energy is known to be an important acoustic cue to sound source distance, human sensitivity to changes in this cue is largely unknown. Here, direct-to-reverberant energy discrimination thresholds were measured for six listeners using virtual sound source techniques that allow for convenient and precise control of this stimulus parameter. Four different types of source stimuli were tested: a 50 ms noise burst with abrupt onset/offset, a 300 ms duration noise burst with gradual onset/offset, a speech syllable, and an impulse. Over a range of direct-to-reverberant ratios from 0 to 20 dB, an adaptive 2AFC procedure (3-down, 1-up) was used to measure discrimination thresholds. For all stimuli, these thresholds ranged from 5 to 6 dB. A post hoc fitting procedure confirmed that slopes of the psychometric functions were homogeneous across stimulus conditions and listeners. These threshold results suggest that direct-to-reverberant energy ratio by itself provides only a course coding of sound source distance, because threshold values correspond to greater than 2-fold changes in physical distance for the acoustic environment under examination.

Acoustics↗

PubMed2002

Dissociation between location and shape in visual space.

There are often large perceptual distortions of shapes lying on the ground plane, even in well-lit environments. These distortions occur under conditions for which the perception of location i saccurate. Four hypotheses are considered for reconciling these seemingly paradoxical results, after which 2 experiments are reported that lend further support to 1 of them--that perception of shapeand perception of location are sometimes dissociable. The 2 experiments show that whereas perception of location does not depend on whether viewing is monocular or binocular (when other distance cues are abundant), perception of shape becomes more veridical when viewing is binocular. This means that perception of shape is not fully constrained by the perceived locations of the vertices that define the shape.

Adolescent↗