Variation and assimilation in German - Institut für Phonetik

538 COENEN, ZWITSERLOOD, AND BOÈLTE
Some psycholinguistic models also allow for a less than perfect match
between input and representation. For the TRACE model of spoken word
recognition (McClelland & Elman, 1986), with its featural, phonemic, and
lexical levels, and with bi-directional and excitatory connections between
layers, assimilation does not pose severe problems. An input such as
/greem/ will activate word nodes (e.g., green, grief, gleam, cream), even if
there is no perfect match. Mismatch has no direct negative consequences
for word units, although recognition might be delayed. One exception in
TRACE is when another word form represents a closer match to the input.
When a word such as gun is assimilated to /gum/ (as in a gumpowder), the
existing word node gum provides a closer match to the input than the
assimilated word (see Gaskell, this issue; Gow, 2000; Koster, 1987). In that
case, competition between word nodes will delay or even prevent
recognition. Importantly, since TRACE was not designed to differentiate
between fortuitous mispronunciations and lawful variation, it does not
predict any differences between legal and illegal deviations. Moreover, the
context which licenses variation (e.g., the [p] in powder) should be
irrelevant.
The rst psycholinguistic model to incorporate underspecication was
the Cohort model (Marslen-Wilson, 1993). It is as intolerant to mismatch
between input and lexical representation as earlier versions of the model
(Marslen-Wilson, 1987), but this intolerance does not apply in all cases.
Based on data from Bengali and English (Lahiri & Marslen-Wilson, 1991),
an underspecication view of the mental lexicon was adopted, such that
legal variations due to coarticulation or assimilation no longer constitute a
mismatch at the lexical level. Phonological context was not taken into
account at this stage.
Phonological context does play a role in a recent (distributed)
connectionist instantiation of the Cohort model (Gaskell, Hare, &
Marslen-Wilson, 1995; Gaskell & Marslen-Wilson, 1997, 1998, 1999). The
most prominent properties of the model are a direct and simultaneous
mapping of the featural input onto semantic and phonological output
representations at the lexical layer. To allow for a broader time scope, a set
of hidden units is linked in a recurrent way to the state of hidden units at
previous time-steps. This allows for an evaluation of featural context, and
thus of contextual appropriateness.
EXPERIMENTS ON ASSIMILATION
Whereas there is a long research tradition into effects of coarticulation on
speech perception (e.g., Howell, 1983; Mann & Repp, 1980; Martin &
Bunnell, 1982; Meyer & Gordon, 1985), few studies have investigated the
type of variation we are interested in here. Koster (1987), for Dutch,