The final acoustic attribute that defines the sine-wave tone is its starting phase. Thit does not mean that this phase is not encoded by the auditory system. As phase differences between the sounds reaching each ear result in differences in perceived location of the sound source. The two sounds differ in frequency, with the sound cycling between periods of higher and lower air pressure at a lower rate, or frequency. These physical properties influence how it is displaced by sound; higher frequencies vibrate the stiffer base to a greater extent than do lower frequencies, creating a place code along the basilar membrane such that different locations are maximally displaced by different sound frequencies. As difficult as it has been to characterize the encoding and processing of single complex sounds, determining …show more content…
The visual analogy implied in that title was carried further by Bregman, who wondered if the basic perceptual principles of sound event segmentation may resemble those for visual organization developed by the Gestalt psychologists. At faster presentation rates, however, the perceived organization of the tones changes; they are heard as two pulsating simultaneous sound events or 'streams', one high-frequency and the other low-frequency grouping by frequency similarity. These perceptual streams no longer interact with each other perceptually, so that listeners can no longer tell the relative ordering of the tones in the two streams or hear rhythmic or melodic patterns that include tones from both streams. Gregg and Samuel have developed an interesting methodology for answering these types of questions using an auditory analog of the well-established 'change blindness' for visual displays. In this 'change deafness' paradigm, listeners are presented an 'auditory scene' consisting of four to six simultaneously presented sound events (e.g., dog barking, bell