Hearing in Distance Or Where is that sound? Today: Isabelle Peretz Musical & Non-musical Brains Nov. 12 noon + Lunch Rm 2068B South Building

Improving Accuracy How do listeners judge distance? –Metrics of perception Absolute distance: objective scale –Euclidean Egocentric distance: metric in body relations –Gibsonian (J.J. Gibson*) Finding a source in distance (Russell, 2004) –Experiment: test distance of a sound source meters Blindfolded walk to position or declare distance in Euclidean Units –When are people better?

Results of Walk vs. Metric Greater accuracy with walking judgments –Much less variability –Overestimation of metric close distances –Underestimation of metric long distances Why did we find this result?

Is It Just Experience? Judge Sound Source –Walking –Pull board Laying on stomach, walking on hands –Metrical declaration Blindfold listening –Full vision movement to source position Judge distances 2 – 30 meters

Results with the Crawl Experiment Walk & Crawl very accurate –Some underestimation at very long distances Much more variation with metric judgment –Tendency for overestimation Golfers show improved accuracy judging metric distance –No underestimation tendency at greater distances with body- relevant units

The Affordance Paradigm Why are listeners better judging distances using body-relevant actions? –Use of Affordances Gibson’s simple idea –World is perceived in action relevant units All perception evolved to support action Best perception when subjects interact with environment Affordances –Action/body-relevant properties of the world Graspable, Eatable, Sitable, Walkable

Hearing the Silent World Localization –Study of sound sources Sound producing objects relative to listener Are sound sources the basis of hearing? –Visual world Light producing objects –Sun, lamps Light reflecting surfaces –Tables, faces, trees –Can we detect sound obscuring/reflecting surfaces?

Hearing the Silent World Sound obstructing surfaces –Diffuse sound field set behind sound attenuating surfaces Are listeners sensitive to position of surfaces? Test behavioral judgment –Is the aperture large enough to allow passage? Ego-centric judgment facilitates accuracy –Aperture size affects intensity, spectra Randomize intensities, sine wave signals –Listeners can detect position of sound obstructing surfaces

Elevation Height relative to listener –How can this be determined? Interaural cues? –Timing difference between the ears Mid-Saggital plane –Loudness difference between the ears Absorption by head & pinna –Front-back confusions Pinna cues –Forward, downward facing –Partially resolve front-back errors

Distance How far away is a sound source? –Interaural cues? Azimuth does not indicate relative distance –Pinna cues? Slight-downward facing –More distant cues higher in the perceptual plane Salient cues for distance –Intensity Attenuation over distance –Frequency dependent Unreliable indicator –Reverberation Increase in number and lag of echoes –DEMO