Auditory Events and Auditory-Figure Stability

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Category:Now See Hear!

Successive snapshots of the auditory image can be used to produce animated cartoons that track changes in a sound as they occur. These cartoons illustrate how the auditory figures of communication sounds emerge, evolve, and dissolve in time, and they allow us to simulate the internal representation of auditory events produced by acoustic events in the environment. The auditory images associated with musical notes, or tones, are dominated by a static auditory figures that appear out of the floor of the auditory image as the tone comes on and remains in a fixed position for as long as that tone is sustained. A single tone can be regarded as an auditory event, but it is not very interesting. Melodies are sequences of tones and they are more interesting as auditory events. A QuickTime movie of the auditory image produced by a simple seven note melody (do, re, mi, so, mi, re, do) is presented below. It shows how the auditory figure of a click train moves in discrete steps as the melody proceeds. In this example, it is only the pitch that is changing, and as a result, the motion in the image predominantly horizontal. This is the characteristic of the perceptual property, pitch; it determines the position of the set of auditory figures in the auditory image.

A Click Train Melody as an auditory event

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When a person says a word like ‘leo’, it produces an auditory event that is dominated by the changes in vowel type. In this case, the image is dominated by formation of the /i/ figure produced by the initial vowel and the transition to the /o/ figure associated with the final vowel. In this example, the word is spoken in a monotone voice, and so the event is dominated by the vertical motion of the formants. In the word "leo," the second formant of the auditory figure is observed to rise rapidly at the onset of the word into the high position associated the /i/ vowel and then drop back into the lower position associated with the second formant of the final /o/ vowel.

The word leo as an auditory event

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The videos of auditory events illustrate one of the most important properties of AIM as a model of auditory perception: change in the simulated auditory image occurs in synchrony with change in our perception of the sound. That is, any change in the position of the auditory figure, or any change in the shape of the figure, occurs in synchrony with the changes we hear in the sound. High-resolution, real-time displays of dynamic auditory events cannot be created from the traditional representation of sound, the spectrogram. The temporal fine structure that defines the auditory figure and its texture are integrated out during the production of the spectrogram. The chapters in Part 2 of the book explain how the temporal integration mechanism in AIM converts temporal information on the physiological time scale (milliseconds and hundreds of microseconds) into position information that appears as the shape, texture and pattern of auditory figures as they evolve in the auditory image. The integration mechanism preserves temporal information on the psychological time scale (tens of milliseconds and hundreds of milliseconds) and synchronizes the motion in the image to our experience of the change in the sound over time.

Category:Now See Hear!
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