Preaspiration in the Nordic Languages: Synchronic and Diachronic ...

are better discriminated than are adapted responses (i.e., with low neural
discharge rates). In one experiment, Lacerda investigated the difference
in discriminability between short, synthetic vowel stimuli with abrupt vs.
gradual onsets. F2-values for the stimuli varied, ranging from 1510 Hz to
1690 Hz in 30-Hz increments. F1 was fixed at 200 Hz, F3 at 2600 Hz,
and F4 at 3600 Hz. A two-alternative forced choice paradigm was used
and subjects were asked to note whether or not the two alternatives presented
were different. Lacerda found that when the F2 difference between
two stimuli was 60–90 Hz, the stimuli with abrupt onsets had significantly
better discrimination rates than did gradual stimuli. This indicates
that the F2 differences have more auditory salience in abrupt than
in gradual stimuli.
However, in an identical experiment using aperiodic instead of periodic
stimuli (thus essentially synthesising an aspiration, but possibly using
a more fricative than aspirative source), Lacerda did not find that
gradualness of onset lessened discriminability at all. Instead, discriminability
scores for stimuli with abrupt and gradual onsets were almost
identical. The scores lay somewhat below those for abrupt periodic stimuli,
but above those for gradual periodic stimuli. (This applies to the
cases in which F2 differs by 60 Hz or 90 Hz; other differences are much
smaller). Thus the abrupt vs. gradual difference found in the first experiment
does not appear in the second.
One may note that aperiodic sounds with abrupt and gradual onset
are both “natural” in speech (abrupt onset = affricate, gradual onset =
fricative). Periodic sounds with an abrupt onset (vowels) are also “natural”
in speech. However, periodic sounds with a gradual onset (such as
the one synthetically created by Lacerda) are not. Perhaps subjects are
better able to discriminate sound patterns that are used consistently in
speech than sound patterns that humans may not even be able to produce
(such as the periodic gradual onset vowel stimulus used in Lacerda’s
experiment).
Reviewing these facts, one may perhaps conclude that there is some
degree of correlation between discharge rate and auditory salience, but
that the two can in no way be equated directly. Thus a three-fold increase
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