From CNBH Acoustic Scale Wiki
This example is the word "Leo," which has been spoken slowly in this case so that the formant motion can be observed visually. The video shows how the second formant in the auditory figure rises rapidly from a very low starting position in the consonant /l/, up to the relatively high frequency appropriate for the first vowel, /i/, and then back down to the lower frequency appropriate for the second vowel, /o/. This is the form of phonological information in speech -- an orderly, rapid progression through a sequence of auditory figures, each of which represents a phoneme of the language. Note that the motion in the video proceeds in synchrony with the changes taking place in the auditory event that we hear. This is a defining characteristic of auditory events, that is to say, when the activity in the auditory image proceeds in an orderly fashion through a sequence of related auditory figures, we hear the activity as an auditory event. The current event is heard as a word because central auditory processes monitoring the auditory image rapidly conclude that there is just one, very probably, interpretation for this event, especially given the context of the current discussion.
The word "leo" (cycles format) as an example of an auditory event
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Download Leo_Cycles.mov [103.77 kB]
The word "leo" (cycles format) spoken slowly as an example of an auditory event
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Download Leo_LongCycles.mov [372.48 kB]
In this example, the word "leo" is spoken in a monotone voice, and as a result, the event is dominated by the vertical motion of the formants. The pulse rate of the vowel, which we hear as the pitch of the voice, appears as the spacing between the copies of the auditory figure that appear across the width of the auditory image. The phonological information in a word is largely independent of the pitch of the voice, so the horizontal spacing of the copies of the figure can change over a wide range and we will still hear the word "leo."
Monosyllabic words like "leo" are simple auditory events. Multi-syllabic words and short phrases can be regarded as compound auditory events in which the simple events associated with the individual syllables cascade through the auditory image in coordinated sequences.